Some noodling about my dream scope

Fair warning: this post is just me thinking out loud about my dream scope. If you’d rather read about the stars, good on ya–there are plenty of other posts here about that stuff, that will be more interesting than this extended episode of navel-gazing about gear. Feel free to skip backward or–hopefully soon–forward.

As I’ve mentioned here a few times before, eventually I want to have a bigger scope, something in the 14″-18″ range. There are four boundaries that define it:

1. It has to be enough of a gain over my current scope to be worth the expense. Some people say that small gains in aperture are not worth it, that you won’t notice enough of an improvement to make it worthwhile. I have looked through 8″ and 10″ scopes in quick succession, and 10″ and 12″ scopes in quick succession, and in both cases the gain in light gathering and resolution was immediately noticeable at the eyepiece. But it’s the “to make it worthwhile” part that’s the kicker. As we saw in What Aperture Costs, above 10″ prices increase sharply. As long as I’m saving up for my dream scope, I might as well save a little longer and get the wow factor instead of settling for a scope I’ll want to trade up from before long. To really get the wow factor from a bigger scope, most people recommend doubling your light grasp–which for me means going from 10″ to 14″ (78.5 to 154 in^2)–or going one magnitude deeper, a factor of 2.5, which for me means going to 16″ (200 in^2).

2. It has to be small enough to fit in my current vehicle or any foreseeable future vehicle not specifically purchased for hauling around big telescopes. That means it has to be collapsible. But it has to be collapsible anyway, because I’ve had a solid-tube 12″ and didn’t keep it. In that case, the gain over the XT10 was noticeable but not worth it. And it still has to fit in a regular car. My friend Ron has a minivan that he bought specifically for hauling around his 22″, but I will probably never be in the position to base my vehicular purchases around my telescopes.

3. The pieces have to be light enough that I can set it up by myself. My friend Jeff has a collapsible 16″–it’s the scope we took on the LCROSS impact watch–but the mirror box is so damn heavy it takes both of us to get it up into the back of his pickup. I’d prefer a max weight for each piece under 75 lbs, and under 50 would be better still. If those sound like light loads for a healthy 6’2″ dude, go move big scopes around for a while. It’s like moving furniture–awkward weight with a center of gravity far from your body that makes the load on your back a lot worse than when you’re pumping iron. My XT10 weighs 55 lbs assembled. I can move it around in one piece if I have to, but I usually feel it in the morning. A 55-lb chunk of a bigger scope would probably be smaller, less awkward, and hurt my back less.

4. I have to be able to afford it. More specifically, I’d like to be able to afford it with no more than a year or three of saving up. Maybe someday I’ll save for a decade or two and get a custom-made ultralight 25″ that packs into the back of a compact car (such things do exist), but that would be my last scope, not my next scope. For me, right now, given the disposable income I can afford to dedicate to astronomy, the one-to-a-few year saving duration means a one-to-a-few thousand dollar budget. (If that sounds low, hey, congrats, feel free to buy me a scope. I promise to use it for outreach! If it sounds high, go price ATVs or boats or campers or any of the really high-end grown-up toys.)

Those conditions give me a range of options to think about while I’m saving up.

For a long time, my dream-scope ideal was a T-Scope, a custom 14″ truss-tube dob with a low rocker box, starting at $3195. Pros: light, 65 lbs total and heaviest single component is 35 lbs; very high quality, very compact when disassembled. Cons: among the pricier options I’m looking at, cost does not include shipping from New York state (not a jab against T-Scopes, almost no-one has free shipping on scopes like these, it’s just one more thing I have to think about). UPDATE: another con is this negative customer experience reported on CN. I’m going to try to find out more about it–stay tuned.

These days I’m thinking more and more about DobStuff. Dennis Steele makes big scopes that  look awesome, weigh next to nothing, and cost surprisingly little for ultralight custom scopes. A 14″ weighs 70 lbs assembled, heaviest single component is 30 lbs, and goes for $2195. A 16″ would weigh about 90 lbs assembled, heaviest single component 45 lbs, for $3495. Apparently there is a price jump from 14″ to 16″ optics, which explains why the 16″ costs so much more than the 14″. Anyway, super-cool scopes that are pretty much exactly what I’m looking for. One CN member says his 16″ DobStuff has a footprint of 24″x24″ and sits in the back seat of his car when collapsed for travel. I need something like that.

Turning to mass-produced scopes, there’s the Orion XX14i, a 14″ semi-truss dob, starting at $1899. That’s a lot of scope for not a lot of dough, especially considering it comes with digital setting circles (i.e., non-motorized “push-to” object locator). And I could drive to someplace that actually has them in stock and save on shipping. Downsides: compared to the other scopes I’m considering, it’s a pig. I call it a semi-truss dob because although it has trusses connecting the ends of the tube, and they do allow it to break down into smaller pieces, they don’t actually lighten the scope. Orion’s 12″ truss dob weighs just as much as the solid-tube version. The assembled weight is 120 lbs, and the heaviest single component is 55 lbs, as much as my XT10 and almost as much as an entire T-Scope. Also, there’s no way to get the scope without the digital setting circles, and it irks me to know that I’d be paying a few hundred more for a feature I’d happily do without. Finally, there have been some quality control issues; at least one Cloudy Nights user got an optical dud and Orion did not replace it, which is the first time I’ve ever heard of that happening. In fairness, Orion has apparently improved the quality of the optics shipping with the newer XX14s, so maybe–hopefully–the optical disappointments are all in the past.

I discovered as I was writing this post that Orion has just introduced a 16″ semi-truss scope, the XX16g. Apparently it’s just like the XX14i but more so: more weight (195 lbs assembled), more cost ($3599), and more paying through the nose for stuff I don’t need–unlike the XX12 and XX14, which can be ordered in the “i” push-to versions or the “g” go-to versions, the XX16 is so far only available with go-to. So I’d be paying even more money for even more stuff I’d happily do without. I’m sure go-to is nice and if I had it I’d get addicted. My objections to go-to basically fall into three categories: (1) I spend at least half of each day working at a computer. I go stargazing to get away from all that. (2) At any given cost, adding electronics means taking away aperture. Given my limited budget, I prefer to buy aperture, for which there is no substitute, rather than electronics, which don’t do anything I can’t do myself with a star atlas and some elbow grease.* And (3) like all electronics, all go-to systems eventually fail. This is why Uncle Rod recommends buying CATs on equatorial mounts instead of fork mounts–EQ-mounted tubes are a lot easier to remount when the motorized mount craps out. I should say that these are my personal reasons for not wanting go-to for myself. If you have, love, or want go-to, that’s cool–may a thousand gardens grow. No need to sell me on it; it’s just not my scene, man.

* John Dobson says that dobsonian telescopes are held together by gravity and powered by yogurt (you eat the yogurt, and push the scope around with your muscles). Preach it, Brother Dobson.**

** That’s funny, see, because Dobson actually was a monk (before he got kicked out for doing too much sidewalk astronomy).

Meade’s 16″ LightBridge is a contender. At about $2000 it costs only a shade more than the XX14, but delivers a third again as much light. Another way to look at it is that it delivers the same light grasp as the XX16g for a little over half as much dough. The weight is high, but no worse than the XX14i: 128 lbs total, and heaviest single component is 58 lbs. Downsides? From everything I’ve read, the LightBridge series do not  quite match the comparable Orion scopes on build quality. They seem to be “work in progress” scopes. This is especially true of the 16″–I’ve heard of lots of people who have rebuilt the base, which is apparently too wobbly for such a heavy scope, and Dennis Steele at DobStuff offers replacement base kits for just this purpose. When there’s a thriving aftermarket to fix the problems with a telescope as delivered, that’s a problem. I’m saving up for my dream scope, not a project scope. But it’s a lot of scope for two grand; even budgeting an addition $395 for a replacement base, it’s a solid deal.

And it’s an affordable way to lay one’s hands on a set of 16″ optics. I realized something odd the other night. A 16″ DobStuff is $3495, but a DobStuff makeover, where you supply the optics, is only $895 for a 16″, plus another $150 for the Easy Transport Telescope option. So it’s actually about $400 cheaper to buy a 16″ LightBridge ($2000) and have it made over ($1045, for $3040 total) than to buy a 16″ DobStuff straight up. About the only risk I can see is the possibility of variable quality control in the LightBridge optics, although from what I’ve read the baseline quality is quite good and I haven’t read any horror stories.

Two options I haven’t discussed are building my own and buying used. Regarding building my own, see comments above about dream scope vs project scope. And although I am normally a big fan of buying and selling used telescopes, I am a little leery in the case of my dream scope. If this is either going to be my last scope or my last scope for many years, I want to get exactly the right thing. I’ve already taken one poorly-considered leap into larger aperture and regretted it. I don’t want to make that mistake again.

And yet…a used scope could just be a delivery mechanism for big optics. The other day someone on CN was selling a used 16″ LightBridge for $1500, and I have seen them go for even less. That plus a DobStuff makeover could be a faster, cheaper track to my dream scope than going all-new. It’s something to think about, anyway–I’m sure I’ll have plenty of time to consider, and reconsider,  and rereconsider, etc., over the next few months and probably years.

Why aperture matters

Most people who have gotten as far as even doing research on buying a telescope can probably rattle off the two benefits of aperture: greater diameter allows increased angular resolution–the ability to resolve fine details–and greater collecting area simply gathers more light. But what do these advantages really mean? Just in the past month I’ve read a couple of explanations that gave me new ways to think about this, and that I think need to be more widely read.

The first comes from Richard Panek’s fine little book, Seeing and Believing: How the Telescope Opened Our Eyes and Minds to the Heavens (page 111):

Double the diameter of the aperture, and its light-gathering capacity increases fourfold; triple it, and the capacity goes up ninefold. At the same time the brightness of the object under observation depends on the square of the distance. Double the distance of a light source, and its brightness decreases fourfold; triple it, and the brightness drops off ninefold. The implication was clear: Double the diameter of the aperture, and you double the distance the mirror can see. Herschel understood that for the purpose of investigating the starry depths the major advantage of a reflecting telescope wasn’t in greater magnification, but in gathering more light–wasn’t in seeing more detail, but in seeing farther.

Okay, cool stuff. I knew that light grasp increases proportional to the square of the diameter, and that brightness drops off proportional to the square of the distance, but I’d never thought to put those two thoughts together.

Still, deep sky observers usually start with the bright stuff, like the Messier objects, and with sufficiently dark skies even the Herschel 400 are within reach of a 2-inch scope. Given that you’re already looking out more than 60 million light years to see the most distant Messiers, does seeing father really help?

There’s another piece to this, and it’s one I’d never considered until I read a very clear explanation of it by Ed Moreno (CN username Eddgie) on Cloudy Nights. Here’s the link to the CN post, but it’s so good I’m just going to copy and paste the whole thing here:

Make no mistake here. If you want to see more structure or detail in any kind of extended target such as nebula, galaxies, or planets, there is absolutely no substitute for clear aperture.

Almost all of the design discussions totally omit the function of image brightness/image scale that is offered by a larger aperture. We tend to discuss equipment like we don’t have eyeballs.

But we do have eyeballs… Or Cameras.

The image brightness and the ability to trade it for image scale is a huge part of the value of a larger aperture.

Keep in mind that a 16″ telescope and a 4″ telescope can both show the Orion Nebula with the exact same brigntness. Is all one has to do is use an eyepeice in each scope that has the same exit pupil.

For example, if I use a 16″ telescope at 100x, this will give about a 4mm exit pupil for the observer. In a 4″ scope, to get the same exit pupil (same image brightness), you will have to use 25x.

Now in the 4″ scope, the image is exactly as bright as in the 16″ scope, but the scale is only 1/4th as large.

Now is where it gets interesting. The structure inside the nebula is often very low contrast and very fine.

It is often stated on these forums that the human eye can resolve down to one arc minuted. This actually greatly overstates the eye performance of the scotopic eye for low contrast detail. This figure (one arc minute) is only achievable when the target is well illuminated and the contrast is 100%.

If the eye is in scotopic mode, and the contrast is very low, the eye may struggle to resolve detail that is smaller than about 3 or 4 arc minutes of apparent field unless the contrast is very high or the target is well illuminated.

There are two ways to increase the likelihood of the human eye (or camera) being able to resolve this very low contrast detail. They are to A: Make it bigger by magnifying it more, or B: make it brighter. Of course if you can make it slightly bigger and slightly brighter, this greatly enhances your ability to resolve fine, low contrast structure present in the extended target.

Now, lets take our 16″ scope and our 4″ scope and use the 16″ scope with our 4mm exit pupil. Remember, the illumination (determined by the exit pupil) is the same, but the angular size of any detail in the target will be four times as large. Detail within the target that does not have the angular magnification to be resolved in the smaller scope is now presented as four times as large. This means that there is now a lot more detail that has been magnified enough to be seen in the much bigger scope. Of course I can make the detail larger in the smaller telescope but this comes at the expense of loosing illumination (smaller exit pupil) which makes it harder for the eye to see the detail.

The other option is to make the image bigger and brighter in the bigger scope. Suppose I use the bigger scope with a 6mm exit pupil. Now, the exit pupil being larger gives me a brighter image. Once again, the eye likes illumination as one of the two ways to improve the ability to detect detail. When I make the image brighter in the larger scope, I see the extended target as extending over more area. The added brightness expands the extent of a nebula or galaxy. And guess what…. With the 6mm exit pupil in the 400mm scope, the magnification is 66x, so every detail present is still presented at almost 2.5 times the image scale as it would be in the 4″ aperture!!!!!! So now I have an image that is both bigger AND brighter in the larger aperture. I don’t care what kind of scope this is… It can be a refractor, a reflector, or a compound scope. If I make the image bigger and brighter, even if the contrast of the detail is exactly the same, my eye will have a better chance of seeing that detail if I make it bigger or brighter, or both at the same time.

Again, make no mistake about it… For seeing the most detail in extended targets of all types, clear aperture is king. You cannot isolate the telescope from the detector, and when the human eye is the detector, with a larger aperture you usually get both increased scale AND better illumination of the target and all of the structure present in the target.

I have owned perhaps 40 telescopes in the last 10 years, and for all classes of extended targets I would rank them in terms of performance in almost 100% agreement with the amount of clear aperture the scopes provided. I personally have never compared two telescope (even of different types) that the scope with the most clear aperture didn’t equal or exceed the performance of the smaller clear aperture.

There is no substitute for aperture. That is why the Hubble is a 2.4 meter instrument and not a 4″ refractor.

Aperture gives you image scale and illumination. It doesn’t even matter how you get that aperture (design). It is only important to have a lot of it.

Big telescopes simply show more. At the end of the day, if you want to see more structure in all class of extended targets, or if you want to see these extended targets at their maximum size, the best way to do this is to use as much aperture as you can manage.

The problem with refractors is that to get any meaningful amount of clear aperure (I recommend 8″ to 10″ for seeing a lot of structure in most deep sky extended targets) the expense becomes impractical as does the physical size of the instrument.

Everyone gets to use what they like, but the physics of image formation give clear aperture the best image formation, and lots of aperture gives the human eye the best chance of seeing any existing detail that might be present in the target.

There really isn’t any substitute for clear aperture. The more you apply to almost any target in the sky, the more structure or detail you will be able to see.

Now, I had experienced this, but I hadn’t thought about it–in fact, hadn’t known about it–in terms of brightness and image scale. And now that I have,  I agree with Ed completely.

I like small scopes. A lot. Maybe more than is healthy. But I will readily admit that my XT10 blows away all of my smaller scopes, on almost every target. Maks are often described as being fine planetary scopes, and they are. My 5″ Mak rocks on planets. But the XT10 just annihilates it on max detail. Even on the moon–I will put one of the smaller scopes on the moon and think I’m getting a good view, and then I put the XT10 on the moon and BAM! It’s the same field of view, but not the same view–suddenly everything is just bursting with details that I couldn’t see before. And now I know why–it’s not just angular resolution and not just light grasp, but rather the ability to get an image that is bigger, brighter, and more detailed, all at the same time.

Fortunately, I didn’t buy the Mak under the illusion that it would outperform the dob–I bought it because it fits in a space only a little bigger than a gallon milk carton, for those times when I don’t have room for anything bigger. And there is in fact one class of targets where I strongly prefer the Maks, and that is double and multiple stars. Oh, there’s no doubt that the XT10 will split closer doubles, period, and split wider doubles more easily, but I have not (so far) been going after doubles that are at the limit of resolution of a 10″ scope. And for things the Maks can split, they provide a more pleasing image than the dob, with no diffraction spikes. There is something entrancing about seeing a just-barely-split star as two clean little balls of light separated by the thinnest of black lines, surrounded by nice concentric diffraction rings but with no other visual noise to clutter the view.

So, dobs are cheap, but people end up buying other scopes for other reasons, and probably the two most important of those reasons are portability and aesthetic “cleanness” of view. Those are, in fact, the very reason that I own scopes other than dobs. BUT if you are interested in the deep sky–or pretty much anything else up there–and you’re on a budget, then clearly it is in your best interest to get as much aperture as you can afford. So this post is a deliberate follow-up to the last one; that one showed which scopes provide the most bang for the buck, and this one explains why you want as much bang as possible.

All of this is just part of an extended run-up to the Suburban Messier Project. I’m not ready to get started on that, not yet. I’m too busy with teaching, and my skies are lousy right now anyway. But I am thinking about the SMP, and when and how to best get started, and what information you may want or need if you’d like to tackle the project with me.

Until next time, clear skies!

What aperture costs

Just for the heck of it, I decided to find out which telescopes are the best deals in terms of light grasp. My comparison group consists of widely available commercial dobsonian reflectors ranging from 3″ to 16″ in aperture. Sometimes I included two models at the same aperture to show the effect of differing features, like the finder scope and better eyepieces on the Orion Funscope versus the Celestron Firstscope, or the collapsing truss-tube design on the Meade Lightbridge scopes. Prices are street, not list, as of this writing. Each entry follows this layout:

Brand Model – mirror diameter (mm) – mirror area (in^2) – price – cost per in^2

Celestron Firstscope – 76mm – 7.065 in^2 – $38 – $5.38/in^2

Orion Funscope – 76mm – 7.065 in^2 – $50 – $7.08/in^2

Orion SkyScanner – 100mm – 12.56 in^2 – $100 – $7.96/in^2

Orion StarBlast 4.5 – 114mm – 15.89 in^2 – $200 – $12.59/in^2

Bushnell Ares 5 – 127mm – 19.63 in^2 – $165 – $8.41/in^2

Orion StarBlast 6 – 150mm – 28.26 in^2 – $280 – $9.91/in^2

Orion XT6 – 150mm – 28.26 in^2 – $280 – $9.91/in^2

Orion XT8 – 200mm – 50.24 in^2 – $350 – $6.97/in^2

Orion XT10 – 250mm – 78.5 in^2 – $580 – $7.39/in^2

Meade 10″ Lightbridge – 250mm – 78.5 in^2 – $700 – $8.92/in^2

Meade 12″ Lightbridge – 300mm – 113 in^2 – $1000 – $8.85/in^2

Orion XT12i – 300mm – 113 in^2 – $1100 – $9.73/in^2

Orion XX14i – 350mm – 154 in^2 – $1700 – $11.04/in^2

Meade 16″ Lightbridge – 400mm – 200 in^2 – $2000 – $10.00/in^2

Interestingly, there are two low points where the price dips below eight bucks per square inch: at the low end, with the 3″ scopes, and in the middle, with the 8″ and 10″ solid-tube dobs. It’s also interesting to note that the StarBlast 4.5, which is an extremely popular scope, is the most expensive in this group in terms of cost per square inch.

I only included dobs because everything else is more expensive–tripod-mounted Newtonians, catadioptrics, and refractors alike. Here are some comparative costs for beginner instruments of those other designs; for fairness, I only picked models with mounts included.

Orion SpaceProbe 3 Alt-Az (reflector) – 76mm – 7.065 in^2 – $100 – $14.15/in^2

Orion GoScope 80 (refractor) – 80mm – 7.74 in^2 – $100 – $12.92/in^2

Orion StarMax 90 Tabletop (catadioptric) – 90mm – 9.85 in^2 – $200 – $20.30/in^2

The difference here is that there is no mid-aperture dip as there is for the dobs, or if there is, it doesn’t bring the price per square inch near the $10 mark, let alone under it. Indeed, one would be hard-pressed to find a new, high quality 4″ achromatic refractor for less than $300-400, which is up in the neighborhood of $30/in^2. Similar prices obtain for mounted 5″ Maks and 8″ SCTs. That’s why I didn’t bother to account for the effect of the central obstructions in calculating the costs of the reflectors and catadioptrics; even what seem to be large secondary obstructions are usually less than 10% of the total collecting area, and dobs cost anywhere from a half to a fifth as much as other popular, “everyman’s” scopes in terms of collecting area.

Now,  I’m not saying that dobs are objectively superior to other scope designs. They’re cheaper. We all knew that, I’ve just quantified it, snapshot style, using currently available models and prices. I did it because I had a gut feeling that 8″ and 10″ solid-tube dobs were in sort of a sweet spot, price-wise, and that actual costs (per square inch of collecting area) rose a bit on either side. And they do.

Finally, these numbers put some classic deals into perspective. When the SkyWatcher 130N was on sale for $100, its cost was just a hair over five bucks per square inch–better than any of the models listed above by a considerable margin. The SkyWatcher 70AR was at one point selling for $36 shipped, or just a hair rover six bucks–a bit more expensive, per square inch, than the Celestron Firstscope, but for a much more capable instrument. I think the  only refractor deal in history that has ever equalled that was the Galileoscope. With 50mm of aperture and an introductory price of $15, it was originally selling for $4.78/in^2, but that was without a mount. Similarly, the value of buying used is now apparent–when I got my XT10 for $350, that was a cost per square inch of $4.46, much less than any of the new scopes, even the cheapies.

What should you buy? That’s a more complicated question, and it can only be answered by reference to your situation and your observing goals. I own a mid-sized Mak because sometimes it’s nice to have 5″ of light grasp in a package a foot long, and I bought it new because sometimes it’s nice to have something fresh off the line. But if you’re interested in deep-sky work, where every photon counts, and you’re on a budget, then you might find the numbers above useful in considering which scope will give you the most bang for your buck, or for evaluating future scopes.

Why you want as much aperture as you can get is the subject of the next post–and for a contrary view, see this post.

Gear reports: Explore Scientific eyepieces, Orion Apex 127 Mak, Celestron Travel Scope 70

Apex 127 (left) and Travel Scope 70 (right) under dark skies on Mount Baldy. The Apex is on a SkyWatcher AZ4 mount, and the TS70 is on a Manfrotto CXPRO4 with a Universal Astronomics DwarfStar alt-az head. Photo by Terry Nakazono.

As promised in the last post, here are my thoughts on the scopes and charts I used up on Mount Baldy Saturday night. I haven’t had half of this stuff long enough for these to be considered true reviews, so I’m calling them “gear reports”.

Explore Scientific eyepieces–For  a long time my workhorse eyepieces have been 32mm and 12mm Plossls and the 6mm Expanse. The 24mm ES68 gives the same true field as the 32mm Plossl but with higher magnification and a larger apparent field–68 degrees versus 52. The 14mm and 8.8mm ES82s give me a nice pair of mid-to-high power options, without taking business away from the 6mm Expanse.

How important is all that apparent field of view? I’ve also had the opportunity recently to look through a few TeleVue Ethos 100-degree eyepieces, and here are my impressions.

• Ethos: I could not quite see all of the field of view at once. I had to actually move my head around to see the field stop. It was nice–when I first looked in the eyepiece, at what was in the middle of the field, I could not immediately see the field stop in any direction. It actually was like looking through a window into space. I can see why people shell out big bucks for this experience (think $600 and up for the TeleVue Ethos models and $400 and up for the other brands).
• ES82: I can see all of the field and the field stop at once, but it is so far out to the edge of my field of view that I am not really aware of it. Very comfortable, too, in terms of eye placement and eye relief.
• ES68 and Orion Expanse (66-degree apparent field): ditto. For me, the jump from 52 degrees to 66 or 68 degrees is much more noticeable than the jump from the sixties up to 82–or back. I never went from one of the 82s to one of the sixties and thought, “oh, hey, where did my extra field go?”, which definitely does happen when I go directly from a widefield to a Plossl. My only explanation is that, at least for me, 66-68 degrees is over a threshold where additional apparent field makes little difference, until the I-can’t-see-it-all-at-once threshold I get with the Ethos.
• Plossls (52-degree apparent field): I like Plossls. They’re good, solid workhorse eyepieces, that can handle a wide range of focal ratios and tend to be sharp and have good light throughput. They were my go-to eyepieces for years. But, like many, many stargazers before me, I am spoiled now. The fact is, after using 66-82 degree eyepieces (I’ve had a pair of 68-degree Orion Stratuses for a couple of years, and just not used them much), going back to the Plossls is like being struck with tunnel vision: I am acutely aware that a lot of my visual real estate is occupied by non-sky inside-of-eyepiece black nothingness. That said, the effect really only jumps out at me when I swap a widefield for a Plossl back to back in the same scope. Saturday night I would be observing with widefields in the Apex and then wander over to the TS70 with the 32mm Plossl and not notice the sudden decrease in field. So I’m not getting rid of my Plossls anytime soon. For one thing, they all weigh much less than their widefield counterparts, and so play better in small scopes and travel kits.

By the way, if you’re in the market for budget Plossls and Expanse clones, check out the Black Knight Super Plossls and Enhanced Super-Wides at OWL Astronomy.

Apex 127–Under dark skies, a potent deep-sky instrument. Its maximum true field of just a bit over a degree will frame almost all deep sky objects, except for the very closest open clusters (like the Pleiades and Hyades). Everything I tried for, I found–my problems with the two open clusters were not that I could not see them, but that I could tell exactly what parts of the rich Milky Way starfields were supposed to be the clusters–more on this farther down. It’s also a planet-killer and excellent double-star scope. One night this spring I was trying to split a particularly tough double with this scope. It refused to budge at 257x, so I Barlowed my 6mm expanse to give 514x, and finally saw that stripe of black sky between the two stars. That’s about 100x per inch of aperture, or twice the rule-of-thumb “maximum effective magnification” of 50x per inch. Which means it’s a damn fine scope.

Travel Scope 70–Four things about this scope, three good, and one not so good. The good stuff first.

• It costs next to nothing. As I’ve pointed out in other posts, you can’t buy a 9×50 right-angle correct-image finder for what they’re charging for this scope.
• It’s small and light. I think it would ride on the same tripod as my SV50 and the scope itself takes up hardly any more room, but 70mm gathers roughly twice as much light as 50mm (5*5=25, 7*7=49). It has the same focal length as the venerable Short Tube 80 but weighs about half as much. You could think of it as a Short Tube 70, but its focal ratio of 5.7 is a hair more forgiving. That combined with the slightly smaller aperture should knock down the chromatic aberration a bit, compared to the ST80, and indeed I’ve found the CA unnoticeable in casual use, even on the moon and  planets (that is, I’m sure it’s there if one goes hunting, but it’s never risen to the level of attracting my attention at the eyepiece).
• The optics are wonderfully clear. The low-power views are really bright and contrasty. I noticed this the first night I had the scope. I was cruising the summer Milky Way from my driveway, trying the 12.5x view with the 32mm Plossl for the first time. Now, Lyra was dead overhead, and atmospheric problems are almost always minimized at the zenith, but still, the view was bright, and I found the Ring Nebula, M57, right away. I thought “No way, there’s just no way the Ring is that easy at 12.5x. Must be an out-of-focus star.” So I started working my way up in magnification, and sure enough, it was the Ring after all. I noticed the same thing again Saturday night. I couldn’t see much detail on most of the Messier objects at that magnification, but they just jumped out of the background starfields, even the smaller ones. If you like low-power scanning, this scope is a blast under dark skies and still a fun ride even under so-so skies.

Now, the not-so-hot:

• It’s hard to push the magnification, and I don’t like the result when I do. A 12mm eyepiece gives 128x in the Apex 127, 108x in the 90mm Mak, and 100x in the XT10, but only 33x in this  scope. A 6mm eyepiece gets you to 67x, but it ain’t worf it. The scope starts to pant around 40x and anything north of 60x is just bad. I noticed this the first night out, looking at Saturn and the moon, and it was still true this weekend. I don’t know if its astigmatism or poor collimation or what, but trying to achieve focus on planets is maddening. Jupiter goes from a vertical fan of red light on one side of focus to a horizontal fan of blue light on the other, and only sort of flirts with being a clean disk in between those extremes, at an infinitesimally tiny point that the rack-and-pinion focuser tends to shoot right past. It’s actually really puzzling to me that a scope that gives such clear, contrasty images at low power goes to crap so fast as the magnification goes up. (In case you’re wondering, we used exclusively low-power eyepieces with this scope for the Venus transit.)

So in the end the TS70 is kind of a one-trick pony. It is awesome for scanning around at low power and surfing the Milky Way. That’s the one thing it can do that neither of my Maks can. But unless you get a much better sample than I did, forget about doing any serious work at even moderate magnifications. The 90mm Mak is a much more versatile tool–it can do almost everything except widefield scanning. So at least the two small scopes complement each other.

Actually the awesome low-power views of the TS70 have inspired me. A small ED refractor like the Astro-Tech AT72ED ought to give equally good low-power views and be able to take magnification well, and could potentially put both the TS70 and the 90mm Mak out of business. I don’t know if it actually will, but I aim to find out. So I think one of those will be my next big astro purchase–once I save up for it.

In the meantime, since the TS70 performs like a superfinder anyway, I’m going to keep scheming on how to turn it into one. I’d love to have it mounted side-by-side with the Apex 127, so I’d have a rich-field scope and a planet-killer on the same mount.

Pocket Sky Atlas–Since I started out in astronomy, the PSA has been essentially the only atlas I’ve used. It has stars down to magnitude 7.6 and about 1600 deep-sky objects. That includes all the Messiers, all the Caldwells, and all the Herschel 400s, plus another thousand or so, so it’s covered my needs and then some. The only time I’ve printed up my own finder charts has been for hunting quasars. I haven’t felt the need to move up to a “deeper” atlas until very recently.

I started thinking about a deeper atlas after observing with Terry Nakazono last month. His most-used atlas is the Observer’s Sky Atlas, which covers the whole sky to mag 6 but also has enlarged charts to mag 9 for finding 250 deep sky objects, including all the Messiers. He also prints out detailed finder charts from the Tri-Atlas (a huge free atlas in three versions: mag 9, 11, and 13). He was surprised that I’ve gotten along as well as I have with just the PSA.

Part of the difference in preference probably has to do with the instruments that we use and how we get on target. Terry’s most-used scope is the SkyScanner 100, which has a red-dot finder. So he gets in the neighborhood–or closer, sometimes you can really bullseye things with an RDF–with the dot finder and then star-hops to his targets at the eyepiece. In contrast, I use a 9×50 RACI finder on whatever scope I am observing with (I only have one, and just move it around among scopes), and do almost all of my star-hopping with the finder alone. The 50mm finder does not go nearly as deep as the 100mm reflector–it simply shows fewer stars–so I often use the geometrical method of centering the finder on an unseen target (this is detailed by Harvard Pennington in The Year-Round Messier Marathon Field Guide and by Stephen Saber in his post on “sharpshooting” deep-sky objects–search for it here). I hadn’t given this much thought before Terry brought it up, but my less-deep atlas suits my finder-driven navigation, whereas eyepiece starhopping really requires that you be able to see as many charted stars as possible to keep from getting lost. So we have each gravitated toward the atlas that best suits our observing style–or rather, I started with PSA and never had a reason to gravitate away.

Until now, that is. The problem is not that the PSA doesn’t show enough deep-sky objects. I’ve only seen about a fifth of its 1600 plotted DSOs. The problem, as Terry pointed out, is that it just doesn’t show enough stars, at least for some problems. In trying to track down some of those small open clusters in Cygnus and Cassiopeia, I found that the plotted symbol in the PSA covered a good-sized field that was striped and mottled with star chains and asterisms of the summer Milky Way. The geometrical relationships shown in the PSA just weren’t enough. I couldn’t go to “the” cluster of stars that made an equilateral triangle (or whatever) with the nearest guide stars, because there half a dozen plausible candidates (actually, this might be a not-enough-DSOs plotted problem as well as a not-enough-stars problem). I need to see some of the fainter stars in between plotted on the chart, to break up those rich starfields into manageable–and interpretable–chunks.

So, to make a long story short, I ordered the first volume of Uranometria 2000.0, a mag 9 atlas, and I’ll get the other two volumes as funds allow. Stay tuned.

More low-cost solar observing

In preparation for the transit of Venus tomorrow, I did a little hacking and tinkering late this afternoon. Although the sun funnel worked well enough for watching the eclipse, as we’ll see below it is not perfect for photographing the sun in any detail. My full-aperture solar filter still hasn’t arrived, but I got to thinking about how to make a safe direct viewing setup.

I recently acquired a Celestron Travel Scope 70, a little 70mm (2.75 inch) f/5.7 achromatic refractor. Like a lot of small refractors, the dust cap for the objective lens has a smaller removable cap in the middle, in case you want to stop down the scope for more pleasant viewing of bright targets like the full moon. The diameter of the small hole in the middle of the big cap is 40mm, so with big cap on but the small cap off, the scope functions as a 40mm f/10.

I don’t have any loose solar film to make a 70mm solar filter or even a 40mm solar filter. But I do have a stack of eclipse glasses, each of which has two 1×1.5 inch eye holes covered with solar film. So I cut one of the eclipse glasses in half, made a round 25mm aperture in a square piece of cardboard, and mounted the eclipse glasses ‘lens’ (solar film still surrounded by two sheets of thin cardboard) and the 25mm aperture stop on the back side of the big dust cap. I didn’t think to take any pictures of the inside of the dust cap to show how it all goes together, but hopefully the general idea is clear enough. With the big dust cap on and the small dust cap off, the scope admits a 25mm beam of fully solar-filtered light to the objective, turning the scope into a 25mm f/16 solar refractor. And because the solar filter is on the inside of the big dust cap and protected by the small dust cap (in front) and the second piece of cardboard with the 25mm aperture stop (behind), I can leave it in all the time. Take the big dust cap off, the scope functions normally. Take only the small one off, I’ve got a 1-inch solar scope.

Two other design decisions to note. First, the finder–and I use the term advisedly–that came with this scope is without doubt the worst finder I have ever seen on a commercial scope from a brand name manufacturer. It looks like a 5×20 straight-through magnifying finder. However, right behind the (single, plastic) objective lens is an aperture stop with only a 1-cm hole in the middle. So in fact it’s a 5×10 finder with a plastic singlet objective. The immense irony is that the scope doesn’t need a finder at all; throw in a 32mm Plossl and you get 12.5x and 4-degree true field of view, so the scope effectively functions as its own superfinder. So I unscrewed both ends of the finder and dumped out all the plastic optics, turning it into a hollow sight tube. Why is this important right now? Because it’s really dumb to leave a magnifying finder on a telescope being used for solar observing; it’s too easy to forget what you’re doing and accidentally looking through the unfiltered finder and cause serious eye damage or blindness. There’s a good reason that every commercial telescope comes with a “don’t point the scope at the sun, dummy” tag or sticker or both. This is not something to mess around with. If you’re going to observe the sun with a telescope, cultivate the same habits of awareness and deliberate action that you would use around loaded firearms and power saws.

Oh, the included 45-degree prism diagonal is also rubbish and the light tripod looks pretty dodgy. Today I used my standard small-scope setup–an AstroTech 90-degree dielectric star diagonal and a Universal Astronomics DwarfStar alt-az head on a Bogen/Manfrotto tripod–and I’ll doubtless do the same in the future.

The other design thing was the sun shield. At first I tried going without but look into a dark eyepiece to catch a filtered (= comparatively dim) view of the filtered sun while unfiltered sunlight was hitting the top of my head and my upper eyelid had me squinting and developing a minor headache almost immediately. The plastic dewshield on this scope pulls right off, so I got a handy piece of cardboard (part of the packaging of a picture frame), cut a hole just big enough to admit the front end of the scope without the dewshield, slid the cardboard sunshield on and used the plastic dew shield (and dust cap with solar filter) to hold it in place. I also cut a second, smaller hole to let light in to my sight tube sun finder.

If you do something similar, make sure that the sun shield can’t get blown off and take the solar filter with it. In my case, the dewshield slides on a long way and grips both the sun shield and telescope tube firmly; a strong enough breeze might upend the whole setup, but it couldn’t blow off just the shield and filter. Again, eye safety is paramount; don’t take any chances.

Okay, so how did it work in practice? Pretty darned well. I had already aligned the sight tube with the telescope, so all I had to do was rotate the sun shield a bit to make sure the second, smaller hole lined up with the sight tube. Then I could point the scope roughly at the sun and pan around until a perfectly round beam of sunlight (projected on my hand) emerged from the sight tube. That always put the sun in the field of view of a 25mm Plossl (16x, 3 degree true field of view). The view of the sun at the eyepiece was reasonably bright–for an astronomical object, not compared to the unfiltered sunlight streaming down all around–and razor-sharp. The sunspots with their umbrae (dark centers) and penumbrae (lighter borders) were striking, like they’d been etched on stained glass.

Happily, the filtered scope yielded nice, even light all over the surface of the sun, no matter where it roamed in the field of the view. My one beef with the sun funnel is that it can be hard to get really good photos because of the inherent granularity of the screen material. Inevitably some part of the projected sun is brighter than another, and if you manage to get the light perfectly centered, it can easily wipe out the sunspots. The best way I’ve found to avoid this flashlight-beam effect is to photograph the sun from a bit to the side, out of the direct path of the projected light (that’s how I got this very sharp photo), but then the sun is out of round–not ideal if you’re hoping to combine images into a composite or movie, or even get a nice, square-on shot of a circular sun.

For example, in the photo above the sunspots on the left are sharp enough–the big one even shows the umbra and penumbra clearly–but the dimmer two on the right are lost in the flashlight glow of the sun lighting up the screen material from behind. And in this view the sun is already way out of round.

Also note that this image is flipped horizontally compared with the image from the refractor. In fact, this image is correctly oriented. Normally Newtonian reflectors show things rotated by 180 degrees, but projecting the image on the screen undoes that and gets everything back to normal. The solar filter on the refractor just cuts down the intensity of the light, it does nothing to reorient the image, so the image at the eyepiece is right side up but, because of the 90-degree mirror, flipped left-to-right.

I didn’t go to all of this trouble just for the transit of Venus. I mean, I happily would have, had the transit been the only game in town. But it’s not–the Astronomical League has a Sunspotters observing program, and now that I have the gear for solar observing, I might as well start logging. I’ll keep you posted on that.

Now, I should point out that the flashlight-beam effect washing out the sunspots in the sun funnel is mostly a photographic concern. For visual appreciation, even solo, I think the sun funnel still wins. A 4-inch image scale and the ability to put your head and eyes wherever you want–and even wear polarized sunglasses to observe–can’t be beat. But for photography, I prefer the filtered direct view–even in a one-inch scope.

Fortunately I’ll be rolling with both tomorrow. Now if the weather just cooperates…

Guest post: Four-way diagonal comparison!

I’m happy to host another guest post (here’s his last one) by frequent commenter and indefatigable scope hacker David DeLano. In this one David compares four 90-degree diagonals: a high-end prism and mirror, and a low-end prism and mirror.

The Test Scope and Target

Here are pictures of the setup I used to test the diagonals.  But first, here’s the dovetail on spare ring that I made for my RDF.

Here is a picture of the target I shot.  It’s the AC unit in the middle of the picture.  This picture is taken at the same zoom level as I used for the pictures taken through the scope.

Here is the scope setup.

The Contenders

Here are the StellarVue prism diagonal on the left and the Astro-Tech mirror diagonal on the right.

Here are the generic diagonals, prism on the left (with SV helical focuser) and mirror on the right.

Here is a shot of the SV diag to show that it’s stopped down.  The generic has similar baffling.

The Camera Mount

Here are the parts to the camera setup, the part that fits onto the camera mount hole to give a T-thread, the barrel that holds the EP and provides a T-thread, and both together.

    

The Comparison

I used my 80AR on my AZ mount for this test.  I had to extend the legs all the way to get a decent target in sight, and then had to pull out my step stool to be able to see into the camera.  I used the bracket I have that puts a T-thread on my Sony P71.  I put a SkyWatcher 10mm Super Plossl into the barrel I have, and attached it to the T-thread.  I’m just not steady enough to shoot freehand like Matt does.  I picked an AC unit about a block away, and was shooting at 91x.  I could see heat waves, so took a couple pictures with each diagonal.  I had the camera set to macro, so the telescope was doing all the focusing.  I still found it very difficult to get a decent focus on my LCD screen, and it shows in the pictures.  I shot the pictures to get email versions, but have the full versions for closer examination.  I tried to use the same zoom for each picture, though one set is one setting wider.  I used the timer on my camera so that I wasn’t touching anything when the picture was taken.

The prisms are on top, the mirrors on the bottom, the generic versions on the right, and a diagonal-less shot at the end.  It was a lot more difficult to get the straight shot, believe it or not, and I didn’t realize that it had drooped on me as much as it did.  The collage is from the full sized pictures, reduced by 50%. I can zoom in and inspect specific data on the originals, but it really only tells me that there was a light breeze blowing.  I took at least two pictures from each setup and took the best picture.

I still have the same conclusions.  The generic prism is the worst, but probably not as bad as the one Matt has.  Definitely good enough for a finder or lower power viewing.  The A-T is slightly brighter, but note that it’s a little less bright than straight through.  The generic mirror holds its own, and I don’t think anyone would be disappointed using it.  That is the main message here for the posters that didn’t want to buy the A-T but wondered if a generic mirror was good enough – it is.

I think this convinces me that I’m not losing much with my SV prism, but it also shows me that I should give the A-T a decent shot in the 80AR.  Zooming in on the pictures, I can almost read some of the tags in the A-T shot (though the text is backwards), but I can also see purple edges with the A-T that aren’t there with the SV.  People disagree with Vic [Maris, of StellarVue] that their prism takes out some CA, but these pictures would say that he’s right (and I’ve not heard an explanation as to why it reduces CA).

An interesting note…..there is a seam on the electrical box going down the middle of the edge.  On all these shots, I used that to focus on, to be as consistent as possible.  It was definitely there in the camera LCD.  You can’t see it very much at all in any of the pictures.

Conclusions

Well, this isn’t quite what I expected.  I’m guessing my ability to focus is a variable that needs to be removed.  But, I’d be happy with any of these, with the generic prism coming in last.  If your prism is of worse quality, I can see you not wanting to use it.  But the SV appears to hold its own, and knocks down some of the CA (which it is rumored to do – I won’t say advertised).  The A-T is definitely a brighter view, and I look forward to getting it out under the stars to see how it does.  For those worried about a generic mirror, it holds its own.  My guess is that I spent $15-20 for this one and it’s the one I started with several years ago.

BTW, I have a third prism that I didn’t test.  I have an Orion brand in the GS.  It too is stopped down more than a mirror.  I’m guessing that stopping down an underperforming prism would help with the reflections.

Going dark for a while

Hey folks,

I am sorry to say that I will probably be around much less frequently for the next two or three months. I have severely overcommitted myself this spring and for the next few weeks I have to pay a succession of pipers. I hope I can find little spaces here and there to post. I will certainly try, but no promises.

In the meantime, I’m happy to see that comment-thread conversations are rolling along just fine without me. I hate to take off when it feels like things are really hopping around here, but that’s the shape of life right now.

Before I go, here’s how David DeLano put his GalileoScope on his SkyWatcher 114N OTA as a superfinder, which itself has a red-dot finder. David was already working on this before I posted about homebrew finders, so I can’t claim any inspirational credit, it’s just a nice example using, in this case, some commercial rings David found on sale.

See you in the future!

Thinking about cheap finders–and cheap finder mounts

This all started because Orion’s Maks are “wrong-handed” for their VersaGo II alt-az mount. Here, I’ll show you what I mean. Here’s my Apex 127 on the VersaGo II.

If the scope is sitting on its dovetail bar, the dovetail shoe for the finderscope is on the left side of the scope, at about 10:30 (viewed from the eyepiece end). So when the scope is mounted sidesaddle on the VersaGo II, where the dovetail faces left, the finder ends up at about 7:30. The eyepiece of the finderscope is a bit below the eyepiece of the main scope (the effect is exaggerated in this picture, which was taken looking down at the mount). This isn’t terribly inconvenient, it just looks weird, and it can cause some slight balance problems when the scope is aimed up high.

What I’d like is to have the finder sticking straight out sideways from the scope. That way the eyepieces would be at the same height, and the altitude axis of the mount would run through the centers of mass of both scopes so there would be no balance problems. I could achieve that by moving either the dovetail shoe for the finder or the main dovetail rail, but that would require drilling holes in the scope and I’m not willing to do that. A better solution is just to get some tube rings, so I can orient the scope and the finder shoe however I want.

Thinking about that led me to think about how nice it would be to have a small refractor mounted alongside the 5″ Mak. Something in the 70-80mm range could function as both a “superfinder” and rich-field telescope, so on one mount I’d have a low-power, widefield scope and a planet-killer.

Stellarvue sells an 80mm superfinder that some folks use as a stand-alone rich-field and spotting scope, but that runs something like $250. I’m sure it’s nice, Stellarvue gear is top notch, but as always I am interested in less expensive options. Celestron’s Travel Scope 70 is not much smaller,  it’s gotten generally good reviews (at CN, for example), and it can be found for $60-80 (the Amazon price fluctuates a lot, but other vendors usually have it for $60). That would work for a finder, but I’d have to mount it somehow. I could just buy some mounting rings, but adjustable mounting rings for a 70mm scope would cost more than the scope itself. There has to be a better way.

So that’s the first thread: moving up from a 50mm finder without breaking the bank.

The other issue is that I have several scopes that I use regularly, and only one 9×50 RACI finder. So I keep moving the finder around, and this is kind of a pain, because I have to realign it for every scope. It would be nice to just park it on one scope, but that means I’d need finders for the other scopes. As before, I could just buy some more RACI finders, but the 6×30 models are about $60 and the 9x50s, which I really prefer, are $90 or more.

Now, I could build my own finder. I have spare 50mm objectives from some cheap binoculars, and I have an erecting prism diagonal, and I could build the tube out of plumbing parts. But that still leaves the problem of mounting, and as before, the mounting rings would set me back almost as much as a new finder anyway.

That’s the second thread: adding 50mm finders without breaking the bank.

It’s been a while since I’ve bought a new finder, and I have to admit that the prices kind of took me aback. I can’t shake the thought that the Celestron Travel Scope 50 runs about $45 and the Travelscope 70 is $60. If only I could find some way to mount them, I could have easily focusable luxury finders for less than new RACIs of smaller aperture! And that’s really the rub in both of the threads of thought outlined above: building a finder-quality scope is not hard. Mounting it solidly, reliably, and conveniently is hard. Part of what you pay for in a commercial finder is a sturdy, easily-adjustable finder stalk with a standard dovetail foot.

Well, what if I built my own finder stalk?

There are examples out there. My favorite, because they look easy to fabricate, are what I call the “half-pipe” mounts that consist of two half-cylinders mounted back to back. Here are a couple from the “Frugal Astronomer” thread on CN:

This one is by CN user Grendel, and is made from cardboard tube–as is the finder, as shown in this post.

I think this one is from the same thread, but derned if I can find the original post now. Anyway, it’s not my photo, I’ll credit it properly if I figure out where I found it,  if it’s yours please chime in, etc. The nice thing about this one is that it’s easily adjustable, thanks to the combination of thumbscrews through the half-pipe and rubber bands pulling the finder against them. Note the zip ties holding the half-pipe mount to the main scope.

So these got me thinking about the possibilities of the half-pipe mount. Here are some sketches I knocked up in GIMP.

The one at the top is simplest, just a V-slot, essentially the same as in the previous photo. The finder would have to be held in with rubber bands, elastic, velcro straps, or zip ties. Alignment could be done with bolts (you could either tap threaded holes or drill simple holes and epoxy nuts on the outside) or shims.

At lower left everything is the same except a trough has been added to cradle the finder, which might make it easier to use. I don’t know that, obviously, just kicking ideas around here.

At lower right is a full ring holder. I figured, if you’re putting alignment bolts through anyway, just make two more holes and you’ve got a six-bolt alignment system just like on the commercial rings (see an example in the photos here).

The key thing isn’t finder alignment, though, since even rubber bands and shims would work there. The key thing is convenient and repeatable mounting and unmounting to the OTA. I got to thinking: with an inverted V-shaped foot, like all of these have, is there any reason it coulnd’t be cut and sanded to fit into the existing dovetail shoes, so that the dovetail retaining screw tightens on one side of the inverted V? If that could be made to work, this kind of finder base could be mounted and unmounted and moved between scopes just as conveniently as one of the commercial jobs.

The end of all of this thinking? I got a piece of ABS pipe when I was at the hardware store to get parts for my sun funnel. I’m going to play around and see what I can come up with. If I find a workable solution, I’ll post it.

Reading PDFs on the Kindle

About three weeks ago Vicki and I traded Kindles, as combination late anniversary/early Christmas presents. She’d gotten hooked on e-books using the free Kindle app on her Droid smartphone, and wanted to get something dedicated.

I’d been skeptical about e-readers for a long time. I’m a book guy; the second-best job I ever had was working in a used book store. I like curling up with books. I doubted that an another Damned Machine (the usual appellation for the electronic devices in my life) could offer the same cuddliness.

Well, I’m a believer now. The Kindle is lighter than hardbacks and even lighter than some paperbacks (I’m lookin’ at you, swollen fantasy epics), and a lot easier to read one-handed than either one. I topped up the charge when I got it, and it’s still at about a quarter of a tank three weeks later, so the promised month of battery life looks legit. I’ve taken it to the park and read in full sunlight, and it looked even better.

It is such a nice piece of kit that I have actually found myself reading more than I did before. At first I wondered if this was just infatuation with the new toy. But it’s been three weeks and I’m not only still reading more, period, but also more kinds of things. Right now on the Kindle I have:

• about a dozen of my favorite essays, copied from the web into Word docs and sent to my Kindle wirelessly (and freely) using its dedicated e-mail address;
• about 30 short stories, most of which I haven’t read, courtesy of Tor.com and Cory Doctorow (also free);
• a whole shedload of classic literature from the Kindle store, from the Bible to the Origin of Species (yes, I value them both) to G.K. Chesterton’s The Man Who Was Thursday to The Adventures of Sherlock Holmes to the first five novels in Edgar Rice Burroughs’ Barsoom series (also free);
• and a handful of paid-for novels that I really desired.

The Kindle is so small that my default now is to just take it wherever I go, and then if the mood strikes, I have a whole range of things on hand to choose from. I don’t have to decide in advance whether to take a book along, or which book to take; to a first approximation, whatever I might want to read, I have with me just about all the time.

One thing I haven’t put much of on the Kindle yet is PDFs. As a scientist I both produce (a little) and consume (a LOT) of scientific literature, and almost all of it these days is in the form of PDFs. Unfortunately the Kindle is not going to replace the PDF vault on my hard drive, or even a good fraction of it. I have something like 20 gigs of paleontology papers in PDF form on my laptop, and the Kindle has about 3 gigs of user-available space, so if I want to take it all with me I’m going to have to wait a couple of hardware generations (at least). Taking it all with me is attractive because I never know when I’m going to be in a museum basement, looking at the vertebrae of some weird dinosaur, and have a sudden and quite desperate need for a paper on Apatosaurus or Dicraeosaurus or whatnot.

For this very reason, my friend, colleague, and frequent commenter Mike Taylor asked me to test-drive a PDF on my Kindle. Thanks to some dumb rules at Amazon, he has a shedload of Amazon.com credit that is useless at Amazon.co.uk, and a Kindle would be a convenient and possibly useful way to dump some of it. So I loaded up the 2007 paper in which he and Darren Naish described the new dinosaur Xenoposeidon, and took it for a spin. The rest of this post is basically copied and pasted from what I reported back to Mike.

It works surprisingly well. Just opening the PDF gives one entire page per screen. At that scale I have no problem making out the text, but it’s too small to be comfortable. The screen is 6″ on the diagonal, so that’s no surprise, and I don’t regard it as being either a pro or a con. The device is what it is.

Adjacent to the space bar is a button with two capital As, one larger than the other, that controls page size, contrast, and screen rotation (for PDFs; with Kindle format docs you can also choose among 3 typesets, 3 line spacings, more or fewer words per line [independent of font size], and text-to-speech [wherein the device will read to you if you have headphones on]). Page size options include fit-to-screen (the default), 150%, 200%, 300%, and actual size. Going to 150% lets me get a bit over half a page on the screen at once, so I can see a whole page with four clicks in portrait view, or just two, I’d reckon, in landscape view.  I set it to ‘actual size’ which turns out not to be far off of 150% and had a good close look at the specimen photos. Resolution was fine. I noticed some pixellation so I opened up the PDF to compare, and the pixellation I noticed on the Kindle is just what’s present in the PDF, and nothing worse. The one downcheck here is that the Kindle screen background is not white but a very subdued gray. I imagine that this is deliberate, to prevent eyestrain during marathon reading sessions, but it does noticeably decrease the contrast range for photographs.

Final analysis: (1) using the clicker button to navigate around on a zoomed in page is slightly less invisible than using a mouse, but only slightly, and I’ve only done the former for about 30 seconds so the device might disappear more from my notice with longer use; and (2) the contrast range is reduced which sucks some of the life (and information) out of illustrations.

Other than that, based on my exhaustive 5-minute trial, the Kindle makes an acceptable PDF reader. You couldn’t tote your entire collection, but you could load it up with a gig or two of stuff you’d most likely need on any given trip.

Getting back to books–and to the stated purpose of this blog–the Kindle is kind of a dead end, astronomically speaking. Few astro books are available, and astronomy is a very visual thing but most Kindle versions (of everything) have the illustrations stripped out. There are a couple of compilations of star maps but these terrible reviews. I did find a handful of older astro books–as in, 19th and early 20th century–but I haven’t had the inclination to check them out yet. If anything good turns up, I’ll let you know.

Telescope tradeoff: aperture vs portability

In a comment on the last post, Jon Lindberg brought up some good points about the aperture/portability tradeoff with telescopes. It’s fertile ground for discussion, because there is always a tradeoff.

The big up-front ground rule for this discussion is that when it comes to portability, your mileage may vary. Some people consider 8″ or even 10″ scopes to be “grab-n-go”. For me, scopes break roughly into two categories: those that require one hand and one trip–my definition of grab-n-go–and those that require some more setup, either two hands or multiple trips or other fiddling. And at any given time, there is only one scope in each category that I’m using heavily.

Right now my big gun is a 10″ Orion dob. It weighs about 55 lbs assembled, which is about half in the tube and half in the base. I can move it while it’s assembled, but usually not without having a few twinges in my back the next day. So I usually carry the base to where it’s going to be set up, then put the tube on, then set up  some kind of  chair next to the eyepiece. Including a trip for my eyepiece case and some charts, it’s usually about four trips. But that’s okay, because I only tend to set it up when I’ve got some serious observing to do, or when I want to impress houseguests.

My old “big gun” was my first telescope, a 6″ Orion dob. It weighs about 33 lbs assembled, and I always carry it out in one piece. But it lives out in the garage with the 10″ and also requires a chair, so I’m still making two or three trips to get it set up. If I’m going to go to that much effort, I might as well get out the 10″ and get the benefit of nearly three times the light-gathering ability and almost twice the angular resolution. So I’ve barely used the 6″ at all since I got the 10″.

The 6″ is also facing competition from the other end, from my 5″ Skywatcher reflector on a homemade Dob mount. That one weighs just under 20 pounds and is short enough that I can use it sitting on the ground, so it’s more grab-n-go-able and still delivers most of the performance of the 6″ scope.

One of the lessons of all of this might be that I have too many telescopes. The more broadly applicable point is that the goodness or badness of a telescope for any particular application depends on what else you’ve got in the stable. When I only had one telescope, it was of necessity both my big gun and my grab-n-go scope. But my enthusiasm for hauling out a 30 lb scope on short notice declined markedly when I had something under 10 lbs to use for quick peeks.

But let’s get on to the meat of Jon’s question, which I am going to interpret as, at what point as you go down in aperture do you start noticing the compromises?

Again, the answer will be different for different observers. Some people think that anything smaller than 8″ is a waste of time. Obviously I disagree. I think that the vast majority of observers would say that a 3.5″-4″ telescope is probably at a threshold between noticeable compromise and being to see most familiar targets–moon, planets, Messier objects, the occasional comet–with rewarding vibrancy and detail. I base that in part on the massive commercial success of 90mm Maksutovs and 4″ refractors, especially apochromats. Also, some of the best deep-sky observers in the world like Stephen O’Meara and Sue French use 4″ refractors as their primary scopes.

That’s not to say that smaller telescopes aren’t popular as well. Refractors in the range of 60-80mm have always sold well and probably always will, especially short focal length, widefield scopes like Orion’s ShortTube 80 (pictured above). And you can have a lot fun pushing these little scopes to their limits, as Jay Reynolds Freeman did when he completed the Herchel 400 with a 55mm scope. But achievements like that get noticed because nobody expects to be doing serious deep-sky work with a tiny telescope. Sub-3″ scopes are almost always intended to be either introductory-level instruments or purpose-built grab-n-go and travel scopes.

So what’s the real word? My little SV50 is well into the realm of trading away performance for portability. So far it has shown every Messier object I’ve tried for, but all but the biggest and brightest have been faint fuzzies at the eyepiece, without a great deal of detail. And a scope that small absolutely requires dark skies to do any meaningful deep-sky work. Here in town it just doesn’t have the horsepower to cut through the light pollution. But that’s okay, because I didn’t get it to use here in town. I got it mainly for airline travel, and if I’m flying, it’s usually to someplace darker than the LA area, so it fills its very specialized niche admirably.

One thing that the little scope excels at is putting a truckload of stars in my eyes. Bigger scopes with longer focal lengths have smaller fields of view, that’s just an inescapable fact of optics. I’ve noticed that when I’m using bigger scopes I’m usually hunting for particular targets. With the SV50 I have a lot of fun just panning around the sky. It is the only scope that I have used that delivers the same super-wide field of binoculars, but with the advantages of being solidly and comfortably mounted (image crouching behind a pair of  mounted binoculars when they’re pointed at a target more than 45 degrees above the horizon) and having variable magnification.

For a little more than double the weight and volume, the C90 is still very portable and delivers a LOT more light and a LOT more detail. But for me it has two distinct disadvantages compared to the SV50. First, it’s just big and heavy enough to require a bigger tripod, so the whole kit-and-kaboodle won’t fit into a tiny bag that I can stuff into the bottom third of my backpack. So if I’m traveling with it, it becomes one of the focuses of my packing, instead of something I just shove in the bag and forget about until I reach my destination. Also, the folded light path gives the C90 a very long focal length for its size–900 mm–which makes reaching high powers a breeze. That makes it easy to power up on planets and specific deep-sky targets, but it also means that the scope has a fairly narrow field of view. So my mindset when I’m using it is more along the lines of, “what individual small thing am I going to look at next”, and not, “let me pan around the sky and see what I stumble across”. If you want the latter experience in a more capable scope than the SV50 that still only weighs about 5 lbs and is eminently airline portable, consider a Short Tube 80.

If you’ve got a little more space and don’t mind a little more weight, a 4″ Mak or a 5″-6″ Schmidt-Cassegrain will put a lot of aperture into a decently small space. Something like a Celestron C5 is about the size of a big coffee can but gives you enough light grasp and resolution to go after just about anything you want, especially if you have dark skies. The caveat I’ll add from my own bitter experience is that at this size of scope you have to put as much or more thought into the mount. When I got my first Mak, a 4″, I put it on a cheapo camera tripod from Wal-Mart. That was a disaster–the mount was so shaky that using the scope was an exercise in almost terminal frustration. Moving down to a 90mm scope didn’t really help, and my little scopes didn’t get much use until I got a decent tripod. And by “decent” I mean “costing as much or more than the telescope itself”.

I brought up the Short Tube 80 and all of the catadioptric scopes (Maksutov-Cassegrains and Schmidt-Cassegrains) first because they’re probably the most airline-portable of the bigger scopes. If portability is important but you don’t plan on flying with the scope, at least not regularly, the Orion StarBlast 4.5 and Edmund Astroscan both put some serious aperture into a one-hand telescope. Both are bulkier than a 5″-6″ SCT, but in both cases the bulk includes a base so you don’t have to worry about buying a separate mount and tripod (although you may want something, even a picnic table, to get them up off the ground). The StarBlast has better optics and a better focuser, but the Astroscan is almost indestrucible. As with any optics purchase, read around to find out the good and bad about them both before you make any decisions. The links to telescope reviews on the sidebar are good places to start.

Most telescopes are made in China and Taiwan these days, and the same models that are sold by Orion and Celestron in the US are usually available from SkyWatcher or Konus in the rest of the world. Happily, just about all of the scopes I’ve discussed can be had for $200-300 or even less if you’re willing to shop used (for example, at the Cloudy Nights Classifieds, where I’ve bought and sold just about all of my astro gear). If you have any questions, feel free to ask in the comments. I’m always happy to talk about telescopes.

UPDATE March 11, 2013: Here’s Doug Rennie’s StarBlast 6 hanging out amongst the flora–see comments for explanation!