Archive for October 11th, 2011

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Cheap Scope Review: the Celestron FirstScope

October 11, 2011

Update: This post seems to get a lot of traffic, especially around the holidays. If you’re looking for good gifts for amateur astronomers, including telescopes and binoculars that won’t break the bank, you may also be interested in my astronomical wish list for beginning stargazers.

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My fascination with small, cheap scopes is probably obvious by now. Don’t get me wrong, I love my 10″ reflector, and if someone said I could only have one scope for the rest of my life, that would be it. But there is still something about wee little scopes that tugs at my heartstrings. I want to try out every one I come across, and see what it can show me. Partly this is an internal, personal fascination with small telescopes, probably akin to the fascination that some people have for very small trains or very small dogs. But it also has a social component. I do a fair amount of sidewalk astronomy, showing the moon and various other things to passersby, and I like to be able to recommend inexpensive telescopes to people. So I’ve been on a quest not only to find the perfect small scope for myself (a quest that is complete…for now), but also the perfect small scope to recommend to other people.

You might think those would be the same thing, but they’re not. If there is a posh end of the little tiny scope market, the SV50 is it. It’s a nice instrument–very sharp optics, within in the limitations of a 50mm f/4 optical train, a smooth focuser, and a rugged build. All this comes at a price. It was a price I was happy to pay, to get a scope that fit my peculiar requirements (being able to be stuffed into the bottom third of my backpack for long airplane flights to dark skies in other hemispheres), but for most people the SV50 is build quality overkill and optical underkill. For the same $150, you can get a 3 or even 4 inch scope on a solid mount, and those larger scopes are still nice enough to be all the scope that some people will ever need.

A few years ago the conventional wisdom–which can still be found in quite a few places out in the wilds of teh intarwebz–was that first-time scope buyers should avoid anything under $300. Then the recommended cutoff fell to $200. Then some manufacturers started building very well received scopes for $150, like the Orion StarBlast 4.5 (which is now up to $200, although you can get the tube alone for $150).

It’s not that there weren’t scopes available for less. Depending on your tolerance for plastic and frustration, the low-end department store scopes grade into toys that go all the way down to about a buck. But these were not in any sense “good” telescopes, and between bad optics and shaky mounts, standard department store telescopes have probably driven thousands of potential stargazers away from one of the most rewarding hobbies. For a long time, the minimum buy-in for a new telescope that actually worked as advertised was between $100 and $150.

That changed, bigtime, during 2009, the International Year of Astronomy. First there was the GalileoScope, which originally sold for $15 but nevertheless managed to attract plenty of good reviews and a strong following online. Galileoscopes are still available, although now that IYA2009 is over, the economy of scale isn’t working as well and the price has gone up to $50.

In the same year, Celestron released the FirstScope, a 3-inch reflecting telescope on a one-armed tabletop mount. The FirstScope was an official product of IYA2009 and was heavily promoted and ended up in a lot of places, including electronics stores and even department stores. It originally sold for $50, but the price has periodically been lower. As of this writing they are $45 with free shipping, but I have seen them as low as $36 online and people report finding them in Fry’s and other electronics stores for as little as $25. The box includes the assembled scope, two eyepieces, and a single sheet of instructions. As far as I know, it’s the most inexpensive, reasonably capable, complete telescope ever brought to the market. So naturally I was curious about it, and the combination of a temporary sale and an Amazon gift card put one in my hands for a while last year.

Let’s start with first impressions. This is a sharp-looking scope, right out of the box. It includes dust covers for the end of the tube and the focuser, and the two eyepieces come with plastic caps, and in general it has the same fit and finish of other mass-produced scopes. The tube is printed in spiraling script with the names of famous astronomers from the past, which I think is not only commemorative but also educational, in that people are supposed to read the tube, see names they don’t recognize, and go learn about them. The tension on the altitude axis is easily adjustable with a big knob that turns against a Teflon bearing surface. The mount turns easily on its base, and the base has three big rubber feet widely spaced for stability. No finder is included, but there are a couple of pre-drilled holes with screws for mounting one.

As usual with “tabletop” scopes, observing with the FirstScope may require some ingenuity if you don’t have an actual table handy. It’s small enough and the useful magnifications are low enough–more on this in a second–that you could just hold it by hand or cradle it in your lap. I used to prop mine on the trunk of the car, back when I still had a car with a trunk. The base is a big plus here–the three rubber feet give solid footing with no rocking, even on uneven surfaces, and the mount is small enough and strong enough that vibration isn’t a factor. The altitude and azimuth motions are also very smooth, so once you get something in the eyepiece, it’s generally pretty easy to keep track of it.

So far, so good; most cheap scopes are so wobbly and shaky that finding targets and then tracking them is an exercise in almost terminal frustration. Mechanically, the FirstScope is as smooth, steady, and convenient as any scope I’ve ever used, and that’s an unbelievable achievement in a bargain-basement scope.

Back to the ease of tracking things at the eyepiece: there’s the rub. How do you get the scope pointed at things, so that you can see them in the eyepiece? With most scopes, you point the tube in the rough direction of your target, look in the finder scope, center the target, and then go to the eyepiece. Without a finder, you’re down a step: all you can do is point the scope in roughly the right direction and hope for the best when you look in the eyepiece. With the moon this is almost foolproof; with anything else it can be surprisingly tricky. Admittedly, with the low power eyepiece the scope has a huge field of view, which makes acquiring objects somewhat easier, but I still found that observing anything other than the moon usually involved at least a little faffing about.

Once on target, how are the views? Here’s where you have to steel yourself to some unavoidable facts of optics and economics. First the optics: it’s dead easy to make a mirror whose surface is a segment of a sphere, all you have to do is rub two flat round pieces of glass together with abrasive in between and that’s the shape that emerges naturally. The problem is that a spherical surface doesn’t bring all of the parallel rays of light that fall on it to the same focal point. The shape that does is a parabola, which is not that hard to generate but still takes some extra figuring from the basic spherical shape.

Now the economics come in: for Celestron to produce FirstScopes at their target price point and still stay in business, they could not afford to parabolize the primary mirrors. That wouldn’t be a big deal if the focal ratio were longer. When the cone of light from the primary mirror to the focal plane is long and skinny, the rays converge well enough that past a certain point spherical mirrors perform just as well as parabolic mirrors. The Orion XT4.5 has a spherical mirror and most reviewers have been very complimentary about how sharp the views are. But the XT4.5 operates at f/8, meaning the light cone is eight times as long as wide (or to put it in more technical terms, the focal length is eight times the diameter of primary mirror). The FirstScope operates at f/4, which means a pretty steep light cone. Even parabolic f/4 systems are hard on eyepieces: it’s difficult to gather up that steeply angled light and turn it into a pleasing image. Without some kind of complex and expensive corrective lens, objects in the center of the field will be sharp but those toward the edge of the field take on interesting, compressed shapes, sort of like a photo taken with a fish-eye lens. With an f/4 spherical mirror, the visible aberrations are worse, and even objects in the center of the field may not be truly sharp.

This is in fact exactly what I found. I could see plenty of craters on the moon, but the views were fuzzy rather than razor-sharp. Jupiter would go from being an elongate smear on one side of focus to an elongate smear on the other side, but in between it never really settled down into a nice circle. The best I could get was a modestly flaring egg shape, although the moons on either side were easy to see. Stars went from being vertically elongated dashes to horizontally elongated ones without ever becoming nice round little points of light. And that was in the center of the field. Toward the edge, the stars became commas, parentheses, and seagulls.

Not only were the eyepiece views pretty underwhelming in terms of quality, they were also small. Economics again: a decent, well-corrected eyepiece with a comfortable apparent field, like a generic Plossl, costs about as much as the entire FirstScope package. The included eyepieces are a 20mm Huygenian yielding 15x and a 4mm Ramsden giving 75x. The Huygenian has a tiny field of view, like looking through a soda straw, but the views are at the sharp end of what this scope is capable of. The 4mm Ramsden has a wider apparent field, not as good as a Plossl but not entirely claustrophobic, but unfortunately 75x is really pushing what this scope can do. Orion packages their almost identical FunScope with 20mm and 10mm eyepieces giving 15x and 30x, and I think those are much more reasonable magnifications for this type of scope. Happily, the focuser accepts standard 1.25″ eyepieces so if you can use other eyepieces, and frankly almost any other eyepieces are going to be better than what comes in the box.

Regardless of what eyepiece you use, focus gets critical at fast focal ratios, because the steep angle of the incoming light means that the focal plane is extremely shallow. With a long light cone, the eyepiece travels through the comparatively long region where the light rays are almost imperceptibly out of line on either side of perfect focus, which means that you can adjust focus very precisely with reasonably big turns to the focuser wheels. With a steep light cone, even minute turns of the focuser can throw you from out of focus on one side to out of focus on the other. Sometimes the distance between visibly out of focus in both directions is less than the spacing between the teeth on a rack-and-pinion focuser, so the perceptible ratcheting of the focuser can throw you past focus. I also found this to be the case; the focuser had an almost imperceptible amount of slack which was greater in one direction than the other, so I had to deliberately overshoot the focus in the “bad” direction and then try to sneak up on it from the “good” one. If I went even a hair too far, I couldn’t simply reverse into focus, but had to go way past in the wrong direction so I could start sneaking up again.

Needless to say, this kind of monkeying around gets old pretty fast. It might have been worth it for reasonably sharp views, but not for a fuzzy moon or egg-shaped planets. I used my FirstScope off and on, halfheartedly, for a few months, and then passed it on to someone who was happy to get it.

PROS

  • Extremely light and portable
  • Solid mount with good motions
  • Good fit-n-finish, comparable to what you’d get on much more expensive telescopes
  • Visually attractive, commemoration of prominent historical astronomers is a nice touch
  • Usable right out of the box
  • Dirt cheap

CONS

  • Almost zero instructions (in the box; more are available online, but for what telescope is that not true?)
  • No included finder
  • Included eyepieces are usable, but barely
  • No provision for primary mirror collimation
  • Very limited magnification potential
  • Underwhelming image quality

It may seem mean to bring up these cons on a complete telescope that costs about as much as a cheap eyepiece. After all, fixing any one of them–adding a finder, or better eyepieces, or an adjustable mirror cell, or parabolizing the mirror–would drive up the cost, and then this scope wouldn’t be filling the same niche anymore. In fact, the telescope ecosystem includes a whole array of small reflectors that improve on the FirstScope in some way, so you can see what the upgrades cost. For $60, the Orion FunScope is virtually a clone of the FirstScope, but it adds a red dot finder, better eyepieces, and a socket in the base of the mount so the whole thing can be put up on a tripod. For $100, the SkyScanner 100 adds (in addition to the RDF, better eyepieces, and base socket) a parabolic mirror with twice the light-gathering area (but still no collimation), or the SpaceProbe 3 Alt-az adds (with RDF and better eyepieces) a full-size tripod, a collimatable primary mirror cell, and a longer focal length for more magnification and sharper images. And things go on up from there.

Still, somebody has to be at the bottom of the price ladder. Considering that it costs almost nothing, the FirstScope is actually a remarkable success. It is certainly not useless. It will show a lot of stuff, and I think it is much more likely to pull first-time telescope users farther into astronomy instead of driving them away like most department-store scopes–although the pull may soon be to a bigger or better scope.

Should you get one? Although I’m sympathetic to the design philosophy of the FirstScope, I’m going to recommend against. Here’s the deal: the Orion FunScope currently costs a full third more, but that full third is still only $15. Most people who can afford $45 for a telescope can afford $60, and the addition of the red dot finder alone (which sells for about $36 as a stand-alone item!) is worth the extra layout, in terms of the convenience it will bring to using the scope.

But honestly, I wouldn’t stop there. The FirstScope and FunScope are fine for getting your feet wet, or for having a well built (if optically wanting) small scope to play with, but I have serious doubts about how long they will hold most people’s attention. In my opinion, the next rung up ($100) is where the “keepers” start. What I mean by that is that the SkyScanner 100 and SpaceProbe 3 have good enough optics to be useful for a lifetime, and recently received very favorable reviews in Sky & Telescope. Even if you already have or someday move on to bigger scopes, they’d be worth keeping around as quick-look, grab-n-go, and travel scopes. Bottom line, if I got marooned on a desert island with a FirstScope, I’d grudgingly make the best of it, but if I got marooned with a SpaceProbe 3 I could probably keep myself happily occupied for the duration.

So what’s the final word? I think most people, even casual observers or kids, will be better served with a slightly more capable–but inevitably somewhat more expensive–scope. Nevertheless, I am glad that the FirstScope exists. It serves an extremely useful purpose: providing a rock-bottom entry-level scope that actually works.