A quick observation about aperture

August 22, 2012

I had an epiphany last night. The busier I am, the less often I get out to observe, the more likely I am to use the XT10. The rationale: if I’m only getting out once or twice a month, I want to enjoy myself as much as possible, and that means using the biggest available scope. The only exceptions are (1) truly quick peeks, under half an hour, where I’ll usually grab the 90mm Mak, (2) sidewalk astronomy, where I use the 90mm Mak just because it’s the most portable, and (3) double star work, where I prefer the slightly cleaner, sharper views provided by the Maks. Any other small-scope observing is a luxury, for stretches when I’m already getting plenty of dark-sky time with a bigger scope–not my current situation, unfortunately. But fall is coming, and that’s traditionally my season for getting out to the desert on dark weekends. I can’t wait.

Maybe this would not even be worthy of comment for most observers, but I’ve always had a thing for small scopes. I still do, and probably always will. But now that I’m sort of settling into my current lineup and not especially wanting or needing another (small) scope, I’m spending more time thinking about the scopes I have and their strengths and weaknesses. Although every one of my current scopes fills a need, I am finding that the overall enjoyment they provide correlates with aperture more than anything else. It’s one thing to hear that aperture rules, another thing to really understand why, and still another thing to discover that for yourself, out of your own experience.


  1. That’s why I use a 15″ Dob. When I bought it (an F 4.5) it was the biggest aperture I could buy that still allowed me to stand flat on the ground while observing at the zenith. Now, with shorter focal lengths one can use an even bigger aperture than 15″ ( without a ladder); but it does depend on your height too. My balance isn’t the best and climbing up in the middle of the night is not something I want to do a lot of. Still, occasionally when I get the opportunity to observe with friends larger scopes I gladly climb up on ladders to do so. I am always struck by the better views of DSO’s the larger apertures yield. The biggest scope I’ve viewed through, so far, had a 25″ mirror. I’ll be truly gazed if I some day get to observe through even larger aperture under dark a dark sky. I also love the desert and go out to Red Cloud Rd, about 3 miles south of the I-10 freeway. Other than aperture, for me, it is all about dark skies. For this reason I’ll be at the Central Nevada Star Party next month for a few nights.

  2. I had this same revelation, with a bit of frustration attached, just before summer started. It seemed like forever since my last observing session, things were busy at work with some overtime, and my weekends seemed packed. The itch to observe was growing and along with it my frustration at living in the heart of LA.

    Sometimes I drive out to Malibu Canyon to try to get away from the light, but I can really only take my Celestron C6. It’s a capable instrument, but I’m always wondering what a particular object would look like with the extra aperture of my 8″ dob. It’s really easy for me to let the perfect become the enemy of the good… I can decide not to go out and observe at all because I can’t take out the larger scope. So I end up observing even less than I would.

    This led me to two resolutions of sorts. First, I was going to get a ‘really nice scope’ so that when I had the opportunity to use the large scope, the experience would be even better. Second, I was going to try to get over my tendency to pass up less than perfect observing opportunities.

    There is always a cost to observing… for some it’s the time it takes to take the scope out to the driveway or back yard. For me, I have to get in a car and drive at least a little bit. This cost makes me want to maximize the return, which is a good thing; making sure I have the best equipment I can for that particular situation. However, when I think back to my local/quick-ish observing sessions with my smaller scope, I still enjoy them. Actually, I enjoy them quite a bit, maybe not as much as if I would have had the big scope, but I stil get that great feeling of being out under the stars. I just need to remind myself that the cost benefit ratio is still good, even with the smaller scope 🙂

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