Large aperture-light pollution

[aatt]

This is my first post here. I was just reading David Kriege's Dob book and one thing leaped off of the page where he said that a 12" will show you just as much as a 25" in typical suburban LP conditions. I have a 15" which, judging for some of the sigs here, makes me a tiny fish in the scope pond. I live in orange/red skies and have been thinking about going to a 20" which seems to be the limit of what I want to handle. I know I am not a ladder guy, but a step stool I can deal with. In all honesty, what are your thoughts about moving up to that aperture in those conditions? Is it worth it? I do know that definitively detecting Abell 262 members ( 732, 759 753 and 712 less so) are a challenge to me with my 15" scope, eyes,age, experience and lp levels. Would those be unambiguous in a 20" (and show detail)? I would think they would, but I have never looked through a 20" before.

[Dragan]

This is my first post here. I was just reading David Kriege's Dob book and one thing leaped off of the page where he said that a 12" will show you just as much as a 25" in typical suburban LP conditions. I have a 15" which, judging for some of the sigs here, makes me a tiny fish in the scope pond. I live in orange/red skies and have been thinking about going to a 20" which seems to be the limit of what I want to handle. I know I am not a ladder guy, but a step stool I can deal with. In all honesty, what are your thoughts about moving up to that aperture in those conditions? Is it worth it? I do know that definitively detecting Abell 262 members ( 732, 759 753 and 712 less so) are a challenge to me with my 15" scope, eyes,age, experience and lp levels. Would those be unambiguous in a 20" (and show detail)? I would think they would, but I have never looked through a 20" before.

Welcome to the group! And don't sell yourself short with your 15. The purpose of DSF is to educate and push our observing skills no matter scope size. There's a wealth of information here that applies to everyone and anyone, regardless of aperture.

I don't have the exact quote from Dave's book in front of me, (what page was it on?) but I'd go out on a limb and guess his intent was that a 12" from DARK skies would show just as much as a 25" from typical suburban LP conditions. That could be plausible. But never would a 12" outperform a 25" where both scopes are under the same conditions. I just can't see that happening and I don't think anyone on the group would disagree.

Is it worth it? That would be up to you to decide. A 20" will give you just shy of twice the light gathering of a 15". (A 22 will give you a bit more than twice) The 20" will allow you to, theoretically, go a full magnitude fainter as well as have the added benefit of increased resolution by going bigger. (Lets not forget a little added FL which I am a fan of) The downside of course is cost, storage and transport. Would you ever have the opportunity to take it to a truly dark sky? If so, while under those skies, you would never regret going bigger. The old adage "aperture rules" has never been truer than when under dark skies.

I'm starting to ramble. My point is that going bigger is always a personal choice and its one only you can answer. Will you see more? Absolutely. Will it be earth shattering improved views? Probably not. A jump from 15 to 20 won't have the same wow factor that someone with an 8" would experience when looking thru a 20". I can't say just how much improved difficult objects like 262 will be. Every observing session/location/condtion is different. But, even under light polluted skies, I believe that you'll see some improvement. Whether or not that improvement is justified is up to you to decide.

I didn't help much, did I! :scared:

[Ivan Maly]

Austin, since you (like me!) are interested in galaxies, consider that 20" at 4/3 the magnification shows the same surface brightness as 15". So (taking into account that you are not traveling with either aperture) I'd say move up to 20" only if you really feel like getting a new scope. You mention a step-stool for 20"; if you observe seated with your 15", then I'd say definitely stay with 15".

[aatt]

Thanks folks! The reference in Kriege's book is on page 40 of the latest edition.I stand mostly, but that needs to be rectified to much crouching and off angle body skewing when the scope is at 40 deg and below.My main thing is I want to be able to easily pull in those pesky Abell 262 members that I mentioned and have the Messiers and majority of the NGC's being bright and definitive and leave the eye strain for the Hicksons etc.My 15" is a great scope and I am addicted to it, but it lacks the firepower I thought it might have. However, in dark skies it can perform pretty well. My first view of the Sombrero galaxy was unforgettable from a dark site. By the same token the 15" scope on the pinwheel galaxy showed, indirectly, the HIII regions in the arms, but the 17.5" next door revealed them directly. I am probably sunk ;)