Question for Astro Photographers

[johnleveritt]

Sorry for the double post.

I have a question for you astro photographers. I will be using my Meade LX200 8" scope for photography, it has an f/10 focal length. Should I get a focal reducer as seen here http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=202595&is=REG to bring down to f/6.3?

I had one before my stuff was stolen a few years back, and didn't replace it with the insurance money, should I do it now that I'm getting back into astro photography.

[Jon]

For point sources and light emitters like stars, the absolute aperture (absolute area of the opening; 50ish sq. in. in your case) is what's critical for light-gathering. If you're concentrating on planetary photography, the f/stop comes into play. What you will find, in either case, with a focal reducer, is that your angle of view will change, so you'll be covering more of the sky.

[johnleveritt]

For point sources and light emitters like stars, the absolute aperture (absolute area of the opening; 50ish sq. in. in your case) is what's critical for light-gathering. If you're concentrating on planetary photography, the f/stop comes into play. What you will find, in either case, with a focal reducer, is that your angle of view will change, so you'll be covering more of the sky.

Thank you.

[Tom W]

I see that it's also a field flattener. I'm not the greatest expert on astrophotography, but I've seen images without flatteners where the image quality falls off (out of focus, specifically) considerably towards the corners. Most telescopes present a slightly curved field of view to the eyepiece, which goes unnoticed to the human eye, but doesn't work well with the flat film/sensor plane.