Re: [APML]: Re: [APML] Help

[Chuck Vaughn <aa6g@aa6g.org>]

John Lumpp wrote:
>
> 
> I'm having a problem with deep sky photos using my 12" LX F10. I tried to
> use the 6.3 focal reducer to reduce exposure times and make guiding
> easier.The results were terrible.I had severe vignetting(central glow) in
> the center of the print with a darker outer region.

Pretty lousy deal isn't it? This is why focal reducers are not all
they're
cracked up to be. Same thing happend to me when I used the Lumicon giant
Easy Guider and reducer with a C14. I had about a 25mm evenly
illuminated
circle. When I tried the Celestron reducer/flattener it was even worse.

A focal reducer does it's job by reducing your field to a smaller area
on the film. The diameter of the image circle is reduced by the amount
of reduction - in your case .63. Add to that any vignetting your system
already has and some of these reducers have a smaller aperture then the
original image circle size so you end up with a small useable circle on
a 35mm frame.

It's better to get a telescope that's designed to operate at the f/
ratio
you want as opposed to focal reducing an existing one.

Chuck Vaughn  <aa6g@aa6g.org>