Re: [APML] Achromats?

["Bert Katzung" <katzung1@attbi.com>]

It wasn't clear to me whether Blair was proposing to do this on color film
or b/w (eg, techpan).  It has been done for years, of course, with highly
corrected scopes (Chuck Vaughn, Loke Tan, etc) with techpan tricolor.
Techpan on a  "cheap" scope would still be subject to all the nonchromatic
aberrations associated with cheap scopes. If Blair is proposing to do this
on color film, I can't see any advantage over b/w and a lot of extra
trouble.
Bert

Bert Katzung
katzung1@attbi.com
www.astronomy-images.com

----- Original Message -----
From: "Matt BenDaniel" <matt@starmatt.com>
To: <astro-photo@seds.org>
Sent: Monday, July 08, 2002 7:42 AM
Subject: Re: [APML] Achromats?


> Blair,
>
> That won't work well.
>
> 1. Doing that will bias colors in favor of the in-focus channel (i.e.
green).
> 2. You lose signal to noise ratio in the L channel because you throw away
signal (in the unused channels).
> 2. The green channel is often noisy.
>
> Matt
>
> At 10:30 AM 7/8/2002, Blair Batty wrote:
> >Relatively inexpensive achromats aren't used in
> >astrophotography because the various colours are
> >out of focus to each other (you know what I mean).
> >
> >Why couldn't you use an achromat to take a photo;
> >focusing it sharply with one central colour (perhaps
> >using a filter over your eye so you only focus on
> >one colour). Then:
> >
> >1) Digitize
> >2) split into separate photos of RGB
> >3) Go into Lab mode and use the "in-focus" colour
> >     as the L channel.
> >4) restack in registar
> >5) combine the original colour information with the
> >      "in-focus" L channel.
> >
> >I admit I don't know what I'm talking about. But I wonder
> >if something like this would allow taking sharp photos
> >with a cheaper telescope? There are all those fast,
> >wide, inexpensive Chinese 'scope available now...
> >
> >Sincerely
> >Blair Batty
> >
> >
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>
> --
> Matt BenDaniel
> matt@starmatt.com
> http://starmatt.com
>
>
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