Does this not depend on the quality of the achromat? The cheap Sky Instruments ones have colour issues, but I have seen some remarkable views through a Stellarvue achromat. The 101EDT is a triplet that has one ED element in it. You pay more for it, but you know what, I could not tell the difference between it and the new Televue 101NP, even looking at a bright moon.
In any case, wouldn't a Lumicon Minus Violet filter fix and issue swith the cheaper ones?
-Bill
-----Original Message-----
From: Matt BenDaniel [mailto:matt@starmatt.com]
Sent: July 8, 2002 10:43 AM
To: astro-photo@seds.org
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
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http://starmatt.com
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