Re: [APML] Equivalent ISO of an ST10E CCD

[James Foster <jrfcomet@pacbell.net>]

To:  Jerry,

You hit the nail on the head!   I think you can equal film images with
equivalent (or less) exposure, but to surpass film you have to take many
(relatively) short exposures, to minimize seeming and get good S/N to exceed
the resolution and depth of a film image(s). All in all a "proper"  CCD
image maybe take longer for a cumulated set of images the film images.  I
bet Mr. Gendler is much more picky with his CCD shots (i.e. throws more
away) than he would taking film shots.

James Foster
Los Angeles, CA

p.s. I have gone to the dark side too...ST-7E + CFW8.


----- Original Message -----
From: "Jerry Lodriguss" <jml@astropix.com>
To: <astro-photo@seds.org>
Sent: Saturday, April 06, 2002 7:12 PM
Subject: Re: [APML] Equivalent ISO of an ST10E CCD


> Hi Chuck,
>
> Thanks, that's a good idea.
>
> Here is another thought...  lets just look at exposure times for, say,
> Rob's pictures of a given object, and, say, your tri-color images of the
> same object, and say, someone else's stacked color neg/slide images of the
> same object.
>
> It's easy to say a CCD has an equivalent ISO of 20,000 but if you have to
> stack so many exposures together that the total exposure time goes way up,
> what does it really mean to say the ISO is that high? To me, it's
meaningless.
>
> Jerry
>
>
>
> >Just a thought on my part... If you want to compare CCD speed to film,
> >maybe you should take the RMS noise of a specific film and then adjust
> >the exposure time of the CCD camera on the same shot until the RMS
> >noise is the same and then compare the exposure times between the
> >two. The number of f stops faster the CCD was compared to the film
> >would be the equivalent ASA for that particular situation. Similarly
> >adjusted images of a grayscale step wedge or a MacBeth Color Checker
> >might be appropriate.
>
> Photoshop for Astrophotography Book:
> http://www.astropix.com/APBOOK/0_PROMO/PROMO.HTM
>
> Astrophotography, Tips and Techniques
> for Digital Enhancement in Photoshop:
> http://www.astropix.com
>
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