RE: [APML] Alternative Anti-Vignetting Photoshop Technique

["George Whitney" <gwhitney@maine.rr.com>]

Matt,
Thank you.  Those are some great points and suggestions.  I look forward to
trying out your techniques on some shots.  I wonder if using the dodge/burn
tool of Photoshop will correct for some of the color shift due to differing
reciprocity of the film layers (dodge/burn the inverse color in the shadows,
midtones, highlights)?
Let me say that I thoroughly enjoy your images...their beauty provides me
with inspiration.  Your "labor of love" has certainly paid off.  <G>
George




-----Original Message-----
From: owner-astro-photo@seds.org [mailto:owner-astro-photo@seds.org]On
Behalf Of Matt BenDaniel
Sent: Monday, January 07, 2002 5:47 PM
To: astro-photo@seds.org
Subject: Re: [APML] Alternative Anti-Vignetting Photoshop Technique


George,

I'm sure the technique you describe provides some AV help to an image,
but it is not a total solution.

* During a long exposure, reciprocity failure affects the film response,
which is not replicated by a short flat-field exposure.
* Differential reciprocity failure also significantly affects color
balance.
* Only a form of multiplication or screening provides a true inverse
function of light falloff.

I use an AV technique which allows use of the entire frame, as long as
the background is recorded above the toe in the corners.  For more info
see:
http://www.millennics.com/olympus/tope/tope1/pictures/tope1_17.jpg

My imaging system has fairly severe vignetting, but you will see few
signs of it in my images.

The big problem with the technique I use is that it is labor intensive.
But AP is a labor of love, right?

Matt

George Whitney wrote:
> Jeff,
> The best way to fix uneven illumination is by flat fielding, just like in
> CCD photography.  Photograph an evenly light square of white foam core
> through an opal glass using a continuous tone film, reverse the image in
> Photoshop, and stack the result with your scanned image and...presto...no
> vignetting!
> George
--
Matt BenDaniel
http://starmatt.com

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