RE: [APML] Matt, Jeff, Chris, Jerry and stuff like dat dere

["Jeff Ball" <jeffball@zoominternet.net>]

Warren,
Here are my thoughts on the exposure times.  I guess the longest exposures
we take are star trails.  Some of those are over 6 hours long. Has anyone
analyzed a star trail shot to determine if there is a reduction is
sensitivity during the exposure?  Is it accurate to analyze star trails
since they are significantly brighter than deep sky objects?  I believe the
longest deep sky exposures are by Chuck Vaughn at 3 hours with TP and
filters.  My guess is that Chuck has data to demonstrate the benefit of
shooting 3 hours vs. 2 hours with Techpan.  Now, how does this compare to
print or slide films we use today?  I guess Don Westergren's tests are as
close as we can get there.  He has data on exposures over 4 hours.  Of
course they are of one light source and I guess it is difficult to infer the
decrease in sensitivity to low light objects based on this data.  The
longest I have shot with any success is 90 minutes and there is more on my
90 minute than 60 minute negatives.

Regarding the LRGB:  I used Rob Gendler's technique with some RGB data.  My
RGB data was very robust and matched up well with the luminosity data.  You
really need to nearly match the level of signal of the luminance data with
your RGB data or the Halpha will overwhelm the image.  I do several
iterations of making a mixed Lrgb with less than 50% contribution of the
Halpha channel until there is no benefit.  Hope that helps.

Regarding slide/print.  My experience with the slide film on my f8 system is
that if I am shooting from a very dark sky, I may not get the sky fog I need
to be able to scan the slide properly.  That is why I am shooting some film.
With my TV101 at f5.4, slide films will probably be a great choice.  Hope
that helps and is somewhat accurate and pertinent.

Jeff Ball


-Jeff, et al- How many of us think that even the best color emulsions are
recording significantly after 90-120 min? Also, when I tried to slap my
color HH/Flame on your FANTASTIC ccd image, the color diminished to very
pale despite changing blend methods, opacity and percentages. What's an
appropriate way to blend an L w/ RGB in PS and PW?

-If the slide film is working so well, why are we still hypering, storing
and purging print?


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