Re: [APML] stacking & adding film images

["Don Westergren" <westergren@netzero.net>]

Wade and all,

The reciprocity losses for E200 occur in the first hour of exposure (for
standard processing).  You can see the effects out to 273 minutes exposure
at my website:
http://home.nethere.net/mpd/FilmTestData/KodakE200.htm.
Beyond 1 hour, the E200 responds nearly linear to increased exposure time.

I don't have the equipment to measure the precise sensitivities of slide vs.
color neg film.  I have found that shooting slide film with an f5 scope
catches a lot of sky fog after one hour at a reasonable dark site (Laguna
Mountain, east of San Diego).  I can easily shoot twice as long with Supra
400 negative film without sky fog at the same site.  The slide film (Provia
400) seems to pick up more dim nebula in one hour than a two hour shot with
Supra 400.  For objects with a large brightness ratio (like galaxy cores,
the Trapezium, etc) the Supra picks up a wider range of brightness in a
single exposure.

Don


> One more thing to consider is the possibility that exposing E200 beyond 1
> hour makes very little difference due to the film's reciprocity failure.
> At some point, the film just can't record any more "photons"; hence, it
> may never make it to a very dark skies' limiting magnitude before
> quiting; whereas, a CCD easily can achieve this given enough exposure
> and/or stacking.
>
> Wade



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