Re: [APML] Supra 400 Reciprocity

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

Steve,

The old Supra 400 is like the pink bunny, it keeps going and going and
going.  We have used it at f7.5 , f9, and f11 for shots up to 4-1/2 hours,
and can see the difference compared to shorter exposures.  Remember that one
stop increase of exposure takes twice the time.  Your 180 minute exposure
has one stop over a 90 minute one.  To get additional stop would take 6
hours.  Supra 400 can do it. It has some reciprocity in the first hour, then
almost no further losses.  See my data on Supra at
http://home.nethere.net/mpd/FilmTestData/KodakSupra400.htm

Good luck with your long exposures.

Don


> I have been attempting some long focal length shots (f11 with my 10" SCT)
on
> Supra 400 (old formula) for some smaller faint galaxies to get tighter
stars
> than on slide film.  My goal has been to do 1 to 2 180 min shots on each
> object (preferrably 2 and stack).  The last couple of times out I keep
> getting cut off by wind, clouds or the mount running out of travel at
about
> 100 to 120 minutes.  For object like M101 or M106 or M65/66 I don't pick
up
> anywhere near enough detail to use for a decent image.  Is this just not
> long enough exposure at that FL or does Supra 400 just run out of gas past
> about 60 to 90 min and maybe is better suited of shorter FL scopes?  I
don't
> recall seeing really long exposures images on this film for comparison.
>
> Steve
>
>
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