Re: [APML] Push Processing (was Scanning slides)

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

Alan,

Push processing gains light sensitivity but also increases contrast and
grain size for just about all films (I don't know of any films that don't
fit this).  So deciding whether or how much to push process is a compromise.
Slide films like E200 and Provia400 are easily push processed with the E-6
chemistry and the push+1 and +2 processes are well established.  However,
the push +1 and +2 was established for normal film use, with short exposures
of daylight (or flash) subjects.  My exposure tests of both these films
processed for +2 show that for astrophotography long exposures, the result
is an honest +1 light sensitivity increase.

Contrast increase with slide films is a concern because slide films are
already high contrast with standard processing, compared to color negative
films.  This is why color negatives can produce a nice print even with under
exposed or over exposed pictures.  Slides have a much narrower range of
acceptable exposures for good pictures.  This is called the "latitude" of
the film.  This may explain some of your slide scanning problems, since most
of your scanning experience has been with negative films.  To get a good
astro picture with slide film, you have to expose long enough to get an
image of the deep sky object without a  light sky background.  For slide
film in particular, you also have to avoid "sky fog" where the background
sky shows up as gray rather than black in the picture.  You should expose
slide film at various times to find where the sky fog limit is for your
film, equipment and sky darkness, then always expose shorter to avoid sky
fog.  Slide film exposed this way will scan easier.  Slide film that is
underexposed is difficult to scan, as you are finding out.

May you have Clear, Dark Skies,
Don

>
> Most likely it would  be an improper scan and I plan to post a question
> regarding that ASAP. I have always had my film developed by the
> recommeneded process, C-41 for Supra, E-6 (?) for the one roll of E200
> I've done. John's comment indicated that push processing wouldn't be
> needed unless it would help get the hump of the histogram fully into
> the box. Is pushing a good idea?
>
> Alan



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