Re: [APML] Film Creep

[George Anderson <georgea@cam.org>]

Hi Steve

I don't shoot medium format so a vacuume back is not a problem for me,
but a thought did come to mind.
Any chance that the suction from the vacuume back is greater than your
nitrogen purge? In other words is the vacuume back also pulling in damp
outside air as well as sucking out all of your nitrogen? Have you tried
experimenting with higher flow rates?

George Anderson
Montreal Canada

Clear skies and good health


Steve Walters wrote:
> 
> Hi Jon,
> 
> Thanks for the suggestion but it already has a vac back. I had problems with
> the original vac pump that allowed the film to lift up during exposures but
> I replaced it and solved that problem.
> 
> In any case, a vac back will not keep the film from changing dimensions due
> to temp or humidity levels. It can only keep it flat.
> 
> Steve...
> 
> ----- Original Message -----
> From: "Jon Kolb" <jkolb@datawest.net>
> To: "'Discussion of Film Astrophotography'" <astro-photo@seds.org>
> Sent: Sunday, September 28, 2003 12:15 AM
> Subject: RE: [APML] Film Creep
> 
> > Hi Steve,
> >
> > > Any suggestions on solving this problem would be very welcome.
> >
> > I haven't tried to verify your calculations, but I will say that going
> > with a vacuum back may solve the problem.  I bought the Hutech version
> > that replaces the standard Pentax 67 back, and although I thought it was
> > a little pricey, it sure helped cure some of my shots of the same
> > symptoms you describe.  Understand, however, that I have pretty dry
> > conditions to begin with - my meter said the dewpoint was -3.5F Friday
> > night with an ambient temp of 28F.  Still my camera sweeps close to the
> > ground with my long refractor, down where it's wetter, and the vacuum
> > back did make a very noticeable difference once I started using it.
> >
> > Sincerely,
> > Jon Kolb
> > Adventures in Astrophotography
> > http://home.datawest.net/jkolb/
> > jkolb@datawest.net
> >
> >
> >
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