Re: [APML] Out-gassing(sp?)

["Andy Homeyer" <homeyer@starband.net>]

----- Original Message -----
From: "Philip Perkins" <philip@astrocruise.com>
To: <astro-photo@seds.org>
Sent: Thursday, September 27, 2001 7:05 AM
Subject: Re: [APML] Out-gassing(sp?)


I finally decided to throw my 2 cents worth in (for what it is worth) after
all the various ideas regarding the "black art" of hypering, these ideas
based on my past 10 years of hypering. I used to build ultra high vacuum
systems b/4 I retired so I know a little about vacumm workings. I built my
own system-but not to ultra high standards-using a high quality rotary
ruffing vacxuum pump that will goto < 1 micron. I had considered adding an
oil diffusion pump, but that was going WAY to far. I pump down to about 12
to 15 microns while the chamber is at temperature (50C) which is controlled
to < 1/2 degree. My chamber comes to temp. and stabilizes in about 3
minutes. On 35 mm film I hyper in the cassette, BUT I reload to only have
about 12 exposures per cassette, this way there is plenty of room for the
film to relax in and not be tightly wound. Depending on the film type, the
pump down to 15 microns can take as long as 4+ hours. Contrary to what you
may have heard color neg. film is not affected by the 50 C temperature,
remember that is only 122 F. I want all the "water" and uncombined oxygen to
be removed, read "outgassing", yes the film is outgassing. I have not
noticed any film embrittlement due to plasticizers being removed. I have
never had a problem with film becoming brittle or curling at these pressures
and temp. Some films are really "dirty" and take longer to pump down, Fugi
SHQ being one of them.  I can hyper 14 sheets of 4x5 tech pan with no
trouble except for loading the darn stuff in its rack type holder, and it
stays as flat as it was in the box it came in. Regarding the various
comments on Fugi SHQ, it does respond to hypering, but the hyper times are
much shorter than other films. I have found that PPF in 120 format also
responds slightly to hypering, but the job of loading in onto a reel is a
real pain in the - - - Hypering it as it is wound on the core is risky in
that the pump down time can be very, very long  and then you can not be
certain that the inner parts do out gas, it's easier to use it as it comes.
At my dark site I can expose any of the films I use for over 2 hours and not
pick up back ground fog, and yes I'm at a very dark place.

Since I do not know how to post images to the group, I'm not to computer
savvy, I can only say look at my images on my web page and judge for
yourself. www.intint.com/andy   I'd like to hear any responces you may care
to make, even from those who know me ;-))))>

Andy

> With colour film, I would recommend purging rather than any specific
> attempts at outgassing.  Out gassing will mostly expel water vapour from
> the film and my experience is that when you do that to any significant
> degree then a number of undesirable things start to happen.  A small
amount
> of out gassing is OK - after all this happens even with the hand pump when
> the chamber is heated, except in that case we would call it evaporation.
I
> believe that the term outgassing strictly means driving off gases under
> high vacuum, and that (in my experience) is definitely undesirable with
> colour film.
>
> --Philip
>
> At 22:25 26/09/01 -0400, you wrote:
> >Hello All,
> >I am curious as to the best method for outgassing film prior to hypering.
I
> >have the 600 Lumicon chamber and 50Deg probe.  Thanks for any help on
this.
> >
> >Jeff Ball



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