RE: [APML] Adapting Nikon F3/T for gas purge

["R. Scott Ireland" <ireland@gate.net>]

Hi, Kent:

> Using the interchangeable backs on the F3's is an interesting
> solution, but N2 is usually introduced in front of the film, either in the
mirror box,
> coupling adapter, or off-axis guider body. If introduced through the
camera
> back it's difficult for the N2 to get to the mirror box to keep the
emulsion
> dry. It will keep the film dry in the cassette and take-up area and may
> eventually get into the mirror box, forward of the shutter.


Very good point.  I wonder, though, given that the film pressure plate only
holds the film against the guide rails (remember the discussion of tape on
the guide rails to hold the thin-based tech pan flat?), perhaps the N2 will
flow over the film surface.  I'm thinking now that I'll insert the N2 at the
take-up side (film exposed and more susceptible to moisture).


> Using nitrogen you will need serveral things:
> 1. Nitrogen tank of appropriate capacity
>     They usually come in 20, 40, 80, 200 cu. ft. sizes. In the smaller
sizes you
>      usually have to buy them. The 200 can be rented. For ease of
transportation,
>      the 40 or 80 are best. The 200 is fine for permanent observatories.
> 2. Pressure regulator with Flow meter
>     The regulator controls and lowers the pressure.
>      The flow meter allows you to regulate the flow of N2 down to very
small levels.
>       The N2, tanks, regulator with flow meter are available from welding
supply co.
> 3. I use drip-irrigation tubing and valves, available at Home Depost, etc.
>       All kinds of on-off, splitter valves are available and they are
cheap.
>       Once the N2 leaves the flow meter, there is very little pressure.


Great advice, thanks!  I can feel my learning curve shrinking already :-)


> If you proceed with the F3 Back N2 Introduction idea, please post your
results.


I think I will give it a try, and I will of course post the results.  It may
take me a little while to get this set up and going (I've just ordered the
extra backs, etc.)

Scott


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