Re: [APML]: Density of Hypered Tech Pan?

[Steve Bell <sb635@delphi.com>]

John F. Wall wrote:
> 
> 
> I just finished developing an unexposed strip of Tech Pan  (hypered for
> 24hr./50C/+3psi) in stock D-19 (finally found the stuff) for 8 min. at 20C.
>   The result is the fog on the film is darker than say my sunglasses. It is
> not black. I can see though it if I hold it up to a light.  But is this
> what I should be seeing?   I know the film is fresh, the chemistry is
> correct, the film was not exposed to light etc, etc, etc.  Even hypering
> time and temp. was right on. The only thing I can't confirm is the quality
> of the forming gas but I can't do anything about that (it came from Lumicon).
> 
> When I process ordinary B&W film I get relatively a relatively clear
> emulsion where it is unexposed and I thought I should be getting the same
> thing with Tech Pan.  After a little more research it appears that the film
> should be fogged to a point.  Like we're talking sort of grey not clear. Am
> I correct?
> 
> I could reduce developing times to get less fog but if you consider that I
> have already reduced hypering times from 100hrs. to 24 hours, this in
> itself is a large deviation from the base line as described by Lumicon.
> Now I'm going to change developing time by almost 50%? - this too is rather
> extreme , is it not.
> 
> The 24 dollar question is "am I on the right track or is there a major flaw
> in my process that I can't see?"
> 

And Chuck Vaughn wrote:

> You can get a rough estimate by holding a piece of the film right in front
> of your camera with a 50mm lens on it and compare the metering with and
> without the film. There should be a 1 to 2 f-stop difference (0.3 to 0.6).

While Chuck's answer is undoubtedly sound, the practical answer is that
John's TP is way over-hypered. At least to me that's true if his
unexposed hypered TP has a base fog that's darker than common
sunglasses. Even without then exposing such film to the sky, that degree
of darkness would give my scanner problems.

With regards to 50C at 3 psi being the base line as described by
Lumicon, I've said this before but I'll say it again, Lumicon officially
does not recommend hypering TP *in the cassette* at 50C for any length
of time. Lumicon recommends 50C for TP openly exposed on a reel, but
when left in its cassette, Lumicom recommends dropping the temp to 30C,
upping the pressure to 15 psi and hypering for at least 8 days (yes,
days). I've done that, and gotten a base fog of somewhat less dark than
half as dark as sunglasses, which is still way too dark for my tastes. I
like a base fog that has a noticably grayish tint compared to un-hypered
TP, but still no where near to even half sunglasses density. The density
I like is about 0.3D, which according to my Kodak step wedge, is the
grayish look I'm talking about. But, I also shoot from a light polluted
site, which plays an important part. I can get my desired base fog using
30C at 15 psi for 4 days. Oh, and that's using a development time of 6
min in D-19 at 68F. Six mins is also what Lumicon recommends when using
D-19, as explained in the literature that comes with their Model 300
hypering kit.

If you still want to hyper TP in the cassette at 50C at 3 psi (and a lot
of people do this successfully - it really saves on gas), I'd recommend
reducing the time to something like 8 hrs and see what happens. If it's
not hypered enough (which can only really be determined by actually
exposing it at the scope under your given sky conditions), then you can
put the rest of the unused cassettes back in the chamber and hyper for a
little more time. By trial and error, you should be able to determine
what degree of hypering is the best for your particular imaging
conditions.

-- 
Clear skies,
Steve Bell
email: sb635@delphi.com
Astrophoto page: http://www.mindspring.com/~sb635