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chris jordan
1-Nov-2004, 14:17
Greetings,
My question pertains to the slowing of film speed due to cold storage. I am a huge fan of Tech Pan and now that it is gone I am looking for a replacement. One of the wierder ideas I had was to send out some Plus-X or T-Max 100 and have it cryo treated( cool to -300 degrees F and bring is back up slowly). My idea for this comes from the fact that supposedly some of Admiral Byrds film was recovered and showed a definite slowing of the film speed. Just a whim but it might work. Thanks to all for the info.
Cheers,
Chris

roger michel
1-Nov-2004, 14:28
just buy some pan f plus and call it a day. i like the tonal range of pan f plus much better than tech pan anyway.

i must say, i am curious to hear why tech pan was your film of preference. to me, it always made (some) sense for miniature format users who were trying to get fine grained enlargements at the inevitable high mags. LF users are more or less liberated from that concern, and can select their film purely based on tonal scale, zonability, etc.

and whilst on the subject, tech pan is notoriously hard to zone. individual treatment of negs is one of the great plusses of LF. using tech pan, you more or less have to give up this great advantage. people try really hard, but never seem to get beyond an n-1/n+0.

anyway, i guess i'm just curious to know why tech pan would be appealing to a LF shooter.

best regards, roger

tim atherton
1-Nov-2004, 14:51
Just wondering where you find Sheet Pan F+? especially 8x10. I thought it only came in 35mm and roll film?

chris jordan
1-Nov-2004, 16:49
Roger,
You got me. My Tech Pan fetish goes back to my minature format but I have also wanted to try fine line so...

Eric Woodbury
1-Nov-2004, 16:56
Although not my standard, I have used TechPan over the years in large format. When the light is low and the contrast from lighting is gone, I can shoot Techpan at about N+4. If you get the exposure just right, the results are unusual and the contrast is that that comes from the subject's coloring. Something no other film can do. The red sensitivity is a bonus.

Ralph Barker
1-Nov-2004, 17:35
I've heard of astrophotographers cold-treating their film, but I was under the impression it actually increased their effective film speed. Either way, I'm not sure that cryo-treating film would change the grain structure. So, you might end up with slow grainy film instead of a substitute for Tech Pan. Unless, of course, you were to also subject the cryo-frozen film to the loud roar of a Polar bear while frozen, thereby breaking up the silver halide crystals. ;-)

Michael Rosenberg
1-Nov-2004, 17:42
I would like to echo what Eric mentioned. I have shot T-Pan in 4x5 and 120 on my 4x5 camera. Not only can you expand it to N+4, but also N+6! This works great for abstracts, architectural, and pictographs. In addition, if I ran out of 4x5 I could shoot 120 roll film normally and enlarge it the same as 4x5. The red sensitivity definitely helped photographing out west. I have bought 200 rolls and frozen them down. I use about 10 rolls/year, so......hopefully in 20 years there will be a substitute.

Mike

Kevin M Bourque
1-Nov-2004, 18:11
Back in the days of film, astronomers would chill some emulsions to gain film speed. The camera body was built to carry a coolant, usually dry ice. The speed boost was only present while the film was cold, so you couldn't warm it up and expect to see any difference.


http://members.shaw.ca/jmirtle/coldcam.htm (http://members.shaw.ca/jmirtle/coldcam.htm)

If Admiral Byrd's film was lost for a lengthy time and then recovered, it lost speed because it was fogged, not because it was cold.

Jim Rice
1-Nov-2004, 18:18
From what I understand, Ralph, the the chilling of film for astrophotography is to mitigate the effects of reprocity failure.

Ralph Barker
1-Nov-2004, 18:31
I think you're correct, Jim.

I've also heard that eating expedition food from lead-soldered tins will slow down the photographer, too. ;-)

tim atherton
1-Nov-2004, 19:04
actually I was photogorpahing some of Franklin's lead soldered tins of food (empty) not so long ago - but it was canned tripe - so I'm not sure if it was the lead or the tripe that did the damage.

However, I believe they found some of Scott's b=jars of Marmite at one of his base camps down at the other Pole. Apparently it was still completely edible. Only two things can survive a nuclear holocaust - cockroaches and marmite.....

Jim Rice
1-Nov-2004, 19:14
Well what the hell do I know? *Eating crunchy raisin bran*

Jim Rice
1-Nov-2004, 21:26
If liquor and ciggies don't bury me, don't expect much more in the way of a death wish.

Jim Rice
1-Nov-2004, 21:30
Okay, I lust after a Calumet C-1......death wish broadened. :P

chris jordan
2-Nov-2004, 10:25
Uhmmmm, Right.
Actually I was refering to the transformation that occures in steels when they are subjected to extreme cold followed by a very slow return to room temp. This has the effect of causing the carbide grains to precipitate from austinite to soemthing or another-ite (been too long since my basic metallurgy classes) which has a MUCH FINER GRAIN structure. I know silver, not carbide, but hey! maybe.
Cheers,
Chris

Tim Curry
2-Nov-2004, 11:58
Chris, just get some Efke 25 and have at it.

Tim Stahl
2-Nov-2004, 14:43
Efke 25 does not look the same as Tech Pan. Also, Efke does not have the extended red sensitivity the TP does.

Chris Gittins
2-Nov-2004, 17:37
>One of the wierder ideas I had was to send out some Plus-X or T-Max 100 and have it cryo treated( cool to -300 degrees F and bring is back up slowly).

What are you talking for a temperature vs time profile?

Chris

chris jordan
2-Nov-2004, 18:04
Chris, the company I am ging to use quotes a 72 hr run down from 0 degrees F to -300 degrees F followed by a 72 hr hold and then 72 hrs back up to zero. At this point a low temp heat soak occures but I think I'd pass on that and just let the film come back to room temp. What did you have in mind?

Cheers,
Chris Jordan

Ralph Barker
2-Nov-2004, 18:12
The nice thing about experiments of this nature is that they don't hurt, and might actually provide a useful technique. Go for it, and let us know what you discover.

I think Chris Gittins was making a joke - if it's 10 min @ 68°, what would the time be at -300°? 8^)

Chris Gittins
2-Nov-2004, 18:48
>I think Chris Gittins was making a joke - if it's 10 min @ 68°, what would the time be at -300°? 8^)

Actually I meant it as a serious question, although when you phrase it that way it is pretty funny. I'm just not that quick witted.

My thought was: "Liquid nitrogen is cheap and plentiful. Might be an easy experiment to do at home." LN2 boils at 77 K which is what, about -320 F? The hard part is doing a gentle decent down to 77 and then back up to ambient. Any moron can drop a box of film in a dewar of LN2 , but doing a smooth 3 K per hour ramp from 300 down to 77 sounds like a challenge without a pretty fancy refrigerator. I'm going to think about this for awhile. Might be able to pull it off with nested styrofoam coolers? Maybe three? LN2 between the outer and middle and an air gap between the middle and inner? Adjust the LN2 level between the outer and middle to control the cooling rate.

Chris

Paul Fitzgerald
2-Nov-2004, 21:17
Hi there,

Just a thought or two:

1)The way I had heard it explained is that the astro film jumped in actual film speed by being drawn down in a heated vacuum to remove the water vapor from the emulsion and that the vacuum bell was filled with a hydrogen/nitrogen mix to replace the air. This speed increase only lasted a short while, until humidity in the air affected the film.

2)Doesn't water expand about 115% by volume when frozen?, and will this not wreak havoc on the emulsion?. It doesn't sound like fine grain Tech-Pan. I think it would be a good idea to vacuum down the film before freezing it.

Smile.

Chris Gittins
3-Nov-2004, 11:13
>Doesn't water expand about 115% by volume when frozen?

Ice is about 9% less dense than water, so figure a 9% volume increase.

>and will this not wreak havoc on the emulsion?

That's a distinct possibility.

On a related note, how much water is in the emulsion? If you drive it off by heating is that going to change the emulsion properties? Is gentle heating going to have any significant effect on grain size distribution?

What I'd worry about a bit more than water content within the emulsion is that the emulsion and base likely have very different coefficients of thermal expansion - probably a significant risk of cracking and peeling when you're change the temp by 300 deg F. My guess is the slow temperature ramp is necessary in order to minimize the risk of that happening.

>I think it would be a good idea to vacuum down the film before freezing it.

It's a pain to hold vacuum. I'd just purge the vessel with dry nitrogen to displace the ambient water vapor.

Chris

MIke Sherck
3-Nov-2004, 13:47
Astrophotographers used to "bake" film in forming gas (formaldahyde, I think,) to boost film speed and shoot it in cold cameras to reduce reciprocity effects, convenient when exposures are measured in multiples of hours.

Mike