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  1. #1

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    Advanced Film Drying--vacuum?

    Dear Group:

    I would appreciate a bit of information from the photo emulsion engineers and experts on methods of advanced film drying post development.

    I am scanning 135 format film at a resolution of 50 MP+. The scanner is resolving 4um. I have considerable success with eeeeeeeking out a lot information content from the New TMAX-2 400 film developed in PyroCat MC with the Hasselblad X1 scanner.

    The problem my lab is having is with dust and dirt getting onto the film surface during drying. They are using a standard stainless steel drying cabinet with a pre-filter on the air supply. Very small particles still seem to enter the system and stick to the surface, producing 1000s of small particles seen on the final scan. While the particles are small, the sheer number is enough to make one good crazy during dust and spotting.

    Rather then trying to modify the conventional drying scenario with HEPA filters, etc, I am wondering about drying the film in a partial vacuum with a desiccant.

    Does any one have experience in so doing and are there risks to the emulsion if too strong a vacuum is pulled and the boiling point approaches room temperature?

    with kind regards,

    Pete Myers
    Santa Fe, NM

  2. #2
    Akki14's Avatar
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    You need more moisture not less, especially in NM. That'll drop the dust out of the air so it isn't floating around to attach itself to your film.
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  3. #3

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    If you go the vacuum drying method, you will need sub 10 micron filters for the air inlet when you turn the vacuum off. Better off to up the humidity in the lab to 50%, clean the drying cabinet and add a hepa filter, and use distilled water for two final rinses, the second with a wetting agent. Adding filtration to the water supply will help as well, tap water usually has lots of very fine particulate in suspension.

  4. #4
    JBrunner's Avatar
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    Hi Pete, welcome to APUG.

    As has been indicated, the humidity in the lab is too low. A good humidifier would go a long way towards cleaning things up.

  5. #5

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    Thanks for the welcome

    Thanks for the welcome!

    The lab doing my development work is not in New Mexico, and they have plenty of humidity and a pretty clean system and HEPA filters running throughout the lab. It is likely about the best setup around for a commercial lab.

    I really need to take it to the next level---so the question remains whether any one has had experience with vacuum drying. If I pull too deep a vacuum, will the 'boiling' off the surface affect the emulsion?

    The idea would be to simply pump down a bell jar containing the film with a lower desiccant layer---oil free vacuum pump. Kind of hard to have dust floating around when there is no air.

    Thanks for kicking this around...

    Pete

  6. #6
    MikeSeb's Avatar
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    If anything, the drying chamber/vessel should have positive pressure rather than negative pressure, similar to what is done for clean rooms and operating suites. Filtration of processing water and of incoming air flow is key.
    Michael Sebastian
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  7. #7
    JBrunner's Avatar
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    Quote Originally Posted by Pete Myers View Post
    Thanks for the welcome!

    The lab doing my development work is not in New Mexico, and they have plenty of humidity and a pretty clean system and HEPA filters running throughout the lab. It is likely about the best setup around for a commercial lab.

    I really need to take it to the next level---so the question remains whether any one has had experience with vacuum drying. If I pull too deep a vacuum, will the 'boiling' off the surface affect the emulsion?

    The idea would be to simply pump down a bell jar containing the film with a lower desiccant layer---oil free vacuum pump. Kind of hard to have dust floating around when there is no air.

    Thanks for kicking this around...

    Pete
    Hi Pete,

    Beyond what I wrote, I'm over my head. I've never had such issues from a lab even for commercial work. Yes there is the odd bit that needs to be cleaned up, but usually no more than the opposite spot or two on the film I turned in. We have a retired photo engineer from Kodak who participates here, and a few lab owners, perhaps they will chime in.

  8. #8
    Nicholas Lindan's Avatar
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    There was a desiccant film drier made by Honeywell. It used a large desiccant can, a fan and a filter and had room for a 120 reel. Made from beige plastic, it looked like an over sized developing tank. They show up on ebay, a WTB plea on APUG or rpmd and a google should yield some result. Small laboratory desicators, some with air fittings, show up on ebay with regularity, there is no reason to get a bell jar.

    I agree with the other posters here: if you are having a lot of dust then I suggest the cure is not in heroic measures, however much more fun they may be, but in the basics. There is no reason you should be having a major dust problem - there is obviously something wrong in the process and the goal should be to find out what.

    If your lab is providing negatives with "1000's of dust particles" then it is not "the best set up for a commercial lab" but most likely the worst. Switch labs if this is the best they can do.

    As the lab is probably providing clean negatives, logic would say that there is a very high probability that the "1000 points of dust" aren't dust at all, but something else entirely. They could be a defect or artifact in the scanning process - what do enlargements of the negatives show? It could be the developer, pyro being known for strange unexplained effects - what does D-76 do? Maybe the spots are in the film, and as no-one else is scanning with as fine a resolution the spots have never been a problem until now.

    Have a roll processed off site, have someone bring in some 120 negatives from an unrelated source, try a different film and then compare the scan results - an experiment that should cost less than $10 and yield an immediate 'Ah Ha!'.

    Of course, if the goal is to have a fun project and the "dust" is merely the excuse, then carry on.
    Last edited by Nicholas Lindan; 12-09-2008 at 11:23 PM. Click to view previous post history.
    DARKROOM AUTOMATION
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  9. #9
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    Quote Originally Posted by Nicholas Lindan View Post
    There was a desiccant film drier made by Honeywell.
    Never ever use one of those dryers. Your film will come out like a coiled spring. The one I bought back in the 70's was made by Kinderman. I quit using it after the second roll. Bad news.
    Don Bryant

  10. #10
    Nicholas Lindan's Avatar
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    Quote Originally Posted by donbga View Post
    Never ever use one of those dryers. Your film will come out like a coiled spring. ... Bad news.
    My take on it is that if it works then everyone will be using one, sooner or later.

    Hear that, everyone? Get yer red hot f-stop timers here! Enlarging meters too! Buy both and get a free footswitch... Guaranteed not to curl your film.

    It gets depressing, if I could sell 10,000 of the bleedin' timers they would sell for $29.95 each [though they would have to come in a tacky made-in-china plastic box, instead of a tung oil varnished, stained, finger-joined cabinet work enclosure].
    DARKROOM AUTOMATION
    f-Stop Timers - Enlarging Meters
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