Advanced Film Drying--vacuum?

[Pete Myers]

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

 

[Akki14]

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.

 

[Bob-D659]

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.

 

[JBrunner]

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.

 

[Pete Myers]

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

 

[MikeSeb]

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.

 

[JBrunner]

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.

 

[Nicholas Lindan]

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.

 

[donbga]

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.

 

[Nicholas Lindan]

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].

 

[Pete Myers]

Desiccant

Oooops. Looks like one of my posts did not make it. I will try again.

I am not sure what the reason is for the desiccant. It is common with commercial lab grade vacuum drying systems---see the example below.

http://www.coleparmer.com/catalog/product_view.asp?sku=0891260

I think I will proceed with the experiment in the new year and will report back my results. There is so much experience with APUG members that I thought it was worth a try to tap into the collective knowledge and see if some one had already had a go at vacuum drying. I do appreciate all your replies and ideas---most grateful for the interest.

I like 135 format, but tend to push its use to an extreme. With a rangefinder camera and optics and the new emulsions (TMAX-2 400), I find it possible to get an extraordinary amount of information content off of a negative.

When I use to scan with my Imacon 343, the dust issues never showed to this extent---but that was at 3200 ppi. Now I am at 6300 ppi with the X1 and its a whole new ball game.

I do occasionally get film back from the lab that 'lucks out' and is nearly dust free, so it is not a scanner issue. But it may be a good idea for me to check reference with a XTOL D&D to make sure it is not a PyroCat issue---though I have seen the problem over multiple batches of developer. Further, I have seen the same trend of problems with tests at different labs, and even with color negatives.

Most grateful for the interest---I will report back when I have done the experiments.

Pete

 

[michaelbsc]

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].

Boy I understand that feeling. In my line of work we usually build *ONE* of whatever it is, then never see another one. Every customer on the planet wants to know why things aren't cheap like TVs are in Wal-Mart. You can't get them to understand that the prototype TV wasn't so cheap, and what they're ask us to quote is really just like a prototype.

I'll take one in a plastic box if you've got it.

MB

 

[Martin Aislabie]

Pete, you are quite right - pulling a vacuum will boil off the water on your films.

The drying cabinet for a vacuum would effectively need to be a Pressure Vessel - which is a serious piece of Engineering

To pull enough vacuum to dry the film, you would need to reduce the pressure inside the drying cabinet down to only a few Pascals (I can tell you how many if you want to persist with the idea)

However, it will have to be one heck of a drying cabinet - with a hermetically sealed opening and cabinet sides that will each sustain aprox 6 tonnes of load without deformation.

Half inch think steel plate will do the trick for the walls.

No idea who you would talk to about a sealed opening - do you know anyone in the Submarine or Pressure Vessel manufacturing industry?


Alternatively you could try a sealed volume and a Chemical Desiccant Salt arrangement - but I have no idea how you control the chemical dust levels to the levels you require


Or - you could go back to your Lab and ask them about their levels of cleanliness and general house keeping – they obviously can do it, as they meet your standards – if only occasionally

Martin

 

[Nicholas Lindan]

I'll take one in a plastic box if you've got it.

Well, we haven't made one in a plastic box yet. Lets see ... $80,000 for the tooling, $29.99 for the timer.

 

[aparat]

I can share my experience with you because I used to have the exact same problem you describe. I solved it by using a Senrac on-reel dryer. After a quick soak in distilled water with Photo Flo, I dry the film on-reel for 8 min. with warm air, followed by 8 min. of cool air. The negatives are absolutely spotless. However, the film curls. I solve it by winding it against the curl and putting it in a 1 inch tube for a couple of hours. Works great!

The other source of dust is your scanner, and in particular the film holder. If you're using a glass holder, you will have to clean the holder really well.

The other thing that works great is an anti-static film cleaner like this one. It works wonders, at least for me .

I second the advice about humidifiers.

Hope this helps.

 

[dancqu]

Dear Group:
I would appreciate a bit of information from the photo
emulsion engineers and experts on methods of advanced
film drying post development. Pete Myers Santa Fe, NM

The accumulation of dust on film is a function of time.
All things being equal, the dryer the film at start the less
time required. So first eliminate the surface water using the
designed for film eight blade squeegee. A pre or post soak in
alcohol may be possible although I do not know if it would be
compatible with squeegeeing.

I squeegee for fast drying. I find no cabinet needed. If you
try the eight blade be sure it and your film have had a soak
in a weak PhotoFlo solution. Draw it slowly down the full
length of the film. Dan

 

[CBG]

Back to basics. No extreme measures until you've eliminated the usual suspects.

If your film comes back from other labs with less or no dust issues, your current lab is the likely problem.

Do your films, when processed by other labs, have the same issue? If so, you may be the source of the dust problem. Anti static brush and various measures may help.

Best,

C

 

[GraemeMitchell]

I'm going to venture that scanning a 400 speed film at 6400dpi isn't resolving 1000 of specs of dust, but maybe it's the films structure you're seeing. Might be wrong. I'd try asking around in scanner or digital forums to see if they can offer ideas in this direction. Just a thought.

 

[wogster]

I'm going to venture that scanning a 400 speed film at 6400dpi isn't resolving 1000 of specs of dust, but maybe it's the films structure you're seeing. Might be wrong. I'd try asking around in scanner or digital forums to see if they can offer ideas in this direction. Just a thought.

You know, I was thinking along that line as well, there is a limit to scanning, where you start to see the structure of the film itself, which isn't perfect..... Same goes for enlarging, for example a 4x6m image from a 35mm negative will look pretty ugly, same thing from an 8x10 negative will look pretty good.