Large contact printer with AIR BAG?

[lightwriter]

I'm wondering if anybody has ever encountered a contact printer that has any sort of "airbag" as part of it. I am competing for a contract in which my incumbant is integral with the contact printing of Aerial negs. I have been in a darkroom professionally for 45+ years. Never heard of such an accessory or its use. Anybody clue me in. Learn something new every day!

[William Whitaker]

I believe it was designed to maintain full contact between the paper and the negative against the platen. It would provide more even pressure than conventional springs which would be important in critical applications such as aerial work and photogrammetry.

[David R Munson]

In serigraphy (screen printing), I've used UV exposure units that have a vacuum back of sorts that involves a piece of vinyl or rubberized fabric of sorts connected to a vacuum to suck it flat against the glass, keeping the sensitized screen and the stencil tightly against one another. I don't see why you couldn't use something similar (whether a vacuum sucking things flat or an airbag pushing things flat) for contact printing.

[Jim Jones]

Vacuum printing frames don't exert much strain on the glass. An air bag would. The frames I once used for 32x40 film would have exerted over a ton of pressure on the glass if they used a bag instead of vacuum. Glass under constant or repeated stress can be permently distorted.

[Jay DeFehr]

A friend is helping me to build a pneumatic contact print frame, even as I type. My design doesn't use an air bag, but a diaphragm, and more closely resembles a diaphragm pump than the bladder-type aero contact printers. My design is only good for developing out processes, as it's not a split back, but for its intended purpose it works superbly. I don't know how it would fare at 32x40, but at 14x17 it works great. We're working now to incorporate a registration system, which will be useful for multiple transfer carbon printing, and many other applications, and an integrated light source.

[Jim Noel]

Years ago I had a contact printer with an air bag. It was pumped up with bicycle pump. The light source(s) were 20 argon or xenon lamps, each with its own switch so it could be used for burning and dodging to some extent. I don't remember he maker. It was a pleasure to use, but large, bulky and hot.

[KOG]

You need an aerial film contact printer. The air bag acts as a pressure plate to keep the negative pressed against the paper or diapositive film. Look at http://www.egoltronics.com/markv.html or perhaps look for military surplus.

Kevin

[nolindan]

A vacuum system will work far better than any air bladder.

Atmospheric pressure is 15 lb/sq in. Even a 14x17" vacuum frame will exert a clamping force of 3,500 lb. while putting very little strain on the glass. A 32x40 vacuum frame has a total clamping force of 19,000 lb - close to 10 tons!.

Needless to say if you used an air bladder and tried to pump it up to more than 1psi you would break the glass. At 1 psi the bladder would exert 238lb of force in a 14x17" frame. Small systems might use a bladder if contact isn't critical as the mechanics are simpler (cheaper) and it can use shop air, saving the price of a pump. Another reason for using a bladder is if one is printing frames from a long roll of film - the film and paper can't 'flow through' a vacuum frame because it would break the vacuum seal.

But even 1 psi of evenly distributed clamping force is more than a spring-back frame exerts. If a 3-spring 14x17 frame has 30lb of clamping force the average pressure on the material is a puny 1/8 psi - distributed unevenly so some areas have almost no force.

If you are going to build a DIY air bladder system it might be a very good idea to use a piece of thick tempered safety glass. Tempered glass is quite strong and safety glass will crumble into pebbles rather than sharp shards when (er, hopefully 'if') it breaks.

[Mark Sampson]

At a former job we used a '50s? vintage contact printer made by Miller-Holzwarth for the USAF. It was a console-sized box with a lamp below and a glass top. Aerial long-roll negatives ran across this emulsion-up, and copying film or paper was placed emulsion-down on top of the neg. There was a lever-clamping setup, not unlike a dry-mount press, on top, that forced the air bag down onto the film to make proper contact- the bladder was filled with a bike pump. It was a workable artifact in the '80s, I'm sure the company is long gone now.

[Tracy Storer]

I just picked up a 9"x18" contact printer for aerial negs, 40's-50s era, uses an air bladder as pressure-plate.
Photos tomorrow.

[David A. Goldfarb]

We had one in our high school darkroom, which was also used by a vocational program in offset printing. There was also a big copy camera with the shooting stage in its own room, and a vacuum back that opened into a space adjacent to the darkroom.

I remember the way it worked was you would put your negs emulsion side up on the glass (the bulbs, individually switchable, were underneath), paper face down on the negs, and then you would lower the back. When the lock clicked in, the bag inflated, and when it was full, the lights came on for the exposure and turned off at the end of a preset time. Click--bzhzhzhzhzhzh--zap.

[Peter Galea]

I have one for sale in the Santa Cruz area.
$20.
It is very heavy, I will ship however there may be sticker shock.
PM for further info.

Also an Adams Retouching Machine.
Pete

[Tracy Storer]

A quick iphone shot of the front of the unit, something like 60 switches are for each exposure bulb, there are also switchable safelights etc.......it is heavy. I'm looking forward to giving it a go, once I get the new darkroom built.

[jb7]

I've done some tests using a computer monitor as a light source-
but I concluded that it wasn't possible without a vacuum frame.

However, a monitor will give millions of light sources, controlled graphically by coupling it to a scan of the negative, which can be overlaid by colour layers, acting as filter grades, or areas of greater or lesser brightness, to burn or dodge.

A monitor might be problematic in one sense, that the pixels illuminate over a wide arc, though that problem is not insurmountable, and I reckon it would easily be possible to get definition down to about 3mm.

[rjmeyer314]

I have a Morse contact printer with an air bag. The top pressure plate lacation is fixed when closed and held by a very hefty clamp affair. If you put too much pressure in the air bag and then close the lid you will definitely break the glass. You really don't want much pressure at all in the air bag.