Contact print max glass size

Discussion in 'Contact Printing' started by padraigm, Feb 18, 2013.

  1. padraigm

    padraigm Member

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    Hi All,

    I just have a 8X10 spring loaded contact frame. I ultimately want to go bigger and have read that 8X10 is really the limit for contact printing frames. Is this true? Would say 2 ~16X20 1/4 inch sheets of glass with regular (rubber feet) clamps provide enough pressure for a reasonable print or would i really be pushing it? This would be for pd/pt printing.

    Thanks
     
  2. Shawn Dougherty

    Shawn Dougherty Subscriber

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    You can get much bigger frames from many different places. Do a google search, do an apug search. You'll find lots of examples, suggestions and prices.
     
  3. Nicholas Lindan

    Nicholas Lindan Advertiser

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    I have an 11x14 that works tolerably well.

    The key to contact printing is the psi [pounds per square inch/pressure]. 16x20 is 320 sq inches - to apply a pressure of 1/2 psi (a not-too-well filled party balloon's worth - about what most frames can manage) you would need 160 pounds of clamping force.

    You only need one sheet of glass. You can make the backing from 3/4" plywood. You will need to cover the plywood with thick felt. A frame around the glass will help to distribute the pressure from the clamps.

    Large contacting frames use vacuum to clamp. One side of the frame is glass, the other has a rubber blanket attached to it. Air is evacuated and the blanket clamps the artwork to the glass with atmospheric pressure - 14 psi. A 16x20 frame would have over 2 >tons< of total clamping force. With the rubber blanket there is no net force on the glass. There are contacting schemes that use a box with holes as the evacuated side and a thin sheet of plastic that goes over the artwork to allow evacuation of the space between the a/w and the film.

    You used to be able to get contacting frames for free as print shops were converting to digital and 'laser plates' right and left. You can find them on ebay - the larger ones cost much less than the smaller ones. And they weigh a ton [almost literally for the large 40x48" ones]. Search for "vacuum frames" and "exposure units".
     
    Last edited by a moderator: Feb 18, 2013
  4. Allen Friday

    Allen Friday Member

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    I have a spring back 16x20 frame that I got from B&S. It works fine. I also have a much larger frame that I hand built. I do 20x24 inch prints with it. I had 4 custom springs fabricated for it by a local metal shop. It is fine for pt/pl prints.
     
  5. Mainecoonmaniac

    Mainecoonmaniac Subscriber

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    I made a 20x24 for my light box. I ripped the molding on my table saw out of oak and used scrap plywood with felt for the back. It cumbersome. I'm thinking of making a smaller one.
     
  6. Photo Engineer

    Photo Engineer Subscriber

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  7. DWThomas

    DWThomas Subscriber

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    I might think a thin layer of foam of other elastic material on top of a sturdy piece of plywood (maybe 3/4 birch) would help to take up any surface irregularities to promote solid contact. One would want relatively thick glass (or maybe acrylic) so as not to have it explode from the force. Wingnuts and bolts, or some toggle clamps, could be used to clamp the frame.

    Heh, I think I have a 2 1/4 x 3 1/4 Kodak contact frame somewhere that's been in the family since 19-ought-48 or so. (Velox and a Tri-Chem Pack anyone. :D )
     
  8. Ken Nadvornick

    Ken Nadvornick Subscriber

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  9. richard ide

    richard ide Subscriber

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    I had a 66" x 96" vacuum contact frame and I have seen one 24' long.
     
  10. padraigm

    padraigm Member

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    Thank you everyone. I think my follow on question is where would I see a decrease in quality above 8x10?
     
  11. richard ide

    richard ide Subscriber

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    I think that you would not experience quality issues if you were contact printing negatives exposed in camera. I had one client that I copied fine art drawings for. I made same size camera negatives on 30" x 40" Plus X Pan film and then made contact prints. The quality was outstanding. I have also made large size duplicate negatives from smaller format film for either enlarging or contact printing. Unfortunately the variety of films available today is very restricted with a corresponding reduction in the options available for reproduction. I guess at one time I had at least twenty BW films in my shop to choose from and many choices available for procedure.
     
  12. dpurdy

    dpurdy Subscriber

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    padraigm, I apparently live in a world with different physical laws than everyone else.
    I started platinum printing trying to use an 11x14 contact printing frame and could never get tight enough contact until I started jamming pieces of card behind my paper to force it to be tighter. I finally gave up when I started getting little wood chips to deal with.
    I decided to just use 1/4" plate glass, two sheets. I found I needed clamps to really get it tight. The glass was 11x14.
    Then I started printing on 11x14 paper and needed oversized glass. I tried 16x20 glass with 4 clamps and could never get it tight enough. I tried foam behind the paper and card or mat board behind the paper and could not get it to work. Very small areas would be out of focus. So I got glass cut 14x18 and started using 8 small size industrial clamps. 3 on each side and 1 on each end. Now I get tight registration. I have never seen any newton rings.
    Awhile back I was hired to print some antique 11x14 glass negs in platinum. I needed over size paper to print on so I went back to the 16x20 glass and sandwiched the 11x14 glass negs between 2 sheets. A couple of the glass negs were not perfectly flat and some small areas printed a little soft.. I should have gotten a vacuum easel.
    Perhaps you should consider a vacuum easel. You can make one pretty easily.
    Dennis
     
  13. Mike Wilde

    Mike Wilde Member

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    I have a frame that comforatble holds 11x14 negatives. It came out of a mid 70's plate burner.
    It has glass plates on both sides of the frame , and has a piece of black 'velvet' bonded to both sides of some kind of cardboard board that sits between the glass panes.

    Originally the frame was hinged mid long edge to swing in the middle on a support so that you could load one side, then flip over and load the other side. I guess you flipped it while the burner was on so as to do two burns for one start of the arc lamp.

    The velvet is stiff to crush, and keeps the sensitized paper in good contact with the negative up against the glass.

    I have yet to use it by loading two sides at once.
     
  14. padraigm

    padraigm Member

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    Thank you so much everyone for your input. At the moment I am limited to 8x10 and happy so far with the contact frame I have. Looking to go bigger especially with some pan shots and will be dipping my toes in digital negs soon. It seems there are some who get good prints with bigger contact frames and others that don't. I think I will try Dennis solution with clamps first while keeping my eye out of a vacuum frame.

    Again the input has been invaluable, thank you again
     
  15. JMB

    JMB Member

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    Will insufficient pressure from the glass on the negative and paper cause Newton rings? I am going to take a shot at 20 x 24 inch contact prints, and I want to be sure that I set up in such a way that I do not have a problem with Newton rings. It appears from your post that anti Newton ring glass is unnecessary. In fact, it seems to me that I have read posts from individuals that encounter problems with Newton rings in making enlargements despite their investments in anti Newton glass.
     
  16. nicholai

    nicholai Member

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    I'm making a crude 17x17 frame, i'll let you know how well it goes! :D
     
  17. JMB

    JMB Member

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    Best of luck. Please keep me posted.