Optical Quality of Glass in Contact Printer

Discussion in 'Contact Printing' started by seadrive, May 24, 2006.

  1. seadrive

    seadrive Member

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    Hi guys and gals,

    Okay, I know I'm gonna get thrashed for this, but...

    Does the optical quality of the glass in a contact printing frame make any difference in the apparent sharpness and/or contrast of the print?

    Common sense tells me it shouldn't, as the neg and paper are in direct contact with each other. But none of my prints have the feeling of sharpness and detail I get when viewing the negatives.

    What say you?

    Regards,

    Steve
     
  2. Dave Parker

    Dave Parker Inactive

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    Can you post a scan and give us a bit of an idea what your talking about?

    Different variations of the quality of glass, can and does make a difference..most current glass, will project a pretty good image through it without a lot of problems, however there is some really poor glass around that can distort light as it passes through it.

    R.
     
  3. User Removed

    User Removed Guest

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    This is been discussed several times here on APUG, but I cannot recall what people's final conclusions were. It might be worth it to do a seach and see.

    I'm using cheep picture framing glass from the local framing store, and never had any complains about the results. When it gets scratched or old I will just buy a new one.

    I would think if your using like UV resistant glass, or that non-glare glass...its going to mess with your image.
     
  4. PaulH

    PaulH Subscriber

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    I sandwich the film and paper between 2 pieces of 1/4 inch plate glass. I also push it down so that the negative and paper are in contact all over (more or less). I get good results this way. Maybe your frame is not making good contact between the film and the paper. You could try adding a piece of mat board and see if that makes a difference.
     
  5. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    What format are you shooting and what kind of frame do you have? Bigger than 8x10" and the quality of the frame and evenness of spring tension become bigger issues.
     
  6. Oren Grad

    Oren Grad Subscriber

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    The likeliest cause of problems with sharpness or microcontrast is inadequate contact between negative and paper due to insufficient and/or uneven pressure across the sandwich.
     
  7. seadrive

    seadrive Member

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    I'm using a cheap Premier 8x10 metal frame, with 5x7 film.

    With the amount of pressure required to get the "wings" under the frame of the printer, it's hard to believe that the neg and paper aren't making a flat sandwich, but ya never know.

    I'll try some other things to see if I can pin down the problem, or maybe there isn't one. Doesn't sound like anyone thinks the quality of the glass should matter too much.

    Thanks for your help, everyone!

    Steve
     
  8. Donald Miller

    Donald Miller Member

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    Based on my experience, the light source used to expose the contact print will have more effect on accutence then the optical qualities of the glass used up to a point at which the glass is visibly unparallel.

    The more diffuse the light source, the more light scatter you have coming through the negative. This affects contact prints just as it does enlargements.
     
  9. Jim Noel

    Jim Noel Member

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    You answered your own questio when you stated the brand of print frame. ALthough the springs may be hard to get under the edge, the center where the hinges are located has a tendency to rise up.

    One possible solution:
    Place a piece of mount board between the printing paper and the back of the frame.

    I do this with all of my frames and I have quite a variety of all vintages. I threw my frame similar to yours in the trash because of its problems.
     
  10. Jim Jones

    Jim Jones Subscriber

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    I haven't noticed problems with acutance or contrast due to the quality of glass, but have seen slightly uneven exposure, even though the glass appeared to be homogeneous. As I recall, a Premier frame I used years ago had felt padding. That can compact until it doesn't maintain really good contact between negative and paper. I replace such padding with velvet.
     
  11. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Yeah, I have a wooden Premier frame as well as a couple of others, and it's not as good. It's an 11x14" frame, but I usually only use it for 8x10" and smaller. I'd suspect the frame before I'd suspect the glass. Better frames are heavier and have heavier springs. My best frame is an 11x14" Kodak frame with registration pins, originally for dye transfer. I have an old 8x10" Folmer and Schwing frame that's also pretty good.
     
  12. Mike A

    Mike A Member

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    Donald, can you expand on this? I'm curiouss this to mean a bare bulb is better than an enlarger.

    Mike
     
  13. Donald Miller

    Donald Miller Member

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    Mike, I believe that it is demonstrable that the quality of light is quite influential on accutence which obtained on a print. I would not go so far as to say that a bare bulb would be inherently superior to a condenser enlarger for exposing a contact print. But I believe that a bare bulb would be superior to a diffusion enlarger or a frosted bulb used as the light source for a contact print.

    Contrast and edge effects or what I call accutence is effected by the size of the light source in relation to the object that it is illuminating.

    A frosted bulb is a larger effective light source than a bare bulb where only the filament is the light source. A diffusion light source whether that is a frosted bulb or a diffusion enlarger suffers from greater light scatter then a collimated and small light source.

    This information is what I have garnered from lighting engineers and from my own personal experience.
     
  14. Mike A

    Mike A Member

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    Thank you Donald, I Never new this.
     
  15. Jim Jones

    Jim Jones Subscriber

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    Whether a diffusion or condenser enlarger, or a bare bulb, is used as a light source on contact printing, the angle the light source subtends from the contact frame is similar. An enlarger is a light source rather less than an inch in diameter; a bare frosted bulb, rather larger than an inch. If intimate contact is maintained between negative and paper, this angle isn't important. Even a large diffuse source gives similar results in practice. In graphic arts we used a fairly small light source when contacting onto litho film because we didn't need the intensity of a large source. When contacting onto diazo film we used 5,000 watts of metal halide lights in a reflector subtending an angle of maybe 45 degrees from the vacuum frame. There was little difference between the two in the ability to hold 99% and 1% dots at 133 dpi. However, maintaining intimate contact between negative and paper or film was important, especially with the metal halide sources.
     
  16. seadrive

    seadrive Member

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    Interesting info, guys.

    I never thought about the quality of the light being used to expose the paper...

    I'm using a bullet lamp with a tiny 30 watt frosted flood. Because of the proximity of the light to my work surface, I've had to attach a piece of translucent (white, not clear) plexiglass and several layers of tissue paper to the rim of the reflector, in order to get exposure times in a usable range. As a result, I would say that the light itself is very soft, emanating as it does from a circle 6" in diameter.

    Fred Picker always said that cold light heads were superior to condensers, primarily due to the Callier effect, which he claimed was evident in enlargements, but not in contact prints. Since I'm only making contact prints, I never gave any thought to the softness or hardness of the light.

    As Picker would have said, "TRY IT!" I'll try it again with a naked bulb (5 watts???), and see what happens.

    Ain't real photography wonderful? If I was a digi-guy, I could just click the "sharpen" button in PS, and my problem would be solved, eh?

    Steve