Optical Quality of Glass in Contact Printer

[seadrive]

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

[Dave Parker]

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.

[User Removed]

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.

[PaulH]

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.

[David A. Goldfarb]

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.

[Oren Grad]

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.

[seadrive]

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.

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

[Donald Miller]

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

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.

[Jim Noel]

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.

[Jim Jones]

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.