Optical Quality of Glass in Contact Printer

[David A. Goldfarb]

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.

[Mike A]

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.

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

Mike

[Donald Miller]

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

Mike

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.

[Mike A]

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.

Thank you Donald, I Never new this.

[Jim Jones]

. . . 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.

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.

[seadrive]

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