Diffusion Plates and Cold Light As Enlarger Light Sources

[ed_balko3]

The cold light sources which I've seen, the Aristo and an old Beseler

source, employ a diffusion plate, plastic or ground glass, between

the light tube and the negative.

 

Can the same light source characteristics be obtained by placing a

similar diffusion plate between the lower condensing lens of a

condensor light source and the negative? I recall that Durst used to

supply a diffusion plate with some of their condensor enlargers.

[ken_lee11]

Perhaps plastics and frosted glass have changed over the years, but I tried this 30 years ago, with frosted glass, and ended up buying a cold light head instead. The cold light head stays truly cold, whereas the lightbulb got hot and threatened to cause problems. Besides, the "frosting" in the glass showed up, being near the film, and there was a noticeable hot spot from the light source. So I tried painting the inside of the enlarger white - this time, with some heat-resistant paint. It didn't work. It smelled badddd.

 

If you've used a real cold light head, you see the advantage in that it produces light of the correct color at a consistent level of brightness, with little time required to warm up. Because they are not hot, plastic can be used as a diffusion plate, with no fear of melting. That plastic is really diffuse.

[ernie_gec]

If you are using a beseler condenser setup with a diffusion-plate-above-the-negative-carrier, the results should be identical to cold light in terms of print quality. The practical problem, aside from heat as mentioned above, is that you'll really increase your print times dramatically. I tried it, despaired, & got a cold light.

[scott_eaton]

I agree with Ernie.

 

I've used counltess enlargers commercially and have yet to see a difference between modifying a condensor with a chunk of milk-plexi, dichroics, and a straight cold-light. Al produce a large, illuminated light source with the same optical properties and hence the same effects.

 

All the cold-lights I've used tend to get pretty warm and cause the same amount of thermal induced negative flex as a incandescent based condensor.

 

The disadvantage of a diffusion plate (usually milk plexi) is that they eat a lot of light. Most Dichroics use a diffusion plate above the neg stage, but have halogen bulbs that burn much brighter (150-300 watts) compared to the typical 50-75 watts of a condensor.