UV glass in negative carrier

[Michael R 1974]

Any reason NOT to use UV glass in a negative carrier (Saunders VCCE diffusion head - quartz halogen)? It's not that I want UV glass per se, just that one of the particular glasses I'm experimenting with only comes a UV coating.

Is there even a meaningful amount of UV-range light in the system? I'm just wondering because I suppose if there was, and you filtered it out, and further assume enlarging paper sensitivity extends into that range, you'd need longer exposures, or even slightly different filtration with VC papers (need to boost contrast slightly due to filtering of some blue-violet spectrum.

[Bob-D659]

Shouldn't make a difference, most halogen bulbs made these days already have a UV blocking coating on them already. On the other hand, quartz capsule halogens can put out a lot of UV if you run them hot enough.

[Sal Santamaura]

Any reason NOT to use UV glass in a negative carrier (Saunders VCCE diffusion head - quartz halogen)?...Is there even a meaningful amount of UV-range light in the system?...

No reason NOT to. In fact, I suspect doing so would be beneficial. Of all enlarger light sources I'm familiar with, halogen lamps are the only ones that emit UV.

...I'm just wondering because I suppose if there was, and you filtered it out, and further assume enlarging paper sensitivity extends into that range...

See page 81 of Ctien's Post Exposure

http://ctein.com/PostExposure2ndIllustrated.pdf

for the full explanation of why you might experience focus shift with certain enlarging lenses in this situation.

[Michael R 1974]

Yeah I started a lengthy thread a while back on here regarding that residual-short wavelength focus shift thing. I ran detailed tests (initial tests posted in the thread) and found zero evidence of it in my system with the papers I use. There was some disagreement in the thread regarding whether the amounts of UV-range light (if any) in quartz halogen systems is anything more than trivial. In the end I'm not sure we answered that particular question.

I think you're probably right though, I can't see how it would hurt to use UV glass. In fact, I'm just thinking, doesn't the base of TMax 100 filter UV? In the end I guess as long as you standardize for a certain set of equipment you're fine.

Thanks Bob and Sal. I'll include this particular glass in my experiments.

[ic-racer]

Is there even a meaningful amount of UV-range light in the system?

Most tungsten/halogen light source in enlargers that I am familiar with have a UV filter somewhere in the system. Maybe incorporated into the light box if you don't see an obvious glass in front of the lamp.

[Sal Santamaura]

...doesn't the base of TMax 100 filter UV?...

Indeed it does. Yet another reason the glass won't hurt if that's the film you're printing from.

[chimneyfinder]

Certainly there is heat absorbing glass in some enlargers - in my Devere condensor head it has a slight green cast - but I don't know if it filters UV as a by product. I suspect there would be no stong reason to suggest that a UV filter would be detrimental to the projected image and I would think it would have good enough optical quality when sandwiched to the negative.
Regards, Mark Walker.