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cyrus
13-Apr-2008, 21:04
One of the biggest hassles in alt processes is making a full-size positive which is then usually contact-printed using a uv light source. However, instead of making an enlarged positive and then contact printing it using the sun or a uv exposure unit, what would happen if you put a uv lightbulb in the enlarger, and then simply enlarging a negative as usual like you were making a "straight" print?

Ron Marshall
13-Apr-2008, 21:14
Unfortunately, the glass will absorb most of the UV, unless you are using a quartz enlarging lens.

cyrus
13-Apr-2008, 21:39
Unfortunately, the glass will absorb most of the UV, unless you are using a quartz enlarging lens.

Which glass? Don't contact print frames use glass too?

Donald Miller
13-Apr-2008, 21:41
It has been done before with Azo...which was and is (I guess that some still have it) very sensitive to UVA radiation. Jensen had a high wattage enlarger built to enlarge on Azo. Unfortunately Azo is much, much more sensitive than the alt processes. John Zdral had one of the Azo enlargers at one time...

Jensen (Durst Pro) had a Pt pd enlarger in the works at one time too...but I don't know that it ever reached production. As I recall the Azo enlarger had something like a 5KW lamp...read that to mean installing a new electrical main and new air conditioning.

Going on what Jensen said, according to his tests, the El Nikkor enlarging lenses did a pretty good job of passing UVA...much better than Rodenstock or Schneider. He went on to say that the Durst condensers (as in the 138 and the 184 did a pretty good job of passing UVA as well).

So yes it is possible but it requires something with a well selected light source and very high wattage to do what you want to do...the cost...priceless!!!

For your information, I converted my Durst 138 from the opal Thorn lamp (150 watt) to a lamp that approximates more closely a point light source and I designed it to use a 1200 watt lamp....this lamp requires a supplemental cooling fan for the lamp house and it allows very short and provides very sharp enlargements...much sharper than a conventional condenser/opal lamp configuration.

If I were going to do something along the lines of what you asked about, I would opt for a mercury or HID lamp and since these have a slow start characteristics, I would leave it on in a continual burn mode and use a shutter on the lens to control exposures.

John O'Connell
14-Apr-2008, 06:54
Well, there's a relatively long history to Pt/Pd enlargement:

http://www.usask.ca/lists/alt-photo-process/1996/alt96a/1087.html

You also might not need a much bigger lamp than the one used for the Azo enlargers, unless you really wanted a short exposure on the ferric-sensitized paper. It doesn't seem like a big deal if the exposure takes seven minutes on the enlarger for Pt.

The bigger issue I see for Pt enlarging is the potential focus shift from UVA to the visible range.

Nathan Potter
14-Apr-2008, 09:21
Seems that projection UV exposure would be possible for Pt/Pd. If UVA source is used, say around 365 nm line of a mercury lamp, there is some absorption in the condenser lenses and the imaging optics, esp. if the condensers are soda lime glass. But, so you may lose 50% of the light - you use a longer exposure. The heat from these lamps is pretty intense and might cook the conventional enlarger lamp house. They are high pressure gas filled lamps and are expensive. You may need a 250 to 500 watt version for reasonable exposures. Seems to me that you want to deliver 50 to 100 mW/cm2 to the exposing surface - but I'm only guessing. Don't know about the effect of such high optical flux on your negative! Don't worry about focus shift - you'll do focusing using the visible UV part of the emission spectrum (about 420 nm) and a bit of stray blue visible light. Just watch your eyes for damage from the reflected light and don't use a mirror focusing device unless you use protective glasses! Google for info on UV lamps for industrial use. Good thought!

Nate Potter

nolindan
14-Apr-2008, 10:29
a uv light bulb in the enlarger

The old Solar enlargers - the sort that used the sun and look a bit like an over sized Polaroid DayLab - might give you enough UV. But the sun isn't all that bright: solar radiation is only 1kW/Square meter. To get a printing time equivalent to a solar contact print would need a Fresnel condenser the size of the print being made. And then there is the issue of cooling the negative ...

Interesting thread on the subject on photo.net http://photo.net/bboard/q-and-a-fetch-msg?msg_id=00G5lN.

Negative cooling would be a lot easier to handle if you used a 'Kokomo filter' before the negative so only the UV would get through.

Google will get you more.

cyrus
14-Apr-2008, 14:53
I have a platemaker, and you're right - the heat/radiation would frizzle my neg, melt my enlarger and burn out my eyes.
Oh well, worth a shot.