Exposure unit with halogen AND Flourescent Sockets???

The halogen bulb is used for screen exposure, as halogen light is brighter & more intense, which allows for faster screen exposure, plus better exposure of halftones. The flour tubes, which are probably controlled by a separate switch, are used mainly so that your exposure unit can double as a light table. Some people have used black light flour tubes in addition to the halogen light to achieve better screen exposure with halftones, but then the black lite tubes defeat the ability to use as a light table. I had this same type of exposure unit, and found that just the halogen light was sufficient for very good screen exposure, and I liked the idea of the standard flour tubes to use as a light table to lay my film positives onto, to make sure they all lined up correctly before I used them to expose my screens. Bear in mind that since your using a halogen light source to expose your screens, your exposure time will be much faster, depending on the type of emulsion you use.

I used to use a 500w halogen unit and yes, it is enough to give relatively good or better exposures. The UV lights are supposed to shorten exposure time and if a detailed comparison is to be made, I think it will contribute to poorer, not better, exposures than just using halogen alone.

A 500w halogen worklamps placed 18-24 feet away, a common distance, has about the same exposure time as 4 regular 20w household fluorescent placed 4-6 inches below the image(also a common distance for fluorescent). It should take at least 3 times as long for a 500w halogen to expose the same emulsion compared to 4 20w UV lamps at 4-6 inches. I don't think even a 1000w halogen will beat 4 20w UV lamps in exposure time. I have a 1500w halogen but it got too hot even under 1 minute so I don't use it for exposures.

Different emulsions have different exposure times that's for sure. An 1.5minute exposure on the using the above UV sources, wattages at the specified heights is not impossible although I have not tried such quick curing emulsions that works on 500w halogens or household fluorescent. However, UV-rich light sources like 4 pcs 18-20w UV fluorescent and 400w metal halides are known to expose most emulsions in about 1.5minutes or so. My not so ideal mercury lamp with a not so high wattage of 250w(compared to 2000-5000w halides) can expose in under 2 minutes.

LegitScreening, can you post a picture of your unit.

Brian, you you said "I had this same type of exposure unit" so does that mean you are using a different unit now? Would you still remember the setup to do a simple illustration? I am asking because I found out that fluorescent lamps does a better job in exposing "taped" film positives and I am thinking of making a UV exposure units. By "taped" I mean large images that prints on 2 or more film positives on a regular printer and therefore have to be taped together for the exposure. My mercury lamp, like my halogen earlier, does not expose the edges of the cuts well leaving some unexposed lines. This is why I am now interested in such unit that combines single and multi point light sources.

That's what I am curious about. How are the 4 fluorescent placed on the unit to still let the halogen UV through? I could try some imagination though but the fluorescent at 10" won't be evenly spaced. A picture or some illustration would be nice.

I've only tried 24" at the most but at 36" a 500w halogen should take about 10 minutes for a workable underexposure and at about 20 minutes for a good exposure. Later figures are guesses though.

To wash out underexposed screens, wet the emulsion and let stand for a minute or so, then wash with light water pressure. Some people swear their underexposed emulsion served them well, and frankly I do not doubt that. But to follow proper exposure methods, underexposure should only be an alternative and a transparency with greater opacity should be more desirable to enable you to expose properly.