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Exposure unit with halogen AND Flourescent Sockets???

3471 Views 15 Replies 3 Participants Last post by  BroJames
Hey guys I have an exposure unit i picked up from a local shop for cheap, my dilemma is this. It has both a halogen socket in the bottom as well has spots for 4 flourescent bulbs. There were two black light blue 40w 48" bulbs, which were no good, so naturally I'm headed out to buy four more to fit all the sockets but after this thread I'm a little un sure about my decision. Will this be good for half tones and fine detail? Will this thing just expose the heck out of my screens before i know it? Also it has a vacuum lid. Please any advice would be great.
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Is this correct?

1 halogen socket
4 CFL socket
2 40w fluorescent socket

I am thinking that maybe the 4 CFLs, if they are for CFLs, are for registration purposes or viewing of film positives. As to the 2 40w 48" fluorescent sockets they may be added to shorten exposure time. I have never tried combining 2 UV source but I know there are commercial exposure units with 2 different UV source which the manufacturer claims to shorten exposure time. I believe it is also a halogen based exposure unit in relation to the box and to each other.

Maybe you could post some pictures so we can see how the sockets are positioned.
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.
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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.
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However, there are some really "fast" emulsions out there that will render a good exposure in about 1.5 minutes based on the above light sources.
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.
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Hey guys, thanks for all the great insight. It turned out the tubes weren't broken, just plugged in incorrectly :mad: so now its ready to rock. It turns out the timer built in has seen better days so I had to rewire everything directly to the toggles (national screen printing went out of business so my hands were tied I think). Anyhow, I'll be taking this thing on its maiden voyage with both the 500w Halogen and 2 40w uv tubes, I'll keep you updated as well as post some pics. Just one question though, how long should I expose for? I'm gonna use the dual cure emulsion from ryonets starter kit.
Hmm...I posted a reply yesterday...must'be been pulled, anyhow, I'll be taking this on its maiden voyage tomorrow. I'll post pics and my results.
Ok so my first four attempts have been in despair. Three didn't fully expose (this I found in the washout process) some just had thin lines fall out, others emulsion just washed out. Finally the one that worked, after increasing exposure time each time (20 minutes by the way) showed us a basic issue...my positives I had printed locally were not solid black but rather lots of tiny small black dots. The light had made its way through these and exposed tiny bits of emulsion. After one print we realized how big an issue this is. Raised ink everywhere, fuzzy edges, just terrible. Now we need 112 shirts printed by Friday for a stores grand opening saturday and we are drastically behind. Anyone willing to offer advice to help us succeed in this golden opportunity please do.
Thanks again all.
...I'll be taking this thing on its maiden voyage with both the 500w Halogen and 2 40w uv tubes...

Ok so my first four attempts have been in despair. ...Finally the one that worked, after increasing exposure time each time (20 minutes by the way) showed us a basic issue...my positives I had printed locally were not solid black but rather lots of tiny small black dots. ...
What is the distance of the halogen, and the UV lights to the glass?

If your printer is not as opaque as ideally should, depending on the opacity or lack thereof, you may underexpose the emulsion. Of course underexposure is not recommended but if you do not have access to a more appropriate printer it may be an interim solution. Actually, many commercial printers underexpose as a routine.

A 500w halogen 24 inches of so below the glass should produce "workable" exposures in 5-7 minutes(for most emulsion). But from what I gather based on posted information, to get a step 7 on the stouffer would require at 12-20 minutes.
The bulb is no more than 24" away. Is it possible the emulsion hadn't properly dried before we exposed? This round we cleaned up all moisture possible in our dark room and left a fan on them. It's going to be almost 20 hours before we can get to them. Also we have found some other prospects as far as large format printers for the transparancies. We may just double up this round and see where that gets us
Also how would you go about washing out an under exposed screen? As it were we were washing emulsion and parts of letters out.
Now that I think about it...the halogen has be more like 36 inches and the black lights are more than ten inches away
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.
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Success! Good solid transparancy and completely dried emulsion prior to exposing did the trick! I measure and the hal. Is 24" and the black lights are about half that distance. We were able to get a solid exposure in 15 min. We could probably go less but this close to deadline didnt seem fitting for experimentation
That's nice. Hope you can update us on the best exposure time when you have the time to experiment.

Is the 15 minutes with both the halogen and UV lights on? Are the fluorescents evenly spaced?
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