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View Full Version : Tracing table as UV light source?



gneissgirl
03-18-2006, 08:42 PM
I have a nice desktop light table (tracing table, Port-a-trace). Its dimensions are approx. 16" x 18" x 2". The translucent plastic surface is removeable to replace the 2 fluorescent bulbs inside. Today I saw 18" UV bulbs in the hardware store, but forgot to note the wattage. Presumably my light table uses 18" bulbs, but I haven't checked the wattage on those, either. the label on the side of the case says 30 W, but I don't know if that means total or per-bulb. I'll have to take the screws off and look at the bulbs.

But I'm thinking this would be a good place to start for an UV light source, if I just replaced the fluorescents with UVs. I'd simply (ha) have to make some kind of shallow enclosure where it could shine face-down. Only one plug for the whole unit.
After seeing marv's setup my concern is whether only 2 bulbs would provide sufficient light for reasonably short exposure times.
Any comments on whether this is realistic? I'm thinking I could try it because I wouldn't have to destroy it to rig something temporary up.
thanks!

earlj
03-18-2006, 09:08 PM
gg -

I am sure that two 18" bulbs would work for exposing up to about 8" wide. You probably wouldn't even have to revamp the table - just replace the frosted glass with clear and make sure that you put something (black cloth) over it during the exposures. Do you have a contact frame? I made a nice one out of some hobby store lumber and a piece of 3/16 thick glass from a mirror and window store. It has a hinged back for checking on exposure without losing registration. Actually, you could just tape the negative to the paper and the paper to the glass and put a book or a board on it.

I bought one of those articulated desk lamps and a compact fluorescent spiral BLB type lamp for it, and it works just fine - it takes longer than a big fancy unit is all. Find yourself some tubes with the right length and the right ends whose number ends in either BL or BLB, and you will be in business. Coat up some paper and expose away.

Good reference sites:

www.unblinkingeye.com
http://www.ferguson-photo-design.com/alternative/index.html
http://www.mikeware.demon.co.uk/
http://www.bostick-sullivan.com/

buggy
03-18-2006, 10:54 PM
It's my understanding that fluorescent bulbs do emit UV. A normal fluorescent bulb would probably not emit as much UV as a BLB black light though. I use a clamp on work reflector with a screw in 13W spiral black light BLB. I have also used a normal spiral white fluorescent 30W and both work well. These single spiral lights require more exposure time but your setup with 2 18" lights should provide alot more UV than my setup with therefore much shorter exposure times.

I don't know how much 2 - 18 inch black light tubes cost but it might be worth trying a print with the fluorescent bulbs you currently have to see how that works. If it doesn't work to your liking then you're only out 1 sheet of paper and a small amount of chemicals.

IMHO regarding exposure times two things. 1. Extremely short exposure times have very little margin for error. and 2. In my workflow I only do a couple prints at a time so the longer exposure times don't bother me.

Anyway, Good luck on whatever system you come up with.

Marv
03-18-2006, 11:07 PM
IMHO regarding exposure times two things. 1. Extremely short exposure times have very little margin for error. and 2. In my workflow I only do a couple prints at a time so the longer exposure times don't bother me.


Dittos to what Buggy said. I only do a couple a couple images at a time also so 10 to 30 minutes isn't too long. Besides, I can have a light on, it is dim, and catch up on filing, sorting etc., etc.

I would compare bulbs to make sure the ones you are looking at are the same. The bulbs in my set up are 17 watt if I remember correctly. I haven't seen any high powered bulbs for the consumer market in my area. The lamps I used are self contained, hence the spaghetti at the end of the unit. Even at that they only ran $9.95 ea. They were the expsense to my unit, everything esle was recycled.

If I give up on it there will be some real happy college kids at my garage sale!!!

ImageMaker
03-18-2006, 11:10 PM
Relative to wattage, all standard tubes of a given size have the same wattage rating; it's only in compact fluorescent that you have to think about it. All T8 24" tubes are 20 W, for instance. Your 18" are probably the smaller T5 tubes, which are (IIRC) 13 W or so each (give about the same light as a 40 W incandescent). Bottom line, if they're a straight-line tube, any tube that physically fits will work.

And yes, two 18" T5 tubes ought to give enough light to expose an 8x10.

There's little difference in the UV output of BL vs. BL-B tubes; the difference is the BL don't have the dark filter, so they look more like a mercury vapor street lamp (if you're old enough to remember those, from before sodium vapor took over that market). If you can get plain BL for less, take 'em, but usually BL-B is all you'll find in places like hardware stores, and they'll do just fine. Standard "white" fluorescent tubes, however, don't emit enough UV to be useful for exposure; the phosophor layer inside the tube is designed to capture as much of this as possible, in order to give the most visible light output possible for a given electrical consumption.

gneissgirl
03-19-2006, 12:50 AM
Thanks, everyone! Good information. The UV tubes I saw today were in the $6-$7 range (just tubes, no fixtures). Looks like things don't have to be very elaborate to do small or medium-sized prints. After seeing buggy's setup, and reading about earl's, I may look at prices for those materials. I'm reluctant to transform my light table because I use it fairly often. Anyway, looks like I'll be able to do something simple and not too spendy ;)

murrayatuptowngallery
03-19-2006, 01:49 AM
Here's my short form comment on UV transmission of glass & acrylic.

I tried to leave a long one & got bumped out by E-blah & my firewall fighting.

Yes, I guess you need glass over a negative to contact print. I suppose no way around that.

'Regular' picture framing glass has roughly 44% filtering of UV below (shorter than) 380 nm. I don't know if two layers = 0.44*0.44 transmission...something to look into. Some suppliers say their non-glare (fine single-sided acid-etched) glass has 53% blockage below 380 nm.

'Regular' acrylic doesn't have a UV filtering rating because manufacturers never intended it as a UV blocker, since they make UV filtering and UV transmitting materials for those applications. However, AtoHaas gave me some data on regular framing grade acrylic (not the UVF museum type), and while not guaranteed, subject to change etc, UV filtering was about 70%, the wavelengths filtered were different than glass etc. Genreal point was that it did block significantly more medium to long wavelength UV, just not readily compared in a meaningful way.

So, if you have problems with long exposure times, the glass/plastic duiffuser over UV lamps will make the problem worse.

Most homebrew UV fluorescent fixtures I see, and the one commercial one I have, do not use a diffuser. I worry about uniformity of exposure, but it's apparently not a concern when the lamps are close together. How close is close enough? With multiple straight lamps, my fixture has the 1.5" (T12) tubes 1/4" apart (gap between tubes).

I haven't tried mine for alt-process yet. Former employer gave it to me. The process they bought it for didn't do what they wanted. Used it twice and stored it until they needed space & thought of me.

earlj
03-19-2006, 07:25 AM
All of these questions are discussed by Sandy King on the unblinkingeye website, in a article about UV light sources for alt process:

http://unblinkingeye.com/Articles/Light/light.html

In his testing, there is no discernable difference between the results with BL and with BLB fluorescent bulbs. In aquarium stores, you can buy super actinic (SA) bulbs, but they are more expensive than the other two. Here is an example of info from the article:

" . . .here is a little information on the nomenclature of fluorescent tubes. They are usually designated by a series of letters and numbers. For example, the GE Blacklight Blue tube carries the designation F20T12.BLB.

- The F stands for fluorescent.
- The next number, 20, indicates the wattage of this particular tube.
- The T number indicates the diameter of the tube in eighths of an inch. A T 12 tube, for example, is 12/8, or 1 1/2 in diameter.
- The letters describe the lighting characteristics of the tube. In the above case, BLB designates a Black Light Blue tube.
- Tubes sometime carry further indicators, such as IS (Instant Start), RS (Rapid Start), or even letters showing kind of usage, for example R for reptiles, A for Aquarium, etc. "

I am sure that two tubes would work well for 4 X 5 cyanotypes. This is enough to help a person decide if they want to start developing negatives especially for alt process, try other processes, go to a bigger format, etc.

I don't have any cyanotype images that I am happy enough with to post yet, but I am working on it.