Safelight

arturo · Post by **arturo** » Mon Jun 14, 2004 3:47 pm

Hi there!

I am preparing my next try on shooting holograms with both, red laser pointer and HeNe, but this time I'd like to use a safelight during development, because I am afraid that is my weak link - I need to know what is going on during development instead of just listening to the alarm clock after X minutes.

Now, I was wondering what would be more suitable (I will be working with PFG-01 plates) to make a safelight?, to use a normal light, covered as needed with color gel, or a gree diode (or assembly of these)? This is, are the green diodes out there really clean of red light wavelengths?

On the other hand, I *think* i remember someone posted a while ago that a nice test for a safelight could be to see the dispersion of its light produced by a CD... any red component there would mean that it is not a good light at all.

Any thoughts on this topic would be greatly appreciated.

JohnFP · Post by **JohnFP** » Mon Jun 14, 2004 4:01 pm

Well, if you take a look at Slavich info page on PFG-01 you will see that even if you have a pure green diode that emulsion is slightly sensitive to green also. So to answer you questions. One - A green diode is probably as pure as you are going to get so I do not think you will have a problem with red being in it. But as I previously stated the emulsion you are using, as is most silver halides, will be slightly sensitive to green. So not only should you use a very thin lined green but it should not shined directly or concentrated on the plate. I used to bounce the light off a back wall or off the ceiling and use just enought light when absolutely necessary as needed. I always loaded the plate blind and in the dark. let settle in teh dark, unloaded and put in a light tight box. Then I would turn on the safe light and let my eyes get used to the very dim safe light. Then process. I never let the plate, even if it is red sesitive, see any light even green, unless I had to.

I am not sure of the CD thing but I bet it would work as they diffract ligh pretty good. When you use the CD you are correct, you do not want to see any red, orange or yellow. But lime green, green and blue should be your best bets.

Colin Kaminski · Post by **Colin Kaminski** » Mon Jun 14, 2004 4:04 pm

Here is some old random information from my web site. Perhaps some of it will be helpful. I really need to start to revise my web site. Perhap this fall...

http://www.designerinlight.com/holo/safe.htm

Safelights for Holography

In order to see while you are working it is important to have some light. Fortunately if you are using film that is only sensitive to red you can make a green safelight. You should test your safelight before you use it.

I do a preliminary test of reflecting the light off of a diffraction grating, CD or DVD. Shine the safe light at the grating and bounce the reflection back to your eyes. If it looks the same then you are looking at the zero order reflection, rotate the grating or CD until you see a reflection that looks like a rainbow. This is a higher order reflection. If you can see red in this reflection then your light is not safe.

The next test is to get out a piece of your film. Find the uncoated side. Place a piece of electrical tape down one side to make a test patch that has not been exposed. Put the film about a foot from your safelight with the tape facing the light. Add one piece of tape at 15 seconds, 30 seconds, 60 seconds, 10 minutes, 30 minutes. At 60 minutes put the plate in developer. If your plate turns completely black then your safelight is not usable. If only the 60 minute or 30 minute lines develop you are probably OK.

If you are using long settle times it is wise to make sure no safelight hits the bench during the settle period.

The easiest light to use is a "Limelight" night light. It is very low power and mostly green. If you add a Rosco Gel #90 available from a theatrical supply shop it will be very good but very low power. Attach the gel with electrical tape. John Klayer uses a row of gelled Limelights above his bench. This is a good idea but I have not found a way to do this yet because of my space constraints.

Just using a piece of #90 over a conventional bulb is not enough. I like to use 2 layers of #90 inside my mini mag light. Lately I have found it better to have one layer of #90 and one layer of #95. #95 lets in too much deep red to use alone and #90 lets in too much yellow that the Slavich materials are sensitive to. I only use it to find something in a hurry and never shine it at the plate.

The main safelight in my studio is a 4' fluorescent shop light with two T40 bulbs. I have it covered with a sheet of Rosco #90 and have it aimed up to the ceiling to spread the light. Since I close my holography table for settling and exposure I can leave the light on all the time.

I also never open my box of plates/film in any light at all. I can perform all of the functions of manipulating the box in complete darkness. I am sure I am being over cautious but film is expensive.

I found a reference to a paper about using the T40 EncapSulite fluorescent bulb covers for holographic safelights. I did not read the paper so I am not sure what bulb he was suggesting or what film he tested with. Because of the expense I have not tried it yet.

Data from:

http://www.flexopress.com/production/en ... eeves.html

ENC-SOS15ND225* 48"
96" S15ND2.25 Dark Green 535 to 560 nm $46.95
$69.95
ENC-SOT20ND75* 48"
96" T20ND.75 Blue-Green 470 to 530 nm $46.95
$69.95
ENC-SOT20ND105* 48"
96" T20ND1.05 Blue-Green 471 to 528 nm $46.95
$69.95
ENC-SOT30ND105* 48"
96" T30ND1.05 Blue-Green 483 to 518 nm $46.95
$69.95

For general information about Safelights see:

http://www.kodak.com/global/en/consumer ... acts.shtml

Kodak makes a #7B and #3 green saflelight filters (#3 is recomended by Shoebox Holography) suitable for red sensitive holographic films. Since I have so much theater gel lying around I have not tested it. Let me know if you try some.

Dinesh · Post by **Dinesh** » Mon Jun 14, 2004 5:42 pm

Silver Halide is naturally blue sensitive, somewhere in the 350-400nm region. Any other sensitivities need dyes. PFG-01 is designed for HeNe (633nm) and Ruby (694nm). You can use anything dispersive - a DVD, a CD, another Laser transmssion H1, a prism etc. The idea is to disperse the spectrum of the bulb. If there's any red there, the dispersed spectrum will show it up. If there's only a little red and the dispersive element does not disperse enough, you may not see it. But in this case, I suspect there's not enough to fog the plate.
With Slavich VRP-M, I use a 25W red bulb with no fogging. Remember also that holographic film is fairly insensitive (even Silver Halide!). If it takes laser light many seconds to "fog" the plate (remember that all exposure is fogging) then it'll take many times that time to fog it with incoherent light.

arturo · Post by **arturo** » Mon Jun 14, 2004 5:51 pm

Thanks to the three of you... I think that the three have helped me to cover the different issues related to safelight! Next week I will finally have some time off, and hopefully I will get something done, at last!

BTW, if anyone is interested, these are the transmitance curves of the Rosco filters Colin uses:

Tony · Post by **Tony** » Tue Jun 15, 2004 2:22 am

I use the luminescent night lights that plug into the wall. At first I was concerned, but had no problems. I added a second one and still no problems. I have had the film as close as 1 foot from the night light with no apparent fogging. Actually, a little fogging still won't totally prevent a hologram the way it ruins a photo...

This with PFG-01 and 8E75...

-Tony

Colin Kaminski · Post by **Colin Kaminski** » Tue Jun 15, 2004 3:16 am

I use the luminescent night lights that plug into the wall. At first I was concerned, but had no problems. I added a second one and still no problems. I have had the film as close as 1 foot from the night light with no apparent fogging.

If you add a piece of Rosco #90 over the top there is very little red indeed. I have two of these I use.

Colin Kaminski · Post by **Colin Kaminski** » Tue Jun 15, 2004 3:29 am

You might find this interesting as well from Vidar's website:

http://www.techsoft.no/holography/be_ca ... elight.htm

Martin · Post by **Martin** » Tue Jun 15, 2004 5:37 am

There is an interesting paper by Valery Petrov, Reflection and transmission silver-halide holograms recorded an processed in white light, SPIE 1732.
"Denisyuk reflection holograms and Fourier transmission microholograms were recorded. 10 mW He-Ne laser and incandescent lamps were used as the sources of coherent and incoherent light. No wavelength filters were used to limit the intensitiy of incoherent light."
The paper demonstrates that despite strong background white light exposure, high quality holograms at high DE could be recorded.
"It is seen that even 200 lx level of incoherent illumination during
recording may be neglected if exposure time does not exceed 10s."

I guess most holographic silver halide emulsions are very forgiving with
respect to additional incoherent background white light illumination
(provided that it's below a certain threshold of intensity/time). Incidentally, I don't agree with the statement made about DCG requiring much less precise exposure energy than silver halides. Actually I think it's the opposite.
Most silver halides can be "fine tuned" along development
time/temperature/developer concentration etc.

In his paper Petrov mentions an interesting additional effect:
"It may be concluded (...) that optimal coherent light exposures for given
incoherent illumination are decreasing by applying more intense incoherent light. And again insufficiently exposed holograms may gain in DE by applying more intense white light illumination during processing in SP." SP is a special developer ("momental developer"), said to be used for 1 - 10s only.

HoloM · Post by **HoloM** » Tue Jun 15, 2004 12:31 pm

With PFG-01 I use 15 very bright green LEDs as safelight. I light the laboratory indirect by pointing the LEDs on a white wall. No problems with pfg-01 so far.