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View Full Version : Using a OA safelight filter in a darkroom with OC filters????



Bogdan Karasek
21-Feb-2016, 20:32
My darkroom has the following safelight setup: three 5 in. OC filters on the Kodak round safelights and a 10x12in OC on a rectangular safelight. I was recently given a 10x12 safelight with an OA filter. I work in B+W only, do enlargements and contact prints. The Kodak Wratten Safelight chart ( http://www.kodak.com/global/en/professional/support/techPubs/ti0845/ti0845.pdf ) gives the following:

OA....Black-and-white contact and
duplicating materials, projection
films

OC....Contact and enlarging papers

I don't quite understand the description for the OA filter.

Anyway my question is whether I can mount the OA Safelight in my darkroom or whether I should be looking for a 8x10 OC filter as a replacement in the safelight ????

Randy Moe
21-Feb-2016, 21:10
I cannot answer your question, but I never did find the round Kodak OA filters I thought I had and had told you I would look for them.

I looked hard.

You already know how I recommend about 'other' options.

Doremus Scudder
22-Feb-2016, 03:04
Kodak lists the OA as "Greenish yellow" and the OC as "Light amber." In later editions of Kodak's safelight filter list they indicate that the OA filter was replaced by the OC filter, "*The OC filter has been formulated so it can be used with photographic materials in place of an OA filter". The OA is greener and likely darker, i.e., less illumination. Since it was formulated for slower contact papers (i.e. Azo, etc.) and duplicating materials, both of which were mostly only blue sensitive, I would guess that it passes a bit more green than the OC and therefore may not be safe with faster projection papers, especially VC papers that are more sensitive to the green component. Do a safelight test with the OA filter as described here: http://www.kodak.com/global/en/consumer/products/pdf/k4.pdf . I think you'll find it isn't much good for modern papers.

Best,

Doremus

Michael R
22-Feb-2016, 07:41
The OA filter was for older materials. Those materials for contact printing and duplicating were usually blue sensitive. Contact papers are also much slower than enlarging papers.

For current materials (other than a few exceptions), the OA filter passes too much green. If you want to try to use the OA, do a proper safe time test with the papers you are using.

Jim Jones
22-Feb-2016, 10:08
The type of filter is not the only consideration. The placement of the safelight may be equally important. While an OC is preferable, the OA might work well enough if used at enough distance or with an in-line dimmer. I like a rather dark darkroom, but have a brighter safelight above the developer tray for brief checks of development. a comprehensive test of any safelight is always a good idea.

Bogdan Karasek
23-Feb-2016, 05:50
The type of filter is not the only consideration. The placement of the safelight may be equally important. While an OC is preferable, the OA might work well enough if used at enough distance or with an in-line dimmer. I like a rather dark darkroom, but have a brighter safelight above the developer tray for brief checks of development. a comprehensive test of any safelight is always a good idea.

What would be the best test for a safelight filter?

Cor
23-Feb-2016, 06:12
What would be the best test for a safelight filter?

See link in Doremus post (#3)

Randy Moe
23-Feb-2016, 07:18
What would be the best test for a safelight filter?

Since you are finally going to test, I will send you a free LED, I and many others use. Not just any LED, a specific one.

https://www.superbrightleds.com/moreinfo/led-globe/2-watt-g11-globe-bulb-360-degree/440/

https://www.superbrightleds.com/moreinfo/led-globe/2-watt-g11-globe-bulb-360-degree/440/#/tab/Specifications

It still needs to be 4 or more feet away.

PM with address.

Jim Jones
23-Feb-2016, 07:32
See link in Doremus post (#3)

That's a better test than most experts quote. I use a more informative test that is simpler to do, although complicated to explain. In total darkness place a sheet of unexposed paper in the easel. Raise the enlarger all the way and stop the lens down to its smallest aperture. If this still provides too much light, an evenly fogged negative can reduce the light more. Cover 1/6 of the paper and expose for 1/2 second. Cover an additional 1/6 of the paper and again expose for 1/2 second. Cover an additional 1/6 of the paper and expose for 1 second. Cover an additional 1/6 of the paper and expose for 2 seconds. Cover an additional 1/6 of the paper and expose for 4 seconds. Expose the remaining 1/6 of the paper for 8 seconds. You have done a test strip with exposures increasing in increments of one stop from 1/2 second to 16 seconds. Now repeat the test on that same piece of paper under the safelight, but at right angles to the enlarger test and using minutes instead of seconds. Develop the paper normally. Interpreting the data from this test suggests a way to flash a print to slightly increase highlight contrast in prints in addition to providing a safelight check.

David Lobato
23-Feb-2016, 07:52
This thread is a nice example of responses with reliable and detailed information. Randy, what color bulb do you suggest? Your links don't show me the specific color. Or are you saying to use the white bulbs in the safelight housings?

bigdog
23-Feb-2016, 08:05
... I and many others use. Not just any LED, a specific one.

https://www.superbrightleds.com/moreinfo/led-globe/2-watt-g11-globe-bulb-360-degree/440/

https://www.superbrightleds.com/moreinfo/led-globe/2-watt-g11-globe-bulb-360-degree/440/#/tab/Specifications


Randy, what color bulb do you suggest? Your links don't show me the specific color. Or are you saying to use the white bulbs in the safelight housings?

Not to scoop Randy, but I am one of the "others" he mentions. It's the red one. I have tested it with Ilford Multigrade paper (using the Kodak method) and it tested "safe" to 10 minutes. It may be good longer, but I did not test longer than that.

I had long been a sceptic of red led bulbs for safelights, but a number of reliable people swore by this particular bulb, and they are cheap so I bought a couple, did the proper tests, and was pleasantly surprised. I have a combination of these bulbs and conventional safelights with OC filters in my darkroom.

Regardless of what one uses, proper testing is paramount!

Randy Moe
23-Feb-2016, 08:33
This thread is a nice example of responses with reliable and detailed information. Randy, what color bulb do you suggest? Your links don't show me the specific color. Or are you saying to use the white bulbs in the safelight housings?


Yes Red. Everybody should look at the second link and examine the spectrum of these bulbs. That's how I found this bulb. I may have been the first to recommend this RED LED and only this exact bulb. I have tried many others and they are no good for our purposes.

Of course test yourself.

I have 6 of them in my roomy darkroom and cut X-Ray in relatively bright light. I have one 30" over my paper trays and have no issues.

David Lobato
23-Feb-2016, 08:38
Thanks.

Randy Moe
23-Feb-2016, 08:45
Sorry Bogdan and guys. I feel I have written about this bulb so many times on this forum I thought by now most are aware of it. I am well aware I post too much.

I know I suggested this bulb some time ago to OP and he was not responsive.

Also many try OTHER Led and have a bad experience. :(

Michael R
23-Feb-2016, 09:18
The Kodak safelight test linked by Doremus (Ilford is the same) is THE safe time test to do as it accounts for the cumulative exposure of safelight and enlarger. The results can be surprising.

There is no such thing as a safelight that is 100% safe. It is simply a matter of how much safe time you get.

It will depend on the paper - an important variable. I would caution OP to do a proper safe time test with this bulb from SuperBright. While the peak output at 635nm is "ok" (higher would be better), output extends well below that wavelength. Also note typical of red LEDs, there are small amounts of output in the green and blue wavelengths - exactly where you don't want any output. It may or may not cause issues depending on the paper, brightness, and the length of safe time you require, but always test first.

Randy Moe
23-Feb-2016, 09:57
I always limit any sensitive materials to the shortest possible exposure to any safelight.

The mention of enlargers is somewhat secondary, but most produce a lot of stray light.

Which come from the traditional Hot Head with heat producing bulbs requiring cooling.

But LED enlarger Heads are another topic.

Michael R
23-Feb-2016, 10:49
Sorry I should have been clearer regarding enlarger exposure. I'm referring to the combined effect of image exposure and all non-image exposure. Even under the ideal scenario with zero light leakage from the enlarger, the safe time is still dependent on the cumulative effects of image exposure and safelight exposure. That is why the Kodak/Ilford test is informative.

Bill Burk
23-Feb-2016, 15:13
I looked at the graphs of the OA and OC filters and notice the difference seems to be that OC cuts about 20 NM more out of the green. When I thought about variable contrast paper using blue and green light, it suddenly made sense to me that the OC filter which cuts more green would be safer than the OA which is suited to older material.

Doremus Scudder
24-Feb-2016, 02:30
I looked at the graphs of the OA and OC filters and notice the difference seems to be that OC cuts about 20 NM more out of the green. When I thought about variable contrast paper using blue and green light, it suddenly made sense to me that the OC filter which cuts more green would be safer than the OA which is suited to older material.

Hey Bill,

Where did you find the spectral graphs for the safelight filters? Is there an online source? I'd sure like to take a look at them.

Best,

Doremus

Michael R
24-Feb-2016, 05:58
Doremus - see link:

http://www.kodak.com/global/en/professional/support/techPubs/ti0845/ti0845.pdf

There is also some info here: (but the link above is more comprehensive)

http://motion.kodak.com/US/en/motion/Products/Lab_And_Post_Production/Kodak_Filters/Safelights/default.htm

IanG
24-Feb-2016, 06:19
There are hidden issues that most safe-light tests miss and that's the adverse effects on contrast with Multigrade papers and the best filter is definitely the OC/902.

If you have some red gel you could add a couple of layers and probably convert an OA into an OC, however OC filters turn up now and again quite cheaply.

Ian

Bill Burk
24-Feb-2016, 13:58
Hey Bill,

Where did you find the spectral graphs for the safelight filters? Is there an online source? I'd sure like to take a look at them.

Best,

Doremus

Oh good, Michael R posted a good link. I was looking at Kodak Filters for Scientific and Technical Uses, CAT 152 8108, but the graphs in his link look just as good.