Using a OA safelight filter in a darkroom with OC filters????

[Bogdan Karasek]

My darkroom has the following safelight setup: three 5½ 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/profe...845/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 ????

[Tin Can]

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]

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/consu...cts/pdf/k4.pdf . I think you'll find it isn't much good for modern papers.

Best,

Doremus

[Michael R]

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]

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]

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]

What would be the best test for a safelight filter?

See link in Doremus post (#3)

[Tin Can]

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/more...60-degree/440/

https://www.superbrightleds.com/more...Specifications

It still needs to be 4 or more feet away.

PM with address.

[Jim Jones]

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]

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?