Darkroom Fogging?

[ray_g]

Please excuse this very basic question. I have read different threads about fogging the paper from safelights, and testing (with coins, etc).

How is it that using the enlarger's swingout red filter under the lens makes it "safe" for the paper (to check focus, etc) despite the intensity of the light (usually 75w or more) from the enlarger, while a 10w red bulb from 3-4 ft away may not be?

 

[Roman]

The kind of red light through the filter is definitely safe for all kinds of B&W paper, as are most red bulbs (you can get pretty close with those - only the darkroom kind, though, not the party type); it's the orange/amber light distributed by various kinds of darkroom lamps that is not safe for all kinds of paper, and with those you should do a fogging test.

Roman

 

[jlw]

How is it that using the enlarger's swingout red filter under the lens makes it "safe" for the paper (to check focus, etc) despite the intensity of the light (usually 75w or more) from the enlarger, while a 10w red bulb from 3-4 ft away may not be?

It's (usually) safe because you don't leave it on very long -- what, 15 or 20 seconds? Your main safelights expose the paper during the entire printing cycle, from the moment you take the sheet out of the box until it's fully fixed, so the cumulative effects are much larger.

If you swung in that red filter and then left the enlarger on for five or ten minutes, you'd probably see an effect from that, too.

 

[Fred]

Hi,

Normal B&W paper is not anywhere near as sensitive to red light as to the other colours. This allows the red darkroom safelight and the enlarger swing filter not to fog the paper. If left over a long time though you might notice slight fogging.

Generally I focus on an old piece of paper using the un filtered enlarger light, then stopping down and adding contrast filters. The en;arger is switshed off when the paper is placed on the frame.

Hope this helps.