So there is no fog unless the paper was slightly exposed, in which case these lights would add to the fog? Why is there such a difference?
Originally Posted by Ken Nadvornick
Safelight fog manifests itself in two ways:
Originally Posted by imush
1) visible fogging in areas of the print that otherwise show at least some tone; and
2) degradation of highlight "sparkle" in areas that don't otherwise show any tone (think specular highlights).
The first type is easy to see with a rudimentary test. The second type is a little harder to detect.
One detects the second type by first fogging the paper slightly - just enough to overcome the paper's "inertia" to low level light. That fogging exposure is done in otherwise absolute darkness. Next, an opaque item (e.g. a ruler) is placed on the paper and different sections of the paper are exposed to the safelight for different times (e.g. 1 minute, 2 minutes, 4 minutes, 8 minutes, etc.). Then the paper is developed (again in absolute darkness).
If the safelights are completely safe the developed paper will exhibit a consistent light gray tone - you won't be able to tell where the ruler was.
If, however, the safelights are only partially safe, the sections exposed for shorter periods will be the same tone as the part hidden by the ruler, while the sections exposed for longer periods will be a darker tone than the part hidden by the ruler.
If however, the safelights are not at all safe, none of the exposed sections will be the same tone as the part hidden by the ruler.
Without the initial slight fogging, some or all of the subsequent safelight exposures may not be enough to make their effect obviously visible (in the test) even if they are enough to cause the degradation of highlights referred to above.
Hope this helps.
“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2
I have my darkroom lit with these in red. I have done extensive fog tests and I get no fog on paper or film designed for red light. I have one of these red bulbs just about a meter away from my developer tray and it is fine.
What Matt said...
Paper has a certain exposure threshold which must be reached before a minimum tone will register. The danger in safelight fogging is not really a gross darkening of the paper. That's easy to recognize. Instead, it's the tendency to "use up" that pre-tone threshold with non-image forming exposure. When the intended image is then projected on top of that, the resulting highlight tone will end up developing out too dark.
And to make things even worse, when that now too dark highlight tone is allowed to dry, the "dry down" effect will render it even darker yet. The net effect is one of an unexpectedly lower contrast, flat looking print. These are the "degraded highlights" referred to above.
Often the source of the problem is not readily apparent. The printer will claim to have already tested for safelight fogging and found none. But if the test was not a version of that second, pre-fogged test as described by Matt, then chances are good the source of the effect will be missed.
Last edited by Ken Nadvornick; 01-04-2011 at 08:48 PM. Click to view previous post history.
Reason: Reworded for more clarity...
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—'blanksy', December 13, 2013
Red works but is less efficient than proper amber filter, ie less usefull light to human eye b/4 fogging.
Good news it preserves night vision better
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I built my safelight using an amber led module of 12 or 16 leds, it worked great and spectrally was an almost perfect match for an OC filter. I can't remember the manufacturer, it have been Luxeon.
I got official data from Polybrite, maker of these 1W bulbs. These seem to be not as bright as OptiLED, but should be adequate for a small darkroom.
Here is their document with the spectrum graph. There is slight blue noise; probably not enough to worry.
Last edited by imush; 01-10-2011 at 02:36 PM. Click to view previous post history.
I have been using Polybrite's M60 red, which has a bigger bulb than the S11. Five years leaving it on day and night. The only time I shut it off is when I am working with film.
I use these (red or amber, depending on the paper type). I put them in a small clamp-on housing, hang them from the rafters about 10 feet from the trays, and bounce them off the white walls. I tested them with a couple papers when I first got them but didn't have any fogging after 10 minutes so I stopped.
Originally Posted by 23mjm