Fog

[lensmagic]

Ansel Adams, in his book "The Negative" talks about "filmbase-plus-fog level" going up with a certain developing procedure, but he goes on to say that this (the fog) "is simply 'printed through' to achieve the desired black values in the print." But what are the advantages and disadvantages of "printing through" a negative with elevated fog?? Does fog affect contrast in any way?

 

[Trevor Crone]

I wouldn't say there were any advantages. A small amount of development fog can indeed be easily printed through without any need to adjust contrast. Large amounts of fog will effect contrast and will need to be accounted for in the print.

Some developers, because of their composition are more prone to higher levels of fogging then others.

Retrainers are used to contain fogging, eg. Potassium bromide.

See Carroll's Photographic Lab Handbook.

 

[David A. Goldfarb]

Generally one tries to minimize the fog level, because that's silver that could be used in the image, but if the film has enough density range, as most film does, you can just print through the base fog. It's more of a problem, though with alt processes, where elevated fog can seriously increase exposure times and you need all the density range the film can offer.

The only possible advantage might be if a little fog density pushes the shadows up the curve to improve shadow detail, sort of like flashing, but you would have to do some testing to see if that really works.

On prints no base fog is acceptable, so print developers usually include restrainers or anti-foggants to eliminate it.

 

[Trevor Crone]

The only possible advantage might be if a little fog density pushes the shadows up the curve to improve shadow detail, sort of like flashing, but you would have to do some testing to see if that really works.

QUOTE]

David, I think it would be better to pre-expose the film to a low density (zone I/II) to control shadow detail then chemical fog.

 

[David A. Goldfarb]

I agree, but just speculating on what the upside of base fog could possibly be, that was something that came to mind.

 

[dancqu]

I agree, but just speculating on what the upside of
base fog could possibly be, that was something
that came to mind.

I've wrestled with that one; fb+f or pre-exposure.
Still do not have it in mind that they affect the image
in the same way. Pre-exposure effectively UPS the ISO
and so low values move up the curve. Fb+f clouds or
vails recorded low values so LOWERS the ISO. Dan