28 days

[zippyt]

Filters wouldn't do much since the emulsion is essentially B&W. Or Brown, orange and white.

I am no expert but you can lighten and darken and do other things with BW film if you use a colored filter , Orange lightens the pic , light blue darkens it , red has an effect as well , look around on the web for BW film filter info . Just a thought .

[footfootfoot]

Originally Posted by zippyt

Filters wouldn't do much since the emulsion is essentially B&W. Or Brown, orange and white.

I am no expert but you can lighten and darken and do other things with BW film if you use a colored filter , Orange lightens the pic , light blue darkens it , red has an effect as well , look around on the web for BW film filter info . Just a thought .

Zippyt,
True. Most bw film is panchromatic,ie sensitive to all wavelengths or colors of light, falling off in sensitivity at the near infrared end. Some emulsions are hypersensitive to blue light or UV. Some films are more sensitive under incandescent. Tri-x for example, is rated at asa 400 but under incandescent light it is about 500 asa. There are IR films and some that are blue sensitive only. Using filters with these films changes the tonal relationship of the subjects by allowing more or less relative exposure to the subjects depending if they are similarly or differently colored than the filters. eg Red lightens red and darkens blue. Green lightens green and darkens red, etc.

The film for these cameras is actually Printing out paper (http://www.albumenworks.com/printing-out-paper.html)
it is sensitive to the blue end (UV) of the spectrum and is fairly insensitive at that. to make a contact print form a negative it needs about 2 minutes to 5 hours of exposure to direct sunlight. That is why it needs days or weeks in a pinhole camera.

So you could put a filter in front of the camera but two things would happen. First, most filter material inherently filters out UV light, so you would be cutting down your overall exposure. Second, since the emulsion is sensitive to blue light only, then any filter that cuts blue light (yellow, orange, red) would also only be reducing overall exposure, without lightening the reds, yellows and oranges since the film isn't sensitive to those colors anyway.

A filter that passed blue light (blue, violet, green) would still have an exposure limiting effect by virtue of the filter's density and inherent UV filtering and wouldn't lighten those areas relative to the other ones since the film is blind to anything but blue light.

Probably more than you wanted to know, and quite possibly some errors here. This is off the top of my head and I have been suffering a bit from CRAFT lately...

I'll dig around and see if I can find some of my bw filter experiments.