Film vs digital for long exposures

[barnacle]

I take your point about the various reasons for the long exposure, Willie, but in any case when a long exposure is used there is very little light arriving at the film or sensor. Either there isn't much light out there in the world - the night sky, the dark cathedral interior - or you have a very small aperture and/or ND filters in front of the lens to restrict the amount of light coming in.

Either way, there's not a lot of photons arriving at the film/sensor, and in the case of the sensor, the thermal noise is adding to the signal generated by the photons. With halide emulsions, this doesn't significantly happen; if enough electrons fail to arrive in a given time, the activated halide decays to its ground state - hence the toe of the response curve and the low-light reciprocity effect.

Neil

[AtlantaTerry]

Back in the '70s, I photographed an old vaudeville theatre that was being restored near Pittsburgh, Pennsylvania USA. After I lit it and then composed one particular view from the balcony using my 90mm f/5.6 Super Angulon on my Toyo monorail view camera, the exposure using 4x5" Kodak tungsten color sheet film calculated to be 30 minutes for one exposure, which is what I did. I seriously doubt if I could do the same thing with my current Nikon digital cameras.

One thing that I have learned is that tungsten film has fewer problems with long exposures. I believe some photographers use tungsten film in daylight (with color filters to adjust the white balance) when they know they are going to need a long exposure.

Every tool is different. We as photographers need to know what to use and when.

[Pere Casals]

Back in the '70s, I photographed an old vaudeville theatre that was being restored near Pittsburgh, Pennsylvania USA. After I lit it and then composed one particular view from the balcony using my 90mm f/5.6 Super Angulon on my Toyo monorail view camera, the exposure using 4x5" Kodak tungsten color sheet film calculated to be 30 minutes for one exposure, which is what I did. I seriously doubt if I could do the same thing with my current Nikon digital cameras.

One thing that I learned was that tungsten film has fewer problems with long exposures. I believe some photographers use tungsten film in daylight (with color filters to adjust the white balance) when they know they are going to need a long exposure.

Every tool is different. We as photographers need to know what to use and when.

This should have a technical reason.

My guess is that different color sensitive layers in the emulsion have different reciprocity failure behaviour that ends in a color shift, this can be solved at taking time by using the proper correction filter. By using Tungsten equilibrated film for daylight long exposures we just enhance sensitivity to blue light, solving a share of the problem.

Perhaps silver halide emulsion for different color layers have different speeds, for example to compensate for the practical optical density the image forming rays have to cross to reach a particular color layer. So if there are different kinds of emulsion this may result in different LIRF, so in color shifts for long exposure.

Just my guess

[Corran]

the exposure using 4x5" Kodak tungsten color sheet film calculated to be 30 minutes for one exposure, which is what I did. I seriously doubt if I could do the same thing with my current Nikon digital cameras.

I don't know what Nikon DSLR you have, but the exposure on digital using the base ISO at a reasonably equivalent aperture for depth of field and with no reciprocity issues of course would probably be much, much less time. Consider that the Milky Way can be reasonably captured with a 10-20 second exposure with a reasonably bright lens and ISO 400 or so on digital. I've shot in very dim abandoned places with my DSLR and not needed more than 30 seconds of exposure.

Your experience with long exposures and such on film may trump the ability to do the same on digital. More importantly in my view is that sometimes I want longer exposures on digital but need ND filters to achieve them due to the higher sensitivity and wider f/stops in general use before diffraction.

[Corran]

Steve asked though "I also wonder on bw film if filters would be needed after a certain length of exposure." The answer is no. As far as I understand, there is no change in spectral response of b&w materials with long exposure. Someone can correct me if I am wrong. I don't believe the question was posed in terms of color film vs. b&w film though. The suggestion to shoot color film and convert to b&w later as a method of "control" is only valid if one is not printing traditionally in the darkroom, unless the idea is to use color filtration and make an intermediate b&w negative via contact printing off the chrome, which seems to me to be a rather roundabout way of doing it. Or burning a new image via LVT.

[Pere Casals]

spectral response of b&w materials with long exposure.

Hello Bryan,

BW films have some changes in its spectral sensitivity depending on some factors. But IMHO this is not a concern because this a minor change compared with the strong filtering a photographer may use.

Kodak charts Density vs Spectral response:



(This Kodak TMY graph has an error, 0.3D under top curve should read 3.0D)

As LIRF changes density balance it also has to change linear response for different colors, but IMHO nothing to worry about.

Modern films can have two layers of silver halide emulsions, the deeper one may be a low speed cubic emulsion, while the outer one may be a predominantly tabular one. Each emulsion may have a different LIRF and a different spectral response, so from it we can expect some change in the same way some an also multilayered color film can have color shifts when LIRF stressed.

[barnacle]

I might expect - absent further information - that B&W film might be somewhat more sensitive to blue than red light at very long exposures, simply because blue light has more energy than red. I'd *guess* that you need fewer blue-frequency photons to sensitise the halides than red-frequency, but this guess is *not* based on any rigorous analysis or knowledge.

Neil

[Pere Casals]

I might expect - absent further information - that B&W film might be somewhat more sensitive to blue than red light at very long exposures, simply because blue light has more energy than red. I'd *guess* that you need fewer blue-frequency photons to sensitise the halides than red-frequency, but this guess is *not* based on any rigorous analysis or knowledge.

Neil

Hello Neil,

Your reasoning makes sense, but the thing may be very complex...

Let me show you two graphs from "A Manual of Advanced Celestial Photography" from two slide films, sensitometric 1 hour exposures for color slide film, see blue channel behaviour, one shows a clear blue loss of speed compared with green/red, the counter for the effect you point (Note inverted curve because it is slide film). The other one shows a contrast shift for blue, it gains or loses depending on exposure/density. It is color film, not BW, but we see a complex behaviour from single channel silver halide emulsions !








Also with Velvia we have a Green shift and not a Blue shift with long exposures...

Well, here we compare emulsions from different layers, that can be different, not same emulsion for different color, but in these particular graphs we see same behaviour for Green and Red, so IMHO there are some complex effects that are not easy if not analyzed by a photochemical engineer knowing the particular emulsion tricks...

[Drew Wiley]

B&W films absolutely can shift in spectral sensitivity as well as contrast over long exposures. But you can't make a generalized statement about it. Even TMax 100 and 400 differ in this respect. Lesser quality films might even differ per emulsion batch. I did a lot of testing and curve plotting a few years ago regarding this very question. When in doubt, do your own specific tests under anticipated circumstances. As far as color films go, Fuji Astia 100F was the most predictable. Their CDUII duplicating film was simply a tungsten-balanced version of the previous Astia. Nothing comparable on the market today, though Portra 160 seems quite predictable under relatively long tungsten exposure.

[Jac@stafford.net]

For digital, there was the Leica M Monochrom with sensor with no bayer tiles, this is an exception.

Leica limits long exposure time and forces an equal time post-exposure black frame to map hot spots. Leica sucks for long exposures.