Are slower films more contrasty or less contrasty than faster ASA films ?

[Andy F]

I am trying to understand how film works with light. In black and white photography are slower films more contrasty or less contrasty than faster ASA films ? Which is better for a contrasty scene and which is better to use on an overcast day that is less contrast? I was once told that a slower film can absorb more contrast but I am not sure what is meant by that.

[Michael R]

When it comes to current negative films, “slow” means lower than ISO 100 (the ISO 100 range is generally referred to as medium speed). Today’s medium speed films aren’t more contrasty than fast (ISO 400) films and there is no real relationship per se between film speed and contrast.

Some slow films do have high contrast but that is because they are special purpose emulsions. Few of these are available as large format/sheet film anyway.

Long story short, virtually any medium or high speed film will handle whatever you throw at it.

I am trying to understand how film works with light. In black and white photography are slower films more contrasty or less contrasty than faster ASA films ? Which is better for a contrasty scene and which is better to use on an overcast day that is less contrast? I was once told that a slower film can absorb more contrast but I am not sure what is meant by that.

[Andreas]

If my memory serves me well, slow films have a thinner emulsion, fast films a thicker one. The ability to record a large range of densities is in function of that thickness, therefore HP5 can handle a wider contrast than Pan-F.
The extreme is lith film: extremely thin, extreme definition but very short range of exposure.
Best
Andreas

[Mark Sampson]

I think that it's more a matter of the laws of physics, although I can't quote which one. But slower emulsions are inherently higher in contrast than faster ones- it has to do with the size of the film grains. This is an advantage with aerial films, where high resolution and high contrast are desirable, and the tradeoff in speed can be dealt with. Less so with people on the ground using Tech Pan, or who torment document films in attempts to a full tonal scale.
In the range of 'normal' photographic emulsions, of course you can adjust exposure and development to get the negative contrast range you want.

[tokyo_blues]

There are people out there (mostly wet printing practitioners) who hold the view that contrast 'is a function of development'.

The idea I think is that, given enough development, any two film stocks can yield equally contrasty negatives.

I'd be interested in people's thoughts on the matter.

[Vaughn]

The idea I think is that, given enough development, any two film stocks can yield equally contrasty negatives.

Nope -- too much variation in emulsion formulas and production methods for that. That is a well know fact to us who regularly torment films.

And one needs to be careful about the word contrast. Two negatives can have equal amount of contrast, but one be continuous tone and the other only whites and blacks.

[Michael R]

There are people out there (mostly wet printing practitioners) who hold the view that contrast 'is a function of development'.

The idea I think is that, given enough development, any two film stocks can yield equally contrasty negatives.

I'd be interested in people's thoughts on the matter.

It is true that the gradient can always be adjusted with development (though the maximum gradient depends on the emulsion). However from a practical perspective giving any film maximum development will also tend to change the shape of the characteristic curve, reducing its effective exposure range. A way around this in certain cases is to use an imagewise staining developer instead of giving maximum development in a regular developer. With a staining developer, the density range/contrast of the negative comes from both the developed silver and imagewise stain. The film itself is of course a key variable. For example it is easier to get a high contrast/high density range negative out of Tri-X 320 than HP5+.

Likewise, severe underdevelopment of an inherently contrasty film will change its curve shape, reducing its already limited exposure range, as well as severely reducing the effective film speed. Exceptions to this case would be the use of special purpose low contrast/high speed developers specifically designed for this purpose. High Phenidone ratio developers such as Adox/SPUR Adotech are used to get reasonable (to varying degrees) exposure ranges and medium contrast out of micro/copy/document films without the penalty of massive speed losses.

[tokyo_blues]

Thank you both for clarifying.

I was particularly interested in the following

It is true that the gradient can always be adjusted with development (though the maximum gradient depends on the emulsion).

Michael - what do you mean by 'the maximum gradient depends on the emulsion'? Am I correct in saying you mean there is something like a 'characteristic' maximum contrast which is a function of the emulsion?

Taking it from another angle, I guess then OP's query around slower films being in general more contrasty than faster films will hold true if exact same development is used?

I guess what I'm trying to understand is - if we remove 'development' as a variable by using (say) 'optimal/leaflet' instructions and same developer for a range of emulsions, will it be possible to rank these emulsions by some definition of 'characteristic' contrast (= differences in the slope of the exposure/density curves in the linear portion at recommended development conditions). Many thanks indeed for the discussion.

[Drew Wiley]

Not even all rubber bands are the same. And if you stretch any of them too far, they'll snap. Some films are capable of very wide ranges of contrast gamma development; many others are not. IT HAS VERY LITTLE TO DO WITH FILM SPEED PER SE. Some slow fine grained films like Pan F have very little contrast malleability, which the recently extinct Efke 25 had miles or it. It depends what any specific film was engineered for to begin with.

The adaptation of extremely fine show films of the technical or microfilm category for pictorial purposes using special low-contrast developers comes with a big penalty in terms of what range of scene tonality those films will accept to begin with; it can be pretty disappointing compared to film engineered for general photographic usage to begin with.

[Michael R]

This can get complicated, but the maximum silver density a film can produce is largely a property of the emulsion, and this is related to maximum contrast. The emulsion design is also a key determinant of how contrast is built - ie the shape of the characteristic curve. Different developers can impact these characteristics to varying degrees.

Regarding your second question (the other angle), basically no on both fronts:
Take any two films of the same speed and a developer. The films will likely require different development times to reach the same contrast. Film A might need longer than film B. Now change the developer. You might find film B needs longer than film A.

While very generally speaking it often turns out faster films need longer development times than slower films, this is not a rule. It depends on the emulsion, and development kinematics. And there is no rule slow films have to necessarily be more contrasty than faster films. The classic example of this was Kodak Panatomic-X, which was nominally an ISO 32 film (ie slow) but wasn’t contrasty and had a long exposure scale typical of medium speed films. Again, it all depends on the emulsion.

Regarding your ranking question, it is hard to rank them by contrast because contrast is variable depending on how much development is given. I suppose one could choose a contrast level, determine how much development time is needed for each film to reach that contrast level in a given developer and rank them that way. For example for a normal gradient in the 0.5-0.6 range using D-76 you might find Tri-X needs 8 minutes and Adox CMS 20 needs 1 minute, so CMS 20 is the contrastier film. But this doesn’t tell you very much. What would be more important to see for any given gradient are speed and exposure range/shape of curve. A gradient over a fixed exposure range is part of the ISO speed criteria, for example.

Thank you both for clarifying.

I was particularly interested in the following



Michael - what do you mean by 'the maximum gradient depends on the emulsion'? Am I correct in saying you mean there is something like a 'characteristic' maximum contrast which is a function of the emulsion?

Taking it from another angle, I guess then OP's query around slower films being in general more contrasty than faster films will hold true if exact same development is used?

I guess what I'm trying to understand is - if we remove 'development' as a variable by using (say) 'optimal/leaflet' instructions and same developer for a range of emulsions, will it be possible to rank these emulsions by some definition of 'characteristic' contrast (= differences in the slope of the exposure/density curves in the linear portion at recommended development conditions). Many thanks indeed for the discussion.