Millions of photographs have been taken with simple cameras with no exposure control, under very varied lighting conditions (scenes, that if they were metered for, would entail several stops' difference between them) - and yet millions of acceptable prints have come back from ordinary labs.
This, as I understand it, is a function of the wide tolerance of film and the development process.
What I understand already
(please correct me if this is not right)
- that a film with exposure latitude will allow you to get your exposure settings "wrong" and still end up with a usable image
- that colour negative film (or perhaps C41 in particular) has a great deal of latitude
- that colour slide film has little latitude
What I think that this must imply
Let's say that for reference, the most tolerant film has a dynamic range from nominal values of 0 (darkest) to 100 (brightest). That is, if a scene contains a range of 100 brightness values, this film, when correctly exposed, will capture all of them.
On the other hand if the scene has a range of say only 50 brightness values, then the film can comfortably capture all of them even if the exposure is off target - as long as the brightness range of 50 can be accommodated somewhere within the range of the film.
As for a less tolerant film, say with a range of only 50 brightness values itself, then you could never capture all of the range of the first scene of 100 values - you'd have to choose whether to lose detail in the dark parts or the light parts of the scene. And to capture all of the range of the scene of 50 values, you'd need to have the exposure spot on.
Is this more or less correct?
Things I don't understand
Say I take two photos with my most tolerant film with a dynamic range of 100, of a scene that has a range of 50.
I take one photo that lands in the film's range 0-50, and one that lands in the film's range 51-100 - i.e. the same scene, with different exposure values.
When the film is developed, there won't be a single point in either frame that has the same brightness as any point in the other frame.
So, how do we get good prints from these two completely different negative frames? Does it depend on the expertise of the person doing the printing to make judgements about how the range of 50 brightness values in each frame should be translated to brightness values in the final print?
If the film is sent to a typical lab for printing, what happens - does the printing machine make a guess at the what the average brightness of the scene should be, and expose each print to bring it closer to that average?
Where does this latitude for exposure come from: is it in the film, in the developing process, or in the printing process?