A bit confused about film speed...
Coming from digital (I'm sorry, I have seen the light in only 2 rolls and I apologize for my many digital sins over the past 2 years ) I'm a bit confused about film speed, it seems much more subjective in metering, perhaps I am missing something but when I shot with my digis it was always set the ISO and meter for what its set. However I seem to be reading all kinds of stuff aobut people exposing at a different film speed then the listed, what is the reason for this? Is it coupled with expanding and contracting in development? I had thought that epanding and contracting delt only with contrast and though required slight exposure adjustment I dont think thats what this is. Is it simply finding what the "acctual speed is with your meter/lens/bellows etc.? Or is there something else I'm misisng? Any recomendations would be appreciated, I'm am working my way through AA series, finnsihed the camera and aobut halfway through the neg. In the appendix he tests for effective film speed (I think he uses a different term) but once that speed is found, is there still reason to shoot at a different speed (pushing and pulling in development would be one I suppose but if I have the light I need to get the exposure I want at the shutter I need would this ever be superior?) I guess I'm getting the feeling that film speed is mroe subjective in analog than in digital, is that true? If so why? Thanks for the help.
The ISO speed of negative film is biased towards underexposure. For better shadow detail many of us shoot at an exposure index lower than the ISO speed. Negative film has more latitude than digital, so it can be more subjective. Most film makers say that the ISO is a starting point to be modified according to the photographer's preferences. By the time you've finished the AA series and applied that knowledge to practice, you should be able to confidently alter exposure and developing as situations require.
Use the box speed and dev as normal, or rate at one stop lower and cut dev by 15%. i belive when you do this you get the tonal range compressed and it is flat. if you push you get higher contrast and you lose detail
Ishotharold, keep in the mind the two responses you have concern B&W film, color film is a different ballgame.
thanks for the quick responses guys, sounds like I'm not missing anything "too" major and I will learn for myself with time what my preference is. Guess I better buy and shoot lots more film to test with :-D.
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Lots of people like to set the exposure slightly different than the speed on the box. Sometimes an image result can be more pleasing if slightly underexposed, or slightly overexposed. You have more room with colour negative films than with colour positive (transparency, or sometimes called slide). Even with transparency films, quite often you can find many films are fine within 1/2 stop of proper exposure.
A separate issue is that some people have cameras that are not super precise on exposure settings. Then they might find that always setting the film speed lower/higher might work better for them.
Outside of that is push or pull, terms you might see used in different ways. A very generalized way to look at this: say you have ISO 100 transparency film, and you set your camera to ISO 200, then you have the film processed as if it were ISO 200 film. What you would find in such a push situation would often be slightly higher contrast, at least with transparency films. Pull processing is done less often by some people, though in a very general sense you could expect slightly less contrast. You would notice more of this using colour transparency films; you could have this done with colour negative, though some labs don't do that, and you might not notice much difference.
Now for B/W films, the only film I have ever had pull processed was TriX. I would set my exposure meter for ISO 200, shoot accordingly, then process the film as if it were ISO 200 film; resulting in a somewhat lesser contrast. I have more often push processed, especially films like Ilford Delta 3200 (B/W), Kodak P1600 (transparency), and Kodak E200 (transparency). The E200 is an odd film for this, since the pushis not linear, and much exposure compensation is needed for each step; though I have worked out settings and processing to 4 2/3 stops push.
Anyway, hopefully I was not too oversimplifying things. This type of discussion could probably be much more technical in nature, especially with some films.
Transparency film is (or was) sometimes slightly underrated to increase color saturation, but I would defer to Robert on this point.
To add to the confusion, you do not get box speed with some film/developer combinations. You could change the developing accordingly, but often you get better results by underrating speed for that particular combination. Also, a particularly thick negative for some printing methods is desireable,
and film is sometimes rated with that result in mind.
Slide and digital speeds are determined with reference to the highlights, because if you over-expose you will get 'blown' highlights (lots of pure white, plus washed-out colours).
Black and white speeds are determined with reference to the shadows, to be sure you get adequate shadow detail: it's quite hard to blow the highlights with negatives (mono or colour) though at the printing stage you may need to burn in to get the highlight detail you want from the denser parts of the negatives.
Mono ISO speeds for the same ISO 400 film can run from ISO 200 or below in a fine grain developer to ISO 650 or even a little above in a speed increasing developer such as Ilford Microphen.
There's a free module on ISO film speeds in the Photo School at www.rogerandfrances.com.
For colour negative film (and chromogenic B&W negative film - ie XP2 etc), which has lots of latitude, it is common practice to set the meter to one stop or more below the box speed. The graph below illustrates one of the main reasons. For colour negative film the graininess decreases with increasing exposure. This effect is most pronounced at the low end of the film's sensitivity.
You can see the effect in the graph below. Exposure increases from left to right.
Conventional (ie silver-image) B&W negative film behaves the other way round, so you may want to avoid overexposure - you may even want to sacrifice shadow detail in some cases.
All good answers above. One test you can do might help quite a bit here. Use a roll of film and play with exposure. Do a series of three shots of each exposure. Do one under, one at and one over the box speed. You can use a full stop for this experiment and see what happens. Use the same method each time (this is called bracketing). I think you will find it an interesting experience and may decide that "box speed" is not always correct. This should give you a better understanding of exposure (one side of the print) as it relates to film.
Looking forward to your posts about development in a little while! tim