FILM ISO Speed and changing it.

[Lookin4filters]

Say if I put a roll of ISO 400 in, but I change the ISO on the camera to something else, does this adversely effect the photo or can it be done without harm. Say like in an environment that calls for maybe 100 ISO or maybe 800-1600 ISO etc etc...

[DocFrankenstein]

Depends on film, if you're developing it yourself your can just increase/decrease development and the film is still going to be fine.

That's called pushing and pulling the film - google it.

With color films you'll need to pay extra if they pro lab can even do it, many won't.

[Johnsoir]

As far as I know if you put a roll of 100 ISO in and set the camera to 800, you would under-expos, and vice-versa.
Test it:
Put your digital camera in M, set ISO to 100, correct other settings, now change the ISO to 800, see what happens.

[DC Fan]

Assuming you're using a film camera that reads the DX coding on the 35mm canister: you'll underexpose or overexpose the film, depending on how you switch the settings. Your average one-hour minilab probably won't be able to deal with that and you'll get a wrongly exposed negative.

A little more explanation: years ago, when film was king, photographers would deliberately do that with something called "push processing," where they would underexpose film by one stop, then overdevelop the film by leaving it in the developer chemical for a longer time. That usually resulted in a properly exposed negative, but one that was grainier than if the film was handled at its native ISO. Some photographers say switching the ISO settings on digital cameras is just an electronic form of push processing, except that the results are usually less grainy than with film.

[PhotosGuy]

You can also "Pull process". Over expose & under develop for some nice color shifts & contrast variations. We would shoot 4X5 & 8X10 sheets at -2, -1, 0, +1, +2, and another at 0 EC. Then process one 0 exposure & adjust processing on the other 5 sheets based on that.

Sometimes we'd shoot several frames of small format on the start of a roll to cut off (Clips) to check developing time before the rest of the roll was processed.

[Mark_Cohran]

Originally Posted by Lookin4filters

Say if I put a roll of ISO 400 in, but I change the ISO on the camera to something else, does this adversely effect the photo or can it be done without harm. Say like in an environment that calls for maybe 100 ISO or maybe 800-1600 ISO etc etc...

Will it adversely effect the image quality? Yes, it will. But by what amount depends on how much you under or over-expose it and how competent the lab is in pushing or pulling the development.

[Stocky]

I am not sure what you are trying to do. The ISO setting on the camera will just change how the internal light meter reads the scene. If you really want to over expose everything for some reason then just tell the camera you have slower film than what you actually put in.

[Lowner]

Stocky,

In the days of film I've seen wonderful images using push or pull processing. I never managed to achieve anything that was not best put straight in the waste bin, but some of the effects by masters of the art could be dramatic.

Remember, this fear of noise in an image, and wanting a very "plastic" look is a modern attitude. Film users actually often wanted to increase grain and contrast for the effect they wanted.