ISO: changing on slr depending on actual film speed

[hotrocks]

so i know what film speed is and how it affects exposure..but say i have film that says 100 on it but i set my camera to 400...what happens? does the meter go two stops up to compensate, but on the film everything will be dark because it (so im fooling the meter)? im confused with this... also same question with 400 iso film and setting it to 100 (or any speed film setting it to something else)

also, what if i switch the cameras iso setting multiple times thru out one roll?

 

[frXnz kafka]

so i know what film speed is and how it affects exposure..but say i have film that says 100 on it but i set my camera to 400...what happens? does the meter go two stops up to compensate, but on the film everything will be dark because it (so im fooling the meter)? im confused with this... also same question with 400 iso film and setting it to 100 (or any speed film setting it to something else)

also, what if i switch the cameras iso setting multiple times thru out one roll?

If you shoot ISO 100 film with your camera set to 400, it will meter is if it has ISO 400 film in it. So basically, all of your shots will be underexposed by 2 stops. Just switch that around for 400 set to 100.

You can compensate for this by using longer or shorter developing times. This is called push or pull processing, respectively. For push processing you'll gain some contrast and there will be more grain. Pull processing will give you less contrast (not sure about the grain, I've never done it).

 

[hotrocks]

so iso setting on cameras is basically the base on which the meter works

and changing iso on dslrs is the equivalent to pushpull processing

well thanks

 

[djacobox372]

Changing iso on a digital is akin to changing film along with iso setting.

The old film trick of increasing the iso on the camera to something different then the film you have loaded doesn't apply to digital.

All modern digitals have ample exposure compensation that should be used if you want to over/under expose a photo.

 

[frXnz kafka]

so iso setting on cameras is basically the base on which the meter works

and changing iso on dslrs is the equivalent to pushpull processing

well thanks

No, changing the ISO on a dSLR would be like actually changing the film in your camera.

The "equivalent" to push/pull processing in digital would be to under or overexpose the image in camera, and then adjust the exposure in Photoshop.

 

[Alex_B]

i would not carry this analogy too far.

changing ISO on a digital camera is not really the same as changing film on a film camera. changing film means changing the actual sensitivity of the recording medium to light.

however, sensor pixels always have the same sensitivity in a sense. it does not depend on your ISO setting.
Increasing the ISO setting on the digital camera does however increase the signal amplification (hence the increase in noise). Technically speaking this is more similar to push and pull processing than to changing film in a way.
But practically, it is like changing film in a way as well.

As I said, it is not really transferable 100%.

But for us photographers all that does not matter anyway. we want a certain exposure, and that you can calculate from ISO, shutter speed and aperture (plus light meter) ... this is the same in the digital and the film world.

 

[Moglex]

No, changing the ISO on a dSLR would be like actually changing the film in your camera.

The "equivalent" to push/pull processing in digital would be to under or overexpose the image in camera, and then adjust the exposure in Photoshop.

The answer to your questions is complex and different from different angles.

As a DSLR photographer all you have to consider with the ISO setting is:

1) Start off with the assumption that you want it set as low as possible to keep sensor noise to a minimum.

2) If the low setting will not allow you to take the shot you require at a suitable speed and aperture, you have to increase it.

3) Where you have options on aperture or speed and can exercise those options based on the ISO setting, your tradeoff is between ability of overcome camera shake/subject movement, the depth of field, and noise from the sensor.

As Alex_B said, there is not a great deal of point in trying to understand a digital ISO setting from the POV of film ISO and they really don't compare apart from the basic sensitivity issues.