Question re ISO and exposure compensation

[Richard K]

Advertisement (gone after registration)

What does increasing the ISO actually do? You’re decreasing the exposure, so you must be increasing the gain? So everything is amplified including noise? What does exposure compensation do? It doesn’t change f-stop or aperture (exposure set manually), so it too must affect the gain? Would there be a difference in decreasing the ISO by one stop vs +1 exposure compensation?

[M11 for me]

Great question. In practice we speak of change of Light Value (LV). When you want to give your sensor double the light to get a lighter picture then you have 3 options. You can increase the aperture: Lets assume from f/4 to f/5.6. That is doubling the amount of light that comes onto your sensor. Instead you can leave your aperure at f/4 and double your exposure time insted: Lets assume from 1/250s to 1/125s. Or you can leave your exposure time at 1/250s but instead increase your ISO from 100 to 200. Whatever you do will increase the brightness of your image. Try this out in practice: All 3 images will have the same brightness.

But there are differences . . .

[Advertisement]

The Leica Q3 is available for pre-order at B&H Photo Video and Adorama

[M11 for me]

What does exposure compensation do when you have manually set the exposure time and the aperture. Then it will change the ISO. If you have set the ISO manually as well then the exposure compensation is doing NOTHING.

[M11 for me]

vor 38 Minuten schrieb Richard K:

So everything is amplified including noise?

You have noise even at base ISO. But when the ISO go up then that will increase the noise. You can test that very easily. Take the triangle from post #2. Take a picture that you expose "correctly" (lightbalance is in the middle). Then put up the exposuretime and the ISO by +1 LV at a time. The brightness of your image will remain the same. But the grain that you will see will increase.

[01af]

vor 17 Minuten schrieb M11 for me:

In practice we speak of change of Light Value (LV).

No, we don't.

.

vor 18 Minuten schrieb M11 for me:

You can increase the aperture: Lets assume from f/4 to f/5.6. That is doubling the amount of light that comes onto your sensor.

No, it doesn't.

.

vor 16 Minuten schrieb M11 for me:

What does exposure compensation do when you have manually set the exposure time and the aperture. Then it will change the ISO.

No, it won't.

.

vor 54 Minuten schrieb Richard K:

What does increasing the ISO actually do? You’re decreasing the exposure, so you must be increasing the gain? So everything is amplified including noise?

That's right.

.

vor 56 Minuten schrieb Richard K:

What does exposure compensation do? It doesn’t change f-stop or aperture (exposure set manually), so it too must affect the gain?

No, it doesn't. It just shifts the light meter's bias.

.

vor 57 Minuten schrieb Richard K:

Would there be a difference in decreasing the ISO by one stop vs +1 exposure compensation?

Yes, there would.

[marchyman]

On my Q with fixed ISO, Aperture, and Speed the exposure compensation dial will modify the speed in 1/3 step increments up to 2/3 of a stop.   That is, if I've set the speed to 1/60 I can use dial to go +/- 2/3 of a stop.  I don't remember if that is stock operation or something I changed in the menus.

If I set the ISO to auto the dial does the same thing: +/1 2/3 of a stop in 1/3 steps.  Auto ISO is set upon initial half button shutter press according to the selected aperture and speed.  It does not with the dial.

[M11 for me]

Advertisement (gone after registration)

vor 12 Stunden schrieb M11 for me:

Great question. In practice we speak of change of Light Value (LV). When you want to give your sensor double the light to get a lighter picture then you have 3 options. You can increase the aperture: Lets assume from f/4 to f/5.6. That is doubling the amount of light that comes onto your sensor. Instead you can leave your aperure at f/4 and double your exposure time insted: Lets assume from 1/250s to 1/125s. Or you can leave your exposure time at 1/250s but instead increase your ISO from 100 to 200. Whatever you do will increase the brightness of your image. Try this out in practice: All 3 images will have the same brightness.

But there are differences . . .

It should of course be from f/5.6 to f/4. Sorry for that.

Edited December 31, 2022 by M11 for me

[M11 for me]

vor 7 Stunden schrieb marchyman:

On my Q with fixed ISO, Aperture, and Speed the exposure compensation dial will modify the speed in 1/3 step increments up to 2/3 of a stop.   That is, if I've set the speed to 1/60 I can use dial to go +/- 2/3 of a stop.  I don't remember if that is stock operation or something I changed in the menus.

If I set the ISO to auto the dial does the same thing: +/1 2/3 of a stop in 1/3 steps.  Auto ISO is set upon initial half button shutter press according to the selected aperture and speed.  It does not with the dial.

You could well set the wheel on your Q to exp. compensation (I checked it on my Q2; I have no Q). So its a question of setting only: Your setting is on AUTO.

The Q2 has a queer thing (to me anyway): Its wheel for exposure time has only 1 full LV jumps. The M11 has ½ LV jump and my Canon R5 has even ⅓ jump. Therefore the Q2 needs something to compensate for that. Its a speciality of the Q2. I never liked that 🤪. I presume that it is the same with the Q.

Edited December 31, 2022 by M11 for me