Is ISO selection, even auto ISO, really necessary on digital cameras?

Dave in Wales

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In fact why even have any reference to ISO at all?

Understandable in the days of film yes, but with todays sensors and the camera's computing power surely it's capable of applying a sensitivity value (lets not even call it ISO) that is required in accordance with the ambient lighting conditions and camera settings at the time of taking the shot.

I know what you're gonna say.....AUTO ISO.....but then, why even bother with that?
 
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Not sure if I understand the question but if all that bothers you is the reference to "ISO" then I believe it comes from so many people using digital cameras today that used to shoot film before:; it's a term that is familiar...

But if you are asking, why doesn't the camera just choose it's own sensitivity according to the scene, oh well, that is a much more complex issue.
I for one, choose the "ISO" according to what I want the exposure to be, given the available light. If I desire a certain depth of field and a certain "freeze" (or blur) my only option is to adjust the ISO.
But of course, this mainly applies to images I want to "create" (look, feel) instead of merely just "record" a scene (snapshot)
 

Growltiger

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Because if you underexpose you get more noise in the shadows.

If you don't want to underexpose, then by all means keep ISO low and have a long shutter speed. But if you need a faster shutter speed, then you have no option but to increase the ISO.

The camera already has tha ability to do it all automatically, not just Auto ISO. Turn your dial to iAUTO!
 

wjiang

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What we're talking about is applying exposure gain to a base photo-site efficiency - whether by a silver halide chemical process, analog amplification in the A2D front-end or digitally afterward. ISO just happens to be a way to scale the exposure gain in a way that is somewhat standardised - at least close enough that everybody is on the same page when we talk about it, and so you have an idea of how much you want to dial in for the exposure you want (there is no such thing as a 'correct' exposure). Otherwise, you'd be left with a different base photo-site efficiency and gain characteristic for every different capture device with no easy way to compare them.
 

Brownie

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Do an experiment. Set your camera up in P or one of the auto modes, use Auto ISO, and take pictures. Do it under a variety of conditions. I've found that in lower light the camera tends to choose an ISO much higher than needed in order to provide a different setting in the triangle, usually shutter speed like @royd63uk said. I almost always find I would have used a lower ISO. I would not like it at all if this choice was taken away from me.
 
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I set my own ISO mostly and keep it fixed at 200, aperture priority. When I do need to use Auto ISO I set the lowest upper limit I can get away with according to what light I have and the shutter speeds I need to obtain sharp images. Basically, I'm in control not the camera.
 
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In fact why even have any reference to ISO at all?

Understandable in the days of film yes, but with todays sensors and the camera's computing power surely it's capable of applying a sensitivity value (lets not even call it ISO) that is required in accordance with the ambient lighting conditions and camera settings at the time of taking the shot.

I know what you're gonna say.....AUTO ISO.....but then, why even bother with that?
I guess what you're asking is: "If the camera is applying the ISO value by just digitally amplifying the values captured by the sensor, why would you set the ISO value at the time of shooting?" In that case, you could just always shoot at base ISO and change the exposure when developing the RAW files.

As @wjiang commented, this is often not how it works. When there's some analog amplification going on, this assumption doesn't work so setting the ISO beforehand is still necessary.

Also, when shooting JPEG you would still want to determine the exposure of the image by setting an ISO value (even if the camera were ISO-invariant). And of course (even when shooting RAW) you want to have a clue as to whether the aperture and shutter speed you choose make sense given the amount of light you have. You could say "don't bother with ISO", but with little light, a small aperture and a fast shutter speed, you'd still have to amplify the signal so much that you'd get a lot of noise. (Finally, with the settings I use, using base ISO in a dark environment would mean that I would see very little through the EVF.)
 
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I understand there is not only digital/software amplification applied but a mixture of hardware switched amplification along software value amplification and interpolation between adjacent pixels to fight noise. Every manufacturer chooses a different mix of these techniques along their chosen math formulas.
 

Stanga

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One thing that I have ported over from using the FZ50 over nearly a decade before switching to M43 is to fix the ISO at 100 or 200. I then use the exposure compensation dial to over or under expose. When overexposing I look out for the zebra pattern, and then dial the exposure compensation down by a notch. This is OK in good lighting when using a zoom, but of very little use in moderate to poor lighting with my zooms limited by their maximum aperture.
 

PakkyT

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I know what you're gonna say.....AUTO ISO.....but then, why even bother with that?
Because then you would have ZERO control over your exposure and noise if the camera was allowed (without a way to turn it off or pick your own level) to try and "properly expose" your scene. Often times we don't want our camera to try and "properly expose" a scene if it is meant to be darker.

In your case, if you are fine with your camera doing it all, then set yours up for Auto ISO and go into the menu system and allow the Auto ISO function to be able to use the entire available range of ISO. Now shoot with your camera for a while like that and then come back and let us know how it worked out over a variety of shooting conditions, especially night, indoor, etc. type shooting.
 

ac12

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P and auto ISO may work fine for 80% of the pictures. It does for me.
But what about that last 20%? That is when your brain has to made the decisions. It is this 20% that is the "exception to the general rule" and messes up general statements.

As @PakkyT said, the camera is not always right.

I have to apply exposure compensation to adjust the exposure to what I want, or I have to switch to M because the camera simply cannot properly deal with the difficult lighting conditions.​

  • I used the exposure compensation on a P&S to under expose a sunset to get the colors to come out darker than the camera's meter suggested.
  • Similarly on a night light scene, I do NOT want the camera to brighten the scene. I want it DARK with just the lights showing.
So 'auto ISO' or your option is simply another tool in the tool box, not the silver bullet.

You as the photographer, have to know which modes and options to use for which situations.
Or be satisfied with the 80%, and know that 20% will not come out as you want it to.
 

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