Z7 auto ISO seems seriously flawed

Started 4 months ago | Discussions thread
olyflyer
olyflyer Forum Pro • Posts: 26,682
Re: Z7 auto ISO seems seriously flawed
5

j2scriba wrote:

The auto ISO setting has two adjustable parameters:
"minimum shutter speed" and "maximum sensitivity"
One would expect the algorithm to select ISO as low as possible to achieve the minimum shutter speed in automatic modes and increase ISO if light is too low to do that, until the maximum sensitivity is reached.

Not that simple. Minimum shutter speed depends on the focal length as well. So depending on your focal length and your settings, the camera may chose one shutter speed for one lens as minimum, and another for an other lens. Shutter speed is only floating in A and P modes, in M and S you have fixed it and the camera keeps it fixed at that value.

However, this is not quite what is happening.

It is exactly what's happening with my camera.

A mode: The aperture is fixed, camera selects shutter speed, to the lowest I configured, which is 1/2 FL. ISO is set to 64 to start with, and the ISO is raised to maximum 25600 if needed. The ISO is raised only if the shutter speed reached the minimum shutter speed. If maximum ISO is reached, the camera will lower the shutter speed, below what's been set up by you as minimum shutter speed to preserve the exposure, but will NEVER change the aperture.

S mode: The shutter speed is fixed. The camera opens the aperture to the maximum if the light is not too strong, and "plays" with the ISO between min and max values you have configured. Selecting a shutter speed higher than the minimum shutter speed overrides the minimum shutter speed settings you have set up. The selected shutter speed is NEVER changed, not even if the aperture is already at minimum or maximum opening and the ISO has reached the maximum. Maximum ISO is kept at the set value, even if the image may benefit from raising above the set value.

M mode: The shutter speed and the aperture are fixed, so the camera adjusts the ISO to what's needed, but it will NEVER move outside the min and max settings you have configured.

In P mode: I have no idea. Never used it on any camera.

If maximum ISO is reached, the A-mode increases shutter speed regardless of the minimum shutter speed.

Actually, quite the opposite.

At first I thought there was some hidden option I had overlooked, but Nikon support (Germany) confirmed that this is how it's supposed to work. The reasoning behind it was explained like this: "Since A, S, P are automatic modes, the camera does whatever it takes to achieve good exposure."

That's total nonsense. Se above how it is working. The camera will underexpose in S mode if you have too high shutter speed and too low maximum allowed ISO, but it will try to preserve the exposure in A mode. I think Nikon Germany knows that very well, and if the guy didn't give you the right information then he should throw away his Nikon certificate.

This may be an acceptable design paradigm for a point-and-shoot, but for a presumably professional target group this seems bizarre.

The way it works is EXACTLY as I would like it. I think you have misunderstood something about how it is working.

For me, this feature is useless in this implementation. Here's the scenario I'm looking at: I need to shoot from a moving car and need a minimum shutter speed of 1/250s. I want to shoot wide open to get windscreen dirt out of focus so I select A-mode at open aperture. The camera adjusts shutter speeds shorter than 1/250s.

You should use M mode for this situation.

When things get dark, e.g. in tunnels, ISO is increased. When the scene gets really dark and there's not much to see, there's no point in turning ISO all the way up to max and blow out whatever light patches there might be to reveal only noisy shadows, so I set a max ISO of, say 8000. With the strange auto-ISO design the camera will disregard minimum shutter speed and motion-blurred pictures.

If you really want to freeze motion in a dark tunnel you MUST allow higher ISO. You have created a problem which does NOT exist. Also, you should select the right mode for the right situation. A mode is UTTERLY wrong for action shots, regardless if you are in a dark tunnel or bright racetrack.

As everybody knows, ISO is mostly irrelevant in digital cameras (after hitting a camera-specific optimum ISO) and post processing RAW files to boost shadows will produce very similar or better results to high ISO during exposure, as we have better control over noise and much better preserved highlights. So headline-grabbing extreme-ISO shouldn't be used for serious work, anyway.

Again wrong. I don't know which camera you are using...

The strange disregard for minimum shutter speed pretty much spoils this feature.

It's NOT strange at all and actually the shutter speed is flashing when that happens, so you are warned about the situation. The camera has no idea about the scene, it does as expected, the best it can do considering the settings YOU have configured.

Underexposure can be fixed in post, blurred pictures cannot.

No, not all underexposure can be fixed at PP, and motion blur is not always a problem at all, so it does not need to be fixed.

Am I the only one who thinks that "No" (as in "No longer exposure than I specified") should really mean "No" in this setting?

Well, maybe you are not the only one, but I definitely disagree with most of what you have written here regarding Auto ISO. I like the way Nikon Auto ISO is working, it is very intuitive and reliable. Besides, the camera gives you warning when you are outside the envelop, and you must use the right mode for the right situation. So it is more about you than the camera, I simply think you must play more with it and believe that either you don't have a Nikon, or new to the brand, because this is how how Auto ISO was working ever since I bought the D300s ten years ago and this was one area I really appreciate and like a lot. I have found that Auto ISO is very useful and a very well designed feature. It is also consistent, works similar in all Nikon cameras I know of. Auto ISO can surpise you, but only because you are not familiar with it.

Anyway, regardless which Auto mode you select, none are perfect for everyone in every situation. If you want to have 100% control you must select all manual modes, including WB and focus.

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