Z7 auto ISO seems seriously flawed

Started 5 months ago | Discussions
j2scriba New Member • Posts: 6
Z7 auto ISO seems seriously flawed
3

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 mimimum shutter speed in automatic modes and increase ISO if light is too low to do that, until the maximum sensitivity is reached.

However, this is not quite what is happening.
If maximum ISO is reached, the A-mode increases shutter speed regardless of the mimim shutter speed. 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."

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

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.

The strange disregard for minimum shutter speed pretty much spoils this feature. Underexposure can be fixed in post, blurred pictures cannot. Am I the only one who thinks that "No" (as in "No longer exposure than I specified") should really mean "No" in this setting?

Nikon Z7
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Discombobulate Regular Member • Posts: 182
Re: Z7 auto ISO seems seriously flawed
10

it seems correct in aperture priority mode.  why don't you use shutter speed priority to 1/250?  using full manual mode is more likely in this case.

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masp
masp Forum Member • Posts: 66
Re: Z7 auto ISO seems seriously flawed
12

Have you tried putting it in manual and setting your aperture open and the shutter to 1/250 or higher and let auto iso float to achieve proper exposure? There were similar issues like this with Fuji years ago until they allowed auto iso in full manual mode.

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MayaTlab0
MayaTlab0 Senior Member • Posts: 2,841
Re: Z7 auto ISO seems seriously flawed
1

j2scriba wrote:

The strange disregard for minimum shutter speed pretty much spoils this feature. Underexposure can be fixed in post, blurred pictures cannot. Am I the only one who thinks that "No" (as in "No longer exposure than I specified") should really mean "No" in this setting?

I think that there are two things to consider in your post :

I) Sensors' linear noise behaviour above a certain ISO (invariance) and why most cameras' tendency to amplify the shot instead of boosting it after the raw file is written (with a line in the metadata indicating by how much it should be brightened) is counter-productive as it destroys highlights with no noise benefit, and

II) Auto ISO behaviour.

The first point I'd agree wholeheartedly with you but there may be some reasons why manufacturers may not go there without thinking this process through : some UI issues (if you take an ISO 1600 shot that's meant to be boosted by two stops, do you indicate it as a ISO 1600 or an ISO 6400 shot ? The user needs to know at least by how much it's underexposed. Older Fuji cameras used to behave like this and displayed the resulting ISO, but not the file's real ISO value for example), some wider ecosystem issue (Lightroom didn't display older Fuji cameras' high ISO files properly at launch as the software wouldn't handle the metadata well), etc. Another point to consider is that with dual gain cameras, the notion of "base ISO" has vanished to some capacity - and what about the future ? What if we get sensors with triple, quadruple gain designs ?

Regarding the second point I prefer the way Nikon implements it. The whole point of specifying a max ISO is basically to say that above x value, the IQ is too low for you to consider the file worth it. What Nikon would tell you, if you don't like to see the camera lower the minimum shutter speed when it reaches the max ISO value you specified, is simply to raise the max ISO value if you intend to boost the file in post anyway... of course at the cost of loosing highlight information given the lack of proper implementation of the first point :D.

So I don't think that the auto ISO behaviour is flawed in regards to your concerns. The implementation of higher ISO values, above the highest base ISO value ? More like it.

The notion itself of ISO may also be questioned with digital files. Personally when I take a shot, which, let's say, requires underexposure to preserve some highlight details and then a boost in post, I'd rather know exactly how noisy the boosted areas will look than an ISO value that's lost all meaning. A sort of live view zone system with indicators for the amount of noise for each zone that would result if the darkest zone was raised above 0 would be more helpful to me in these circumstances... and even then far from perfect as I may not even want to boost the darkest parts above 0...

j_photo Veteran Member • Posts: 4,105
Re: Z7 auto ISO seems seriously flawed
19

Just shoot manual shutter, manual aperture, with auto-iso. No big deal.

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MSullivan Regular Member • Posts: 129
Re: Z7 auto ISO seems seriously flawed

j_photo wrote:

Just shoot manual shutter, manual aperture, with auto-iso. No big deal.

I think the OP wants the shutter speed to float at 1/250 or higher, depending on available light, but never go below 1/250. If he switches to M the shutter speed is locked, so if light increases to the point where ISO can't go any lower then the pics will be overexposed (which can't be recovered). Using A mode with minimum shutter solves most of the problem, but when light gets really low it sounds like minimum shutter is being ignored. Probably the only solution is to remove the max ISO cap.

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copyfall Regular Member • Posts: 252
Re: Z7 auto ISO seems seriously flawed
1

Have you tried following?

AUTO can take these value {Slower, , , , Faster}.
i believe camera will try to push the shutter speed more when AUTO is set to Faster, compared to the case when AUTO is set to Slower.

Photo ->ISO Sensitivity Settings ->Minimum shutter speed ->AUTO = {Slower, , , , Faster}

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j_photo Veteran Member • Posts: 4,105
Re: Z7 auto ISO seems seriously flawed
1

MSullivan wrote:

j_photo wrote:

Just shoot manual shutter, manual aperture, with auto-iso. No big deal.

I think the OP wants the shutter speed to float at 1/250 or higher, depending on available light, but never go below 1/250. If he switches to M the shutter speed is locked, so if light increases to the point where ISO can't go any lower then the pics will be overexposed (which can't be recovered). Using A mode with minimum shutter solves most of the problem, but when light gets really low it sounds like minimum shutter is being ignored. Probably the only solution is to remove the max ISO cap.

Yes, good points. Or one can manually raise the shutter speed when needed.

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vockman Contributing Member • Posts: 546
Re: Z7 auto ISO seems seriously flawed
5

Auto Iso, only makes senses to me in manual mode and it works great on the Z.  Other wise you have two auto functions going on and it is hard to figure it out.

giarc
giarc Contributing Member • Posts: 697
Re: Z7 auto ISO seems seriously flawed
9

This is how AUTO-ISO works on the D750 and the D500 as well. The minimum shutter speed is ignored if the exposure would be too dark when using an auto mode, like 'A'. I understand their decision ( and Fuji works this way as well...) and I think its better than the alternative of raising the ISO past the max.  The thing is to know how it behaves, and adjust your settings when the camera isn't doing exactly what you want. Cameras are tools, don't blame your tools, make them work for you.

Peter v.d Werf Contributing Member • Posts: 744
Re: Z7 auto ISO seems seriously flawed
1

vockman wrote:

Auto Iso, only makes senses to me in manual mode and it works great on the Z. Other wise you have two auto functions going on and it is hard to figure it out.

Interesting topic, I just switched from a d750 to z6 and wonder if the behaviour changed or simply went unnoticed for me on the d750 or prior models.

In case I understood the OP correctly then I share the OP’s expectations. That the camera should honor the hard limits that have been set by the user. Otherwise whats the use of setting these limits. So no higher iso then ‘max iso’ and no slower shutter then minimum shutter speed. If that ends up with a too dark image then it’s up to me to manually increase the thresholds. Which in my case is mostly upping the iso because i’d rather have that then subject blurring.

And between those values it’s up to the camera to figure the 2 auto functions out, that’s where I’d rely on camera logic.

Interesting to check my z6 for it’s behaviour.

Horshack Veteran Member • Posts: 8,009
In the manual
6

"Shutter speeds may drop below the selected minimum if optimum exposure cannot be achieved at the ISO sensitivity chosen for Maximum sensitivity."

https://onlinemanual.nikonimglib.com/z7_z6/en-nsg/09_menu_guide_03_08.html

SaltyPeanut
SaltyPeanut Senior Member • Posts: 1,178
Re: Z7 auto ISO seems seriously flawed
2

vockman wrote:

Auto Iso, only makes senses to me in manual mode and it works great on the Z. Other wise you have two auto functions going on and it is hard to figure it out.

Not that hard to figure out.

The camera tries to stay at base ISO and above your min shutter speed. When light is low, camera stays at base ISO and lowers shutter speed down to the minimum shutter speed that you set. Once at the min shutter speed, if light is still low, camera stays at the min shutter speed and now starts to increase ISO up to the max ISO that you set. If light is still low, the camera stays at the max ISO that you set, and now it begins to go lower than the minimum shutter speed to achieve exposure - the other choice would've been to go above the max ISO but Nikon decided to go below the min shutter speed instead.

The Auto ISO icon flashes on screen when the max ISO has been reached to let you know that the camera is now going below your min shutter speed. Simply keep shooting if the lower shutter speed still works for you, increase auto ISO limit, or switch to manual to lock in a min shutter speed and max iso, knowing that you will capture underexposed shots this way. Alternatively, you may stay in A mode and simply dial in a negative exposure compensation, to keep your shutter speed up (haven't tried this, but *should* work).

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SaltyPeanut
SaltyPeanut Senior Member • Posts: 1,178
Re: Z7 auto ISO seems seriously flawed

Peter v.d Werf wrote:

vockman wrote:

Auto Iso, only makes senses to me in manual mode and it works great on the Z. Other wise you have two auto functions going on and it is hard to figure it out.

Interesting topic, I just switched from a d750 to z6 and wonder if the behaviour changed or simply went unnoticed for me on the d750 or prior models.

Behavior should be the same. It was on my D7200.

In case I understood the OP correctly then I share the OP’s expectations. That the camera should honor the hard limits that have been set by the user. Otherwise whats the use of setting these limits. So no higher iso then ‘max iso’ and no slower shutter then minimum shutter speed. If that ends up with a too dark image then it’s up to me to manually increase the thresholds. Which in my case is mostly upping the iso because i’d rather have that then subject blurring.

If that's what you or the OP want, you need to switch to manual mode. In the semi-auto modes, the camera will always try to achieve a good exposure, and it will go below your min shutter limit to do that. Note different meters can make slight differences in exposure, i.e. matrix vs spot or highlight, as well as where the AF point is within the frame in combination with the selected meter (camera tends to prioritize exposure to where the AF point is looking at, even with matrix meter which evaluates the entire scene).

If you want to stay in a semi-auto mode, you need to dial in some negative exp compensation, so the camera doesn't need to go far below your min shutter setpoint to achieve a balanced exposure (you're basically telling the camera make my balanced exposure a -1EV or -2 EV, etc.). Otherwise, switch to manual, dial in your shutter speed, aperture and ISO, and capture whatever light those settings allow you to capture.

And between those values it’s up to the camera to figure the 2 auto functions out, that’s where I’d rely on camera logic.

Interesting to check my z6 for it’s behaviour.

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j_photo Veteran Member • Posts: 4,105
Re: Z7 auto ISO seems seriously flawed
3

Nothing's changed. Same as dslrs.

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aut0maticdan
aut0maticdan Senior Member • Posts: 1,260
it makes sense if context is considered
1

You have two things happening here.  Based on metered data, the aperture priority system affects shutter speed and the auto iso system affects iso.

You are adjusting settings for the auto iso system.  Those settings  don’t affect how aperture priority works.  They can, however, influence what shutter speed gets set to by increasing iso.

What you are looking for is a setting in aperture priority that says, “Don’t go under a shutter speed of 250, even if it means under exposing”

Nikon’s position is apparently that they don’t have their auto exposure modes expose incorrectly.

I would second the recommendations of going to manual mode with auto iso so that you can set shutter speed and aperture where you need it.

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michaeladawson Forum Pro • Posts: 13,439
Re: Z7 auto ISO seems seriously flawed
3

j2scriba wrote:

The strange disregard for minimum shutter speed pretty much spoils this feature. Underexposure can be fixed in post, blurred pictures cannot. Am I the only one who thinks that "No" (as in "No longer exposure than I specified") should really mean "No" in this setting?

Strange disregard?  Spoils it?  For who?  You, not me.  It works the way I expect it to work.  Why would I want the camera to start taking underexposed photos?

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michaeladawson Forum Pro • Posts: 13,439
Re: Z7 auto ISO seems seriously flawed
1

Peter v.d Werf wrote:

In case I understood the OP correctly then I share the OP’s expectations. That the camera should honor the hard limits that have been set by the user. Otherwise whats the use of setting these limits. So no higher iso then ‘max iso’ and no slower shutter then minimum shutter speed. If that ends up with a too dark image then it’s up to me to manually increase the thresholds. Which in my case is mostly upping the iso because i’d rather have that then subject blurring.

Then what's the point of even having an upper ISO limit?  If you're just going to raise it when you run out of ISO just set max ISO to the max ISO to start with then.

If you're working in conditions where you are going to run out of minimum shutter speed AND you're going to run out of max ISO then you should be shooting in manual mode with auto ISO.

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Mike Dawson

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michaeladawson Forum Pro • Posts: 13,439
Re: Z7 auto ISO seems seriously flawed
1

giarc wrote:

This is how AUTO-ISO works on the D750 and the D500 as well. The minimum shutter speed is ignored if the exposure would be too dark when using an auto mode, like 'A'. I understand their decision ( and Fuji works this way as well...) and I think its better than the alternative of raising the ISO past the max. The thing is to know how it behaves, and adjust your settings when the camera isn't doing exactly what you want. Cameras are tools, don't blame your tools, make them work for you.

Think about it... If Nikon were to choose the option of letting the camera go past the max ISO when light is too low then there IS NO POINT to having a max ISO setting.

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Mike Dawson

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Peter v.d Werf Contributing Member • Posts: 744
Re: In the manual

Horshack wrote:

"Shutter speeds may drop below the selected minimum if optimum exposure cannot be achieved at the ISO sensitivity chosen for Maximum sensitivity."

https://onlinemanual.nikonimglib.com/z7_z6/en-nsg/09_menu_guide_03_08.html

Ah, guess I should have RTFM then;-)

The advices to choose manual are appreciated but won’t be the workaround for my specific application of A prio with auto iso for certain situations.

While I still find it odd (even though it’s in the manual) that such user settings are overriden, it has apparantly not led to images where it has actually and noticably affected my images.

But I do allready change/up the thresholds when going from day to evening for instance so I think that prevents the camera from going it’s own way.

The camera also does not close the aperture in A mode when it leads to an overexposed image, so in that sense why ignore one user setting but uphold another if the camera sees A still as one of the auto modes.

I’d like to see an option offered where you can disable/disallow the camera from going lower then the chosen thresholds.

Other then that: @OP Thanks for making me aware so I can take it into consideration when using auto iso

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