Z8 Exposure Variability

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That definitely is a factor. Matrix looks at the entire frame.
Centre waited also looks at the entire frame,.
Centre weighted divides the frame into two segments.
Most of the exposure is determined by a central circle that can often be varied in size though the area outside the central circle is also taken into account when calculating centre weighted exposures.
A bias of 80% for the central Circle and 20% for the outer area is not uncommon.
 
Well, again, using full manual with a mirrorless camera renders the metering choice largely meaningless because one can see the exposure in the viewfinder.

I see your point, I was just saying what i did because in my view the same is also true of any of the auto modes combined with exposure compensation. If one doesn’t like what is seen in the viewfinder they don't have to use it, no matter how they got there. Assuming there is time to make the adjustment.
 
Centre waited also looks at the entire frame,.
Centre weighted divides the frame into two segments.
Most of the exposure is determined by a central circle that can often be varied in size though the area outside the central circle is also taken into account when calculating centre weighted exposures.
A bias of 80% for the central Circle and 20% for the outer area is not uncommon.
Yes. Absolutely but 80% will definitely help lesson the over or under exposure in contrast to matrix metering.
 
While it might be disconcerting, what you’re seeing is normal and the camera’s behaving as expected — I’ve seen the same thing routinely many times with both my own Z8 and D500.
Just look at the histograms — there’s not a huge difference — only what might be explained by a slight change in shooting angle relative to the sun and focus point position relative to different total amount of background light.
The very small amount of clipping you have in the two shots is nearly identical.

Remember that ISO doesn’t control exposure — it’s a consequence of it.
Manual with Auto ISO is just manual. All light hitting the sensor is still controlled by 3 things: ambient light levels plus the shutter speed and aperture you manually set.

So, in post, I’l wager these two shots can be made fairly similar with about the same amount of noise simply by moving the exposure slider (which, on an ISO invariant camera like the Z8, does pretty much the same thing as raising the ISO in camera).
 
Stating the obvious, shooting Auto-ISO is essentially shooting Full Auto and in this case enslaved to the idiosyncrasies of the most idiosyncratic of meter setting. A fraction of movement and the meter would read something completely different and ISO would swing wildly. As you experienced.

In this situation, if you still decide to use Auto, I'd go with a narrower (center or spot) metering and follow the bird as much as possible.
Agree completely
 
I agree that the change in background messed with the auto ISO. This is the perfect example for when to use manual ISO: Same light, same exposure. Get the subject right and ignore the backgrounds.
 
Manual with Auto ISO is just manual.
ISO doesn’t have any effect on exposure — it’s an outcome of it.

When you’re controlling the aperture and shutter speed yourself, the only other change in exposure is change in ambient light.
The camera has no exposure control.
 
Manual with Auto ISO is just manual.
ISO doesn’t have any effect on exposure — it’s an outcome of it.

When you’re controlling the aperture and shutter speed yourself, the only other change in exposure is change in ambient light.
The camera has no exposure control.

Wrong. AUTO ISO changes the signal amplification coming off the sensor, bumping exposure up or down depending on the meter reading. Manual + Auto ISO is a misnomer; it's an auto setting similar to Aperture and Shutter Priority.
 
Wrong. AUTO ISO changes the signal amplification coming off the sensor, bumping exposure up or down depending on the meter reading. Manual + Auto ISO is a misnomer; it's an auto setting similar to Aperture and Shutter Priority.
Nimi, I think you are technically wrong on this.

Exposure, strictly speaking, is the amount of light falling on the sensor. In auto ISO, it is indeed true that the brightness of the image in the viewfinder will change, but (in Manual exposure mode) it changes neither the sensitivity of the sensor nor the shutter speed and f-number...So the exposure remains the same.

And, if the camera is ISO invariant, the outcome in terms of signal and signal-to-noise is the same.
 
I took my shiny new Z8 for its first outing on Friday and it's certainly a step up from my D850. I was however surprised at the occasional radical difference in exposure of images within a 20 fps burst. The two images below were taken within a second (2 frames separate the images) and the light did not visibly change - it was a grey, overcast day with no sun. Shooting RAW, Auto-ISO at 1/3200th, f6.3 at 400mm on a Z 180-600, the first (bright image) is ISO 3200 and the second darker image is ISO 560. It has happened in other bursts as well which is odd as they are a fraction of a second apart - any ideas or is this a known thing?

I accept that my shutter speed was too high for the situation but that surely wouldn't explain why 1 shot in the sequence should be so bright and high ISO would it? Am I missing something obvious?

In Custom Settings, change c1: Shutter-Release Button AE-L to On (burst mode). That will lock the Auto-ISO (exposure) for the first frame in the shot and all subsequent shots in the 20fps (or any multiple fps) burst. When you lift your finger off the shutter release, Auto-ISO will "unlock" and change according to light conditions.

FWIW: I use -1 Exposure Compensation to get a full stop lower ISO with Auto-ISO. There is a point where the ISO is too high for ISO invariance to be a factor, but it may just be wishful thinking on my part.

 
I have experienced this on a few occasions. I am sure it has to do with metering variations as the bird is moving through different backgrounds. I actually asked Steve a while back when this first happened about a year ago. He recommended shooting full manual but I find this difficult to do in many cases so I tend to stay in M-auto iso as in the vast majority of cases the exposure is correct or at least close. I generally use matrix on the z8 and do find I have to pay more attention to exposure compensation than I did on the d850. Using the d850 I tended to prefer center weighted and usually set my exposure compensation to -.3 or -.7. Getting tack sharp images is so much easier on the z8 it almost doesn’t matter as you will have so many more chances to get the shot. I usually use matrix metering and occasionally use single point if the subject is very dark and big in the frame.
 
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