Clunk noise at the end of long exposures when IBIS and VR off?

Any ideas? I have shutter cover to come on when camera turned off, but at the end of a LE I hear a clunk like I have a camera with a shutter? IBIS and VR confirmed off in the menu?

Z8|Z9?
Sensor shield closes down for the LENR dark frame exposure.
Check your noise reduction settings.

This will be it, thank you. I like to do LR NR for daytime LE.

Why do you use LENR? Do you see many hot pixels without it?
LENR has the effect that it increases random (uncorrelated) noise in the image.

Never seen anything but a much cleaner file with it on. I do up to 10 min LR in daytime. It's warmer. You get rid of mostly all hot pixels and it's all combined in one file with no faff.

I have not tested myself, but Jim Kasson measured the noise with Z 9:
blog.kasson.com/z9/nikon-z9-lenr/

Yes but still if you try a 10 min exposure in daytime, and then look at the file without LENR you'll see it is peppered with hot pixels. It's an easier method to just leave it on and end up without all of that. That said this is only going by how my 850 and 810 behave; I haven't tested this on the Z8 yet but assume i'll still leave it on to escape the sea of red green and blue hot pixels.

+1

Note that Jim’s test was carried out only as far as 10 seconds; since 10 minutes is almost two orders of magnitude longer it should be considered separately.

Jim pointed out that the feature can only repair artifacts that repeat from one frame to the next. I’ve made a series of dark frames at exposures of 30 seconds (not as long as the OP’s) and pixel peeped them to see where the hot pixels actually fall. Some were at the exact same locations for as many as 3 or 4 frames in a row then went away. Those would be removed by LENR. But the overall majority did not repeat between any two sequential frames. I therefore leave it switched off. But those weren’t 10 minutes per frame.

LENR was a more useful feature to me with the “generous” level of magenta haze amp glow on the D800, which was also present but to a lesser extent on the D810. But for 30 seconds or less on my Z’s I feel I’m better off doing without. I could be wrong but there may be a good trend going on in this sensor lineage at Sony.

Note that in astrophotography when dark frame subtraction is used the darks are preferentially collected offline outside of precious dark sky time, and a set of them will be combined with per pixel averaging or median.

Just to respond to your last paragraph. I communicated closely with Mark Shelley from Cloudy Nights on my d850 deep sky astro shots who dug through and analysed my flats and dark frames at the time. He concluded that darks didn't need to be used for my then d850 because the sensor has such good dark current suppression. I only shot lights and flats with bias frames. So the point here is...for astro...darks aren't always required. Especially with the Sony sensors. Canon...mostly yes. I of course never use LENR for astro.

I will test the z8 soon with ultra long exposures during the day and comment further on this.

A friend relayed the same thing to me recently from advice she received in an astro workshop. And I’ve not lately been collecting darks for my Z light frames either.

Thumbs up on your plan to experiment.

Yeh your friend is absolutely correct. If you are using a dedicated astro cam it is more likely to need darks but with dslrs or mirrorless sensors sometimes they are not required. Dithering helps alot. My d850 night sky images turned out very clean for a few hours data on targets I felt. Interested to see what the z8 will do. It's gonna be so much easier to focus and frame up with starlight view. Also...the back screen will save my neck too.