Any idea what's going on here?

[pen_y_cae24macro]

Focus stacking, F8, 1/100th, manual. Settings saved to C1. Yesterday, I suddenly found that I had a dark bar along the top of the images. Today, I shot a test stack and it was barless. I took the camera out with me, the first two stacks had no bars and the third and subsequent all had bars. The time between the two was seconds! I've no idea what's causing this. Any suggestions will be gratefully received!!

[Camera Gent]

were you using flash? (It doesn't look like it though). Can you see the exif data on the files? Were the shutter speeds the same? What are your C1 settings?

[pen_y_cae24macro]

Yes, to flash. 1/32, manual. It was flashing away like normal. I have looked and you're correct the shutter speed is not the same. The first stack 1/100 - no bar, second stack 1/125 - no bar, third and all the rest 1/125 with a bar. I must have contorted for the shots and my thumb rolled the shutter speed up. Odd that the second stack was ok? That's probably it. All my gear is packed away at the moment so I'll confirm tomorrow. But in the meantime, thanks very much for the 'point'.

[R99C99]

I asked ChatGPT what might be causing this. Please see response below. Could be complete nonsense, but there could be some causes in there.



That black bar you’re seeing at the top of your focus-stacked images with an OM System (Olympus) camera is a known quirk of how the camera does its in-body focus bracketing/stacking.

Here’s what’s happening:

• OM System cameras don’t just blend the images; they also do slight sensor-shift cropping to align the frames.
• During focus stacking, the field of view can change a tiny bit as the lens shifts focus (focus breathing).
• To compensate, the camera slightly crops into the image so that all the stacked frames overlap perfectly.
• If the subject is near the edge of the frame or if the lens exhibits more breathing than usual, the alignment process can’t fully cover the entire frame. The result: a thin black bar or edge (commonly at the top or side).

You’ll usually notice it more:

• With wide-aperture or telephoto lenses (more focus breathing).
• When stacking a large number of shots.
• If the subject is framed very tightly.

📌 How to avoid it:

1. Leave a little extra space around your composition so the camera has room to crop during stacking.
2. Reduce the number of frames in the stack (fewer steps = less accumulated breathing).
3. If possible, try bracketing in-camera but stacking later in software (Helicon Focus, Zerene Stacker, etc.), which can handle edge alignment more

Here’s a visual example of what happens during in-camera focus stacking:

• The black square is the full sensor frame.
• The colored boxes show how each shot shifts slightly due to focus breathing and lens changes.
• The camera has to crop to the purple overlap area, so all frames align cleanly.
• If the crop doesn’t fully cover the top (or side), you see that black bar appear.

[Camera Gent]

Load of old or, in chatgtps case, new, tosh

[R99C99]

Great to have such experts on the forum then eh?

[R99C99]

[Matt_Hirst]

I had something similar when I was doing some work indoors recently...I had the flash on one of those off camera hotshoe cords and whilst holding the flash rotated 90 degrees (don't ask i was just trying things out) all my images ended up with a top bar....rotating it to a more normal position everything was fine.

I put it down to some form of bad connection / cheap cable I was using so as I was just messing around left the flash in its more normal position.

Doesn't really answer your question but just a similar observation.

Matt

[Camera Gent]

I think your answer is here re the flash sync speed

https://www.e-group.uk.net/forum/forum/cameras-lenses-and-system-accessories/camera-conference/micro-four-thirds/new-om-system-om-1-mark-ii/987803-running-into-problems-straight-away-with-a-new-set-up

[David Mallott]

I think your answer is here re the flash sync speed
https://www.e-group.uk.net/forum/for...h-a-new-set-up

I'm surprised that AI isn't intelligent enough to come up with the obvious and most likely cause. 🙄