Sensor corrosion or something else?

[Herman Zhang]

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I noticed a spot while shooting at f2.8 on a 35mm lens today. It does not seem to be dust, as it is bright in the centre and sharp even when the image is defocused. It is visible at all apertures, and with all lenses that I own(so it is not dust on lens). The sensor is ID11, looks pretty clean under a strong lamp and is claimed to have had the filter replaced by a workshop. I just found today it but it happens to be found in all of my photos in the same spot since I bought it 4 months ago. I suspect that it might be a hot pixel, as allegedly corrosion is only visible at very small apertures (like F/16 or 22). Can anyone tell me what it is, and if it does happen to be a corrosion, can someone tell me which specific filter(which one from Schott) does the M9 originally has (I want the original colour rendering).

The other dark dots should be dust on sensor, as it seems to be somewhat defocused

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[irenedp]

I would examine the sensor with a magnifier before making any assumptions. Sometimes it might be something else 

[mujk]

Agree with @irenedp. If i's dust or corrosion you should be able to see it with the loupe, corrosion possibly only at an angle. If it's a hot pixel you should not be able to see it with a loupe. In an image corrosion is actually visible at least until F/8 and sometimes even with bigger apertures.

[Herman Zhang]

17 minutes ago, mujk said:

Agree with @irenedp. If i's dust or corrosion you should be able to see it with the loupe, corrosion possibly only at an angle. If it's a hot pixel you should not be able to see it with a loupe. In an image corrosion is actually visible at least until F/8 and sometimes even with bigger apertures.

Mine is visible at all apertures. If it possible that it's a very bad corrosion?

[pedaes]

On 2/8/2025 at 4:41 AM, Herman Zhang said:

It does not seem to be dust,

Give the sensor a clean and if it is still there you will know answer.

[Elliot Harper]

Looks like a corrosion to me if it's visible and same shape across all the apertures.

[Casey Jefferson]

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On 2/8/2025 at 12:41 PM, Herman Zhang said:

I noticed a spot while shooting at f2.8 on a 35mm lens today. It does not seem to be dust, as it is bright in the centre and sharp even when the image is defocused. It is visible at all apertures, and with all lenses that I own(so it is not dust on lens). The sensor is ID11, looks pretty clean under a strong lamp and is claimed to have had the filter replaced by a workshop. I just found today it but it happens to be found in all of my photos in the same spot since I bought it 4 months ago. I suspect that it might be a hot pixel, as allegedly corrosion is only visible at very small apertures (like F/16 or 22). Can anyone tell me what it is, and if it does happen to be a corrosion, can someone tell me which specific filter(which one from Schott) does the M9 originally has (I want the original colour rendering).

The other dark dots should be dust on sensor, as it seems to be somewhat defocused

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It's a damaged pixel, I had some on mine as well (sensor glass replaced), fortunately it's around the edges and it's only visible if one pixel peep and look hard for it. I was a little annoyed by it but after shooting it for a while I eventually forgotten about it and never spot it on my images.