Hi Folks,

Should I worry about this mark? No idea how it got there, its not dust. It doesn't seem to be affecting photos.

 

thx!

How do you know it's not dust? If it doesn't show up in your photos (especially when shooting at large apertures) chances are good that the spot is lying on top of the sensor and is not a scratch or droplet on/in the cover glass.

Take a photo at a very small aperture (f/16-22) of e.g. a clear blue sky or a brightly lit white surface. If the spot is in the relevant part of the sensor, it should show up as a black spot on the photo.

At large apertures, light rays are very diffuse and can reach behind a dust particle, so dust particles might not show up on photos. At small apertures, light rays are more parallel so there should be a clearly defined shadow cast by a dust particle.

Edited June 8, 20241 yr by Pieter

Looks like delamination, i.e. the different layer of the sensor that detached.

It happens in screens (and sensors) as a consequence of a knock or because too much pressure is applied in cleaning. 

It could also be a surface treatment (coating) that has been removed due to harsh cleaning, I have seen that often in lenses.

In both cases it has a limited effect on image quality, because it is not blocking light transfer.

Thanks for the responses. I'll try some photos today at a small aperture. I tried the blower tool to see if it was dust, but I haven't touched the sensor

The sensor has a cover on it? Or a top layer?

Edited June 8, 20241 yr by Rudbeckia

1 hour ago, Rudbeckia said:

Thanks for the responses. I'll try some photos today at a small aperture. I tried the blower tool to see if it was dust, but I haven't touched the sensor

The sensor has a cover on it? Or a top layer?

Yes, there's a protective layer of thin glass on top of the sensor.

1 hour ago, Pieter said:

Yes, there's a protective layer of thin glass on top of the sensor.

If this is the case, could be that a faulty coating and/or an aggressive cleaning has removed it.

The good news is that it should have minimal effect on the pictures.

Every piece of glass in the optical path affects image quality. Decent lenses are designed while taking this effect into account. Vintage lenses however were designed for film rather than a digital sensor, which didn't include this sheet of glass. The result is that vintage lenses show poor corner sharpness on digital cameras. Companies like Kolari Vision make a bussiness out of replacing the relatively thick cover glass on Sony sensors by a very thin glass layer, with astounding effects on the corner sharpness when using vintage lenses.