Sensor Dust or not? Only happens with lenses on M to L

[SoCalLeicanator]

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So this is really weird.  I have a Leica Sl2-S that I purchased to primarily use with M-mount lenses and have for the past 8 months without incident until a dust spot appeared in the viewfinder.  I blew on the sensor and tried a several different M-Mount lenses where stopped down to f8+ and the spot is in exactly the same place.  BUT, with my Autofocus lenses (Lumix 50 1.8, 35 1.8, Leica APO SCRon 50) it is not there even stopped down to f22?  

I am obviously going to clean the sensor, but find this to be extremely weird.  Would a lens profile correct a sensor dust spot? Does the adapter increase the distance between lens and the sensor and thus reveal dust in a different plane of focus?

Edited October 12, 2023 by SoCalLeicanator

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[jaapv]

No, the distance is the same, but as native SL lenses are far more telecentric than -in general- M lenses the more parallel light rays will magnify the dust spot - on the cover glass- less on the sensor surface -deeper inside - . 

[dpitt]

Did you use the minimum aperture on the L lenses? Dust disappears at large apertures. Use F16 or F22 when doing test shots for dust.

[hdmesa]

10 hours ago, SoCalLeicanator said:

So this is really weird.  I have a Leica Sl2-S that I purchased to primarily use with M-mount lenses and have for the past 8 months without incident until a dust spot appeared in the viewfinder.  I blew on the sensor and tried a several different M-Mount lenses where stopped down to f8+ and the spot is in exactly the same place.  BUT, with my Autofocus lenses (Lumix 50 1.8, 35 1.8, Leica APO SCRon 50) it is not there even stopped down to f22?  

I am obviously going to clean the sensor, but find this to be extremely weird.  Would a lens profile correct a sensor dust spot? Does the adapter increase the distance between lens and the sensor and thus reveal dust in a different plane of focus?

Most AF lenses remain wide open until the moment of exposure, therefore you won't see dust spots when using AF lenses by just looking through the viewfinder. You should see the dust spots when examining the images. 

[SoCalLeicanator]

Yes, the AF lenses were all shot at f22 and no dust, where it is clearly visible at f8 and up on the M Mounts.  This is true on the pictures as well.  I had a feeling there was a physics explanation.

Now, I have to man up and clean my sensor.  There is a respected photo shop that will do ir for $80.  Have to admit that's tempting.   They are where I woud have to buy the sensor kit so maybe I'll swing by and see.  

[jaapv]

Try blowing the sensor with a rubber ball blower first   There is an extensive sensor cleaning  post in the M FAQ. It is easy and safe and takes about five minutes. 80$ is ridiculously overpriced. 

[SoCalLeicanator]

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So I manned up and did it.  Dust gone. HDMESA was dead on.  The spot WAS visible at f22 with the autofocus lenses but barely.  jaapv Mathphotographer has a video as well.   I followed his rather than the M instructions  because of the IBIS.