Aperture black dot!

A

Alpha Beta Omega

Veteran
I got an email a week ago from a guy having problems with his AF camera and some lenses. Today I looked into how my Voigtländer lenses behaved when stopping down and if this is related to his problem or it's another artefact or whatever you'd like to call it, I don't know. Take a look at this image:

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You have to click it to see it bigger. In the middle of the frame is a black dot. Just to the left of the bulb. First I got worried the sensor was damaged but it seams something else is happening. The spot changes shape and form when changing aperture and it's only visible when stopping down the lens past F4 (Voigtländer 75/1.8). I even tried my Olympus 14-35/2 and sure enough the dot came forward and the image above is with that Olympus lens.

I would guess some sort of blackout happens when the blades on the lens are closed.

And the solution tada! Dirt or objects on the sensor cover/glass. I found a tiny dust speckle and I can image something similar happened to the other guy. Good to know what this is next time it happens.
 
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On this particular image the dot looks like a shadow and I would have never guessed it was anything else. Can you provide another image that isolates the dot a little better?
 
I haven't looked to close on how the whole assembly is put together but there's a glass in front of both ND and sensor and possibly no dust will enter beyond the that first piece of glass.
 
That is correct -- there is sensor protection glass on the outside, and everything else is sealed behind that and won't ever get dusty or dirty. It's just that outer glass that you have to keep clean.
 
On that question - do we have a difinitive answer as to the best way to clean that glass. I have all sorts of cleaners and am reluctant to put anything on there until I know what effects they could have. Lenses are lenses - can this be treated the same? Until now I have been treating that glass like a sensor and making sure its closed off at all times and using a blower from time to time. But eventually I know something like a drop of something or greasy finger may accidentally come in contact with it.
 
Noel Evans said:
On that question - do we have a difinitive answer as to the best way to clean that glass. I have all sorts of cleaners and am reluctant to put anything on there until I know what effects they could have. Lenses are lenses - can this be treated the same? Until now I have been treating that glass like a sensor and making sure its closed off at all times and using a blower from time to time. But eventually I know something like a drop of something or greasy finger may accidentally come in contact with it.
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One of the questions I asked the Panasonic rep when I went to an AF100 demo was about cleaning the sensor as I have known this to be a problem with my early DSLR's. He pointed out that the sensor was completely sealed off behind that front piece of glass so it would not be a problem. I would think your normal lens cleaning procedure should do the trick. Here's a link to the people I bought a sensor cleaning kit from for my original Canon 300D still camera. http://www.copperhillimages.com/index.php?pr=Copper_Hill_Products though I doubt you'll need it for the AF-100.
 
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