Need help for my voigtlander lens

[Viktor Long]

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Hello, everyone. I have a voigtlander 15mm f4.5 (m-mount, version II) for daily photography. When adapted to my Nikon Z camera, the image quality is very good. But I found a problem. When the lens is aimed at the street lamp, table lamp and other light sources, you can see many white spots in f11, f16, especially at f22. I'm sure it's not sensor dust. Observing the lens, there is no obvious dust on the front and rear glass. What's wrong with my lens? 

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[Carlos cruz]

Internal reflections and healthy dose of diffraction. There are not many lenses that can be closed all the way without paying a price and voigtlander is not one pf them. 

[Robert Ardinger]

Looks like internal reflections.  Duplicate the findings while looking through the viewfinder and move the camera around or rotate the camera with the point light source in the center and the "spots" should move around and not be in a constant position in the frame.  Also if the aperture is opened (as referred to in the other comment) the spots should lessen or go away.

Edited July 16 by Robert Ardinger

[Viktor Long]

thanks for your reply, my friend. For the internal reflection problem, I never recognize it before. I check my lens and find many small dust inside the lens, will those dust cause this problem?

[jaapv]

It could cause reflections but it would need to be pretty bad. 

[Viktor Long]

Thanks to Robert Ardinger. Yes the spots will move around when rotate the direction of the camera. Now I know the reason, so I can use it without worries.

[Viktor Long]

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3 minutes ago, jaapv said:

It could cause reflections but it would need to be pretty bad. 

Thank you. I find there are many dust inside the inner glass. Maybe they make the problem worse. At f5.6 and aim at strong light, you can see white spot in images. F22 makes it extremely bad(as my example image).

[Viktor Long]

19 minutes ago, Robert Ardinger said:

Looks like internal reflections.  Duplicate the findings while looking through the viewfinder and move the camera around or rotate the camera with the point light source in the center and the "spots" should move around and not be in a constant position in the frame.  Also if the aperture is opened (as referred to in the other comment) the spots should lessen or go away.

Thank you my friend, you introduced this knowledge to me, I never knew about the problem of internal reflection before. Maybe that's the reason. If it's a common problem, then I'm not worried. I can avoid it when shooting in the reality world.

[spydrxx]

When I owned the LTM version of that lens I encountered the same issue as you. After a little experimentation I learned to shoot wherever possible with the diaphragm almost wide open AND not directly into a bright light source.

[250swb]

With a 15mm you are focusing a mix of dust and snot and flying bugs at small apertures because of DOF.  

Edited July 16 by 250swb

[lct]

The lens will make those sort of spots when shooting bright light sources. At wide aperture the spots will be less visible and larger.