[Leica] 49 to 46 Step down ring was Leica Service in Hong Kong

[red735i at earthlink.net (Frank Filippone)]

Well.. on any M camera, open the back door.  Set lens to F wide open.  Lock 
shutter to B ( shutter open) .  Focus or not.
Look through the rear door at the corners through the extreme other corner 
of the lens.....  If you  see anything other ( darker)
than image, you have vignetting.

Now that is easy.....

Frank Filippone
red735i@earthlink.net 


Not to mention the vignetting is easy to check on the M8 display!   
With film, you have to process a roll, or stick a piece of paper over  
the back and use it like a ground glass to see.

Tom