Question about 50mm F4 Schneider Componon

[Nokton48]

Hi All. I just picked up this 50mm f4 Schneider Componon for $20 including Omega D2 board. But I have a question. When set wide-open to f4, the blades on this one close down slightly. Is this normal for the 50mm f4, or is the f/stop ring out of alignment inside? The lens is clean and if necessary I am not afraid to work on it.
Thanks for responses in advance!

Here is the lens, shot from slightly above, you can see the lens stopped down at F4.
My other Componons don't operate like this one.

 

[Gerald C Koch]

Mine works the same way. Nothing is wrong. What you are seeing is perfectly normal for this lens design. By doing this Schneider reduces the amount of some aberrations. You want to increase the use of paraxial rays or rays close to the optical center of the lens. This is actually an f/2.8 design. However if used wide open this lens would not have the best resolution. So the user is prevented from using apertures larger than f/4.

For the optical reasons the following may be useful.

Dead Link Removed

 

[Nokton48]

Great! Thank you for info. Makes good sense.