Mamiya Universal 65mm Lens Aperture Question

I just picked up a Mamiya 65mm for my Universal Press camera. When I set the aperture to wide open (f6.3) the blades in the lens do not open all the way, they appear to still be closed just a slight bit. I can't find any info online, but I found

and the aperture on the lens in the video does exactly what mine does. You can see at about the 50 second mark that he opens the shutter and the aperture is clearly still closed a bit despite being set wide open to f6.3.

 

Everything else about the lens seems perfect, and there is no oil or grease on the aperture blades.

 

Does anyone have experience with this lens, or does anyone have one you can check and see what the aperture does at f6.3?

 

Much appreciated.

I sold mine a few months ago, but I think that your lens is OK since mine looked the same way and worked perfectly.

Quite a few lens designs are like that. Some enlarging and LF lenses are limited by the aperture blades and not the size of the glass.

 

I suspect that this might be a 'quick fix' after manufacture. Maybe the lens was designed to be f/5.6 and didn't quite make the grade after being turned into a real lens from a theoretical design. The main reason for this is low contrast due to internal reflections/flare. Slightly closing the aperture blades quickly fixes this by acting as light baffles against the reflective edges of the glass elements.

I have a large format lens with the same properties. Works as advertised. My guess this was an acceptable practice and rodeo_joe has probably got as good as an explanation as any.

Thanks for the info everyone. I appreciate the detailed response, Rodeo_Joe.