View Full Version : Pentac Apeture Blades Not Right

19-Jun-2010, 11:09
I went to use my AM Pentac this morning, and noticed after a few twists of the aperture that the circle wasn't quite a circle - it was some weird shape - looking closer, and finally removing the front and rear elements - I noticed something wasn't right. One of the blades may now have a slight bend from trying to open and close the blades (by turning the aperture on the barrel) - thinking it would snap back into place.

I notice the end of each blade has a circular nib and there is a corresponding receptacle in the aperture assembly within the barrel - but it isn't exactly clear which nib goes into what receptacle - I have pulled 3 blades from their receptacles - I'm not sure if the others are in correctly either - I was in a warm climate recently - though the camera has been in an air conditioned environment since then - maybe the blades are sticky?

I might have to bend back that one slightly bent blade?

Hopefully someone here has had a similar experience and can offer pointers.

Perhaps SK Grimes can fix?


I have since unseated all the blades, and I notice they a bit oily/gummy - I'm not sure I can put this back together !!! :(

19-Jun-2010, 13:22
Almost had it back together - still gummy though. Except it wasn't quite right, wouldn't open all the way to f/2.9. I wonder it there's a particular aperture that lends itself to reseating the blades? I'm going to try the middle f/5.6.

Dan Dozer
19-Jun-2010, 14:40
I took my AM Serrac apart because the blades were stuck in one position. With all fo them out, take the opportunity to clean them all. Don't use oil. If there is some present, use some sort of solvent to clean it off of them. The blades all fit around the barrel on with the nibs in the holes. It's hard to explain. Start with one blade with the aprature wide open and slowly work your way around. It is pretty easy to start but gets more difficult as you fit more blades in place. If you're lucky, you can get them all back in. Don't get discouraged -it takes a lot of patience.

Steven Tribe
19-Jun-2010, 16:23
Before you try to put them back - check that there isn't an undetected "nick" on one of the 4 edges of each blade. Touch is better than visual inspection. Run a finger up and down the edges for each blade individuallly. Remove "nicks" with fine abrasive paper ( keeping the blade on a solid surface).