Pancolar 80 - aperture in automatic mode problem

Gonzoo · Joined: 29 Mar 2010 Posts: 231

I recently aquired a Pancolar lens with stuck aperture. I removed the lubricant from the blades and the lens worked like charm - in preset (manual) mode. In automatic mode the lens' aperture should only be closed if the pin at the rear is pressed. With this lens however, the aperture operates from f1,8-f3,5 as if in manual mode (closes down). If I go beyond f3,5 the blades stay at f3,5 position and only close further if I press the pin.

My first thought was, that there still my be some lube hampering the blades movement, so I cleaned them again - to no avail. Might be a weak spring that fails to hold blades in open position? But then I would expect such behavior around f11-f16 where the spring is pulled more than at f1,8-f3,5...

Anybody got an idea on this?

Thx in advance!

Himself · Expire: 2013-05-30

The spring could be the culprit.
Pay attention that even if you see the blades cleaned, it doesn`t mean that they are totally clean.
There is always some gunk at the base impossible to be cleaned unless you dismantle them completely.

Gonzoo · Joined: 29 Mar 2010 Posts: 231

In fact, the blades are not totally clean. I did not disassembled the diaphragm mechanism, instead I cleaned it with cotton buds. But I dont see why this would cause the above mentioned behavior of the aperture.

One could think of this: if set to f16 and closed down to f1,8 the weak spring is not able to move the blades beyond f3,5 because of some grease still left on the blades. But why does this apply to the other way around? If the spring is weak it should not be able to keep the aperture open all the way from f1,8-f16 - not only from f1,8-f3,5. Or, do I miss a point?

Spotmatic · Joined: 18 Aug 2008 Posts: 4045 Location: Netherlands

My first thought is that you installed the back part wrongly. I have disassembled a few 80mm f/1.8 Pancolars so I know the lens inside and out, but not this exact problem. Make sure that you installed everything right, especially lining up the notch in the diaphragm ring with the rod going down to the diaphragm.

As for cleaning the lens: I've removed the front and back lens groups and then dunked the whole (working) barrel in a bath of naphta, after which I regreased the focusing helicoid. It still works as of today: http://forum.mflenses.com/czj-80mm-f-1-8-pancolar-stupid-cleaning-idea-t29774,start,15.html#1047344

Gonzoo · Joined: 29 Mar 2010 Posts: 231

I already checked that and compared to other, working pancolars. Everything is exactly where it should be. As I wrote: in manual/preset mode the aperture works perfectly. Only in automatic mode it shows this strange behavior.

Unless anybody got an idea my next try will be to take out the blades for complete cleaning. Maybe there is just a little bit of grease left between them, hampering the aperture movement spring...

Spotmatic · Joined: 18 Aug 2008 Posts: 4045 Location: Netherlands

If so then you should do it like I did, never disassemble the whole lens or you're in for big trouble. Just dunk it in a cleaning bath of Naphta. regrease the focusing helicoid and you're all set.

Gonzoo · Joined: 29 Mar 2010 Posts: 231

Had taken apart the diaphragm mechanism before with this type of lens, its not that complicated - if documented properly. Love the process of piecing everything together... thats like meditation Smile

Spotmatic · Joined: 18 Aug 2008 Posts: 4045 Location: Netherlands

For me it's like stress, so I wish you much luck Very Happy