Flektogon 50mm f4, fixing stuck diaphragm, some remarks.

[landstrykere]

my zebra Flektogon 50mm f4 ie. the P6 one, had stuck diaphragm. Before unscrewing, I went to find a page with illustration, seen many years ago. It is defunct, I found it on archive.org:
https://web.archive.org/web/20140103172049/http://www.stephenrc.com/flektogon.htm

when I tried to unscrew the front rim with name, in order to access the notches for unscrewing the optic block, it opposed resistance with the improved rubber ring I made. I decided to try a cleaning only from the back. It is doable.

I applied terpentin with cotton tips, only a bit, insisting on the connection of the blades with the rotating ring:



in order to exercise the diaphragm, the automatic spring lever is removed, and a tiny flat screwdriver inserted in the slot, and slided back forth several times, then some more terpentin. After what use several dry cotton tips



then applied ethanol, the same way with cotton, and exercising the diaphragm in between.

the point is that the other side is not accessible with the optic block in place. I used a syringe for sending some ethanol there, holding the lens partially upside down, so the fluid doesn't run in the space between the lens body and the optic block:



still decided to disassemble the front, I finally succeeded, when I checked some cup had the exact diameter.. The body of the cup provided a firm and easy good grip for maximal torsion. I used cuts of bicycle tube for rubber:







after what inspection down showed that the cleaning worked or at least that there was little to remove and the needle trick was enough:



a possible cause for stuck diaphragm may be just mechanical, the small lever of the automatic spring getting stuck if pushed a bit too much by the pin of the mount::



in a short video:

https://youtube.com/shorts/GjhFCxVCIOQ

[BrianSVP]

This is a common diaphragm design for many of the shorter focal length Jena lenses, so worth keeping bookmarked if you plan to work on others.

I'm not really a fan of the design, which I find overengineered and fragile - the outside aperture linkage is finicky in its placement and very prone to breakage.

[jamaeolus]

Clever bit with the coffee cup.