Minolta 50/1.7 AF Repair (updated)

Another post on a very common issue: sticky diaphgram blades.
From old Exakta lenses to Nikkor AF Zooms, apparently anyone gets there.

This time, the classic Minolta 50/1.7 has the issue, although in its AF version.

Dismounting AF lenses can be tricky, but in here everything seems fine, except the Iris. I want to avoid regreasing the helicoids because I haven't yet found a satisfactory Grease, even if I tried several! I will try unmounting as little as possible from the lens as possible to get to the Diaphgram Iris assembly.

We can work from the front, by unscrewing in sequence the cone with the name plate first, then removing 3 screws to remove the the front part with the retractable sun shade. Without these parts, the lens is still fully functional.

From the rear, we can remove the lens bayonet and put it aside and we see the picture like this:

AF Rokkor 50/1.7 from the back, mount removed (left)

The optical assembly is in the middle and has two guides, clearly seen top and bottom in this picture. Mark the helicoid for convenience and unscrew them
Now it is possible to unscrew the optical kernel to the back of the lens.
Getting it back will be a little tricky, since the infinite setting needs to remain. Even if I marked the helicoid, I needed a couple of attempts.

The hard part is done! The 50mm is a double-gauss type and it is easy to take it apart. Removing three screws enables to remove the front part and the same is for the back.

What remains is just the Aluminum barrel with the Iris mechanism inside. Now you can clean it by flushing or by opening it.

My first attempt of repair was done with a flush-clean: often this is enough if just a little oil is astray. However it worked for a couple of months, but then the blades stuck again. This means there was a lot of oil in the non-accessible mechanism (the ring that acts as governor for every pin), so a more drastic solution was needed: remove the blades with their governor ring.

The open diaphgram blades, the governor on top

Mounting everything back is relatively easily, except for getting the right screw thread and not damaging the delicate Aluminum thread when screwing it in.

Check the infinity focus.. and that the diaphgram is snappy again!

Dompilan diaphragm repair

Meyer Optik Görlitz Domiplan was a quite nice 50m/f 2.8 compact and standard lens common in Exakta (especially for the Exa) and M42 (Praktica) mount.

I have two and both of them suffer from a sticky diaphragm (iris aperture) syndrome, like most of old lenses.

I read horror stories about this lens, people ruining it completely, declaring it unrepairable or so. I don't think it is any harder than other lenses I tried to repair, provided it is just stuck and not broken. When it gets stuck, the blades gum up very hard so trying to force it may cause the pin and leverages to break.

I find the lens quality quite nice, for being a triplet! Smooth colors, bokeh and only slight vignetting. I disagree with people calling this a bottle bottom glass or "Holga like"! I think people having bad experiences had badly serviced or broken lenses. See the examples below.


Start by removing the back-part, the bayonet. Then you can remove the barrel holding the lens. You do not need to remove the lens itself. Three screws and you get the parts seen in the picture below.

Remove all the blades carefully, put them on a paper towel.

Clean the blades with petrol, light gas, lighter fluid, what you prefer. They are made out of steel, be careful not to knick them and not to damage their drive pins.

If you had a serious oil problem, then the lens surfaces might be hazy and you need to clean those too.

The blades need to be inserted one over the other, like a spiral stair case. The most difficult are the last and the butlast, because the nose needs to go "below" the first, it can be seen well in the picture below.
Try not to touch the blades with greasy fingers. Once all blades are in, you need to slightly close them before putting the cover ring and screwing it down. To do that, gently actuate the leverage, as shown in the following picture. The three screw both fix the upper part to the diaphragm ring, but also fix the whole assembly to the lens barre.

Once closed and screwed down, the actuator lever should already work smoothly. Don't close it too much or it will stick.

Remount the rest of the lens with care. Take care of the two opposed springs that go into the barrel. Take care that the f-stop-ring is aligned properly.
The Exakta version is easy to remount, the M42 version has a different linkage to the bin, be sure to mount it in the correct open position!

Once everything is reassembled, use the lens! In my experience it is a light, compact lens which works fine with color and b&w films. It works best around 8-11, but 5.6 is already quite fine. Of course at 2.8 it vignettes a bit, but it remains reasonably sharp in the middle,

Here a photo taken with my Exa and the Domiplan:

Here again, wide-open at 2.8: