ISCO Westrogon 24/5 - disassembly help needed

clie · Joined: 18 Sep 2014 Posts: 5

I'm trying to get to the blades to clean it. The blades stick only when pointing the lens at a 45% angle upwards. Any other angles, the blades open and close properly. I suspect there is grease somewhere.

Can someone advise me how to disassemble this lens?

Managed to unscrew the entire front group which contains the 1st and 2nd elements (large glass).

https://www.flickr.com/photos/40638730@N04/15099195868/in/photostream/

There is a cone structure that appears to hold back the 3rd element (small glass), The cone and the surrounding part (where the scratches are) is one piece.
I can't seem to twist this off. There is no retaining ring, nor notches to put a lens spanner into. There are some scratches as the previous owner has tried to get a grip to turn it. I've tried too. No luck as it is too tight.
It's slightly recessed below the focus ring so it is hard to get a good grip

https://www.flickr.com/photos/40638730@N04/15262730506/in/photostream/

One the outside of the lens, there are three rows of screws.
(A) is to allow the focus ring to grip the focusing helicoids.
Not sure what (B) does, but it didn't release the black cone.
(C) doesn't seem to do anything - it just holds a ring surrounding the back of the body.

https://www.flickr.com/photos/40638730@N04/15285766505/

Appreciate any help

Jesito · Expire: 2015-01-07

Probably you know that to clean the diaphragm blades it's not necessary to disassemble the diaphragm, just to have access to the blades, either from the front side or the bottom side. If the top side is too difficult, try to disassemble the back element and then get access to the blades. Once gotten, q-tips wet on isopropyl alcohol and softly rub on the blades with the diaphragm closed at max. Then let the alcohol evaporate, move the diaphragm wide open and close it back and repaat until clean.

Good luck, these not well known lenses are difficult to service...

calvin83 · Joined: 12 Apr 2009 Posts: 7584 Location: Hong Kong

Make sure you pay attention if you go from the back. I break the second rear element when I put the glasses back. Sad

clie · Joined: 18 Sep 2014 Posts: 5

I have actually accessed the back and wiped the blades using a q-tip. Even soak half the lens all the way to the blades in white spirits. THe blades now work when the lens is pointed horizontally or downwards.
Problem is that the blades still get stuck halfway when the lens is pointed 45 degrees upwards. I tap the lens body with my finger, and the blades open fully. When I point the lens horizontally and turn the aperture ring, the blades open and close fully all the time. Very strange. Suspect there is stubborn dirt inside the aperture blades casing or maybe the spring's tension is loose.

---------------------update --------------------------

I've managed to unscrew the cone structure. I drilled two holes on either side and inserted the lens spanner into them and turned hard. It became unstuck and then I could twist it off with my hand. The 3rd element is actually attached to this cone structure. Lifting this out gave me access to the front of the blades. I could see that one of the blades had stubborn grease on it which never came off even though I had soaked it in white spirits. So I gently rubbed off the grease with a q-tip dipped in white spirits and it is now no longer catching at a certain angle.