Iskra Stiff Focus Advice Wanted

[graywolf]

Ever since I got the Iskra the focus has been super stiff. I have positively identified the stiffness as being in the RF mechanism. I just removed the RF cover for a look see.

I think that spring may be the problem. Does anyone who has worked on these know if that spring looks heavier than the one that is supposed to be there?

I posted more details on my blog http://graywolfphoto.com/journal/?p=1908&preview=true

 

[Livesteamer]

Don't know a thing about Iskra's (except that I want one) but as a retired machinist I would tell you that spring making is an art. With Russian quality control being what it is/was, that spring could well be the problem. Disconnect it and see. Good Luck, Joe

 

[jnoir]

Looks regular to me. Does it fully compress when focusing to infinity ?

I also notice from your picture, the long spring that goes from the advance mechanism to the fixed pivot is not fully compressed, when it should be based on my experience. Not sure if that is relevant for your particular issue, though.

How did you discarded the helicoid as the stiffness' source ? That's the most typical point of failure, due to solidified grease. I guess you already cleaned and relubed it ?

 

[Ernst Dinkla]

The lens helicoil is in my opinion the main point where focus friction is created. Both grease/oil and having the body to lens screws not too tight make the difference. In fact turning the focusing helicoil to infinity is not influenced by the rangefinder mechanism at all as the rangefinder follows that movement by the power of another spring. If both directions are equally difficult check the helicoil.

Ernst Dinkla

 

[VictorM.]

From several years ago:

http://www.rangefinderforum.com/forums/showthread.php?t=13574&highlight=iskra+light+leaks

Covers light leaks and stiff focusing...

 

[graywolf]

How do I know it is the RF and not the helical?

The Iskra arrived from the Ukraine supposedly fully serviced. Everything worked fine, but the focus was really stiff. The seller offered to take it back but I decided to keep it.

I checked the helical and felt it needed a bit more grease, which I did. I checked the tightness of the screws holding the bellows to the front standard. I did not find them over tight, but they were tightened unevenly. Tightening them evenly, reduced the stiffness slightly.

Next I checked the external RF linkage. I found a place where it was rubbing and fixed that which again reduced the stiffness slightly.

The linkage is pulled out by the helical/lens/shutter unit when you focus closer. If you grip the end of the RF linkage with a pair of jeweler pliers you and hold it out and move the focus with out the the linkage applying any resistance. When I do that the focus lever and the helical all move easily which indicates the stiffness is in the linkage or the RF itself.

I set the camera aside until I had time to open it up and see what was going on inside the RF. Unfortunately, my health went south about that time and I never got around to it. The other day, only a couple of years late, I did remove the rangefinder housing.

I immediately noticed that that spring looked brand new and heavier than the other spings. At this point I can see nothing but that spring that can be the problem. Hence my inquiry.



Answers to a couple of questions asked or implied:

Yes, the spring is fully compressed at infinity. If you look at the distance scale at the top of the photo, you can see it is set at about 3 meters.

I am not sure about the other spring, it may simply be at an intermediate point as is the RF spring.

The rangefinder is accurate at all distances.

I see no sign of excessive or dried lubricant.

 

[graywolf]

I thought of another possibility. The helical could be worn to the point where the pressure of the RF linkage causes it to cock and jam somewhat.

 

[NorpA]

Albeit I didn't try it yet and albeit I think you already checked this page out, I would suggest you to take a look here. It is written in French and unfortunately it doesn't cover step by step how to service the helicoil, but maybe it could help.

 

[graywolf]

Albeit I didn't try it yet and albeit I think you already checked this page out, I would suggest you to take a look here. It is written in French and unfortunately it doesn't cover step by step how to service the helicoil, but maybe it could help.

I used Google Chrome to translate it. However, it will not help. If the problem is the helical, it is simply worn out, and nothing much I can do about it. Unfortunately, between my disability and the med's they have me on it is very difficult to get started on anything, so I have not gone back into the camera to see if that spring is the problem or the helical is.

On second thought if the helical is worn, maybe some heavier grease may help (by limiting how much it can cock).