Zuiko 50mm f/1.4 slow aperature

[matthew_newton]

I just recently acquired a 50mm f/1.4 silver nose (SN 6xx,xxx). It appears to

be in excellent condition in all respects except that the aperature is slow to

operate. From what I can tell operating the aperature closure on the back of

the lens and when mounted on my OM-1 and snapping the shutter it will stop down

properly and quickly, but after it stops down it is very slow to release

(taking maybe .5-1s to open fully from f/16 when operating by hand, about .25-

.5s when firing the shutter on a faster lens speed). The aperature blades don't

appear to be bent and they are oil free. Any idea what could be causing this

and is there a relatively easy fix?

 

More importantly does this signal a problem that could start causing it to

stick closed or prevent the lens from stopping down properly down the road.

 

I have yet to get my test roll developed to see if this is actually throwing

off exposure because it is not stopping down quiakly enough (it certainly

appears to only be an issue once the aperature closure is released).

 

Thanks!

[skip_williams]

The diaphragm mechanism needs to be cleaned. As they age, most lenses' lubricants evaporate and attract dirt. The result is gummy, dirty mechanisms. It needs to be opened up and cleaned out.

 

That's not an unusual problem, esp for a 20 yr old lens.

 

Skip

[matthew_newton]

Any advice or links to articles on how to acomplish this? Should it just be cleaned out? Or also relubricated, and if so where could I find the lubricant?

 

Thanks.

[patrick j dempsey]

Ive never worked on this particular lens, but it is a common problem with older lenses. Look up information on general camera repair. Remember to keep the parts organized as you disassemble and replace screws in their holes as you go. If you have to make sketches to remember the order, that can help. You shouldnt need to take the lens apart any further than the aperture blades to do the cleaning. Once you get to the aperture blades they can be cleaned with Ronsonol on q-tips... being careful to not leave cotton fibers from the q-tip. Be careful to not let the Ronsonol drip onto the lens elements. It may take many hours to get the fluid worked throughout the aperture blades by opening and closing them over and over. You can then clean them off with dry lens wipes or q-tips. The Ronsonol will leave a slight residue behind as it evaporates and often this is all the lubricant you need. If you accidentally used too much lighter fluid, clean with lens cleaner or alcohol and then apply a little Ronsonol afterwords as a protective and lubricating layer. Let the lens sit, glass up for a day or so to make sure the Ronsonol has fully evaporated before putting it back together.

[matthew_newton]

Thanks for the advice. I might try this on one of my spare 50mm f/1.8s first, just to make sure I manage properly. I figure I would rather mess up one of my two 50mm f/1.8s then my new (well to me) 50mm f/1.4

 

Thanks again!

[richard_oleson]

I have some notes - not very pretty i'm afraid - for disassembly & diaphragm access in the 50/1.8, which you're welcome to. i think the 1.4 and 1.8 are very similar in construction. drop me a note if you'd like a copy.

 

Do not lubricate. The only lubricant in the lens is the grease in the focusing helical, which unfortunately migrates into the diaphragm system and gums it up. you can do a better job of cleaning the blades if you remove them from the lens ... though of course this carries the burden of getting them back in afterwards. your call there...

[tommyinca]

You likely have oil in the aperture iris blade. This is not an easy problem to fix as you will need to take everything out to get to the iris. At the minimum all the lens groups go out. To do this right, the mount and the bellow, focus helicoid will need to be remove and clean as well.

[fred aspen]

I have had this problem with two lenses and it was relatively simple to fix. I removed the screws from the lens mount and underneath the mounting ring is a ring that has an arm that extends into a slot internal in the lens that operates the diaphragm. This ring had minute amounts of grime on it and I simply cleaned with alcohol on a Q-tip and replaced it. Worked great! This ring is spring loaded to provide tension on the diaphragm but doesn't "fly" apart when disassembling. Also, take care in aligning the arm with the diaphragm slot when reassembling. Takes about 4-5 minutes to complete. I am an ex-watchmaker so proceed at your own risk.

[paul_verwer]

Matthew, Ron,

 

I had the same problem with my 50mm 1.4, and did not want to take it all apart, especially because the diaphragm was only slow on return. However, after reading Ron's hint I did take the lens mount off, and cleaned the ring. Indeed, this solved the issue with just a few minutes of work!