Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
12-03-2017, 11:48 AM   #1
Senior Member
Pentaxis's Avatar

Join Date: Jul 2012
Posts: 193
Advice needed to fix a third party K-mount lens

Hello all,
I have acquired a deJur 135mm k-mount lens that is cosmetically sound but has a major functional fault. I bought this lens as a minor part of a package of Pentax cameras and accessories and it has been clear to me from the outset that it had a major problem: namely, the iris diaphragm would not return to the fully open position after the stop-down lever was released. I suspect that oil on the aperture blades might be causing a friction that resists the iris blades from fully opening again.

I tried to fix it and opened up the rear part of the lens. Unfortunately, I must have somehow released, from its mounting position, the spring from the mechanism that operates the aperture stop-down action when the camera shutter is operated. One end of the spring is still fixed to a point near the throat of the lens but I cannot see where the fixing point is for the other end of the spring (presumably at the the iris diaphragm itself).

Can anyone refer me to a relevant internet link, even for a "generic" lens, that shows how to reassemble the spring, in order to complete the shut-down mechanism? Or to advise me in this forum how I could try to fix the lens? I am reluctant to send the lens for professional repair because the likely cost would not be justified for what is a relatively cheap lens. I just don't want the lens to be inoperable if I can fix it myself.

Thanks for any help or advice offered!

12-03-2017, 11:58 AM   #2
Pentaxian
photoptimist's Avatar

Join Date: Jul 2016
Photos: Albums
Posts: 4,496
Alas, there's no "generic" design for these things. Spring posts may be screws, rods, tabs, or even just a hole in a disk.

But I'm sure we can help. If you post some in-focus pictures of the various parts, we may spot where the other end goes. It also helps to think about what direction things are moving so you can guess whether the spring must be mounted clockwise or counterclockwise.
12-03-2017, 12:37 PM   #3
Senior Member
Pentaxis's Avatar

Join Date: Jul 2012
Posts: 193
Original Poster
QuoteOriginally posted by photoptimist Quote
Alas, there's no "generic" design for these things. Spring posts may be screws, rods, tabs, or even just a hole in a disk.

But I'm sure we can help. If you post some in-focus pictures of the various parts, we may spot where the other end goes. It also helps to think about what direction things are moving so you can guess whether the spring must be mounted clockwise or counterclockwise.
Many thanks for your information.
Here are a few photos that I just took on my simple point and shoot camera, showing as well as I can the problem area..
Attached Images
View Picture EXIF
FinePix Z20fd  Photo 
View Picture EXIF
FinePix Z20fd  Photo 
View Picture EXIF
FinePix Z20fd  Photo 
12-04-2017, 04:14 AM   #4
Pentaxian




Join Date: Jul 2009
Location: London
Posts: 1,017
What did you do immediately before the spring came loose?

12-04-2017, 08:21 AM   #5
Senior Member
Pentaxis's Avatar

Join Date: Jul 2012
Posts: 193
Original Poster
QuoteOriginally posted by JohnX Quote
What did you do immediately before the spring came loose?
I had just unscrewed a "clamping plate) (on the left in the first photo attached) and then removed a short "tube" (on the right in the first photo attached and by itself in the second photo attached).

To be clear:
-When I first obtained the lens, and when it was not mounted on the Pentax camera, the aperture control "tab" would stop down the iris diaphragm when I pressed it but when the tab was released the diaphragm was "sticky" i.e. reluctant to open again.
-When I started to investigate the problem I unscrewed three tiny screws on the clamping plate, removed the clamping plate, then removed the short tube (both shown in the attached photos).

As the spring has a loop at its end it must loop over a pin or tab somewhere in the barrel of the lens. Its function, if I understand it correctly, is to stop down the diaphragm at the moment of exposure. that means that the spring must somehow be connected to the diaphragm but at present I cannot see how that connection can be made. I have tried looping the spring over a couple of features on the short barrel thing but that somehow is very tricky and doesn't seem logical.
Attached Images
View Picture EXIF
FinePix Z20fd  Photo 
View Picture EXIF
FinePix Z20fd  Photo 
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
135mm, advice, aperture, blades, dejur, diaphragm, diaphragm actuator, fault, iris, k-mount, lens, mechanism, pentax lens, position, slr lens, third party k-mount
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Third Party Lens Compatibility - M42 Mount pendennis Pentax SLR Lens Discussion 14 12-27-2017 06:49 AM
DA* 50-135-- to fix or not to fix, that is the question... geek-girl Repairs and Warranty Service 9 10-03-2017 03:07 PM
k-70 third-party battery advice Naren Troubleshooting and Beginner Help 12 03-23-2017 04:29 PM
Third-Party Lens Review Database: Help Needed! Adam Site Suggestions and Help 8 03-14-2008 09:32 AM
Using K mount third-party lenses on the K100D... The PIPE Pentax SLR Lens Discussion 3 10-14-2007 09:44 AM



All times are GMT -7. The time now is 05:55 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top