Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
06-17-2021, 02:43 PM   #1
Site Supporter
Site Supporter
vladimiroltean's Avatar

Join Date: Dec 2010
Location: Bucharest, Romania
Photos: Gallery
Posts: 1,435
Cannot remove aperture ring from SMC Pentax-A 28mm f/2.8

One of the screws inside my SMC-A 28mm unscrewed by itself and the focusing ring simply jammed.
After taking it apart, I realized it was one of the 2 screws keeping one of the 2 L brackets in place - those which keep the optical block moving up and down instead of spinning with the focusing helicoid.
That is now solved - both L brackets are properly screwed into place as can be seen in the picture, but there were some issues getting to this point which now need to be solved as well.

First I attempted entry into this lens through its front. I got as far as removing the focusing ring, but I realized that the Pentax-A lenses are not built the same like Takumars, where only the front is removable. Instead, if you want to access the back of the optical block, you need to disassemble from the back.
Which is what I did, except that while the focusing ring was off, the aperture ring had a bit of space to move (towards the front of the lens) and now I can't get it back into position, or move it at all, for the most part.
I don't know exactly what's keeping it locked in place. When I try to pull it out towards the back of the lens, it looks like it's sticking at the contact point between the button that locks the ring in 'A' mode, and the spring that's inside the lens body that presses against that button. What the ring movement that I was talking about earlier did was it shifted the button off of the spring, but in the wrong direction. Unfortunately I cannot take a picture of this, it is between the lens and the aperture ring and I don't have the angle.
Has anyone dealt with this before who has taken apart an A series lens?
In the picture attached below, the sticking point is between the tweezers.

Attached Images
View Picture EXIF
PENTAX K-1 Mark II  Photo 
06-17-2021, 02:54 PM   #2
Moderator
Not a Number's Avatar

Join Date: Mar 2012
Location: Venice, CA
Posts: 8,590
Looks like something behind the leaf spring for the A button mechanism. Part of the "A" pin or maybe the "click" ball bearing?
06-17-2021, 06:16 PM   #3
Site Supporter
Site Supporter
ramseybuckeye's Avatar

Join Date: Apr 2009
Location: Hampstead, NC
Photos: Gallery
Posts: 14,407
A couple of dumb questions, is there any "play" in the ring that you could squeeze the ring to make it a wider opening at that point. I'm guessing not, but sometimes those rings feel a little loose. Can you move the button at all?
06-17-2021, 07:05 PM   #4
Pentaxian
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 5,937
It might be the two opposing leaf springs jammed on the ring somehow. See photos of the A50/1.7 repair for the springs I'm talking about. Maybe some small wedges can hold the springs to the lens body and allow the ring to slide off.

06-18-2021, 03:24 AM   #5
Site Supporter
Site Supporter
vladimiroltean's Avatar

Join Date: Dec 2010
Location: Bucharest, Romania
Photos: Gallery
Posts: 1,435
Original Poster
I don't know exactly what the leaf springs you are talking about are. Certainly googling for leaf springs does not help me identify any in my lens...
https://ars.els-cdn.com/content/image/3-s2.0-B9780750650540500055-f05-20-9780750650540.jpg
I assume you might be talking about the spring-actuated buttons on the sides of the lens barrel that press against the aperture ring, then yes, I've tried.
I noticed that if I press with my tweezers against those silvery buttons, they retract enough in order for me to be able to rotate the aperture ring. The aperture ring has 2 notches cut into its interior in which the spring-actuated buttons depress and keep it in place from rotating further. When pressing those buttons I can freely rotate the aperture ring 360 degrees, but I can still not slide it out towards the lens mount. At this point I have no idea what's keeping it in place, and after so many turns I also lost any frame of reference I had, not knowing any longer what the correct angle of the aperture ring is supposed to be.
Since the ring is able to turn 360 degrees with uniform friction (save for when it crosses the ball bearing of course), I guess it is round and not oval, so I would not try to squeeze it without understanding why it won't go out.
07-04-2021, 07:06 AM   #6
Site Supporter
Site Supporter
vladimiroltean's Avatar

Join Date: Dec 2010
Location: Bucharest, Romania
Photos: Gallery
Posts: 1,435
Original Poster
Small update: I was able to remove the aperture ring. I don't know exactly what was keeping it from going out, but I made a small lever with my pliers somewhere between the lens body and where the ring was already lifted, and it came off.
Then I mounted the ring with the DoF scale back to the lens body, so I had some sort of reference as to which way is up.
With the DoF scale as reference I was able to put the aperture ring back into its place, with the spring-actuated button for the A position working properly, as well as the manually-set aperture ring values from f/2.8 to f/22.
I am now able to reassemble the back of the lens. I have some small objects that I don't know what to do with.
I managed to figure out what to do with the black plastic ring.
For context, the first attached picture shows the lens without the ring I am talking about. The spring-controlled aperture lever at the right (which is actuated by the camera) moves in tandem with the lever on the left side. The chrome triangle shaped piece is fixed in one corner and can press against the lever on the left.
Now, the second picture is with the black plastic ring mounted. Its yellow portion plugs into an inside notch of the aperture ring, and this ring also presses against the chrome triangle, therefore closing the aperture to the value selected by the ring.
This is all fine, but the chrome triangle also had a spring attached to it, which came off (leftmost object from the third picture). What the hell am I supposed to do with that? The mechanism appears to work without it too.
In the third picture there are also three other objects which together form the spring-based pin which tells the camera mount that the aperture ring is in A mode. I compared these objects with what Dave shows in his A50/1.7 disassembly and I don't seem to see any resemblance. I should mention that when I first disassembled the lens, the pin on the right catapulted itself with a lot of force onto the floor. Please tell me I am not missing any piece, because I did search for a spring somewhere but I am not able to find any (whereas I could find the pin). But if there's no spring, I fail to see how this pin is supposed to advance and retract, depending on whether the A mode is set or not on the aperture ring...
Attached Images
View Picture EXIF
PENTAX K-1 Mark II  Photo 
View Picture EXIF
PENTAX K-1 Mark II  Photo 
View Picture EXIF
PENTAX K-1 Mark II  Photo 
07-04-2021, 08:09 AM   #7
Site Supporter
Site Supporter
vladimiroltean's Avatar

Join Date: Dec 2010
Location: Bucharest, Romania
Photos: Gallery
Posts: 1,435
Original Poster
Holy ####, I found it. I swept up the entire room and then I had to sift through a lot of crap, but there it is, now I think I have all the pieces, I just need to figure out how to put them back together

Attached Images
View Picture EXIF
PENTAX K-1 Mark II  Photo 
07-04-2021, 10:16 AM   #8
Moderator
Not a Number's Avatar

Join Date: Mar 2012
Location: Venice, CA
Posts: 8,590
You can see where the spring with fingers goes from you earlier picture.

The other spring, cap and frame with knob are the A-pin assembly. See the A 50mm f1.7 aperture ring repair thread on how this goes together. Last piece is probably the contact for the assembly.
07-04-2021, 04:05 PM   #9
Site Supporter
Site Supporter
vladimiroltean's Avatar

Join Date: Dec 2010
Location: Bucharest, Romania
Photos: Gallery
Posts: 1,435
Original Poster
QuoteOriginally posted by Not a Number Quote
You can see where the spring with fingers goes from you earlier picture.
Either you're a genius, or I'm a dumb doughnut (or possibly both). I guess I'm not used to taking pictures during teardowns, I had forgotten about that.


QuoteOriginally posted by Not a Number Quote
The other spring, cap and frame with knob are the A-pin assembly. See the A 50mm f1.7 aperture ring repair thread on how this goes together. Last piece is probably the contact for the assembly.
Believe it or not, but while I was assembling the A-pin with its spring to put it in place, the spring disappeared again right before my eyes, with nowhere to be seen this time.
I reassembled the lens with no A contact and calibrated it for infinity and currently it is like that. A lens that can be used with the aperture ring is better than a lens which sits in pieces on my work bench...
Amazingly, after a few hours of searching once reassembly was done, I was able to find the spring once again. I am going to hold off from another attempt at putting it back until I have a good plan how not to lose it.
07-04-2021, 08:20 PM   #10
Moderator
Not a Number's Avatar

Join Date: Mar 2012
Location: Venice, CA
Posts: 8,590
Get a storage bin for storing household goods like blankets, clothes or towels and work in there. If you are ambitious you could make a glove box (without gloves).
07-21-2021, 05:20 PM   #11
Site Supporter
Site Supporter
vladimiroltean's Avatar

Join Date: Dec 2010
Location: Bucharest, Romania
Photos: Gallery
Posts: 1,435
Original Poster
Finally I mounted the A pin back today, thanks for the help.
The storage bag for blankets was not a great idea, with so many reflections off the plastic I could barely see anything, so I solved one problem but created another.
I ended up working in a small freezer bag opened towards me, so that I could see what I was doing with my microscope. It is not actually that hard to do if you are able to properly see.
I don't have any more pictures, but I guess I can summarize the steps for other poor souls who might find this thread, because tactics are important.
To reassemble the A pin, you need to:
1. Make sure your aperture ring is off the lens.
2. Take the L-shaped piece with the round hole, and put it on the lens barrel inside the groove where it's supposed to stay.
3. Put the aperture ring back on, at f/22. The ring should slide into the L-shaped piece's round protrusion, and from there, it should be able to slide left and right. If the L-shaped piece does not fall into place properly at this step, there will be no hard stop between f/22 and A mode. Also be careful to not dislodge the aperture ring ball bearing.
4. With a pair of tweezers, slide the sheet of metal with the bent tip beneath the L-shaped piece. I don't exactly know what functional role this plays apart from moral support for the spring.
5. Now slide the aperture ring out slightly. You will need to do this because at this point, the L-shaped piece should move together with the aperture ring (its round protrusion should be engaged with the aperture ring's inner groove), and you need to lift the L-shaped piece slightly in order to put the A pin back.
6. Put your lens in a bag, because here starts the fun part.
7. Put the spring inside the A pin.
8. Pick the A pin up with a pair of tweezers and put it inside the L-shaped piece's (which should be lifted at this point) round hole. Poke it a little bit until the groove in the A pin engages with the L-shaped piece. It is important that the L-shaped piece is lifted at this point, because the lower it is, the more you have to tension the A pin's spring, which in turn means the higher chances you'll have of it just taking off. Done properly, there shouldn't be too much tension in the spring, if any at all.
9. Once the A-pin engages with the L-shaped piece, start sliding the aperture ring back down and into its final position. You will probably need to press the ball bearing and also move the aperture ring a bit towards f/2, but it should go back in, and the A pin's spring should tension.
10. Check that you are able to switch between f/22 and A mode with hard stops (if not, remove the ring and also check the A button's position on the ring, maybe it fell off), and if the A pin retracts and extends when switching between f/22 and A mode.
11. Mount back the aperture actuator's spring, the inner aperture ring, the lens mount.
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!
aperture, block, button, camera, front, lens, move, pentax help, pentax-a, photography, picture, smc pentax-a 28mm, troubleshooting
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
CZJ 50 f2,8 remove spring from aperture ring Phalbert Pentax SLR Lens Discussion 2 06-14-2020 02:08 PM
Cannot remove name ring from 50mm Pentax-M f/1.4 lens :(!! ohaya Pentax SLR Lens Discussion 19 04-13-2016 02:08 AM
Aperture ring or no aperture ring hjoseph7 Pentax SLR Lens Discussion 29 12-02-2014 03:06 PM
How do you remove the dust that cannot be remove by the blower? rustynail925 Pentax DSLR Discussion 3 07-31-2010 10:39 AM
Can I remove the "A" position lock on my aperture ring MikesChevelle Troubleshooting and Beginner Help 17 02-13-2010 02:52 PM



All times are GMT -7. The time now is 11:08 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