Help on sticky apertures

yyyzzz · 07-08-2009, 11:05 PM

My Pentax 28mm f2.8 has sticky apertures. There must be some discussions about how to open the lens from the front.

I have been able to open the lens from the mount. But I could not get access to the mechanism. Thanks.

pbo · 07-08-2009, 11:18 PM

I dunno about Pentax 28/2.8, but on my Sigma 16/1.8 fisheye, the whole rear group is screwed on (without screws, the whole group is screwed in), and beneath it is the aperture mechanism.
Just in case it's your first time doing this, be careful not to make mistakes like I did - that is, be careful not to lose a ball bearing that makes aperture click (of course, if you do, you can say you modified the lens so that it's now stepless

), and clean aperture without actually opening the aperture mechanism - I did, and spent maybe two days putting it back. Great experience, though, feel like I can open a repair shop now

Bo.

wavecurrent · 07-09-2009, 12:25 AM

Well, I have successfully repaired a couple of the Pentax K and M lenses with a sticky apeture(K28/3.5, K35/3.5 & M35/2.8), don't know if you have seen the follwing tread about lens repair? Anyway here it is.

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/44776-disassem...-needed-2.html

But you should be able to access is from the mount side of the lens, check my images on my flickr site.

Mike

yyyzzz · 07-09-2009, 12:52 AM

I had no problem in opening the lens mount and put it back. It took me about 45mins for the first time. See attached photos.

My problem is that I could not open the front. I could open my 50mm without much difficulty. But I could not loosen the cover which has the sign Pentax SMC....

Attached Images

View Picture EXIF

View Picture EXIF

yyyzzz · 07-09-2009, 01:08 AM

Use double side sticky tape. The next step is to find the mechanism and learn to clean a front element. Any suggestions? Thanks.

wavecurrent · 07-09-2009, 04:51 AM

Is it possible to unscrew the front and rear lens assembly, I did that on the M35/2.8. I never had to deal with individual lenses. Then it was relative "easy" to access/ disassemble the aperture and cleaning completely of any grease. Is the front element dirty on the inside?

Mike

yyyzzz · 07-09-2009, 05:31 AM

Please see attached photos. I am not sure what kind of problem it is. They are inside the front element. Any insights?

Attached Images

View Picture EXIF

**Just1MoreDave** · 07-09-2009, 08:33 AM

I like to check the optical diagram first to see how many lens elements there are. It's not always easy to tell which surface is affected.

I know all of the lenses in front of the aperture blades can be removed as one assembly. There are pairs of rectangular slots, 180º apart, easy to see in your second photo above. They are for a tool called a lens spanner that fits the slots and unscrews the rings. I improvise with needlenose pliers or dividers with tips ground to fit the slots. One outer ring removes the group from the lens, and each element can be removed from that group with a similar ring or some other method. Sometimes the rings are stuck in place with lacquer. I use some acetone to dissolve the lacquer.

You have the back apart enough to grab the flat black ring around the rear element and unscrew that group too. That should give you access to both sides of the aperture assembly. It is possible to get the whole assembly out and take all the blades out, but I don't remember the exact steps.

yyyzzz · 07-09-2009, 09:24 AM

Thanks a lot. I will follow the steps. But are these dots fungus or what? They do not seem to have great effect on the picture quality.

wavecurrent · 07-09-2009, 01:12 PM

Originally posted by yyyzzz

Thanks a lot. I will follow the steps. But are these dots fungus or what? They do not seem to have great effect on the picture quality.

Sorry, can't help on that. First time I have seen it!?

Mike

07-08-2009, 11:05 PM	#1
yyyzzz Veteran Member Join Date: Mar 2009 Location: Salt Lake City, UT Photos: Gallery Posts: 509	Help on sticky apertures My Pentax 28mm f2.8 has sticky apertures. There must be some discussions about how to open the lens from the front. I have been able to open the lens from the mount. But I could not get access to the mechanism. Thanks.

07-09-2009, 01:08 AM	#5
yyyzzz Veteran Member Join Date: Mar 2009 Location: Salt Lake City, UT Photos: Gallery Posts: 509 Original Poster	Found a way Use double side sticky tape. The next step is to find the mechanism and learn to clean a front element. Any suggestions? Thanks. Last edited by yyyzzz; 07-09-2009 at 01:26 AM.

07-09-2009, 09:24 AM	#9
yyyzzz Veteran Member Join Date: Mar 2009 Location: Salt Lake City, UT Photos: Gallery Posts: 509 Original Poster	fugus or what? Thanks a lot. I will follow the steps. But are these dots fungus or what? They do not seem to have great effect on the picture quality.

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07-08-2009, 11:18 PM	#2
pbo Veteran Member Join Date: Mar 2009 Location: Ann Arbor, MI Posts: 891	I dunno about Pentax 28/2.8, but on my Sigma 16/1.8 fisheye, the whole rear group is screwed on (without screws, the whole group is screwed in), and beneath it is the aperture mechanism. Just in case it's your first time doing this, be careful not to make mistakes like I did - that is, be careful not to lose a ball bearing that makes aperture click (of course, if you do, you can say you modified the lens so that it's now stepless ), and clean aperture without actually opening the aperture mechanism - I did, and spent maybe two days putting it back. Great experience, though, feel like I can open a repair shop now Bo.

07-09-2009, 12:25 AM	#3
wavecurrent Senior Member Join Date: Jul 2007 Posts: 147	Well, I have successfully repaired a couple of the Pentax K and M lenses with a sticky apeture(K28/3.5, K35/3.5 & M35/2.8), don't know if you have seen the follwing tread about lens repair? Anyway here it is. https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/44776-disassem...-needed-2.html But you should be able to access is from the mount side of the lens, check my images on my flickr site. Mike

07-09-2009, 04:51 AM	#6
wavecurrent Senior Member Join Date: Jul 2007 Posts: 147	Is it possible to unscrew the front and rear lens assembly, I did that on the M35/2.8. I never had to deal with individual lenses. Then it was relative "easy" to access/ disassemble the aperture and cleaning completely of any grease. Is the front element dirty on the inside? Mike

07-09-2009, 08:33 AM	#8
Just1MoreDave Site Supporter Join Date: Feb 2007 Location: Aurora, CO Photos: Gallery \| Albums Posts: 6,340	I like to check the optical diagram first to see how many lens elements there are. It's not always easy to tell which surface is affected. I know all of the lenses in front of the aperture blades can be removed as one assembly. There are pairs of rectangular slots, 180º apart, easy to see in your second photo above. They are for a tool called a lens spanner that fits the slots and unscrews the rings. I improvise with needlenose pliers or dividers with tips ground to fit the slots. One outer ring removes the group from the lens, and each element can be removed from that group with a similar ring or some other method. Sometimes the rings are stuck in place with lacquer. I use some acetone to dissolve the lacquer. You have the back apart enough to grab the flat black ring around the rear element and unscrew that group too. That should give you access to both sides of the aperture assembly. It is possible to get the whole assembly out and take all the blades out, but I don't remember the exact steps.

07-09-2009, 01:12 PM	#10
wavecurrent Senior Member Join Date: Jul 2007 Posts: 147	Originally posted by yyyzzz Thanks a lot. I will follow the steps. But are these dots fungus or what? They do not seem to have great effect on the picture quality. Sorry, can't help on that. First time I have seen it!? Mike

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