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07-26-2009, 04:19 PM   #1
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SMC Pentax 24mm F/2.8 Disassembly

I have an SMC Pentax 24mm F/2.8 that suffers from the 'sticky aperture blades' problem. I've done this before for several other lenses, but the 24mm innards don't look like what I've worked on before.

At this point, I've removed the front name plate ring and the rear of the lens. I want to move slow and don't want to screw up this lens.

Any help (exploded diagram, article, tricks, ....) is appreciated.

Thanks.

07-30-2009, 02:02 AM   #2
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I've recently done just that, it's quite easy if you have some basic skills and tools. There is a thread which covers a very similar lens (K 35/2 ?). Elements are removed as a single front assy & a single rear assy giving you access to the aperture blades.
Will post (dis)assy photos tomorrow.
-Steve
08-31-2009, 11:14 AM   #3
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I have exactly the same defect on an old 24mm F/2.8; blades close too slowly to the stop, so I can use it only at amximum aperture.
Is there a simple way to lubricate the blades or the mechanism, without opening the lens body? Otherwise I would appreciate a lot a guided "maintenance tour", possibly with some photo of the disassembly steps....

thank you a lot

Leonardo
09-07-2009, 12:44 AM   #4
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first step... and now?

Because I never disassembled a lens, I will do it in a very prudential way.

I loosened the 5 screws "A" (see image5.jpg) ; before trying to remove the mount ring: may I unscrew safely the 3 very small screws signed by arrow B (image1.jpg) ? What is their function?

thanks

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09-07-2009, 01:24 AM   #5
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These 3 screws only hold the black light baffle if I'm correct. Try to unscrew one and see if the baffle moves... I think you should leave these alone so that it comes off the lens in one piece (with the bayonet).
09-07-2009, 05:26 AM   #6
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thak you Asahiflex,

this evening I will check.
I know is that the glass and its surrounding black cylinder is moving while focusing, so the 3 little screws "B" are hooked to the "fixed" cylinder / baffle.
I think the screws "B" (sorry in the picture I wrongly labeled it as "A1") are used to enhance the mechanic stiffness of the mounting ring (bayonet)... but if I am wrong??
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Last edited by leoalo; 09-07-2009 at 10:57 AM.
09-07-2009, 06:06 AM   #7
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QuoteOriginally posted by leoalo Quote
Is there a simple way to lubricate the blades or the mechanism, without opening the lens body?
When you do find your way into the lens, the last thing you want to do is lubricate the blades. Any lubriacnt you use will be too viscous and will make the blades move even slower or stop them moving at all. It will almost certainly be oil on the blades that it making them slow as it is. Remove the blades and clean them with a dergreaser, I usually use lighter fluid (petrolium) of methilated spirits. When everything is spotlessly clean, dry and free of oil put it all back together and it should be snappy again. The first time I did this it took hours, now that I have done a few I can strip, clean (optics, aperture blades and everything else) and reassemble a simple prime lens in under two hours. Keep at and don't lose anything and you will get there eventually with the satisfying feeling that you fixed it yourself.
09-07-2009, 11:04 AM   #8
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hi MattGunn,

can you tell me if I must remove the 3 screws "B"?
I do not want to force the opening of the bayonet ring, or to risk to loose the spring or other from the inside of the lens, with a clumsy - and useless - operation.

If it helps, I noticed that this assembly (3 small screws around the bayonet) is the same as Pentax SMC 50/f1.7

thanks

--EDITED---
found it by "myself", this thread:
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/19460-smc-50mm...sassembly.html

for the 50/f1.7, there is no need to unscrew the little "B" screws

09-07-2009, 12:08 PM   #9
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I have never had or dissasembled this lens and anything I suggest is based on other lenses I have repaired.
As asahiflex has said, the screws your refer to probably only hold the baffle on the back of the lens in place, and don't need to be removed.
It is probable that you will be better attacking the lens from the front. You will need to find a suitable rubber tool to remove the trim ring. The tools required and the method to proceed are described for a different lens here:
Disassembly and Cleaning of the F1.4 50mm Super Takumar Lens
If you get the trim ring off, take some more pictures and more suggestions to proceed can be made.
If you are not confident in dismantling things and you value this lens highly then it is probably better to have it repaired professionally. If you want to get into repairing lenses then buy a cheep and otherwise useless one to practice on.
09-07-2009, 01:39 PM   #10
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QuoteOriginally posted by SOldBear Quote
I have an SMC Pentax 24mm F/2.8 that suffers from the 'sticky aperture blades' problem. I've done this before for several other lenses, but the 24mm innards don't look like what I've worked on before.

At this point, I've removed the front name plate ring and the rear of the lens. I want to move slow and don't want to screw up this lens.

Any help (exploded diagram, article, tricks, ....) is appreciated.

Thanks.
Is this what you are looking for? I took my apart my and found it was suffering from lens separation in the front lens assembly
The first picture shows the rear and the second the front.

Mike
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09-07-2009, 05:27 PM   #11
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My bayonet was firmly sticked to the lens, so I tried to remove the baffle, (discovering it is plastic) but this did not help me. I had to firlmly - but "gently" - pop up the bayonet like a snap bottle cap. Examined if I can clean the aperture mechanism without further disassembling, but I am afraid I have to do more work.

Wavecurrent, thank for your picture, but I cannot understand how to reach and disassemble the aperture blades (from front or from back?): would you mind explaining with more detail your approach?

Thank you
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09-07-2009, 08:10 PM   #12
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QuoteOriginally posted by SOldBear Quote
I have an SMC Pentax 24mm F/2.8 that suffers from the 'sticky aperture blades' problem. I've done this before for several other lenses, but the 24mm innards don't look like what I've worked on before.

At this point, I've removed the front name plate ring and the rear of the lens. I want to move slow and don't want to screw up this lens.

Any help (exploded diagram, article, tricks, ....) is appreciated.

Thanks.
You don't need to do anything on the rear end of the lens to reach the aperture blades. Since you already removed the front name plate, just hold the glass element from the front with your finger tips and turn the whole glass element anti-clockwise, you should be able to unscrew the whole front group and take them out. Then you'd see the aperture blades assembly. I don't know about 24/2.8, but mostly there is a plate press on these blades, just take off that plate, and you can shake the whole assembly out. Then clean the blades one by one w/ dry tissue, w/ the help of lens cleanser if they are too oily. And make sure you clean the blades holder and the top plate too, just make sure there isn't any oil on them. Better check the inside of the barrel and see if there is any extra oil there. You can wipe them off easily.

The hard part is to put the aperture blades back. Before you do so, turn the aperture ring to max aperture (F2.8 for this lens), and put in the aperture holder, then the blades in sequence. W/ some try and error, you should be able to figure out how the aperture blades assembly works It's pretty tricky, but not too hard if you know how. Would be great if you could take a photo of the blades or at least remember how they look like before you shake them off. This would help a lot when you put them back in order.

Here is the first lens I've ever opened, a Cosina 50/1.4, w/ the tools I used:



I opened up the whole lens just to see how this thing works. It's simpler than I expected. Here are the oily blades:




I've done quite some lenses ever since this first try

Last edited by frank; 09-07-2009 at 08:16 PM.
09-08-2009, 01:15 AM   #13
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I will follow your suggestion, frank; this morning I tried to remove the front ring with a very professional tool

It is the IKEA ghost light skin, silicon rubber, but it is too chewy.
The front ring seems very hard to unblock, I tried to heat the outside barrel, but with no results.
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09-08-2009, 01:42 AM   #14
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QuoteOriginally posted by leoalo Quote
I will follow your suggestion, frank; this morning I tried to remove the front ring with a very professional tool

It is the IKEA ghost light skin, silicon rubber, but it is too chewy.
The front ring seems very hard to unblock, I tried to heat the outside barrel, but with no results.
That's a nice tool

You can try to unscrew the front ring w/ a rubber eraser, but if can't, you'll need something like these:



Vacuum Pad Camera Parts Opener, Japan Made!

Good luck
09-08-2009, 02:58 AM   #15
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QuoteOriginally posted by frank Quote
Have you bought anything from them? What is the postage like?
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