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03-17-2016, 10:01 AM   #1
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slow aperture on M 50 1.4

Hey friends,

got an M 50 f/1.4 and I was stoked about the condition. at home I discovered in some testing situations that the aperture is kinda sticky and goes only "slow" from f22 to open. Is there anything I can do about that without dismantling or brining it to the repairshop? I talked to the guy and he told me about 200+ Euro for a lens repair...? Wft?
Will it come back to life if I use the blades a lot? open and close them manually? Hmmm I am a bit disappointed. looked so good that glas...

03-17-2016, 10:16 AM - 1 Like   #2
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200 Euros is absolutely outrageous. A blade cleaning on this lens is an easy half hour repair, even for the complete beginner. The only tools needed are a rubber friction tool, some lighter fluid, and some cotton swabs, and a microfiber or lens tissue for cleanup. You don't even have to remove any screws if you do it right.

Honestly, you should tell any photographer friends you have to avoid this guy. 50 Euros would be a reasonable quote for an hour of bench time. 200 Euros is highway robbery.

Unfortunately working the lens proabbly will do nothing to help, but I am sure you can find someone who will do it for less, probably on this MB. Heck, if you were in the U.S., I'd be happy to do it for you, but unfortunately the round-trip postage might be prohibitive.

In the meantime, if you want to use the lens, you can mount it on the camera until just before the pin clicks into place and use it like an m42 lens in manual aperture mode on your camera's Av setting. Just be careful not to accidentally knock it off the camera while in use.

Last edited by dcshooter; 03-17-2016 at 10:24 AM.
03-17-2016, 11:41 AM   #3
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QuoteOriginally posted by i5_david Quote
Hey friends,

got an M 50 f/1.4 and I was stoked about the condition. at home I discovered in some testing situations that the aperture is kinda sticky and goes only "slow" from f22 to open. Is there anything I can do about that without dismantling or brining it to the repairshop? I talked to the guy and he told me about 200+ Euro for a lens repair...? Wft?
Will it come back to life if I use the blades a lot? open and close them manually? Hmmm I am a bit disappointed. looked so good that glas...
If you are feeling adventurous, the disassembly database has an entry for your lens. I cleaned my M 28mm last weekend, it took me 2-3 hours, and I'm a beginner with lenses - but not with screwdrivers
03-17-2016, 11:51 AM - 1 Like   #4
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See this disassembly video:


03-17-2016, 12:13 PM   #5
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Thanks for your help already!!! It doesn't look that crazy hard to open up... but do I need to disassamble the complete unit? The attached video shows the blades at 2:26 already. Is this the moment I can actually clean the blades? Or do I need to get each of them out of the lens to clean them properly?
How do I clean them? alcohol?
I am a bit afraid that dust will get into the lens when I go on my adventure....

EDIT: Do you think the problem are the blades or can it also be the spring that brings the aperture wide open? Then I wouldn't be able to fix that, right?
03-17-2016, 12:21 PM   #6
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The simplest way to clean the blades on this camera:

1. Remove trim ring on front with rubber tool buy turning counter clockwise.

2. remove entire front lens cell by turning it counter clockwise. Now you have access to the blades.

3. put a couple of drops of lighter fluid on the closed blades and flick them back and forth with the lever on the mount of the lens. Soak up the lighter fluid gently with a cotton swab

4. Repeat step 3 50-100 times, using a clean swab tip each time.

5. Allow any fluid inside the lens to evaporate for an hour or so, and then check to see the action on your blades. If they are still slow, repeat the swabbing process several more times.

6. Once you are confident that it is working, carefully use your microfier or lens tissue to clean the element surface behind the blade, whcih will likely now have some oil on it. Blow out any dust left behind.

Put the front cell back on and the trim ring and enjoy your working lens.


This is the absolute simplest way to clean your blades. It requires the removal of only two parts and no tools that can't be found around the house or involve screwdrivers which can strip screw heads or lens spanners that can scratch element surfaces. It also doesn't throw off any of the focus and aperture tuning, since everything is left in one piece.

The disadvantages are 1) since you are only cleaning from the front, you have to let the fluid seep behind the blades instead of accessing them directly, so it takes longer to do than methods where the lens is disassembled further, and 2) the rear cell remains in place, so you have to clean it before reassembly.

Considering you haven't worked on lenses before, don't even try the disassembly shown in Marktax's video unless you are willing to take the risk of likely permanently ruining your lens or losing tiny parts, or at the very least going down the path of insanity that is reassembling and calibrating a disassembled aperture.

---------- Post added 03-17-16 at 12:27 PM ----------

QuoteOriginally posted by i5_david Quote
Thanks for your help already!!! It doesn't look that crazy hard to open up... but do I need to disassamble the complete unit? The attached video shows the blades at 2:26 already. Is this the moment I can actually clean the blades? Or do I need to get each of them out of the lens to clean them properly?
How do I clean them? alcohol?
I am a bit afraid that dust will get into the lens when I go on my adventure....

EDIT: Do you think the problem are the blades or can it also be the spring that brings the aperture wide open? Then I wouldn't be able to fix that, right?

Apparently you posted this while I was writing my last post. 2:26 is exactly where you need to be to do the technique I outlined above.


It is 99% likely that it is oily blades based on your descriptions of its behavior above.

Last edited by dcshooter; 03-17-2016 at 02:53 PM.
03-17-2016, 01:24 PM   #7
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hey dcshooter, thank you for your detailed description. I am right now following this dude: https://www.youtube.com/watch?v=-rlDO5Qj6cU#t=71
since its a bit different with the 50 1.4. but I am ready to work on the blades. In fact I just opened it but I dont have the fluid here and stores are closed since some hours already.

just a couple things:
- you mean the normal fluid I would use to fire up a zippo lighter or any special fluid?
- what happens when the drop goes through the blades into the lens... does it go/fly away/disappear like pure ethanol?

Thanks for your outline I will take a shot tomorrow and try it
03-17-2016, 01:35 PM   #8
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Hi David,

Zippo or Ronsonol are both fine. You are looking for a naptha-based fluid rather than compressed butane. Ethanol itself can be used but takes longer to dry out. Either way, work in a well-ventilated area away from open flames.

Place the drops directly on the blades. If it gets on the lens surface, it will evaporate but will leave any oil dissolved in it behind.

If you are just using a drop or two at a time, it won't spread further into the lens than the exposed surface you see. Just don't flood the entire mechanism, and be patient with the process. When you are done, simply wipe any residue left on the glass away with a lens tissue or cloth. You can actually use a drop of lighter fluid on the tissue on the first pass to clean most of it off, then just the tissue with fog from your breath.

If while you are doing the cleaning the blades get stuck, simply wait a minute or two for the lighter fluid to evaporate and try working the aperture again. The surface tension from the lighter fluid itself can sometimes be stronger than the spring tension in the aperture mechanism and cause things to bind temporarily.


Last edited by dcshooter; 03-17-2016 at 01:49 PM.
03-17-2016, 02:03 PM   #9
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Thanks mate, really appreciate your help here!
I will go downtown and get myself a bottle of lighter fluid and give it a ride. I will be sure to let you know here if it worked. That would be so cool, since I really looked forward to use this lens.
(in fact I got it on ebay (marketplace) in comination with a ME, the 50 1.4 and 200 f4 for 45€ - so happy about this deal, haha )
03-18-2016, 08:56 AM   #10
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QuoteOriginally posted by i5_david Quote

EDIT: Do you think the problem are the blades or can it also be the spring that brings the aperture wide open? Then I wouldn't be able to fix that, right?
It's unusual for the rest of the mechanism to have trouble. I have one lens like that, and it's a screw-mount lens so it doesn't need fast aperture blades. Resist the temptation to put a drop of oil somewhere just in case. .
03-18-2016, 01:26 PM   #11
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So, came back today and after the opening the lens test yesterday I did it. longer story short: I bought a bottle of lighter fluid for 2,20€ and now its working again! HAHA
THANK YOU so much dcshooter!!! Because of your awesome outline I managed to repair my lens. great feeling. love it
After I put it together I noticed a small little tiny hair... that actually bothers me, so I think I have to do it one more time.
(One thing, after I put it together the lens' focus sounded a bit like there is sand in the mechanism (NO WAY, No Chance that that happened). Its better now, but these noises were kinda strange. Turned the focus back and forth and back and forth and now its better but why is this?)

@soti: thanks for pointing this list out of videos how to open up lenses. Great resource!
03-23-2016, 07:56 PM   #12
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dcshooter is The Man :-)

i tore down a canon fd 50/1.4 a couple of days ago for oily blades... i stupidly took it down too far, basically disassembled the focus mechanism, and it took me half a day just to grasp how the internal focus ring could drive the top group assembly straight down: gregpotter.net - Canon New FD 50mm F/1.4 Disassembly from the Front

i got the blades out, blew 'em clean with carb cleaner, but they were still sticky, ended up with all eight blades disassembled in pieces on the bench :-0

the amount of screw torque on the blade assembly is apparently critical to proper operation.

got it all back working, infinity adjusted, then noticed some very tiny bubbles somewhere in one of the rear elements...

live and learn, glad to hear that someone had better luck with their lens teardown.
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