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07-23-2013, 07:21 AM   #1
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Sticky aperture blades?

Hi all, could someone please give me a definition of what 'sticky aperture blades' are? I'd also like to know how to:
  • Prevent sticky aperture blades
  • Identify sticky aperture blades
  • Fix/remedy sticky aperture blades
I'm posting this because I have a Pentax-A 50mm f/2.8 Macro lens which has oily aperture blades but I am unsure if they are 'sticky' (though I have read that I should get this remedied regardless of whether it is sticky or not) and I've recently bought a Pentax-M 35mm f/2.8 lens which is notorious for sticky aperture blades. If anyone has any relevant experience with any of these two lenses (or any similar lenses) could you also post your experience(s)?


Regards,


Michael

07-23-2013, 08:09 AM   #2
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To determine whether you have sticky aperture blades or not, do the following.

With the lens unmounted and the aperture ring set to "A" position (or in case of K or M series lens, set the aperture to minimum), actuate the lever on the rear of the lens to open the diaphragm. When you quickly release the lever, the blades should snap shut immediately, without any hesitation.

Most sticky aperture is caused by excess oil or liquified grease leaking into the aperture mechanism. Unless you're prepared to open up the lens yourself to clean the mechanism, there's no "remedy".

In the case of the M35/2.8, apart from the oil problem, the aperture may not operate properly due to improper repair attempt. This particular lens has a construction whereby the aperture assembly is held in place by a retaining ring. If this ring is tightened too much, it puts pressure on the blades, causing problems.

There is no specific action to prevent sticky aperture blades. Some lenses are more prone to this problem than others, due mainly to the type of oil and grease used. It seems Pentax used different grades or brands of oil/grease at various times during lens production. Some grease tends to "run" at lower temperature than others. It's a normal and common sense advice for any lens, but high temperature situation such as leaving your lens in the car on a hot sunny day should be avoided.
07-23-2013, 08:29 AM   #3
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QuoteOriginally posted by tom1803 Quote
To determine whether you have sticky aperture blades or not, do the following.

With the lens unmounted and the aperture ring set to "A" position (or in case of K or M series lens, set the aperture to minimum), actuate the lever on the rear of the lens to open the diaphragm. When you quickly release the lever, the blades should snap shut immediately, without any hesitation.

Most sticky aperture is caused by excess oil or liquified grease leaking into the aperture mechanism. Unless you're prepared to open up the lens yourself to clean the mechanism, there's no "remedy".

In the case of the M35/2.8, apart from the oil problem, the aperture may not operate properly due to improper repair attempt. This particular lens has a construction whereby the aperture assembly is held in place by a retaining ring. If this ring is tightened too much, it puts pressure on the blades, causing problems.

There is no specific action to prevent sticky aperture blades. Some lenses are more prone to this problem than others, due mainly to the type of oil and grease used. It seems Pentax used different grades or brands of oil/grease at various times during lens production. Some grease tends to "run" at lower temperature than others. It's a normal and common sense advice for any lens, but high temperature situation such as leaving your lens in the car on a hot sunny day should be avoided.
Could you please describe what the lever on the rear of the lens looks like? What is the 'diaphragm' that you refer to?

EDIT: Nevermind, I've found the lever. How quickly should the blades snap shut?

Last edited by mn_raf123; 07-23-2013 at 08:35 AM. Reason: Found the lever
07-23-2013, 09:12 AM   #4
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QuoteOriginally posted by mn_raf123 Quote
Could you please describe what the lever on the rear of the lens looks like? What is the 'diaphragm' that you refer to?

EDIT: Nevermind, I've found the lever. How quickly should the blades snap shut?
Nearly instantaneously.

07-23-2013, 12:08 PM   #5
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The aperture is held wide open for focusing. When you press the shutter button, the blades close to the aperture you have set on the camera, by allowing the spring-loaded lever on the lens to move. DSLR cameras have very short "shutter lag", the time between pressing the button and the camera taking a shot, so the blades have to react in something like a tenth of a second.

Another test is to take a series of shots with the same exposure but different apertures, to compare brightness of the shots. Put the camera on a tripod and aim it at a target with constant lighting, not fluorescent because that flickers. Focus doesn't matter a lot. The A50/2.8 macro will make this easy. Set the camera to Av mode and the aperture to f2.8. Get a meter reading, then press the AE-L button to lock that. Take a shot, then change the aperture to f8. The shutter speed should follow along: you closed the aperture three stops, so the shutter speed should three stops slower. Take a shot at f8, change the aperture to f22 and take another shot. Each shot should have similar brightness and histogram. They won't be identical but close. If you see a trend of overexposure as you stop sown, that is probably slow aperture blades. You may find a point where changing the aperture setting doesn't change the shot brightness much, because the blades only close to a certain point. With the M35/2.8, you have to use M mode and change the shutter speed yourself for this test. Remember you don't take a new meter reading for each shot.
07-23-2013, 01:56 PM   #6
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My two cents...

QuoteOriginally posted by mn_raf123 Quote
Prevent sticky aperture blades
One thing is heat. Never store the lens in a hot car. Excessive heat will cause certain types of lens greases to separate and the lighter oils will invade areas of the lens sensitive to any share.

QuoteOriginally posted by mn_raf123 Quote
Identify sticky aperture blades
...already cover above it looks like...

QuoteOriginally posted by mn_raf123 Quote
Fix/remedy sticky aperture blades
I've not had much luck with the trick of soaking the lens with alcohol or others the like. Tearing the lens down and cleaning a wiping all parts have guaranteed like new performance. However, this means tool and a little knowledge of the inside, re-lube of key parts and ultra clean conditions to end up with a proper lens in the end.
07-23-2013, 02:22 PM - 1 Like   #7
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The old Asahi documentation on Takumar lenses notes that there should NOT be any oil or grease used on the diaphragm or linkage. They originally coated some parts with dry-lube film, and they say NOT to wash the parts with solvent (which would promote corrosion, etc), but to carefully disassemble and wipe each part carefully to remove any oil. Diaphragm blades often had a black-oxide coating that is not rust-proof, and so they said not to touch them with your fingers, but to use tweezers or wear gloves to assemble.
I've followed similar steps to cure sluggish diaphragms, but usually "burnish" sliding parts with moly-disulfide powder, wiping off well until nothing visible wipe off.
Pentax lenses have far fewer problems with such issues than some other makes of the same time period. I've seldom found a Canon FL lens that doesn't need to be serviced! It's common on old Canon FT cameras to find uneven exposures in bright light because the diaphragms are slow to close to small apertures. On film cameras you can open the back and look through the shutter curtains as you fire with high shutter speed and f16 settings, and see if the lens opening is the same on the left and right sides.
12-04-2014, 06:13 AM   #8
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Good info here

07-08-2015, 05:56 PM   #9
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Hi there.

My mint 50-135 f2.8 has sticky aperture blades. Can you recommend anyone in North America that can do a repair?

Thanks!
07-08-2015, 06:58 PM   #10
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mint?
07-08-2015, 08:36 PM   #11
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The M50/1.7 has an aperture assembly that drops completely out if you remove the front element and lock ring. Wipe down with high pecentage alcohol Q tips and set it back in, replace ring and clean front element while you are at it. Its a 15 minute job. You can get to the backside of the aperature just by unscrewing the rear element. Could possible clean it enough from there.
07-09-2015, 08:34 AM   #12
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QuoteOriginally posted by jholthuysen Quote
Hi there.

My mint 50-135 f2.8 has sticky aperture blades. Can you recommend anyone in North America that can do a repair?

Thanks!
Do you mean the Pentax-DA 50-135/2.8? If so, I am surprised that a lens of that age would have developed a problem generally associated with vintage glass. Sticky blades are usually the result of gummed up lubricant that has migrated on the iris diaphragm from elsewhere on the lens. Less common is physical damage to the actuator mechanism.

The Ricoh/Pentax service facility in Canada is Sun Camera Service in Vaughan, ON. They would be your preferred shop due to familiarity with your lens and access to parts.


Steve
07-09-2015, 08:46 AM   #13
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I'd advise using Naptha (lighter fluid) rather than alcohol. It's much more effective at removing oil, dries more quickly, and tends to leave less residue behind. The front and rear groups are easy to remove. I'd advise against attempting to clean it by just removing the rear group, since chances are you'll end up with the oil on the front group glass rather than on the blades...

If you manage to take the whole aperture assembly out, you can dunk the whole thing in Naptha a couple of times, and it will be good as new. I'd avoid taking the aperture assembly itself apart, though, since it takes a LOT of practice to learn to get it reassembled in a reasonable amount of time.

QuoteOriginally posted by pishta Quote
The M50/1.7 has an aperture assembly that drops completely out if you remove the front element and lock ring. Wipe down with high pecentage alcohol Q tips and set it back in, replace ring and clean front element while you are at it. Its a 15 minute job. You can get to the backside of the aperature just by unscrewing the rear element. Could possible clean it enough from there.


---------- Post added 07-09-15 at 08:52 AM ----------

The DA? For something that new, and weather sealed, I'd advise sending it off to the authorized repair center at Precision or Sun. Eric won't touch anything that new, and local repair techs don't have access to new seals if the originals get compromised during the repair.
QuoteOriginally posted by jholthuysen Quote
Hi there.

My mint 50-135 f2.8 has sticky aperture blades. Can you recommend anyone in North America that can do a repair?

Thanks!


---------- Post added 07-09-15 at 08:54 AM ----------

Some of the modern AF lenses use lubricants and some don't. I can't attest to this one, since I've never opened one up myself.

QuoteOriginally posted by stevebrot Quote
Do you mean the Pentax-DA 50-135/2.8? If so, I am surprised that a lens of that age would have developed a problem generally associated with vintage glass. Sticky blades are usually the result of gummed up lubricant that has migrated on the iris diaphragm from elsewhere on the lens. Less common is physical damage to the actuator mechanism.

The Ricoh/Pentax service facility in Canada is Sun Camera Service in Vaughan, ON. They would be your preferred shop due to familiarity with your lens and access to parts.


Steve

Last edited by dcshooter; 07-09-2015 at 08:53 AM.
07-09-2015, 10:44 AM   #14
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QuoteOriginally posted by dcshooter Quote
The DA? For something that new, and weather sealed, I'd advise sending it off to the authorized repair center at Precision or Sun. Eric won't touch anything that new, and local repair techs don't have access to new seals if the originals get compromised during the repair.
Eric worked on my DA 70mm with visable oil on the blades. 1 week turnaround....and need I say, the lens was and still is, perfect. Oh, and incredibly cheap!
07-09-2015, 10:56 AM   #15
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QuoteOriginally posted by pepperberry farm Quote
mint?
Maybe the blades are sticky because someone melted a candy cane on it.
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