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06-30-2017, 02:31 AM   #1
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aperture weakness on SMC DA 70 limited. Help needed. Anybody experienced such issue?

I bought a SMC DA 70 limited second hand two years ago.
It tends to overexpose around 0.7 to 1 stop when I select small apertures, whereas it is OK at full aperture.

I noticed that, compared to my other lenses, the aperture seems slower to close:
When looking at a Pentax lens unmounted, the aperture is closed to its smallest value.
By moving the aperture lever it opens to its maximum value. Then, when releasing the aperture lever, it shuts down back to its smallest value.
On all my other lenses, it closes very fast with a clack when achieved.
On my DA 70, it closes slower and there is no clack.

I think either there is some grip in the aperture blades, or the spring that closes it is worn and weaker than it should be.

I tried to move a hundred times the aperture lever, but it didn't fix it.

Has anybody experienced this issue and what are the ways to fix it other than send the lens for repair?

Any tips welcome

06-30-2017, 03:02 AM   #2
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QuoteQuote:
On all my other lenses, it closes very fast with a clack when achieved.
On my DA 70, it closes slower and there is no clack.
I think you have found the problem your Clack value is knackered . Sorry could not resist .

Seriously, as you probably know the aperture is closing too slowly at the higher speeds leading to the over exposure. Over time and with lots of use it is possible that it could free itself. On the other hand it could just as easily get worse.

Unless you are skilled at taking a lens apart and dealing with cleaning the aperture blades then it is my opinion that a visit to a service centre is in order



06-30-2017, 04:38 AM   #3
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After four years of use, my DA70 Ltd is still functioning as new. Maybe yours had a hard life with its former owner? DC Shooter works on lenses. Send him a message.
06-30-2017, 04:56 AM   #4
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QuoteOriginally posted by AquaDome Quote
After four years of use, my DA70 Ltd is still functioning as new. Maybe yours had a hard life with its former owner? DC Shooter works on lenses. Send him a message.
Didnt find him herevcnor on google.
URL?

06-30-2017, 05:39 AM   #5
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dcshooter - View Profile - PentaxForums.com
Here you go
06-30-2017, 06:35 AM   #6
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I also can recommend DCShooter.
06-30-2017, 07:17 AM   #7
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Thank you alpheios and uncleVania.
Went through dcshooter posts. Lots of interesting tips but nothing about a similar issue, save some do it your self tips for repairing lenses at home.
I might have tried it if the defective lens was a cheap old manual lens from the film era.
But I won't dismantle myself a modern limited lens which costs over 500 euros new, I will rather ask a pro.
06-30-2017, 10:20 AM   #8
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QuoteOriginally posted by Tatouzou Quote
Went through dcshooter posts. Lots of interesting tips but nothing about a similar issue, save some do it your self tips for repairing lenses at home.
PM him. Alternatively, contact a camera repair near your home.

The classic cause for your problem is fouling of the aperture blades with oil and/or botched service attempt. Most competent repair persons should be able to manage the service/repair, assuming that parts (if needed) are available.


Steve

06-30-2017, 12:15 PM   #9
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QuoteOriginally posted by stevebrot Quote
PM him. Alternatively, contact a camera repair near your home.

The classic cause for your problem is fouling of the aperture blades with oil and/or botched service attempt. Most competent repair persons should be able to manage the service/repair, assuming that parts (if needed) are available.


Steve
Thank you Steve
06-30-2017, 04:33 PM   #10
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QuoteOriginally posted by Tatouzou Quote
Thank you alpheios and uncleVania.
Went through dcshooter posts. Lots of interesting tips but nothing about a similar issue, save some do it your self tips for repairing lenses at home.
I might have tried it if the defective lens was a cheap old manual lens from the film era.
But I won't dismantle myself a modern limited lens which costs over 500 euros new, I will rather ask a pro.
This exact same problem happened with my SMC DA 70 which I bought used. Also I noticed it had (and still has), more inner barrel wobble than my other Limited lenses. I sent it to Eric Hendrickson in Tennessee, who is well known on this forum requesting repair of both the barrel wobble and the sluggish aperture blades. When I got the lens back the aperture blades were cleaned and now they snap shut just as quickly as any of my other limited (15, 21, 35 macro and 40) lenses. Minor disappointment the inner barrel still has the wobble but I am reluctant to send it out for another repair, just for this. It is as sharp as my DFA 100 Macro so I do not think the wobble is a real issue in terms of lens performance. Good luck with yours, this can be repaired and is worth repairing. If it is the same issue as I had, it just needs cleaning of the aperture blades.

Last edited by jddwoods; 06-30-2017 at 04:37 PM. Reason: correct typos
07-01-2017, 12:44 AM   #11
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Thank you all.

It took me long to decide I should have the lens serviced, as I mostly use it wide open for subject isolation. But I finally came to the conclusion that I used this lens less often because of this issue.

I am glad you confirmed this kind of issue and it is easily fixed.

As I live in France, I won't send it overseas to USA for service, I will deal with a local repair station.

My DA 70 also shows more wobble than my other limited lenses. I will ask to have it fixed too if they can.
07-02-2017, 08:27 PM   #12
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I had an old 28mm M lens with the same issue and sent it to Eric; he found some sand in it and was fixed in a week. Not an expensive repair.


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