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05-23-2017, 11:41 AM   #1
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Leaving Pentax-A lenses in the green "A" setting?

I have several old Pentax-A lenses which work perfectly fine with more modern Pentax DSLRs. Just wondering if I should keep my Pentax-A lenses in the "A" setting (i.e. at the green "A") when they are not being used. The green "A" setting keeps the aperture closed down, and I am wondering if this puts unnecessary strain on the spring mechanisms that keep the aperture closed down. My question.....should I move my Pentax-A lenses off the green "A" setting when they are being stored? Thanks

05-23-2017, 11:58 AM   #2
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Interesting question. And not what I thought you were going to ask We often see people wanting to know if they can use the 'A' setting on the camera, not in storage, so that part is new.

My opinion (and practice) is to leave them on the 'A' setting. I don't see how it could make any difference. We are talking 30 year old lenses at this point, if they have not broken yet I do not see that happening in the future. YMMV of course. I do not think the strain is "unnecessary" the parts were designed for that strain. Now whether they were designed to operate for 30, 40 or 60 years is another question.
05-23-2017, 12:11 PM   #3
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I have a few Pentax "A" lenses and always leave them in the "A" position. My reason for doing so is that I have read that some of the plastic aperture rings do malfunction and prevent enabling it into the "A" position if it has been left at a specific aperture position.
I have never used them on a camera that does not allow the aperture to be selected on a body so if I cannot get out of the "A" position, I'm not worried.
05-23-2017, 12:31 PM - 1 Like   #4
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Your logic is actually flawed. Yes, the spring closes down the aperture, but it is under the most stress when the lens is wide open, not closed down. You will notice that when the lens is removed, and on the A setting, the aperture closes. The mechanism in the camera opens it back up when attaching the lens to the camera. When you take a picture, the lever inside the camera moves, and the spring action closes down the aperture. If you carefully move the lever on the lens with your finger, you will experience the most pressure when the lens is wide open.

Really, we should all remove the lens from the camera body when we store the unit, to reduce stress to a minimum on the mechanism.

Regards,

05-23-2017, 01:01 PM   #5
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QuoteOriginally posted by Midges Quote
Leaving Pentax-A lenses in the green "A" setting?
All my "Ladies" are left in that condition... without any dramas or rebellions so far.
05-23-2017, 01:33 PM   #6
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The lenses came from the factory in the 'A' position with the aperture fully closed. I figure Pentax knew what they were doing.
05-23-2017, 02:10 PM - 1 Like   #7
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QuoteOriginally posted by BigDave Quote
Your logic is actually flawed. Yes, the spring closes down the aperture, but it is under the most stress when the lens is wide open, not closed down. You will notice that when the lens is removed, and on the A setting, the aperture closes. The mechanism in the camera opens it back up when attaching the lens to the camera. When you take a picture, the lever inside the camera moves, and the spring action closes down the aperture. If you carefully move the lever on the lens with your finger, you will experience the most pressure when the lens is wide open.

Really, we should all remove the lens from the camera body when we store the unit, to reduce stress to a minimum on the mechanism.

Regards,
What he said ^ ^ ^

FWIW, there is at least one A-series lens where leaving the aperture ring on the "A" setting is strongly recommended. That lens is the A 50/1.7. That lens has a fragile detent mechanism that is prone to breaking and making the aperture ring immovable.


Steve

(...My M 50/1.7 has been attached to a camera for most of the last 35 years...What? Me worry?...)
05-23-2017, 02:21 PM   #8
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Both fully open and fully closed will be well within the elastic limit (yield point) of the spring, so you can relax. Any engineer past high school level will have condidered that in their design.

What should worry you more is whether they have ensured that the amplitude of the cycle is within the fatigue limit or whether they decided that some distant fatigue failure is an acceptable risk compared to the additional cost of higher quality or quantity of materials. However, considering the ages of some of these lenses, it is clearly not significantly past the limit.

05-23-2017, 03:24 PM   #9
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Springs are designed for infinite life in most cases. Which doesn't mean they last forever, but they would if they didn't have flaws, or weren't exposed to corrosion. Given these are protected physically and don't really see corrosion, I'd say they will last "forever", with occasional exception due to flaws in the base material.
05-23-2017, 04:39 PM   #10
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There are only two good reasons for a DSLR-only photographer to pull an A lens off the A setting, in my opinion. The first is when you have "blind" extension tubes or bellows fitted and have lost electronic transmission and control as a matter of course. The second is on a camera whose aperture block has failed.

A little while ago, I had the option to purchase a 50/1.7 A lens in a store at a fairly good price. The optics looked great and the contacts were humming sweetly when I put it on the K-5, but I passed because I shoot film on K mount bodies a lot & the aperture ring of this one was already feeling a bit shaky. Had I not been a film shooter, it would have gone home with me.
05-23-2017, 04:59 PM   #11
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I do not have any A series lenses but the questions asked here apply to all F and FA series lenses and the DFA 50 macro. I have an F 28mm and an FA 50mm 1.7 and I leave the aperture ring set on A with both lenses. With a modern digital SLR there is no need to take it off the A setting. You can use Av setting on camera to change aperture settings.
I am not worried about stressing the spring mechanism in the lens. I have had the F 28mm in use exclusively on the A settings for about 28 years now on various film and digital bodies and there is no sign of any problem issue.
05-23-2017, 09:40 PM   #12
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Lens diaphragm springs aren't under enough tension to worry about. Leaf shutter main springs like on Mamiya and Hasselblad cameras are under a fair amount of tension and go bad in storage. Spotmatics and other horizontal curtain focal plane shutter cameras can need tension adjustment if stored cocked and that is what probably makes people concerned.
05-24-2017, 02:44 AM - 1 Like   #13
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Since the DA/DFA lenses without aperture rings are always in the "A" mode it would seem to be okay to always be set in the "A" mode
05-24-2017, 09:49 AM   #14
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Many thanks to everyone who responded and left thoughtful, detailed and helpful responses to my question about leaving Pentax-A lenses on the "A" setting. I will keep my lenses on "A".
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