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11-03-2020, 10:53 AM   #1
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Issue with Aperture ring on A Series lens (50mm f1.7)?

Hi all,

Apologies if this has been asked before but I've been a bit useless at finding an answer in the forum. I've picked up a copy of an SMC Pentax-A 50mm f1.7 and I've loved the results I've gotten at such a low price, as they are. The lens seems to be in good condition and it's resulting in satisfactory shots at f1.7.

Now, I am using it on a K-5 and ensuring that I've got the "using aperture ring: permitted" menu setting enabled and I'm in aperture priority mode. My issue is that no matter what I do, the aperture seems to be fixed at f1.7. I can surmise this not only from the exif showing f1.7 at every aperture ring setting but also the very blatant depth of field and bokeh. I can see the ring moving the blades inside the lens normally when it is not mounted to the camera.

Might anyone have any suggestions on what I may be doing wrong/if this is a common (and fixable) issue?

Many thanks,
Jack

11-03-2020, 11:08 AM - 1 Like   #2
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Hi, did you set the aperture on the lens to the 'A' position ? There's a little black button next to the 'A' you need to push to allow the aperture ring to move to the 'A' position. That should do the trick. Good luck. Fred.
11-03-2020, 11:15 AM   #3
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That is how your camera support this lens.
In any mode except manual mode the aperture will always be wide open if you do not have the aperture ring set to A.

So any lens with A-position on aperture ring it is recommended to have it set to A-position when used on a DSLR.

The "using aperture ring: permitted" is intended for older lenses that lack A-position on aperture ring, but they have the same limitation.
11-03-2020, 11:30 AM   #4
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Hi and welcome!
You might want to look through these articles if you are interested in manual lenses: Using Manual Lenses (M42 Screwmount, M , K) on Pentax DSLRs F-- - PentaxForums.com They mostly deal with lenses older than your Pentax-A 50mm but might be useful. Your lens has the 'A' position on the aperture ring and as noted above you should set it there and use the camera dial to change the aperture setting. With your lens you have the option of using it as a manual lens (using the aperture ring to set the aperture) or in 'A' mode which is the same as modern lenses except it is manual focus. If you want to use the aperture ring then read the articles listed above.

11-03-2020, 12:00 PM   #5
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QuoteOriginally posted by RWJ3399 Quote
Might anyone have any suggestions on what I may be doing wrong/if this is a common (and fixable) issue?
Welcome to the Pentax Forums!

As noted above, when using the aperture ring with K-mount lenses on a Pentax dSLR, the lens will remain full open when shooting in any of the automated exposure modes. Likewise, optical DOF preview will also remain wide open. The modes that support aperture ring are M, X, and B.

Since your lens has the "A" position, it is best to leave it there unless it is being used on a bellows or when using extension tubes for close-focus or macro. Doing so will allow support of all automated exposure modes as well as metered manual in M and X modes. P-TTL flash will also work. There is an additional consideration that applies to the Pentax-A 50/1.7, that being that the aperture ring is prone to becoming difficult to move due to breakage of a small plastic part. Prevention is to leave it on the "A" position and not borrow trouble unless it is being used on an older film camera such as an ME Super. If yours does break, there is a fix, but it requires partial disassembly. The aperture ring on my copy of the lens is still good, but it stays on the "A" position.


Steve
11-03-2020, 12:03 PM   #6
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Hi Jack, welcome. You mention that you got the A50/f1.7 cheaply, so itís worth checking that you can actually set the aperture ring to the A setting by pressing the setting button.

One of the ífeaturesí of this lens (and itís an issue that mine has) is that the spring mechanism in the aperture ring that allows the A position to be set, can jam due to breakage of plastic fixings under the button. The result can be that the button doesnít move, and the A setting canít be engaged, which would mean that youíd be stuck with manual mode only (or aperture priority at full aperture only).

If this affects your lens, there are instructions on this site somewhere (hopefully someone knows) about how you can repair it yourself.

EDIT - Steve responded at the same time that I did! Hope this isnít your problem.
11-03-2020, 12:04 PM   #7
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QuoteOriginally posted by fwwidall Quote
Hi, did you set the aperture on the lens to the 'A' position ? There's a little black button next to the 'A' you need to push to allow the aperture ring to move to the 'A' position. That should do the trick. Good luck. Fred.
Thank you for the prompt and helpful response- likewise, Fogel70.

I think herein lies the issue, I have in the past tried clicking the black button and setting the aperture to "A". When I do, the top side display of my camera shows "F- -". Whatever I press or whichever dials I turn, I'm struggling to do anything that controls the aperture. In your experience is this to be expected or should I be given an option to select my F stop?

Many thanks

---------- Post added 11-03-20 at 12:12 PM ----------

QuoteOriginally posted by microlight Quote
Hi Jack, welcome. You mention that you got the A50/f1.7 cheaply, so itís worth checking that you can actually set the aperture ring to the A setting by pressing the setting button.

One of the ífeaturesí of this lens (and itís an issue that mine has) is that the spring mechanism in the aperture ring that allows the A position to be set, can jam due to breakage of plastic fixings under the button. The result can be that the button doesnít move, and the A setting canít be engaged, which would mean that youíd be stuck with manual mode only (or aperture priority at full aperture only).

If this affects your lens, there are instructions on this site somewhere (hopefully someone knows) about how you can repair it yourself.

EDIT - Steve responded at the same time that I did! Hope this isnít your problem.
I think this is exactly it, I have (rather sheepishly) managed to suss that I can get things working in manual mode. Aperture priority seems to be off the cards for now.

To anyone who has posted and responded so helpfully can I say a big thanks- amazing to have patient and friendly replies so quickly!
11-03-2020, 12:48 PM   #8
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QuoteOriginally posted by RWJ3399 Quote
I have in the past tried clicking the black button and setting the aperture to "A". When I do, the top side display of my camera shows "F- -".
With everything functioning as it should you should see the aperture displayed on the camera screen/viewfinder display and it should work as advertised in Av mode.

Try cleaning the mount and lens contacts first, and fiddle with the "A" setting on the lens itself. As others have advised this particular "A" series 50mm does have a reputation for problems. If you are unable to get it to work then you can still use Av mode but every shot will be at 1.7. Or use the aperture ring set to a physical setting, and Manual mode/green button. This will enable you to get a picture at the aperture selected.

11-03-2020, 02:20 PM   #9
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In addition to pschlute's suggestion to try cleaning the mount and lens contacts, it may also help to rotate the aperture ring back and forth several times. Especially if the lens has been setting for a while the mount contacts and aperture 'click' setting's contacts can oxidize and fail or intermittently fail to make a good connection.
11-03-2020, 06:40 PM   #10
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I don't think it was mentioned yet. About the F--, if using the aperture ring you need to tell the camera it is permitted, The default in the menu is not permitted--for some reason.
11-05-2020, 12:54 PM   #11
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The OP made a point of saying that he had set the camera to permit the use of the aperture ring. Double check that.

If he is still getting the "F---" on the top LCD, that means that the camera is not recognizing that the lens is in A mode.

If the lens is, indeed, in A mode, then cleaning the pins on both the camera and the lens might help.

If the lens is not in A mode, try getting the aperture ring to the A setting. If that is not possible, as others have said, you will have to shoot wide open. That kinda sucks for a couple of reasons: f/1.7 is probably not the sharpest aperture for that lens, and you will have minimum depth of field. The latter may be okay for some shots, but for most shots, its nice to have at least moderate depth of field.
11-06-2020, 03:00 AM   #12
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QuoteOriginally posted by noblepa Quote
try getting the aperture ring to the A setting. If that is not possible, as others have said, you will have to shoot wide open.
If the OP's lens will not work in the "A" position he can still get full aperture control by setting the lens to a physical aperture and shooting the camera in Manual exposure mode.
11-06-2020, 03:55 AM - 1 Like   #13
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Should it be a case of the loose spring under the ring here is an lengthy thread devoted to DIY repair:
Pentax-A 50mm f1.7 Aperture ring repair - PentaxForums.com

Note: some will recommend put grease on the pin assembly to help keep it together for ease of assembly. Unless it is conductive grease do not do this. The grease will eventually block electrical contact in the pin and you'll have to take it apart again to remove the grease. These parts are tiny and difficult to work with and easy to lose.
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