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02-03-2016, 09:03 AM   #1
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how to set aperture with smc pentax-A 50mm F1.7

Hello everyone!
I recieved a smc Pentax-A 50mm F1.7 lens today for my Pentax K-r. I couldn’t change the shutter speed or the aperture, live view wouldn’t start, and my camera wasn’t taking any pictures either. I found a feature in settings where I took permitted to use the aperture ring and after doing that I was able to change the shutter speed and take photos, but I still couldn’t change the aperture. Does anyone know how can I change the aperture and see it on display?

02-03-2016, 09:05 AM   #2
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Put the aperture ring on the 'A' setting (it will lock with the little button) and leave it there forever. Then it will work like any modern lens except without autofocus (and if shake reduction is on it will ask you the focal length).

If you take it off the 'A' setting, it becomes fully manual, like an earlier M-style with no contacts. See this:

https://www.pentaxforums.com/forums/54-pentax-lens-articles/110657-how-use-me...k-x-k-7-a.html

But there is rarely a reason to take it off 'A' for normal use...
02-03-2016, 09:17 AM   #3
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a) Enable Aperture Ring use in the back of the camera's Menu
b) On the lens' aperture ring, push the little button and slide it into A setting (instead of the numbers). Leave it there
c) When you turn on camera, input focal length 50mm for SR.
Now it works just like any DA or DFA lens, only without AF. Camera keeps lens wide open (at f1.7) for focusing purposes, and only stops it down to the selected number when you take the photo. In live view, the lens is often not wide open (to shield sensor for sudden bright light, and to help with composition). This is normal and DA lenses don't show you the aperture in live view, either. In live view, you can press the Info or Ok button (depends on camera model, not sure which it is for K-r), and the camera will zoom in and open the lens aperture. This will help you with focusing in live view.

The camera also has a DoF preview function (check the Manual, you might need to remap a button function), which will move the lens to the selected aperture, so you can see what it will look like.

The lens doesn't have AF, but you can use Catch in Focus with it (aka Focus trapping). Many threads about this feature, even blog posts. It gives you something similar to AF, so you might want to read up on it. CiF works well with my M 50mm f1.7, so it should work well with the A, as well.

Edit: You can check whether the camera stops down the aperture correctly by going into Av mode and choosing something like f14. Now look into the lens and take a photo. You should see the aperture blades mode inside of the lens. If they don't, you probably didn't select A button on aperture ring, or the lens might be damaged. Or the camera's aperture actuation, but that is less likely. Reasons why the camera does not fire when you press the shutter button might be Focus priority, CiF enabled, maybe you have something like timer or another thing that makes the camera behave differently than you would expect. Does it work normally with other lenses?

Last edited by Na Horuk; 02-03-2016 at 09:23 AM.
02-03-2016, 09:20 AM   #4
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QuoteOriginally posted by flwwera Quote
. I found a feature in settings where I took permitted to use the aperture ring and after doing that I was able to change the shutter speed and take photos, but I still couldn’t change the aperture.
This setting only applies to non-'A' lenses, or an 'A' lens that is not in the 'A' position. As vonBaloney says put the lens in the 'A' position by moving the aperture ring and just leave it there.

However, if you do want to use the lens in non-'A" then you must change the aperture by turning the aperture ring on the lens. This sets the aperture, but the camera has no way to know what it is so you have to press the green button on the camera to take a meter reading and set the shutter speed. That's assuming you have the other settings in the menu set to allow that. If you are interested in learning about old Pentax lenses and how to use them read the link provided above. Otherwise, put the lens aperture ring in the 'A' position and forget all of this.

02-03-2016, 09:30 AM   #5
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So I am supposed to twist/turn the aperture ring so that the yellow dot and the "A" are above one another? It is easy to turn the aperture ring in the opposite direction, but when I try turning it in the direction of the A it becomes heavy and difficult. Is this supposed to happen? I don't want to ruin it.
02-03-2016, 09:42 AM   #6
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QuoteOriginally posted by flwwera Quote
So I am supposed to twist/turn the aperture ring so that the yellow dot and the "A" are above one another? It is easy to turn the aperture ring in the opposite direction, but when I try turning it in the direction of the A it becomes heavy and difficult. Is this supposed to happen? I don't want to ruin it.
No the red center line is the setting you are on. See the main picture here:

SMC Pentax-A 50mm F1.7 Reviews - A Prime Lenses - Pentax Lens Reviews & Lens Database

It is on the 'A' setting. You will have to hold down the little button to make the jump from 22 to A, then release the button, and it should be locked on A. (If the lens if not mounted on the camera, the aperture will now be very small, and should open and close snappily if you manually push and release the aperture lever on the mount. Once mounted, it will stay wide open at all times except for the actual shot or the use of a preview function.) And as long as you keep it on A, you never have to touch the aperture ring again ever.
02-03-2016, 09:48 AM   #7
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Greetings, and welcome.

The SMC-A 50/1.7 is a cracker of a lens, but it is notorious for having a sticky or jamming aperture ring, caused by one of the plastic components breaking off inside the ring. Mine is like this. Wiggle the aperture ring gently to rotate the green A setting opposite the red diamond in the centre of the depth-of-field scale - but don't force it. The aperture ring is plastic. You'll need to press the small black button next to the A setting to get it to lock in place. Once it's there, leave it there! In this configuration, you can change the shutter speed and/or aperture on the camera body or use any exposure mode. With catch-in-focus enabled, you'll then have a perfectly good fast short telephoto.
02-03-2016, 10:00 AM   #8
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See I have done that, but the aperture is still not on display.

02-03-2016, 10:03 AM   #9
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When you have the lens in place and turn the camera on, does it ask you to input a focal length? Also, in the viewfinder, you should see the shutter speed and next to the green AF hexagon, the aperture. Do you see the aperture, or 'F--'?
02-03-2016, 10:09 AM   #10
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Yes, it asks for focal length and the aperture says "F--"
02-03-2016, 10:23 AM   #11
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If F-- is showing, then either you haven't got option Custom menu 4, option 22 in the menu system set to 'Permitted', or the lens is not in the A position. The setting for C22 should be 2, or Permitted. If you have this, then the lens is not in the A position. If the aperture ring shows that the A is lined up with the red diamond but the display still reads F--, then the lens may be at fault.
02-03-2016, 10:31 AM   #12
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Thanks for the feedback everyone! I will try and look at it
02-03-2016, 11:10 AM   #13
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QuoteOriginally posted by microlight Quote
If F-- is showing, then either you haven't got option Custom menu 4, option 22 in the menu system set to 'Permitted', or the lens is not in the A position. The setting for C22 should be 2, or Permitted. If you have this, then the lens is not in the A position. If the aperture ring shows that the A is lined up with the red diamond but the display still reads F--, then the lens may be at fault.
If the lens is on A (and is working), then the aperture permitted setting does not matter. When it is on A, it just like a lens with no aperture ring (except for the manual focus part). "Aperture ring permitted" means it is permitting the shutter to fire IF you take it off A (which should only be done in Manual mode on the body or it won't stop down).
02-03-2016, 11:55 AM   #14
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Yeah, if camera says F--, that means the camera does not know what apertures the lens has. This means it is either a manual lens (no communication with camera) or it is not in A-mode on aperture ring.
Other possibilities include damaged A lens, or maybe its not a Pentax A 50mm f1.7, but an older Pentax M 50mm f1.7 or something. Can you post a photo of the aperture ring on the lens?
02-03-2016, 01:00 PM - 1 Like   #15
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Remove the lens and look at the mount. There should be a round pin or bump that sticks out slightly when the ring is set to "A". It should be flush or slightly recessed below the surface of the mount when taken off the "A" setting. You need to press the small black button in order to move the ring on or off the "A" setting. If the retainer for the spring clip has broken as it often does then sometime the clip can prevent you from setting or moving from the "A" position. You can usually get it to move with some gentle jiggling back and forth.

If the pin does not protrude in the "A" setting then there is a problem. If the pin pops out as it should and you still get only the "F---" then there is probably grease on the pin mechanism so the pin isn't conducting electricity. Try cleaning the pin(s) on the camera and the lens with a soft lint free cloth. A tiny bit of lighter fluid or alcohol on the cloth might help - but be sparing so the fluid doesn't go into the contacts.

Otherwise the lens probably needs to be repaired and cleaned.

See this thread for further information on the retainer problem:

https://www.pentaxforums.com/forums/114-maintenance-repair-articles/88051-pen...ng-repair.html
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