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11-20-2011, 04:26 PM   #1
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Problem adjusting f-stop on 50mm prime

I recently bought the Pentax SMCP-FA 50mm f/1.4 lens to use on my K200D.

Unfortunately I cannot work out how to adjust the f-stop on the lens. It seems to only work on the 'A' setting. If I try to manually set the f-stop, the display window on the camera flashes "f--" and it won't take pictures. I've tried using every setting on the camera in combination with different f-stops, but nothing works.

I'm sure there's a really obvious solution but I can't work it out; my apologies for being such a newbie! If there are any kind of useful instructions you can point me towards, please let me know.

Cheers

11-20-2011, 04:58 PM   #2
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Leave the lens aperture ring on "A" for auto, put the camera in "Av" mode, and then you can adjust the aperture with the e-dial on the camera.

Unfortunately all PEntax DSLR's have what's known as a "Crippled K-mount" which means the camera can't tell the aperture from the lens when you use the aperture ring to set it. Yes it is ridiculous that Pentax did this, but they figure like most other manufacturers that aperture rings are obsolete. Like I said, the remedy is just leave the lens in "A".
11-20-2011, 05:39 PM   #3
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In order to take photos with the lens in the non-A postition, you need to go into the custom menu on the camera and set the "using aperture ring" to "permitted".

Then, you need to put the camera in "M" mode - manually set the aperture to whatever you want, use the wheel on the camera to set the shutter speed you want and fire away!!

You'll also be able to take photos in the other (not M) settings, such as Av, but the camera will not stop down the lens - you'll always be using the wide open setting (in this case, f1.4).
11-20-2011, 06:15 PM   #4
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Why would you want to control aperture from the lens when it is far, far more accurate exposure wise when the aperture is controlled by the camera at the A setting. At the A setting, you can use every exposure mode offered by the camera and you get more precise aperture control. Read your camera operating manual.

11-20-2011, 07:04 PM   #5
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Why not use the lens as a "learning tool"? In the event the op gets a fully manual lens, he'll already know how to use it. I give him points for wanting to learn!
11-21-2011, 06:47 AM   #6
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Thanks so much for your help, I really appreciate it! Interesting that there is more than one solution ("read the manual" is one I've already done, ta).

Why make a lens that is only adjustable when it's not actually attached to the camera? *shrug*
11-21-2011, 09:52 AM   #7
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All cameras with open-aperture metering are like that (fortunately), but the main difference here is that Pentax DSLRs can't sense the aperture setting if the aperture ring isn't in the A position.

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

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11-21-2011, 09:53 AM   #8
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QuoteOriginally posted by Unregistered Quote
Why make a lens that is only adjustable when it's not actually attached to the camera? *shrug*
That shouldn't be. If the camera doesn't have Aperture Ring Permitted set, then for any non-A aperture setting, the camera will show F-- and the lens will work wide-open (and maybe stopping-down in M mode with Green button use). If it is set to Permitted, then the camera should know what aperture is set... unless the contacts need cleaning.

EDIT: Oh, you're talking about DA-type lenses. Duh, I missed that. Yeah, loss of the aperture ring sucks. Complain to the bean-counters.


Last edited by RioRico; 11-22-2011 at 12:32 AM.
11-21-2011, 10:21 PM   #9
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QuoteOriginally posted by Unregistered Quote
Why make a lens that is only adjustable when it's not actually attached to the camera?
This lens was designd long before your camera. The cameras that were around when the lens was designed worked differently. Some of them not control the aperture from the body, so lenses had to have aperture rings. But it's been a very long time since Pentax made a camera that cannot control the aperture from the body, So most modern lenses skip the aperture ring as it is irrelevant to any camera made this milenium.
11-21-2011, 10:27 PM   #10
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QuoteOriginally posted by Marc Sabatella Quote
But it's been a very long time since Pentax made a camera that cannot control the aperture from the body
the MZ-S was only discontinued in 2006
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