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03-23-2014, 02:08 AM   #1
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HELP!!! Pentax P50+ Tokina SD 70-210mm

I just got my FIRST SLR, the Pentax P50. I'm using a tokina SD 70-210mm 1:4- 5.6 lens... here's the problem: I cant take it out of automatic mode (with the two 'programs' Landscape and sport) unless the lens is completely screwed on (and clicked). When it isn't fully clicked, I can change from Auto, to Manual, 1/100, and bulb, which I guess is the normal thing. I tried twisting the aperture knob off of 'A' and I successfully did, but still nothing changes Is this normal with this lens? I'm worried that if I unscrew the lens by a but, the focus will be thrown off. How do I get to bulb mode (ex.) without removing the lens? I've tried holding the mode button and changing it, and pressing the two buttons, but NOTHING changes, just the program. (I do have film in) Also, how do I turn off exposure compensation? Is the program not changing because I put ML? Thank you so much for help

03-23-2014, 04:55 AM   #2
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I can't answer your questions but if you don't have an owners manual go here and you will find a downloadable at the bottom of the list.
http://www.lensinc.net/freeuser.html

Last edited by Oldbayrunner; 03-23-2014 at 05:09 AM.
03-23-2014, 08:22 AM   #3
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That is normal behavior for all recent "auto aperture" lenses. When the lens is not mounted, you can see the aperture blades move like you would expect. But as soon as you mount the lens, a spring-loaded aperture lever is held open, which is released only for a split-second during the shutter release. This allows you to can see through the viewfinder and focus with the lens-wide open, instead of presenting a dark and useless viewfinder.
03-24-2014, 01:02 PM   #4
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QuoteOriginally posted by Tanzer Quote
That is normal behavior for all recent "auto aperture" lenses. When the lens is not mounted, you can see the aperture blades move like you would expect. But as soon as you mount the lens, a spring-loaded aperture lever is held open, which is released only for a split-second during the shutter release. This allows you to can see through the viewfinder and focus with the lens-wide open, instead of presenting a dark and useless viewfinder.
So like I can only shoot auto mode with this specific lens? I am looking at a 50mm to get. Will I be able to shoot proper pictures even if the lens is ever-so-slightly dismounted? Even when I do remove it a bit, the viewfinder is still fully functional...

03-24-2014, 03:57 PM   #5
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Oh, I have to apologize. I thought you were referring to something else, related to the way the aperture blades appear. Please disregard my earlier comment, and let's start over.

Where you say: "I cant take it out of automatic mode unless the lens is completely screwed on (and clicked)."

I think you really mean: I can't take it out of automatic mode whenever the lens is completely screwed on. Did I understand this right?

I believe A-type lenses (i.e., those with an "A" setting on the aperture ring) electrically ground the A-pin on the mount when in the A position, but should open (unground) the connection when the lens is taken off the A setting. When you don't have the lens fully mounted, the matching pin on the body is not touching anything, so it thinks a non-A lens is attached, giving you the behavior you expect. This leads me to believe the problem is in the lens itself, not the camera body. You could try cleaning the contacts as a matter of course, but I suspect the problem is that the A contact is somehow electrically fused inside the lens.

If I am correct, and the problem is isolated to the lens, then the good news is that you will probably have better luck with a different lens.

There is a mechanical coupler on the lens which tells the body what aperture you are set to, whenever the lens is off of the A position, and set to a specific aperture value. If the lens is not fully mounted, this will throw off your metering, which will cause your exposures to be off. And anyhow a loose lens might fall off the body.

Hopefully someone else has had experience with this kind of problem and can comment.
03-26-2014, 02:56 PM   #6
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Thank you so much, you did understand correctly. I did not quite get what you meant by the process of fooling it to thing it's a non-A lens? Maybe it is the lens... I will try to clean and my friend has a P30 that I could try the 50mm lens (would that work on the p50?) And check if that works! Thanks so much for a great reply!
03-26-2014, 04:02 PM   #7
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Thanks for clarifying.

What I meant about "fooling" the camera: When any lens with electrical contacts is properly mounted, the pins on the lens and the body match up. If you leave the lens partially unscrewed, then the contacts won't line up correctly. You can see pictures of various vintages of the K-mount, and the contacts they supported, here:
https://www.pentaxforums.com/forums/54-pentax-lens-articles/87589-photos-k-m4...-k-mounts.html

I suspect that the problem is in your lens, i.e., the "A" position isn't working correctly - even though you can turn the aperture ring on the lens, the A-pin is still shorted, so the camera thinks you are still in the A position.

I further suspect that when you leave the lens partially mounted, the A pin on the lens and on the body are not in contact. Since there is no electrical contact, the body thinks you are off the A-position (whether you actually are or not), and so the camera allows you to go into manual or Av mode.

I'm not sure if the P30 works exactly the same way, but it probably does. Here is a list of modes on various non-AF bodies:
Pentax Manual Focus Film SLRs - Pentax Pentax Film Cameras - Pentax Camera Reviews and Specifications

Good luck!
03-26-2014, 04:21 PM   #8
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QuoteOriginally posted by Causmatic Quote
I did not quite get what you meant by the process of fooling it to thing it's a non-A lens?
As Tanzer said, there is no reason to "fool" the camera about whether an A-contact lens is mounted. To disable body-controlled aperture simply move the aperture ring off the "A" position. On your camera that should enable Av mode or M mode depending on how your body mode is set. There are two different kinds of "A" contact pins. One has an actual pin that retracts to break the circuit when off the "A" position. The other has an internal electrical switch that does the same thing. For the first kind you should be able to confirm function by visual inspection. The second type requires a continuity tester (ohmmeter).

If the lens tests out fine, there is probably a problem with your P50.

See Dimitrov's excellent resource page for more information:
Features and Operation of the Ka Mount
Also, as noted above, the user manual is your friend. It is available several places, but I usually direct people to the Butkus site. Drop him a few $ via Paypal if you find it useful.
Pentax P5 manual, user manual, free instruction manual, pdf manuals

Steve


Last edited by stevebrot; 03-26-2014 at 04:27 PM.
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