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06-09-2014, 07:50 PM   #1
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SMC Pentax-M 50mm F1.7 problem

I have an SMC Pentax-M 50mm F1.7 lens that I bought from a Forum member a couple of years ago. It is the only prime or manual lens I have ever used. I can only take a few shots with this lens and then it seems to lock up and I can't focus with it. Turn the ring and nothing happens until I turn the camera off for a second then turn it back on then everything works fine for the next few shots. It has always been like this so I don't know if there is something wrong with the lens or if I'm doing something wrong.

My camera is a K-R and this happens even when I'm using a fully charged battery.

06-09-2014, 08:20 PM   #2
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Hmm, this is confusing, since the camera doesn't have any influence on the lens's focus setting. Is live view freezing up on you or something like that?

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06-09-2014, 08:38 PM   #3
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What do you mean by lock up and can't focus with it? Is the viewfinder black? Does the focus ring refuse to more or move with great effort?
06-09-2014, 08:57 PM   #4
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Do you have AF on or set to manual? At least on my K10D getting focus lock (hex in the viewfinder on) is very twitchy with manual focus lenses. The slightest movement will lose the lock and sometimes I can't get focus lock again unless I move the focus point somewhere else. I just switch the focus to manual if it gets to be a problem. The camera will still beep when focus is achieved but you can fire the shutter without focus lock/confirmation.

06-09-2014, 09:27 PM   #5
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QuoteOriginally posted by Not a Number Quote
Do you have AF on or set to manual? At least on my K10D getting focus lock (hex in the viewfinder on) is very twitchy with manual focus lenses. The slightest movement will lose the lock and sometimes I can't get focus lock again unless I move the focus point somewhere else. I just switch the focus to manual if it gets to be a problem. The camera will still beep when focus is achieved but you can fire the shutter without focus lock/confirmation.
If you're shooting in AF I believe the Custom Menu settings [C] 9 and 10 (p. 309 in the manual) will affect whether or not you can release the shutter. I find sometimes it matters which OOF direction I move from (BF or FF) in getting a good focus confirmation with a MF lens.
06-10-2014, 06:48 PM   #6
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I have my camera set up for Catch-in Focus Mode as on p. 136 with AF Mode set to AF.A. Also have Drive Mode set to Continuous Shooting Low, use Aperture Priority with the camera set to AF. I never use Live View. Although I did read the manual a couple of times when I first got the K-r (my first dSLR) I still refer to it when I need answers, looks like I'm missing something. When it "locks up", turning the focus ring does nothing and what I see in the viewfinder is just unchanging blur and I can't depress the shutter. Turn the camera off and back on and everything works fine for a few more shots of totally different views/subjects and then it locks up again. I just thought there was something wrong with the lens but maybe it's just me not knowing what I'm doing. Does any of the info I just listed tell you anything? I really do love the results I get with the lens but rarely use it since it is just easier to use an auto focus lens. Thanks to all of you for responding to my post and I hope I have given enough info this time for someone to help be solve my dilemma.
06-10-2014, 08:36 PM   #7
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QuoteOriginally posted by sandhilr Quote
I have my camera set up for Catch-in Focus Mode as on p. 136 with AF Mode set to AF.A. Also have Drive Mode set to Continuous Shooting Low, use Aperture Priority with the camera set to AF. I never use Live View. Although I did read the manual a couple of times when I first got the K-r (my first dSLR) I still refer to it when I need answers, looks like I'm missing something. When it "locks up", turning the focus ring does nothing and what I see in the viewfinder is just unchanging blur and I can't depress the shutter. Turn the camera off and back on and everything works fine for a few more shots of totally different views/subjects and then it locks up again. I just thought there was something wrong with the lens but maybe it's just me not knowing what I'm doing. Does any of the info I just listed tell you anything? I really do love the results I get with the lens but rarely use it since it is just easier to use an auto focus lens. Thanks to all of you for responding to my post and I hope I have given enough info this time for someone to help be solve my dilemma.
Your shutter may not be tripping because Catch-in-Focus Mode is not detecting anything in focus. Some things to try:

1. Try setting AF Mode to Manual. If that doesn't help, try...

2. Try setting AF Mode to Manual AND turn Catch-In-Focus Mode to OFF

Also, and I'm asking this only because you say this is your only manual focus lens...are you sure that you are turning the focus ring and not the aperture ring on the lens?
06-10-2014, 09:14 PM   #8
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Thanks for your suggestions, John. I will try both #1 and #2. As far as being sure that I'm turning the focus ring and not the aperture ring? I actually had to go put that lens on my camera just to be sure and, yes, I am turning the focus ring. Tomorrow after work I will go play around with the lens using your suggestions. Thanks a lot for your help.

06-11-2014, 07:19 AM   #9
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I think something with your description is not correct.

The focus setting on this camera/lens combination is fully mechanical, and the light path to your eye is following optical rules and is not in any way influenced by camera settings. The light you'll get through the viewfinder may depend on the aperture setting, but with the correct camera settings this should not happen with a M lens (only green button and shooting should close the aperture to the set value).

If the image in the optical viewfinder REALLY stays blurred all the time even when adjusting distance setting, the only possibility is that the optical light path is not as it should be. No camera setting will influence it. Either the mirror in your camera body is not in its correct position, or the lens is not correctly fixed on the body, or an element inside the lens does not stay where it should.

But I still think something with your description is either wrong or incomplete.

EDIT:
The obvious way to discard some of these possibilities would be to try and exercise to focus with the camera switched OFF!
Focussing manually should NOT depend on whether the camera is switched on or off!
06-11-2014, 11:10 PM   #10
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Is the rubber grip on the focus ring loose? If the focus ring is somewhat stiff, a loose grip might be slipping around the ring. It might feel like the focus ring is turning, but it might just be the grip. I've had an older lens do this before.
12-23-2014, 04:20 AM - 1 Like   #11
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QuoteOriginally posted by Jamfke Quote
Is the rubber grip on the focus ring loose? If the focus ring is somewhat stiff, a loose grip might be slipping around the ring. It might feel like the focus ring is turning, but it might just be the grip. I've had an older lens do this before.
I think the OP experiences problems with the K-r mirror not correctly coming back into place after shooting with a K or M lens. I have the same issue sporadically and it definitely blurs the whole viewfinder image. Taking a few more shots might temporarily solve it (or not). Never happens with a KAF/KAF2 lens. Some other threads here seem to say that using AA batteries can solve the problem but I'm not sure.
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