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03-02-2011, 08:05 AM   #1
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Dead AF?

My K100D suddenly won't recognize my FA 100-300 as an auto focus lens. It's fine with the kit DA's and it does let me use the FA in manual mode. Is this the camera's way of telling me the FA AF motor is dead? Thanks for any opinions.
Brett

03-02-2011, 08:11 AM   #2
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My K-5 does that with a Sigma 18-200 occasionally. I just turn it off and then it recognizes it. Clean the contacts of the lens and camera. They may have some obstruction...
03-02-2011, 08:51 AM   #3
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Cleaned contacts on both lens and camera. Nothing changed but thank you for the idea.
Brett
03-02-2011, 08:59 AM   #4
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Put the lens on the camera, set the camera for AF, hold the lens lock release (the button you press to remove the lens) while holding down the shutter button. Does the camera AF motor activate Then? Remove the lens from the camera and see if you can turn the AF screw on the Lens manually.



03-02-2011, 10:17 AM - 1 Like   #5
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QuoteOriginally posted by afvn72 Quote
My K100D suddenly won't recognize my FA 100-300 as an auto focus lens. It's fine with the kit DA's and it does let me use the FA in manual mode. Is this the camera's way of telling me the FA AF motor is dead? Thanks for any opinions.
Brett
Brett

except for the latest pentax lenses supporting the SDM technology, no other pentax lens has an in lens focusing motor.

Focusing for all F, FA FA-J, DFA, and many DA lenses si done via a screw drive that engages with a coupling on the lens. the drive needs to allign itself correctly with the mating coupling on the lens, and normally this is not a problem but can occasionally not engage.

when you say it does not recognize the lens as an AF lens, exactly what does it do?

Does it try to focus? Do you get focus confirmation?, Does the aperture show F--?, DOes it prompt for focal length at staret up?


speccifically can you tell us exactly how you know it is not recognizing the lens, based upon the feedback you get from the camera.

The reason I ask, is that depending on the responses where to start looking for a solution differs, but the problem is most certainly with the lens.


Take the lens off the back of the camera and look at the mount. Orient the lens locking slot at 12:00.

The aperature activating lever should be at about 11:58 i.e. just to the left of top.

Once you are oriented correctly, look at the 4:00 position. this is the focus drive coupling. Turn the focusing collar, and this shoud also spin does it? If so, the AF linkage is free and OK.

You may wish to try turning the lens focusing collar while the camera body is set to AF. if it takes more pressure than turning the focusing collar with the lens dismounted, then the AF linkage is at least engaged at the camera.

Now depending on the symptoms you list, you need to consider either a failed or dirty pin in the base of the lens.

All AF data and focal length information is fed through the last contact pin when moving clockwise. this pin is at about 1:30 position, but is the 7th position away from the first pin in the mount. If the aperture is reporting but AF is not working this may be the only problem, clean this pin.

If neither aperture or AF is working it may also be just this pin, or the 3rd pin from the lens locking slot as this enables the Auto Aperture. This pin should be a very low resistance to lens mount when in the A position, and open circuit when not in the A position.

Feedback please and good luck
03-02-2011, 05:21 PM   #6
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Jeff, Lowell,
Thank you very much for your assistance.
Jeff, when I do the button pushes you suggested, nothing activates. I'm not sure what you mean about turning the AF screw manually.
Lowell, no matter what mode the camera is in at turn on, I get the Shake Reduction focal length screen. The camera then says I'm in aperture priority mode no matter what mode I switch to, except it will recognize manual and bulb modes. The MF indicator in the viewfinder is active even though the camera is set to AF. The F stop is not reading, stop down metering works. The focus drive coupling does spin when I turn the focus collar. Turning the focusing collar with the camera set to AF does meet more resistance than turning it when off the camera and generates the noise associated with focusing. The lens works fine in manual mode. Earlier I gave the lens contacts a Q-Tip rub with Deoxit D5. Didn't have any effect. Should I try the WD40 and sandpaper? Brett
03-02-2011, 06:44 PM   #7
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Jeff

If it prompts for focal length then clearly there is loss of connection of the data pin or perhaps a total loss of connection from the lensount to the internal circuit

If the data pin functioned properly then you would not get the focal length prompt

That would be my guess so hold offmon sandpaper and chemicals. It probably needs someone who knows the lens to remove the mount to look for a bad connection
03-02-2011, 07:31 PM   #8
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QuoteOriginally posted by afvn72 Quote
Jeff, Lowell,
Thank you very much for your assistance.
Jeff, when I do the button pushes you suggested, nothing activates. I'm not sure what you mean about turning the AF screw manually.
Lowell, no matter what mode the camera is in at turn on, I get the Shake Reduction focal length screen. The camera then says I'm in aperture priority mode no matter what mode I switch to, except it will recognize manual and bulb modes. The MF indicator in the viewfinder is active even though the camera is set to AF. The F stop is not reading, stop down metering works. The focus drive coupling does spin when I turn the focus collar. Turning the focusing collar with the camera set to AF does meet more resistance than turning it when off the camera and generates the noise associated with focusing. The lens works fine in manual mode. Earlier I gave the lens contacts a Q-Tip rub with Deoxit D5. Didn't have any effect. Should I try the WD40 and sandpaper? Brett
QuoteOriginally posted by Lowell Goudge Quote
Jeff

If it prompts for focal length then clearly there is loss of connection of the data pin or perhaps a total loss of connection from the lensount to the internal circuit

If the data pin functioned properly then you would not get the focal length prompt

That would be my guess so hold offmon sandpaper and chemicals. It probably needs someone who knows the lens to remove the mount to look for a bad connection
Lowell, Brett didn't say anything about being prompted for a focal length in the original post, only that it wouldn't autofocus and that he could use the lens manually (unless I read him wrong).

Brett, the AF screw I refer to is the one on the lens that the camera turns to focus the lens. However, if when you push the lens release button on the camera (With the lens mounted), press the shutter release as you would to focus, And nothing happens, then Lowell is probably correct. The lens isn't making electrical contact with the camera. You also stated that the lens Quit working. Suggests to me, something internal. No amount of scrubbing the external contacts is going to change that. Unless it was intermittent before, I doubt a dirty contact is your problem. It Could be that one of the contacts is pushed in slightly and not making contact at all.


And no, I would never use WD40 on a lens.



03-02-2011, 07:38 PM   #9
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Again thank you both very much. I'll probably just continue to use the lens manually and see if I can find another working version. And I was kidding about the WD40 and sandpaper
03-02-2011, 08:01 PM   #10
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Dumb question, but do you have the aperture ring off of "A"?
03-02-2011, 09:54 PM   #11
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QuoteOriginally posted by Wheatfield Quote
Dumb question, but do you have the aperture ring off of "A"?
Not so dumb. I have done that more than once!
03-02-2011, 10:12 PM   #12
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that problem cause by the lens/body contact..

if lens with electronic contact mount on body, the camera would not prompt to set up focal length even the aperture ring is other than A position..

clean the contact..i think your cleaning method is not good enough to clean the contact..try use anti fog cleaner on the contact..it is working well with electronic contact..
03-03-2011, 08:25 AM   #13
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Certainly not a dumb question but in this instance I did remember to check it. As it happens, one of my few nit picks with this lens is that I've never felt the lock into the "A" position is as definite as it should be.

V3to I used Deoxit D5, the best electronic contact cleaner I know of. I'm not familiar with anti-fog cleaner. What is it? Thanks.
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