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04-26-2019, 06:39 PM   #1
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Autofocus problem camera or lens

I have a new to me Sigma 24mm 1:1.8 EX DG on a K-3. On autofocus it makes small clicking noises but otherwise doesn't focus. Manual focus works fine.


is there a good way to tell if the problem is the lens or the camera? The lens looks very nice, no obvious wear.

thanks

04-26-2019, 06:49 PM   #2
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do any other lenses exhibit this behavior?
04-26-2019, 06:53 PM   #3
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Follow up, also the focus ring spins freely in autofocus. Is this normal?
04-26-2019, 06:54 PM   #4
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Assuming that other screw-drive AF lenses work on your camera, the problem is most likely with the lens.

IIRC, this lens has a AF/MF clutch (push-pull?) on the lens barrel. Make sure this is in the AF position and the switch on the camera is also in the AF position. It should not say MF in the viewfinder of on the rear LCD. If MF is displayed, try cleaning the contacts on the lens mount and see if that helps.

Pentax Forums user @pepperberry_farm wrote a recent review on this lens and is likely still an owner. With any luck, they will drop in on this thread with advice.


Steve

04-26-2019, 06:58 PM   #5
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QuoteOriginally posted by pepperberry farm Quote
do any other lenses exhibit this behavior?
Speak of the devil and who shall appear


Steve
04-26-2019, 06:59 PM   #6
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I have two other autofocus lenses...one works, one makes the same clicking sounds, although it used to work. (DA 10-17). I had just blamed that on lots of travel. I also have a fisheye that I rarely use autofocus on just because I never feel like it really hits it well, but it works smoothly.

Back of the camera display says AF when in autofocus...and yes it has the push/pull on the barrel.
04-26-2019, 07:01 PM   #7
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QuoteOriginally posted by tmwellington Quote
Follow up, also the focus ring spins freely in autofocus. Is this normal?
Yes, there is an unusual double mechanism for enabling AF on your lens. This video shows how it works and should be helpful...


Note: This is the Canon version of the lens, which has an in-lens focus motor. Apparently the Pentax version has the push-pull clutch, but not the AF/MF switch.


Steve

Last edited by stevebrot; 04-26-2019 at 09:03 PM.
04-26-2019, 07:07 PM   #8
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Sounds like there might be a problem with the camera pushing out its AF drive shaft. This could be due to a broken af/mf switch mechanism.

To verify, take a look at the camera mount and see if the screw is coming out all the way. Also, verify that the lens focuses smoothly when not on the camera.


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04-26-2019, 07:51 PM   #9
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Adam: is this on the camera? How far out would it come? Right now if I have the right piece, it is not even flush with the end of the mount. Should it come out if the camera is turned on?
04-26-2019, 07:51 PM   #10
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QuoteOriginally posted by stevebrot Quote
Assuming that other screw-drive AF lenses work on your camera, the problem is most likely with the lens.

IIRC, this lens has a AF/MF clutch (push-pull?) on the lens barrel. Make sure this is in the AF position and the switch on the camera is also in the AF position. It should not say MF in the viewfinder of on the rear LCD. If MF is displayed, try cleaning the contacts on the lens mount and see if that helps.

Pentax Forums user @pepperberry_farm wrote a recent review on this lens and is likely still an owner. With any luck, they will drop in on this thread with advice.


Steve


I do still own this lens - it's one of my favorites..

it does not have an AF/MF switch, but has a push/pull clutch as described by Steve....

mine does not click at all in AF mode - it makes the typical screwdrive sound, but nothing unusual...

the focus ring spins freely with the lens is in AF mode... as Adam stated, this may be an issue with the focus pawl in the camera body itself...
04-26-2019, 07:52 PM   #11
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The autofocus lens that does work is an HSM lens....that has its own motor, yes?
04-26-2019, 10:06 PM   #12
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QuoteOriginally posted by tmwellington Quote
The autofocus lens that does work is an HSM lens....that has its own motor, yes?
Yes ....
QuoteOriginally posted by Sigma FAQ:
HSM stands for Hyper Sonic Motor. It is a new type of motor used in some of Sigma’s newer lenses. The technology employed is similar to that used in certain lenses made by other camera manufacturers. The benefits of HSM system are: virtually silent autofocus function, very quick responsive autofocus function
FAQs | Sigma Corporation of America
04-26-2019, 10:46 PM   #13
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Just a thought... When you take a lens off the camera you push the lens release button. I once, without thinking, pushed the same button when I attached a lens and the screw drive autofocus did not engage anymore with the same sound you describe. A feeling of dread came over me and I thought the autofocus did not work anymore... It took a while for me to realise I had done something a bit stupid. Sometimes muscle memory can work against you...
04-27-2019, 05:45 PM   #14
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With no lens on the camera body... Make sure the camera switch on the left side of the camera mount is in AF position and you are not pressing the lens release button on the right side. What looks like the tip of a screwdriver should be sticking above the lens mount flange. This is the AF screw drive. If it is not extended but retracted, use a toothpick to reach in and gently push on either side of the 'screwdriver tip' to see if it pops up on its own as there is a spring behind it and it may simply be misaligned in the flange hole. If not, flip the AF/MF switch a couple times and see what happens.

The lens mounting flange is easily removed by removing the obvious screws. However, unless you have missing screws on the flange, this isn't likely to get you any further along because it sounds like the spring behind the AF drive is no longer functioning. The body should go to a qualified camera repair technician.
04-27-2019, 06:55 PM   #15
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Jim,

Thank you!!!!
After some gentle back and forth rocks and flips of the AF switch, it did indeed pop back up!

Learned something new.

I will still, I think, have a shop give it a good cleaning and tuneup. We go to the beach every year, and last year in particular featured a very windy day, so it is possible that some fine grit got in. Heading out in two months for a trip that will include great image possibilities, so the camera should be in top form. It does lead a rough life, travels with me quite a lot.


Thank you to all who replied, everyone had great suggestions which really helped understand the problem. Pepperberry farm, glad to hear the lens is one of your favorites!
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