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10-28-2022, 02:35 PM   #1
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AF turning off to MF issue

I bought a used K70 and a used 50mm 1.8 recently.

I went to run it today a bit and immediately found that AF (with of course the body set to AF) will turn OFF if you try to autofocus on an object within say, 4 feet or so. Beyond that, if you only AF on objects or a subject further than approx. that distance, it switches to MF mode, regardless that the body is set to AF.

I then cannot get it to go back to AF unless I put it to MF, turn the lens to it's furthest focus point, and then turn the camera to AF again.

Is this an issue with the lens or camera?

The AF/MF button selector works fine it seems (the detent goes up and down). I can rotate the detent that goes in and out a bit too. Not sure if that is normal.

I currently don't have any other Pentax lenses to try or that would be my first idea.

Help!

10-28-2022, 08:47 PM   #2
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It would seem to me most likely a problem with the lens. However, there is no easy way to tell without trying the lens on another body and/or another lens on the K-70.

You could try cleaning the electrical contacts on the camera and lens mount. A lint free cloth or tissue should do the trick. If you use alcohol very sparingly dampen the cloth. Doubtful it will help from the description of the problem but should not hurt unless you go overboard with the alcohol.
10-29-2022, 02:38 AM   #3
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QuoteOriginally posted by nsjohn130 Quote
I bought a used K70 and a used 50mm 1.8 recently.

I went to run it today a bit and immediately found that AF (with of course the body set to AF) will turn OFF if you try to autofocus on an object within say, 4 feet or so. Beyond that, if you only AF on objects or a subject further than approx. that distance, it switches to MF mode, regardless that the body is set to AF.

I then cannot get it to go back to AF unless I put it to MF, turn the lens to it's furthest focus point, and then turn the camera to AF again.

Is this an issue with the lens or camera?
When you say, "it" goes back to MF: Does this mean the switch itself moves? It that would be the (very rare) case, then the K70 would have been opened (probably for solenoid-repair) and the necessary alignement was then forgotten.
But again, this would only count if the AF/MF switch itself would move, which I daubt.

Can you hear any sound (the screwdrive mechanism makes an obvious sound and won't be there if switched to MF)???
If so, does the sound start and then goes off? If so, more likely a lens problem but could be a gear- or AF-Motorproblem.

QuoteOriginally posted by nsjohn130 Quote
The AF/MF button selector works fine it seems (the detent goes up and down). I can rotate the detent that goes in and out a bit too. Not sure if that is normal.
That would have been my first question, if what is called the screwdrive-mechanism pokes out of the hole when in AF-position and retreats when in MF-position.
Don't turn/rotate it because it is a geared mechanism and you can damage it doing so!


But check on your DA50 with an appropriated sized flathead-screwdriver if you can turn that part which would be turned by that mechanism.

The best would be to do a check with another lens of course (no Sigma HSM, Pentax SDM or Pentax with an inbuilt DC-Motor though)
because if then the AF won't work then you got cheated for sure.
10-29-2022, 05:47 AM   #4
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QuoteOriginally posted by photogem Quote
When you say, "it" goes back to MF: Does this mean the switch itself moves? It that would be the (very rare) case, then the K70 would have been opened (probably for solenoid-repair) and the necessary alignement was then forgotten.
But again, this would only count if the AF/MF switch itself would move, which I daubt.

Can you hear any sound (the screwdrive mechanism makes an obvious sound and won't be there if switched to MF)???
If so, does the sound start and then goes off?
If so, more likely a lens problem but could be a gear- or AF-Motorproblem.


That would have been my first question, if what is called the screwdrive-mechanism pokes out of the hole when in AF-position and retreats when in MF-position.
Don't turn/rotate it because it is a geared mechanism and you can damage it doing so!


But check on your DA50 with an appropriated sized flathead-screwdriver if you can turn that part which would be turned by that mechanism.

The best would be to do a check with another lens of course (no Sigma HSM, Pentax SDM or Pentax with an inbuilt DC-Motor though)
because if then the AF won't work then you got cheated for sure.
Hey thank you so much for replying.

The actual button on the body does not switch randomly- just the mode on the camera (think electronic screen). It is like it senses something with targets that are close and thinks the lens is MF. For example, the dog is 10 feet away. I AF on him, shoot a picture. Then, he walks within 3 feet of me, taking up most the frame. I AF on him- and it does AF loudly, but then on the screen the camera says MF and won't AF. Yet(!), the actual button that switches AF/MF has not changed.

Yes the sound (and on the 50 it's loud-ish) of the drive is audible when AF is working. So it's weird, because AF seems to work fine at mild distances and beyond, but once it tries a close object, it AF's, quite hard, and then the camera thinks it's in MF and the lens will not AF. I must manually switch the button to MF, then focus out so to speak, and then I can switch back to AF.

I did turn the little detent mechanism a little to just see if it was loose. From my understanding it is supposed to be in a certain position.

Laslty, if I use a tiny flathead on the lens's slot, what am I looking for?

Thanks!

---------- Post added 10-29-22 at 06:10 AM ----------

Update on the lens screw, I am unsure how easy or not it is supposed to rotate. It does rotate, pretty uniformely. It is hard to tell due to my large hands and this tiny flat head though.


Last edited by nsjohn130; 10-29-2022 at 06:40 AM.
10-29-2022, 06:42 AM - 1 Like   #5
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QuoteOriginally posted by nsjohn130 Quote
Update on the lens screw, there does seem to be some mild grit when turning it at one point. Would this cause the Pentax K70, as a trip, to switch to MF as to preserve the motor?
It is very simple:
When you turn the manual focusring of your DA50, it will make a very soft noice and there should be no real resistance.
At the same time the tiny metal screwdrive-rod will turn quite quickly.


So when you turn the screwdrivemechanism of the lens with a screwdriver, you will feel the focusring of the lens turning same as when you turn it manually. Again there should be zero grit but it should go all the way up and down without really a worrying noice aside the mentioned slight soft noice which remains the same all the way up and down.

If it doesn't turn smooth it can block the AF-motor and even damage it.

It is then as if the motor has to work against a very strong resistance which overheats it.
10-29-2022, 07:13 AM - 1 Like   #6
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With the lens off camera manually set the distance in the range that gives problems. Turn the focus drive shaft with scredriver. Repeat with lens set at range where it works. Compare how the action feels when turning the shaft. If it is different then there is your problem.
10-29-2022, 07:32 AM   #7
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Thanks for all your replies I will be receiving a new lens (One day Amazon, same 50mm 1.8 because it's cheap and quick, but if the body is good I will be buying the 70mm 2.4) tomorrow and I will update with function.

10-30-2022, 07:09 AM   #8
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Great, let us know how it turns out.
10-30-2022, 01:35 PM - 1 Like   #9
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Attention Pentax friends:

It was the lens.

New 50 came, new 50 worked as close as I wanted to AF!

Cheers!
10-30-2022, 04:13 PM   #10
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What I don't quite understand because only know did I read a few of your earlier posts:
You have a K1, a DA35 and a FA77. So why didn't you check with those lenses, all screwdrive?
Wouldn't that be the most obvious to do?
10-30-2022, 04:32 PM - 1 Like   #11
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QuoteOriginally posted by photogem Quote
What I don't quite understand because only know did I read a few of your earlier posts:
You have a K1, a DA35 and a FA77. So why didn't you check with those lenses, all screwdrive?
Wouldn't that be the most obvious to do?
Well firstly, you pointed out something to me that I have not noticed in the past two days.

This is an inactive account. I had not logged in in...perhaps four years? Maybe less.

In 2020 I had to sell my K-1, 35mm, 77mm, Tamron 90mm macro, etc...I have been camera-less since

But, I allowed myself to get a used K70 and looks like I now need to update my profile. We'll see how active I can stay on here with my new setup! Thanks for pointing it out
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