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03-29-2017, 02:31 AM   #1
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Whats wrong with this lens. 200m FA focus issues.

So after posting the other day, i kinda couldn't hold back, attached the 200mm and went out on the balcony and took a few shots (20+-) just to get accustomed to the camera.
After getting back and playing around with the 45mm, i attached the 200mm with the x2 rear converter-A and used the manual focus for a while, then removed them and it seem to me something might have happened while i played with the rear converter or playing with manual.. The focus function in the lens has gone all topsy turvy. I have attached a video illustrating the problem, but basically, it seems to be be stuck within a very small area of the focus ring.


I find it to be a bit upsetting, i am presuming i must have been doing something wrong and i am not blaming the equipment. There is only one single store in the whole country where they officially carry pentax(no joke) So this will be quiet a hassle to deal with unfortunately


/additional question
Is there any chance that the mechanism which "grabs" on to the focus ring or focus latch has come undone and is not latching into the mechanism correctly when i push it into the AF mode. ?


Last edited by synonyms; 03-29-2017 at 05:02 AM. Reason: extra question
03-29-2017, 02:40 AM   #2
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Do you have the lens cap on or off for your video?
03-29-2017, 02:46 AM   #3
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its off
03-29-2017, 02:53 AM   #4
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QuoteOriginally posted by synonyms Quote
its off
Does the lens do the same thing with the lens cap on?

03-29-2017, 02:57 AM   #5
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Yes, the behaviour with the cap on seems very much like the same.
03-29-2017, 03:05 AM   #6
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That's odd. Because, with the cap on, it should be trying to focus through it's entire focus range.
03-29-2017, 03:50 AM   #7
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would it be completly insane to see if the focus screw was tight by using a piece of plastic to turn it ? I would like to see if its a mecanical issue of some sort. (to me it kinda feel like it)
03-29-2017, 03:53 AM   #8
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QuoteOriginally posted by synonyms Quote
would it be completly insane to see if the focus screw was tight by using a piece of plastic to turn it ? I would like to see if its a mechanical issue of some sort. (to me it kinda feel like it)
I imagine it could not hurt if you did so gently.

03-29-2017, 04:07 AM   #9
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It looks like a mechanical thing, when on manual it runs and just keeps on running, when i put it to AF, it runs for a little while and then becomes so tight i dont want to push it.
03-29-2017, 05:01 PM   #10
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Is it possible the auto/manual focus ring isn't slid all the way up? It looks like it's partially trying to move the focus ring.
Greg
03-29-2017, 05:43 PM   #11
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QuoteOriginally posted by dcshooter Quote
The way the AF engage works in these lenses with the push pull collar is that pulling the ring into autofocus mode pulls an internal ring gear on the focusing helical down onto a spur gear on the end of a shaft connecting to the AF gear train which ultimately leads to a spur in the mount.

Since the manual ring ties directly to the helical and seems to move freely in MF mode, the symptoms displayed here seem to indicate a problem in the gearing of the AF portion of the gear train causing the mechanism to bind at a certain point. This likely points to a chipped/broken/otherwise deformed tooth on one of the gears, although it could be as simple as mount screws loosening causing the gearing to go out of alignment. Don't attempt to force anything that has bound, as it is likely to cause more damage. A local general camera tech should at the very least be able to open it up and diagnose the problem for you, although if you need replacement parts, you will likely have to send it off to a Pentax-certified repair facility.

Here are some illustrations from Pentax-FA 85mm that I repaired recently that was having a similar problem. I was fortunate enough to be able to source a new component to do the replacement (the shop had 3 NOS pieces left from back when Pentax still supplied them to shops). It's KAF mount, but the principles are the same:



This photo shows the entire portion of the AF mechanism that sits just above the lower mount. The silver shaft on the bottom is the screw drive that projects through the base. The bronze gear at the top of the shaft and the adjacent black one are the damaged ones. The silver gear at the top interfaces with a gear shaft whose other end engages/disengages with the ring gear on the helical.

Here's the bronze gear removed. Not pretty:
Nice images. How small is that little gear?
03-29-2017, 09:28 PM   #12
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QuoteOriginally posted by dcshooter Quote
The way the AF engage works in these lenses with the push pull collar is that pulling the ring into autofocus mode pulls an internal ring gear on the focusing helical down onto a spur gear on the end of a shaft connecting to the AF gear train which ultimately leads to a spur in the mount.

Since the manual ring ties directly to the helical and seems to move freely in MF mode, the symptoms displayed here seem to indicate a problem in the gearing of the AF portion of the gear train causing the mechanism to bind at a certain point. This likely points to a chipped/broken/otherwise deformed tooth on one of the gears, although it could be as simple as mount screws loosening causing the gearing to go out of alignment. Don't attempt to force anything that has bound, as it is likely to cause more damage. A local general camera tech should at the very least be able to open it up and diagnose the problem for you, although if you need replacement parts, you will likely have to send it off to a Pentax-certified repair facility.

Here are some illustrations from Pentax-FA 85mm that I repaired recently that was having a similar problem. I was fortunate enough to be able to source a new component to do the replacement (the shop had 3 NOS pieces left from back when Pentax still supplied them to shops). It's KAF mount, but the principles are the same:



This photo shows the entire portion of the AF mechanism that sits just above the lower mount. The silver shaft on the bottom is the screw drive that projects through the base. The bronze gear at the top of the shaft and the adjacent black one are the damaged ones. The silver gear at the top interfaces with a gear shaft whose other end engages/disengages with the ring gear on the helical.

Here's the bronze gear removed. Not pretty:
Thank you shooter for such a nice and descriptive post, Im pretty technical and skilled in quiet a few areas, but i think i might be a to much of a fumble finger to disassemble the thing. (i can just imagen small springs shooting small parts all over the place)
I have done some lens fiddeling but its daunting with this beast.

QuoteOriginally posted by Chapel Quote
Is it possible the auto/manual focus ring isn't slid all the way up? It looks like it's partially trying to move the focus ring.
Greg
I was actually thinking about this yesterday and managed to google pictures of the lens to see if i can spot how high its suppose to go.
The 45 2.8 fa seems to clear the top of the A and F in Auto Focus(the letters writte on the barrowl)
The case with this lens is that it seems to not clear the letters totally and kinda hides some of the top. This could indicate that the two small gears are not joining correctly.
04-04-2017, 07:55 PM   #13
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Looking at the video, have you disengaged the AF, click it into manual, then re-engage the AF, and maybe take the lens off and re-mount it, if the lens isnt quite sitting right it may affect the AF performance
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