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11-27-2010, 10:58 AM   #1
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Stiff regions on distance/focus ring.

Some time ago i purchased F50/1.7 lens here on forums. At first i thought that it was just my old F50 that was worn out, and new one is as it should be.
After having used it for some time there are some things that still worry me.

First of all, the focus ring movement has frictional stiffness.

None of my other lenses (except a rusted/oxidized m39 manual lens) has such feel of stiffness. I've had heavy lenses - that seem to have some inertial resistance, but not frictional one.

Secondly, it is uneven. The ring rotates quite well at some parts, but gets noticeably stiffer around 1 meter and beyond (~0.8..5m). When AF'ing i can even hear a lowering of pitch in AF motor sound, as it is getting additional load.

I'm not sure if it's related, but i've also observed minor AF errors in the far range (5..50m). E.g. 2/3 shots are random miss. Just refocus and one might be correct.
Sometimes i think the camera has trouble fine tuning AF.

How uneven the focus ring movement can be?
If it has to be even, where/how can i fix this? Do Pentax service such old lenses and is the charge reasonable (e.g. not = price of some new prime lens)
Is it safe for my camera? Can it burn the AF motor?


P.S. The filter thread on the lens was cracked, but i've heard it's easy to break it for this particular lens, so i don't suspect the lens being mistreated in past.
Previous owner reported flawless operation on his higher end body (i think it was k20), which are known to have stronger AF motors.

11-27-2010, 04:49 PM   #2
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Aw come-on, 85 views and not even a single opinion?
11-27-2010, 06:46 PM   #3
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If the filter ring is broken, the lens has been impacted and given the symptoms, the focus helicoid is damaged.
11-27-2010, 06:55 PM   #4
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I had this happen with a Minolta 55mm f/1.7 a while back, I had to pull the thing apart and it turned out that the heliciod didn't have enough lubrication on the lower half, which caused a distinct stiffening of movement at the 0.8m>0.55m range. Light machine oil is a good temporary solution to the problem.

11-27-2010, 07:03 PM   #5
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Since dropping my DA 12-24mm onto a concrete sidewalk,
the zoom ring now has a slight stiffness at a certain position.
(luckily the brick wall photo test shows no focus/alignment issues)

Hopefully not on concrete like mine, your lens had perhaps suffered an impact in it's previous life.

Michel
11-28-2010, 03:59 AM   #6
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QuoteOriginally posted by Wheatfield Quote
If the filter ring is broken, the lens has been impacted and given the symptoms, the focus helicoid is damaged.
I was afraid that something like that might be the problem. Are there people out there that fix those kind of issues? As i understand Eric does only mechanical/film and camera stuff.
I don't have clean enough space and tools to do this on my own.

Btw.The stiffness also seems to change depending on the orientation of the lens and direction i turn the focus ring.
It gets worse when the lens is oriented as mounted on camera in landscape position and going from far to close distances.

If anyone's interested i made a small demo:
As you see, when AF'ing the sound changes but other than that nothing bad seems to happen. The camera does however fine tune longer and more "harder" than with my kit lens.

Last edited by ytterbium; 11-28-2010 at 04:50 AM.
11-28-2010, 05:19 AM   #7
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Cracked filter rim + uneven stiffness of the focus ring = impact damage. Get a refund while you still can. I doubt Pentax still kept the parts for this lens. Good luck.
11-28-2010, 11:06 AM   #8
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Nah. I bought this some time ago, and now it would be too late to bother the seller. I just have to learn that it's a NONO for used stuff. I've burned too many times already. And they always seems to be honest, easy to contact people. Maybe they just don't know of the problem, same way i fail to judge it objectively during the first testing days.

I suppose then the only options is to use this lens as is until it falls apart. I Just hope my camera wont get hurt.


Last edited by ytterbium; 11-28-2010 at 11:47 AM.
11-28-2010, 07:27 PM   #9
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It's possible it may be repairable without parts replacement. I'd send it to a lens specialist to see if it's fixable.
I would be be concerned with it straining the AF motor to the point of early failure.
04-17-2011, 09:34 AM   #10
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P.S. Do any of you get ridiculously long AF times with this lens as well?

Outdoors it's more or less usable. But indoors under a single 60..100w incandescent bulb, i often get AF times up to few seconds (if the subject is static, and has enough contrast).

Is it because of the k200d, or the lens? How much better are new cameras (K-7, K-r)?
Or replacing the lens to something more up to date (DA35/2.4?) would be enough. Or else i'm unable to use the DSLR for what it was originally purchased.

That is intriguing because in the full throw test, the actual speed of movement is fast.

Last edited by ytterbium; 04-17-2011 at 09:40 AM.
08-16-2011, 10:07 AM   #11
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More on the AF times. Just fooled around a little, and found that lens resistance/AF motor strength has a MAJOR effect on AF speed. Especially while fine tuning, after the initial throw.

It might sound bad to do so (and i highly discourage everyone to try this themselves), but since i'm already quite disappointed by the lens and k200d in general, i did some basic testing. Just to see what exactly makes it so annoying.

At first i went to see what the camera does if i hold the focussing ring still while performing AF. It clicks (like reaching AF scale end) and stops focussing with blinking hexagon. This made me think if the camera even detects AF scale end or just smashes into it every time.

Then applied some force, so that the camera could move the AF ring, but with increased resistance. In situations where it would be snap to focus, it took a lot more correction steps to get the lens in position.

Now i must reconsider my thoughts about screw drive AF and AF speed relation to camera processing time. Maybe when i find it slow it just has some trouble getting the lens in position, because of loose and long feedback chain (many mechanics) as well as driving efficiency.

QuoteQuote:
It's possible it may be repairable without parts replacement. I'd send it to a lens specialist to see if it's fixable.
I would be be concerned with it straining the AF motor to the point of early failure.
Who does that? I don't have anything like that nearby. Where could i send the lens?
08-16-2011, 12:52 PM   #12
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I purchased my DA21 from someone here. The focus ring was so stiff at close distances that the camera could not move it.

I went to a local repair shop, they charged me for disassembly and inspection, and told me that some tumblers inside the lens were misaligned and were causing the resistance. The lens has worked flawlessly since it got repaired.

Your lens possibly suffers from the same kind of problem.
09-08-2011, 10:49 AM   #13
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Well, 60$ and the lens is back on track. Someone has dropped it before. The repairman said it was offset for as much as 1mm. AF is better as well. Locks after 2...3 fine tunes instead of 6..8 or more.

P.S. Now i'm certain. I must NEVER, EVER buy used camera equipment again, unless its price (and expectations - e.g. MF) are already on the "faulty" level.

Last edited by ytterbium; 09-08-2011 at 11:09 AM.
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