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02-04-2017, 08:22 PM   #1
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Pentax DA* 60-250mm autofocus: an exercise in frustration

SMC Pentax-DA* 60-250mm F4 ED [IF] SDM Reviews - DA Zoom Lenses - Pentax Lens Reviews & Lens Database

After running into problems while using my Pentax DA* 60-250mm lens to shoot a basketball game today, I must say that I'm really disappointed by the way the AF mechanism is designed.

It seems the main source of the issues with this lens' AF is the hybrid screwdrive/SDM system. The Quick-Shift Focus System is supposed to prevent the user from turning the focus ring while AF is in progress; however, it seems that when combined with an in-lens SDM, this mechanism can lock up or cause excessive friction, resulting in sluggish AF performance. In some cases, the lock may fail to disengage properly and lock up the focusing mechanism altogether until the lens is dismounted (suggesting that the screwdrive AF coupler connection is part of the issue).

Be sure to read the updated review for more on this issue. At this point, I really cannot recommend this lens for serious professional use as it's just too unreliable. I've gone through five different units and I just don't feel I can trust it to work properly.

I am replacing it with a D FA* 70-200mm in a few days.

Draco

02-04-2017, 08:46 PM   #2
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QuoteOriginally posted by bwDraco Quote
The Quick-Shift Focus System is supposed to prevent the user from turning the focus ring while AF is in progress; however, it seems that when combined with an in-lens SDM, this mechanism can lock up or cause excessive friction
Is it? I thought that was only on the 150-450mm, with QFS-M. If you otherwise turn the ring while SDM is on, you may break the lens.

Adam
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02-04-2017, 08:55 PM   #3
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QuoteOriginally posted by Adam Quote
Is it? I thought that was only on the 150-450mm, with QFS-M. If you otherwise turn the ring while SDM is on, you may break the lens.
To clarify, the issue is the way the lens is supposed to lock the focus ring while focusing with the screwdrive coupler. On a body without SDM support, the QFS is supposed to lock the focus ring during AF until focusing is complete. However, it seems this mechanism can sometimes lock the focusing mechanism as though it was screwdrive focusing depending on how the AF screw is coupled to the lens (meaning that slight rotation of the lens while it is mounted can cause it to latch up).

It's essentially a flaw in the AF mechanism brought on by the mechanical complexity of having to accommodate both screwdrive and SDM.

Too bad there's no way to disable the SDM and fall back on screwdrive focusing...

Draco

---------- Post added 02-04-17 at 11:02 PM ----------

Now my lens is making a friction noise while focusing when the lens is oriented in certain directions (e.g. rotated 90 degrees clockwise). This is quite clearly a mechanical issue.

---------- Post added 02-04-17 at 11:08 PM ----------

Also note this thread: Burnt smell from 60-250 mount - PentaxForums.com

Last edited by bwDraco; 02-04-2017 at 09:00 PM.
02-04-2017, 10:58 PM - 1 Like   #4
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Odd. Mine hasn't ever behaved this way.

02-05-2017, 03:08 AM - 1 Like   #5
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QuoteOriginally posted by UncleVanya Quote
Odd. Mine hasn't ever behaved this way.
+1

I have used mine heavily for more than 5 years, mainly for sport photography.
This lens is around for more than 7 years, I believe. I don't think I have ever read about such a "design flaw".
02-05-2017, 03:14 AM   #6
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I don't have this lens, but do have others with SDM/screw drive, and have never experienced this problem.

My understanding of the QSFS is that it operates through a clutch, and as such surely it's not intended to lock the focus mechanism?

The OP says he's been through 5 copies of this lens, and has had the problem each time. I've not read any other similar reports, so at the moment the common factor seems to be the OP, or possibly the bodies the lenses have been attached to?
02-05-2017, 05:50 AM - 1 Like   #7
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QuoteOriginally posted by UncleVanya Quote
Odd. Mine hasn't ever behaved this way.
Neither has mine.
02-05-2017, 06:31 AM - 1 Like   #8
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If you have had the same problem with five different copies of the lens, I suggest your issue is with the bodies you are mounting the lens on.

Had this lens for years without issue.

02-05-2017, 08:12 AM   #9
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I feel bad for anyone with this level of bad outcomes. Statistically it seems unlikely, but unlikely isn't impossible.

As for the body or behavior bringing this about, I think that kind of seems to dismiss the problems experienced as isolated. The truth is no user level manipulation should result in this.

I wish deep forensic analysis was available in these cases.
02-05-2017, 01:19 PM   #10
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QuoteOriginally posted by JohnX Quote
I don't have this lens, but do have others with SDM/screw drive, and have never experienced this problem.

My understanding of the QSFS is that it operates through a clutch, and as such surely it's not intended to lock the focus mechanism?

The OP says he's been through 5 copies of this lens, and has had the problem each time. I've not read any other similar reports, so at the moment the common factor seems to be the OP, or possibly the bodies the lenses have been attached to?
Not every time, but three of the five units had similar AF issues, including one case of catastrophic failure. See Pentax DA* 60-250mm - my first impressions - PentaxForums.com.

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02-05-2017, 07:15 PM   #11
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I have never had this issue any of my Star lenses, I have three. None of the DA* lenses are known for speedy autofocus. It is well known that SDM motors are a bit sluggish. I always make sure my hand is not on the focus while using autofocus. Normally my hand is laying flat under the bottom of the lens supporting the hood. If you are using Quick Shift focus your hand better be off the autofocus button. The autofocus ring does not lock while the lens is focusing and you can turn it which would be bad news. i have tried to use my 60-250 for sports a few times but just prefer my Tamron 70-200. It focuses faster, locks focus quicker, and is f2.8. However my Tamron can not reproduce the color rendering of a Pentax Star lens. I wish you better luck with the DFA 70-200. That is one heck of a monster lens.
02-05-2017, 08:39 PM   #12
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I might just have been unlucky with the 60-250. I tend to use mine fairly hard, constantly hitting the AF button for two hours or more as I track fast-moving student-athletes. I suppose the 70-200 should be vastly more reliable; I have not heard even one report of a DC motor failure. (From what I can tell, Pentax is using brushless DC motors in these lenses, which are generally very, very reliable.)

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02-05-2017, 09:00 PM   #13
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This is one of oldest lenses I've had it at least 5 years, and never had a problem. You should maybe sen it in for cleaning etc. and see if they find anything wrong with it.
02-06-2017, 04:57 PM   #14
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It seems I'm not the only one with this issue...

The 60-250 screw drive mystery - PentaxForums.com

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02-12-2017, 04:13 PM   #15
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I seem to be having a similar if not the same problem as the OP with my 60-250 mounted to a K1.

When first mounted after some time off camera, I can't turn the focus ring and the K1 won't operate the SDM. Switching the lens to MF doesn't free the focus ring. When I take the lens off the camera the focus ring will turn freely. Off camera, if I move the focus to infinity and remount, the SDM will slowly step the ring to minimum focus and remain in that state. This is very strange behaviour since the SDM is functioning but only in one direction. After several mount/unmount attempts the focus starts to function, SDM operates normally and the quick shift works. I'm trying to find the secret sauce sequence to get this lens to work without the frustration of continuous mounting and cursing.

Does the camera need focus lock to enable quick shift? And/or does the camera somehow sense a SDM focus problem and for some reason won't release the clutch on the screw drive to manually focus?

Unfortunately I don't have my K7 with me to test it on that.
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