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03-27-2015, 04:07 PM   #1
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Do pentax lenses (or 3rd party for Penatx) have higher defect rate?

Well, this is a bit disappointing. After trying a few lenses with little success (except for just one new DA 35mm f2.4 from Adorama,) I ordered a fresh new 50mm 1.8 from B&H after reading such great reviews. To my dismay, this one also looks like a lemon.. I'm losing confidence in buying lenses now.. especially used ones due to the defective rate that I've experienced. Am I just out of luck with Pentax lenses? I've never had this problem with Canon including 3rd party lenses. Maybe just a luck, but it's pretty weird. OK, here's my quick history from this January when I switched from Canon T2i to Pentax K-3 with DA 35mm.

I ordered a used Sigma 17-50 on eBay and it turned out to have bad focusing in some focal lengths, especially near 35mm, so I had to return it. Next, I ordered a 40mm Limited here in the forum, and found the lens was decentered so I had to return it. Next I purchased an FA 50mm f1.7 on eBay and found it front focuses on distant subject while focusing right on close subject or vice versa, so I had to return it. And NOW, having been tired of being disappointed by used lens, I ordered a fresh new 50mm mentioned, and this one suffers from focusing and even -10 adjustment, it front focuses! It hunts and hunts for auto-focus and sometimes even can't focus.

Now I have to return this one again. Would my camera be a culprit? But it produces lazor-sharp images with DA 35mm with +3 fine adjustment. Also, it worked well with Sigma 17-50 except for 35mm range, so I doubt it. I really wish I could settle with this 50mm but now I have to return it again. My wife thinks I'm getting crazy-buy and return, buy and return.. Does anyone have an experience like me? i'm kinda losing confidence in buying lenses..

03-27-2015, 04:27 PM   #2
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Not saying you aren't correct about the 50 being defective but you say it hunts and hunts. That's a different issue than front or back focusing. I have a k50 and my 50/1.8 hunts quite a bit (depending in the subject) even in daylight. Granted I only use center point focussing but half the time I just use manual focus. It's much faster and I can actually focus on my intended point. Matter of fact, even when I do use AF on my 50, it's hit or miss. Again, depending on my subject.
03-27-2015, 04:27 PM   #3
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I never heard of such a problem. Maybe there is something wrong with you camera. Seems like way too many faulty lenses to be the problem.
03-27-2015, 04:37 PM   #4
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Agree with rimfire. While my 50 does hunt, I've not had any problems with any of the lenses I've owned over the past year. And two of my lenses are 40 years old.

03-27-2015, 04:50 PM   #5
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QuoteOriginally posted by Rimfiredude Quote
I never heard of such a problem. Maybe there is something wrong with you camera. Seems like way too many faulty lenses to be the problem.
Thanks for your comment. Well, if the camera is wrong, how come it works pretty well with DA 35mm? Would it be possible that it works very well with one lens and not well with most others? Should I send it to a service center? So at least slow auto-focusing of DA 50mm (or even some focus failing) is something typical, right?
03-27-2015, 04:55 PM   #6
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I assume that you tried your lenses in ideal conditions for the AF: outdoor with good light, like in your garden? What were your AF settings? AF hunting may occur indoor in moderately low lights.

As suggested by rimfiredude, you want to eliminate the camera as a source of pb. LIke others I never had any AF issue with my lenses.But I know that my K-7 and K-01 do not AF well indoor in poor lights, evidenced by a lot of hunting and poor focusing.

My 5 cents....
03-27-2015, 05:05 PM - 1 Like   #7
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QuoteOriginally posted by ychousa Quote
It hunts and hunts for auto-focus and sometimes even can't focus.
My DA 50/1.8 focuses fast and sure on my K-3. I would point to your -10 focus adjust as being the probable cause of both your hunting and the failure to acquire focus. Despite the prevailing wisdom on this site, most lenses require very little, if any, focus adjustment. Unfortunately people will fiddle even when they are getting good results. The problem, particularly with faster lenses, is the inherent imprecision of the system. Even with a proper adjustment and using the f/2.8 center focus point, fully 4 out of 10 focus attempts at f/1.8 will show measurable deviation from the expected and the direction of deviation will vary depending on whether you are focusing up or focusing down.

Undo the -10 adjustment and see if your problem with hunting and focus acquisition disappears.

Edit: Just a quick additional note...A couple of AF nudges prior to lock is not "hunting". Pentax cameras will often double check before lock. Your previous camera (Canon T2i) omits the final confirmation with a resulting higher rate of missed focus. At least that is how it was explained to me by my repair guy, an avid Canon user and dealer.


Steve

Last edited by stevebrot; 03-27-2015 at 05:25 PM.
03-27-2015, 05:05 PM   #8
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QuoteOriginally posted by ychousa Quote
Well, if the camera is wrong, how come it works pretty well with DA 35mm?
Slower maximum aperture.

Let me guess...am I correct that you new DA 35/2.4 did not require any focus adjust?


Steve


Last edited by stevebrot; 03-27-2015 at 05:26 PM.
03-27-2015, 05:07 PM   #9
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QuoteOriginally posted by hcc Quote
What were your AF settings? AF hunting may occur indoor in moderately low lights
My AF settings are: Single shot/center focused. This DA 50mm has the worst auto-focus that I've ever had. Not sure if this is something acceptable or if this is a defective lens, aside from front-focus issue even with -10 adjustment.

---------- Post added 03-27-15 at 05:13 PM ----------

QuoteOriginally posted by stevebrot Quote
My DA 50/1.8 focuses fast and sure on my K-3. I would point to your -10 focus adjust as being the cause of both your hunting and the failure to acquire focus. Despite the prevailing wisdom on this site, most lenses don't require very little, if any, focus adjustment. The problem, particularly with faster lenses, is the inherent imprecision of the system. Even with a proper adjustment and using the f/2.8 center focus point, fully 4 out of 10 focus attempts at f/1.8 will show measurable deviation from the expected and the direction of deviation will vary depending on whether you are focusing up or focusing down.

Undo the -10 adjustment and see if your problem with hunting and focus acquisition disappears.


Steve

Understood, Steve, but if I adjust it to 0, then it badly front-focuses on a distant subject at f1.8, and the subject that I focused is out of focus. That is why I ended up with -10 after trying decremental numbers.

Last edited by ychousa; 03-27-2015 at 05:15 PM.
03-27-2015, 05:14 PM   #10
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A couple of the lens/problems should have been noticed and disclosed by the seller.
03-27-2015, 05:18 PM   #11
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QuoteOriginally posted by SpecialK Quote
A couple of the lens/problems should have been noticed and disclosed by the seller.
Yes, but the sellers happened to use their other lenses mainly and apparently weren't aware of the problems, I guess. Fortunately, they were nice people and accepted return.
03-27-2015, 05:19 PM   #12
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I've never had a problem. 7 Pentax lenses. Had a sigma 70-300 once for a different mount - sucked so bad I didn't want it around to use even as a paper weight.
03-27-2015, 05:34 PM   #13
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Kinda sounds like your camera is just grossly miscalibrated (or the AF sensor is dirty?). See if you can find another Pentax to borrow and try your 50 on it -- I bet it works fine. Or send camera AND lens in for service and tell them to check everything and recalibrate the AF system...
03-27-2015, 05:42 PM   #14
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QuoteOriginally posted by vonBaloney Quote
Kinda sounds like your camera is just grossly miscalibrated (or the AF sensor is dirty?). See if you can find another Pentax to borrow and try your 50 on it -- I bet it works fine. Or send camera AND lens in for service and tell them to check everything and recalibrate the AF system...

Yeh, I guess I probably have to do it if this is something very unusual. In this kind of case, do the lens and camera should be all new and under warranty? or just the camera is under warranty and I can include any old lens? Do you know by chance?
03-27-2015, 05:47 PM   #15
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QuoteOriginally posted by Eagle94VT Quote
I've never had a problem. 7 Pentax lenses. Had a sigma 70-300 once for a different mount - sucked so bad I didn't want it around to use even as a paper weight.
I had, notice I said "I had" a 70-300 Sigma also with the same problem besides being very soft at 300.
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