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12-10-2012, 09:56 AM   #1
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New 50-135 mm, is +10 AF correction a sign of bad copy?

Hello All,

Long time lurker here, finally with a question to which I couldn't find an answer after TONS of searching on this and other forums. This forum has been extremely helpful and most times if I dig around a little I can find answers to all my questions. Thank you all for sharing your expertise!

First, I've rekindled my interest in photography with a K5 purchase almost a year ago and have to say I really love this camera! Second, starting with the 18-55 kit lens, then adding the 35 2.4 plastic wonder, I bit the bullet and took advantage of the Black Friday pricing of the DA* 50-135 mm, my first "real" piece of glass some might say. After the rave reviews across the board how could I go wrong? Well, instead of initially being blown away as so many were, I was initially disappointed. I'll cut to the chase here and say that I seemed to have lost the ability to take a picture in focus! Long story short, I read about front/back focusing issues, printed the test chart kindly provided by Yvon Bourque at pentaxdslrs.com and did my best to be precise in the setup and testing. With an AF fine tuning adjustment of +10 it now seems to be focusing properly, though by my reckoning, it could have used up to a +12 correction (though I couldn't swear my camera was set at exactly 45 degrees).

My question is, if a lens needs the maximum adjustment possible in-camera (+10), could it be a "bad copy"?
In other words, if I can still exchange this at B&H would you recommend it? My hesitation is fearing the next copy may be the same or worse. This lens calibration is a new world to me, so is all of this normal?

I learned so much these past couple of weeks in trying to troubleshoot this, by the way, and if it's helpful to others:

I learned more about how the Pentax autofocus system works and how to better deal with it's limitations in low light and in tracking movement (eg., fasting running dogs), and that the size of the focus points matters.
I learned that just because a lens is "fast" doesn't mean it can either focus quickly, or track a moving object quickly.
I learned not to judge a lens out of the box in a low light situation, or indoors.
I learned that a fast telephoto takes some getting used to in terms of dealing with that beautiful narrow depth-of-field.
I learned that pixel-peeping on a large (27" imac) monitor can drive a person to madness.

Thanks for any input!

Pam

12-10-2012, 11:08 AM   #2
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Could be the case that you have a camera body and a lens at opposite ends of the manufacturing tolerance, so not a 'bad copy' per se, but is bad for you.

If you can take it back, why not? Ideally go in person with your camera and try the replacement lens on it and make sure it's ok before you leave the store.

OR, send both camera and lens off to Pentax and get them to sort it under warranty (it's a mechanical adjustment to the AF so no big deal for them).

On a releted note, I'm intrigued how/why you think +12 would be the optimum correction? I've got/used Yvon's test chart and thought it simply was a measurement tool that didn't translate into actually letting you compute correction?
12-10-2012, 11:46 AM   #3
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I bought a 50-135 f2.8 from B&HPhoto where the copy had to be +9 to be correctly in focus, no problems with it other than that. I still have this copy and plan on keeping it until it withers away alongside with my K-5 and other lens'. If it's a +10 and you plan on keeping it, make sure it isn't backfocusing any further than +10 and take rigorous amounts of testing and a few real non-test photos to insure that.
12-10-2012, 11:53 AM   #4
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I have a K-x and K20D. I test all my lenses when I receive them. I don't tolerate any variation, if the lens needs correction, I send it back. If I want another copy, I send it to the seller, If I want to keep the same lens, I send it to Pentax for calibration, along with a body.

The K-x cannot correct out-of-focus lenses, the K20D does. Even if I didn't have the K-x, I would have my lenses corrected while I have warranty. If you try to resell the lens, it could become a problem.

12-10-2012, 02:51 PM   #5
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QuoteOriginally posted by JohnX Quote
Could be the case that you have a camera body and a lens at opposite ends of the manufacturing tolerance, so not a 'bad copy' per se, but is bad for you.

If you can take it back, why not? Ideally go in person with your camera and try the replacement lens on it and make sure it's ok before you leave the store.

OR, send both camera and lens off to Pentax and get them to sort it under warranty (it's a mechanical adjustment to the AF so no big deal for them).

On a releted note, I'm intrigued how/why you think +12 would be the optimum correction? I've got/used Yvon's test chart and thought it simply was a measurement tool that didn't translate into actually letting you compute correction?
JohnX,

Thanks for your suggestions about the body/lens fit. I would LOVE to walk in to a store and discuss this with sombody, but have found nary a Pentax DSLR in sight in any store in Chicagoland (if anybody know of one, please advise). As for why I used Yvon's "Autofocus Adjustment Chart" (PENTAX DSLRs: PART-1. Autofocus Adjustment charts for front and back focusing problems. Good for Pentax, Canon and Nikon.), I followed those directions assuming that is what it was designed to help with. Using his chart, the line at zero (0mm) should be sharp, but when I tested, the line at 8mm was sharpest. With adjustment it was better, but still sharpest at 2mm. I simply don't have confidence my setup was spot on, but I will retest and try to post an example.

Thanks again,
Pam
12-10-2012, 03:09 PM   #6
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QuoteOriginally posted by LeDave Quote
I bought a 50-135 f2.8 from B&HPhoto where the copy had to be +9 to be correctly in focus, no problems with it other than that. I still have this copy and plan on keeping it until it withers away alongside with my K-5 and other lens'. If it's a +10 and you plan on keeping it, make sure it isn't backfocusing any further than +10 and take rigorous amounts of testing and a few real non-test photos to insure that.
LeDave,

Thanks for your reply. I had specifically read your post about the 50-135 and your experience in trying to make the AF corrections. You helped clarify some things as I attempted mine. I'm pleased to hear you're now happy with it at +9 (it was a +10, yes?) and all is well. I'm also waiting for some decent light. Heavy cloud cover on December days are making the real world testing a bit challenging.

Enjoying your other informative posts as well!
Pam
12-10-2012, 03:23 PM   #7
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QuoteOriginally posted by audiobomber Quote
I have a K-x and K20D. I test all my lenses when I receive them. I don't tolerate any variation, if the lens needs correction, I send it back. If I want another copy, I send it to the seller, If I want to keep the same lens, I send it to Pentax for calibration, along with a body.

The K-x cannot correct out-of-focus lenses, the K20D does. Even if I didn't have the K-x, I would have my lenses corrected while I have warranty. If you try to resell the lens, it could become a problem.
Dan,

Your comment is nudging me in the direction of exchanging it.

Thanks,
Pam
12-10-2012, 03:26 PM   #8
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QuoteOriginally posted by Briton Quote
LeDave,

Thanks for your reply. I had specifically read your post about the 50-135 and your experience in trying to make the AF corrections. You helped clarify some things as I attempted mine. I'm pleased to hear you're now happy with it at +9 (it was a +10, yes?) and all is well. I'm also waiting for some decent light. Heavy cloud cover on December days are making the real world testing a bit challenging.

Enjoying your other informative posts as well!
Pam
I had issues making adjustments due to poor lighting as the AF adjustment varies, when I finally got the chance to do it in sun-light, I was able to single it out to a +9 for perfect AF. I learned the hard way, never adjust your AF in poor lighting conditions. And no, really bright in-door light-bulbs do not count. It can vary from +5 to even +9 when you try to adjust it in really poor conditions. I didn't believe it before but I do now, the K-5 has issues with fluorescent lighting. If you are planning to keep it all the way, as in not planning to resell it in the future like me, then you can consider in keeping it. But if you are someone who likes to switch lenses a lot or is unsure about whether you want to keep it in the long run, then I suggest you send it back for a better copy for higher re-sell-ability/trad-ability. But as this can vary by the specific person, some cannot tolerate that much of a back-focus at all even if they plan to keep it for many years down the road while some can. It all depends on how you feel about it. Also I know how you feel about the weather, where I live right now, the weather is going crazy. It snowed a lot yesterday also and cars were slipping off the road. Good luck adjusting your AF, don't let the +10 fool you until you actually test it out in the light, it could be better or worse, and if anything you should return it if you can't find a good lighting a few weeks before the return policy expires.

12-10-2012, 04:16 PM   #9
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QuoteOriginally posted by LeDave Quote
I had issues making adjustments due to poor lighting as the AF adjustment varies, when I finally got the chance to do it in sun-light, I was able to single it out to a +9 for perfect AF. I learned the hard way, never adjust your AF in poor lighting conditions. And no, really bright in-door light-bulbs do not count. It can vary from +5 to even +9 when you try to adjust it in really poor conditions. I didn't believe it before but I do now, the K-5 has issues with fluorescent lighting. If you are planning to keep it all the way, as in not planning to resell it in the future like me, then you can consider in keeping it. But if you are someone who likes to switch lenses a lot or is unsure about whether you want to keep it in the long run, then I suggest you send it back for a better copy for higher re-sell-ability/trad-ability. But as this can vary by the specific person, some cannot tolerate that much of a back-focus at all even if they plan to keep it for many years down the road while some can. It all depends on how you feel about it. Also I know how you feel about the weather, where I live right now, the weather is going crazy. It snowed a lot yesterday also and cars were slipping off the road. Good luck adjusting your AF, don't let the +10 fool you until you actually test it out in the light, it could be better or worse, and if anything you should return it if you can't find a good lighting a few weeks before the return policy expires.
LeDave,

Funny, you read my mind. I just did some more testing indoors with using two bright light bulbs illuminating the chart, but I had a suspicion this is not making for an accurate test at all. I'm hoping for a sunny day tomorrow. As for the selling/keeping the lens long term, I tend to be a keeper, like you, until the thing dies. Once I have something, I convince myself to make the best of it, for better or for worse (hence the waffling in making an exchange). Usually, everything works out. It's only as a result of using this lens that I've begun to question so many things about the K5, focusing, and lenses in general. Up until now I was satisfied, but perhaps I've just climbed a steep learning curve in becoming more particular. The crazy narrow depth of field combined with focal length makes autofocusing a real challenge, don't you think? Or is it just me? Also, low contrast seems to challenge this lens more than either of my two lesser lenses. By the way, did you use the same testing chart I mentioned? If not, how did you test?

Also, have you tried any AF-C, high speed tracking (continuous frame-high) with this lens? One reason I got it was for getting super sharp outdoor shots of dogs, kids, things in action, as well as for some use indoors (after all, it's supposed to be fast at 2.8). I understand it's a bigger lens to move around, but the AF-C seems much slower than my kit. My choice was between this lens and the 70-200 Tamron, and I'm very satisfied with the range, build, weight, bokeh, colors and IQ (when in focus) of this one, but have learned that I'll have to plan better when shooting fast moving objects.

Did I read somewhere that you had this lens, sold it, and then got a new one? If so, any differences between the two?

I'm going to call B&H and see what my timeframe for exchange is. Their answer may nudge me one way or another.

Stay warm in your snowy climes!

Pam
12-10-2012, 04:26 PM   #10
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The narrow depth of field at wide-open and up-close at the minimal focusing scale of the lens shouldn't be a problem when shooting outside in daylight. At least for me it doesn't, indoors sometimes it hunts and sometimes it doesn't, but yeah it can be a challenge.

I had the Tamron 70-200 and it hunts more than this DA* did. I don't feel like this lens lack contrast but it does lack more contrast than my DA* 16-50 but the 50-135 does have more contrast than the Tamron. This is all in my experience, some may differ.

Yes I had the DA* 50-135, DA* 16-50, and K-7 with battery grip before I sold it all about a year and a half ago. Just several months ago I decided to go back into photography and lacked the commitment due to the fact that I thought it would take forever to get enough funds for these lenses back. Well here I go, several months later with two of my favorite lenses back alongside with an upgraded body, the K-5. I felt the K-7 had better overall quality because it never encountered any problems and works the way it should. Whilst the K-5 has problems in florescent lighting and a couple of people reported having their lens release button falling off. But I am still satisfied due to its' high ISO capabilities, that's the ONLY reason why I am not going back to my K-7 despite issues. But the issues the K-5 has is still minor in my opinion and is not worth switching cameras or brands for. My K-5 and these lenses suit me fine.

Also for you to know something, the Tamron 70-200 f2.8 has dust problems with the front element being a vaccuum for dust unless you use a filter to block it out. The gap is the plastic rounding covering and holding the front element to the lens (Between the plastic and the front optic). I wrote a guide here a long time ago but is now forgotten and dead on how to remove dust from the Tamron. If you do enough research, you'll find that it's hard to find this lens used WITHOUT dust inside it. It's ashame that Tamron doesn't make the new VC version for Pentax K Mount, it'd be a great replacement for the older version that is still technically "new" for K-mount.

There weren't much differences in the two 50-135 that I had, except for the one I now own has backfocus problem that has to be corrected in the camera settings.

EDIT: Google findings, http://forums.dpreview.com/forums/post/35655231

Last edited by LeDave; 12-10-2012 at 04:46 PM.
12-10-2012, 06:00 PM   #11
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QuoteOriginally posted by audiobomber Quote
I have a K-x and K20D. I test all my lenses when I receive them. I don't tolerate any variation, if the lens needs correction, I send it back. If I want another copy, I send it to the seller, If I want to keep the same lens, I send it to Pentax for calibration, along with a body.

The K-x cannot correct out-of-focus lenses, the K20D does. Even if I didn't have the K-x, I would have my lenses corrected while I have warranty. If you try to resell the lens, it could become a problem.
I have to agree here. These DA* lenses are supposed to be top of the line. While I also agree with what I have read about manufacturing tolerances, when I spend that kind of money on a lens I want it to be perfect. If it were a consumer grade lens, I might deal with it if it was <= +/- 5 adjustment.

When you say +9 almost makes it - not good enough for me.

First question is if any of your other lenses needed any AF adjustment. If not, then this tells me that your body is just about right. I will never rule out a body again as I had one of my K-5's come out of AF adjustment 6 months after buying it.

Test your lens again in good light. Also try 2 different tests - one with the paper target, and another with maybe a row of AA batteries placed at a 45deg angle to the lens. Another test to try is on a tripod, choose a flat target on a wall where you are horizontally aligned, and take a test shot with both the viewfinder and live view - then see if there is a difference in the two images. If the live view image is the same as the viewfinder image, than it is definitely the lens.

B&H's exchange period is 30 days.

If you do opt to send it to Pentax, you will need to send in your camera also so they can calibrate them together. With this option you will be without your camera and lens for 2 weeks, plus bear the cost of shipping it to them.

I went through the same thing with the DA*55 lens - needed +10 adjustment. Sent it back and was lucky as the second copy was dead on without any AF adjustment.
12-10-2012, 06:52 PM   #12
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QuoteOriginally posted by stormtech Quote
I have to agree here. These DA* lenses are supposed to be top of the line. While I also agree with what I have read about manufacturing tolerances, when I spend that kind of money on a lens I want it to be perfect. If it were a consumer grade lens, I might deal with it if it was <= +/- 5 adjustment.

When you say +9 almost makes it - not good enough for me.

First question is if any of your other lenses needed any AF adjustment. If not, then this tells me that your body is just about right. I will never rule out a body again as I had one of my K-5's come out of AF adjustment 6 months after buying it.

Test your lens again in good light. Also try 2 different tests - one with the paper target, and another with maybe a row of AA batteries placed at a 45deg angle to the lens. Another test to try is on a tripod, choose a flat target on a wall where you are horizontally aligned, and take a test shot with both the viewfinder and live view - then see if there is a difference in the two images. If the live view image is the same as the viewfinder image, than it is definitely the lens.

B&H's exchange period is 30 days.

If you do opt to send it to Pentax, you will need to send in your camera also so they can calibrate them together. With this option you will be without your camera and lens for 2 weeks, plus bear the cost of shipping it to them.

I went through the same thing with the DA*55 lens - needed +10 adjustment. Sent it back and was lucky as the second copy was dead on without any AF adjustment.
Stan,

I see your point about expecting a DA* lens to be better (than +10) out of the box, and that's why newer people like myself are perplexed when the "pro-grade" lens seems inferior to a cheaper lens. My other lenses, in the testing I did, seemed to be just right. You mentioned live view.....in setting up the test on the tripod I used live view and it had a heck of time finding focus. Not sure why, but could be lighting. I'll try it again using a wall target as you suggested. All this is convincing me to just send it back to B&H for a replacement. I'm well within the 30-day exchange window.

Thanks!
Pam
12-10-2012, 08:35 PM   #13
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Pam - if it was having a hard time finding focus in live view that tells me that you need to do your tests in better light. Live view is using contrast detection for focus which means that you need a good contrasting target to work properly.

I think you are on the right track however - you won't be the first person to return a lens for the same reason. I certainly hope you get one that is right on because these DA* lenses really do shine and well worth the effort to get a properly calibrated one.
12-13-2012, 12:45 PM   #14
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QuoteOriginally posted by Briton Quote
Hello All,

Long time lurker here, finally with a question to which I couldn't find an answer after TONS of searching on this and other forums. This forum has been extremely helpful and most times if I dig around a little I can find answers to all my questions. Thank you all for sharing your expertise!

First, I've rekindled my interest in photography with a K5 purchase almost a year ago and have to say I really love this camera! Second, starting with the 18-55 kit lens, then adding the 35 2.4 plastic wonder, I bit the bullet and took advantage of the Black Friday pricing of the DA* 50-135 mm, my first "real" piece of glass some might say. After the rave reviews across the board how could I go wrong? Well, instead of initially being blown away as so many were, I was initially disappointed. I'll cut to the chase here and say that I seemed to have lost the ability to take a picture in focus! Long story short, I read about front/back focusing issues, printed the test chart kindly provided by Yvon Bourque at pentaxdslrs.com and did my best to be precise in the setup and testing. With an AF fine tuning adjustment of +10 it now seems to be focusing properly, though by my reckoning, it could have used up to a +12 correction (though I couldn't swear my camera was set at exactly 45 degrees).

My question is, if a lens needs the maximum adjustment possible in-camera (+10), could it be a "bad copy"?
In other words, if I can still exchange this at B&H would you recommend it? My hesitation is fearing the next copy may be the same or worse. This lens calibration is a new world to me, so is all of this normal?

I learned so much these past couple of weeks in trying to troubleshoot this, by the way, and if it's helpful to others:

I learned more about how the Pentax autofocus system works and how to better deal with it's limitations in low light and in tracking movement (eg., fasting running dogs), and that the size of the focus points matters.
I learned that just because a lens is "fast" doesn't mean it can either focus quickly, or track a moving object quickly.
I learned not to judge a lens out of the box in a low light situation, or indoors.
I learned that a fast telephoto takes some getting used to in terms of dealing with that beautiful narrow depth-of-field.
I learned that pixel-peeping on a large (27" imac) monitor can drive a person to madness.

Thanks for any input!

Pam
UPDATE: Based on the advice I received here (and my own gut sense), I returned the lens to B&H for an exchange. What an easy process, by the way. After a 2-minute phone call, and receiving an email with pre-paid UPS label, I was set to drop it off. (I'd anticipated more of a rigamarole).

In the end, whether the lens was truly backfocusing or not, something about the image output didn't see right to me, especially given that so many people have the exact opposite experience. As JohnX suggested, the lens copy may not have been the best fit for my K5 copy. Plus, I learned (largely from posts on this forum) that the umbrella term "focus" has multiple parts, and these become very apparent when shooting a fast tele wide open.

So, (and correct me if I'm wrong) if this helps any other beginners out there, FOCUS problems include the following and must be eliminated one by one:
• Human error (camera shake, not selecting spot-focus when necessary, not waiting for SR (shake reduction) icon to appear, etc.)
• Autofocus choosing "wrong" point (tree behind person's head, high contrast area vs. low contrast subject)
• Super narrow DOF making image appear blurry, when in fact a tiny sliver is tack sharp (whether it's the desired sliver, see below)
• Actual back/front focusing error, when all the above eliminated

Another question: I realized I forgot to "unset" the AF correction that was +10. When I put the new lens on, will the camera read it as +10? I assume the camera knows by lens type (ID) vs. individual lens (serial no.)? And then I can just reset it, right?

Even with my focusing frustrations (I'm seriously working on my technique now), I miss the lens already and am looking forward to getting my new copy (fingers crossed).

Thanks,
Pam
12-13-2012, 12:51 PM   #15
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QuoteOriginally posted by Briton Quote
FOCUS problems include the following and must be eliminated one by one:
Human error (camera shake, not selecting spot-focus when necessary, not waiting for SR (shake reduction) icon to appear, etc.)
Autofocus choosing "wrong" point (tree behind person's head, high contrast area vs. low contrast subject)
Super narrow DOF making image appear blurry, when in fact a tiny sliver is tack sharp (whether it's the desired sliver, see below)
Actual back/front focusing error, when all the above eliminated
Good list.

QuoteOriginally posted by Briton Quote
Another question: I realized I forgot to "unset" the AF correction that was +10. When I put the new lens on, will the camera read it as +10? I assume the camera knows by lens type (ID) vs. individual lens (serial no.)? And then I can just reset it, right?
The camera won't distinguish by serial number, it will apply the correction to the new lens unless you reset.
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