[rustynail925]

Staff note: This post may contain affiliate links, which means Pentax Forums may earn a small commission if a visitor clicks through and makes a purchase. If you would like to support the forum directly, you may also make a donation here.

---

found at 260 euro on ebay..
Tamron SP AF 17-50mm f/2.8 XR Di for Pentax on eBay (end time 03-Dec-09 06:23:55 GMT)

[rustynail925]

My eyes are set on the tamron 17-50mm but after reading this thread im having 2nd thoughts.. maybe a da 16-45mm or take a risk

[StevenVH]

Now in hindsight and reading these comments, I'd say it's K10/200 issue under certain circumstances and maybe made worse or more obvious with certain lenses.
I occasionally suspected AF accuracy with K200 and DA*16-50, but it seemed random and rare enough and didn't show up with simple testing.
Now, with the K20, it's like a new and much better lens. AF nails it under reasonable conditions.
My expectations have always been pretty low for AF and easy enough to just bump the focus manually that I didn't pursue the issue at the time.

gl

[causey]

Now in hindsight and reading these comments, I'd say it's K10/200 issue under certain circumstances and maybe made worse or more obvious with certain lenses.

My suspicion, too.

[rustynail925]

But are there any K200D without issue with the lense? or all K200 got issues with tamron 17-50mm?

[Marc Sabatella]

rkt, IMO the focusing charts you can download and print are virtually worthless from a precision perspective. The target area is simply too small. As Marc already mentioned there is no way you can know precisely what the camera has chosen to focus on.

Not sure what you mean by this. A small focus target is *exactly* what you want. If it's too large, then you don't know with any precision which part of the target it used. The smaller the better. Some people complain the target is too *large* on the focustestchart.com version, as you don't know if the camera has focused on the front or back edge of the black bar. But you'd have to be shooting a lens with an incredibly tiny DOF for a difference that small to be visible at all.

[Marc Sabatella]

Marc... I would assume the digits are sufficiently distinct for the K200D AF sensor... otherwise... at the same aperture (2.8) shouldn't the Tam 90 have shown some focussing issues as well?

It's not a question of whether the digits are distinct or not. The issue that the AF sensor is much larger than the red dot - it's about the szie of the entire center bracketed area. So the camera might legitimately to focus on *anything* within that area. The digits might be perfectly clear, but if the lines in front of them are also in range, the camera might well choose to focus on them, You have no control over this - none whatsoever. The camera will choose whatever it feels like choosing within range of that sensor. Sometimes it might choose something closer, sometimes it might choose something farther away. That's why you might get different results each time you do the test, and why the 90mm might have happened to appear produce different results than the 17-50.

with the charts printed and pasted flat on a wall

How, then, did you manage to shoot them at a 45 degree angle like the instructions clearly say, then? Or was this a 3-D test chart that really was designed to be shot straight on?

Rather than continually repeating various different flawed test and trying to rationalize what miht or might not be explaining the results, save yourself a tremendous amount of grief and do the test properly in the first place. A correctly performed focus test shows you *instantly* whether you have a problem or not. An incorrectly performed one does nothing but waste time and cause confusion.

[WheresWaldo]

Not sure what you mean by this. A small focus target is *exactly* what you want. If it's too large, then you don't know with any precision which part of the target it used. The smaller the better. Some people complain the target is too *large* on the focustestchart.com version, as you don't know if the camera has focused on the front or back edge of the black bar. But you'd have to be shooting a lens with an incredibly tiny DOF for a difference that small to be visible at all.

Marc, you took one sentence out of context from the entire response. I am surprised.

My opinion is that are not worth the paper they are printed on for two reasons, the FOCUS HERE line is too small, you are attempting precise focus on a sloped plane which you have no way of knowing whether or not you have achieved.

That is why I also mentioned the LensAlign in the same response! The target is big enough that you know you are focused precisely on the central point of the sloped plane and you can then make proper adjustments knowing that the front or back focus displayed is truly a front or back focus issue and not an imprecise selection by the auto focus sensor.

[Marc Sabatella]

Marc, you took one sentence out of context from the entire response. I am surprised.

I didn't do so deliberately. I was honestly confused about your point.

My opinion is that are not worth the paper they are printed on for two reasons, the FOCUS HERE line is too small, you are attempting precise focus on a sloped plane which you have no way of knowing whether or not you have achieved.

That's what I don't get. What about a small line is bad? I just don't get it. Are you saying AF sensors are not capable of focusing accurately on things that small? That's not my experience at all. And I don't see why the sloped plane in any way complicates things. Either part of that line is in focus or not, whether you shoot straight on or slope, but the sloping is necessary in order to compare the focus at the line with that in front and in back. You know when you have achieved focus because the focus indicator comes on and the camera lets you take the picture. I'm not trying to be difficult here, I just don't understand what the problem you are alluding to is. Is there maybe something in the physics of how light strikes a sloped surface that you are saying somehow interferes with phase detect specifically? Is there some sort of scientific reference for whatever the effect you are referring to is?

BTW, note I'm not saying the approach taken by Lensalignisn't good too. i just honestly don't understand the science behind whatever problem you are describing with the other approach.

[jeffrey r]

But are there any K200D without issue with the lense? or all K200 got issues with tamron 17-50mm?

I have a K200D and Tamron 17-50mm. My photos from this combo look very good to me, and I have some other excellent lenses to compare it to. Some of you would probably tell me my lens front focuses. Some would probably tell me it back focuses. I don't test my lenses other than just taking photographs, so I am not of much help in the technical area.

[causey]

It depends. If you don't use AF with your Tamron 17-50 at f/2.8 a lot, you don't really care about the issue. If you do use it this way but without noticing anything problematic in your pics, then the camera / lens combination works fine in your case. I for one used the second copy I tried while visiting a friend in a hospital room. She had just given birth to a girl, and I wanted to immortalize those precious moments. But the pics were out of focus or at best barely in focus. (There was low, but natural morning light in that room. No tungsten/bulb light.)

[rkt]

...
How, then, did you manage to shoot them at a 45 degree angle like the instructions clearly say, then? Or was this a 3-D test chart that really was designed to be shot straight on?...

Well, if you followed all that I had to say, the 45 degree stuff was done with the yellow scale... and I alread posted some extracts from them... so there was nothing 3D about that... unless you have access to some such special charts (you could drop a link here for the common good then)... and the point about using flat charts was used to indicate that I was not simply testing the AF on a set of homogenous parallel black lines as you were convinced about, but across a variety of test objects... which happened to include some focus test charts as well...

...
Rather than continually repeating various different flawed test and trying to rationalize what miht or might not be explaining the results, save yourself a tremendous amount of grief and do the test properly in the first place. A correctly performed focus test shows you *instantly* whether you have a problem or not. An incorrectly performed one does nothing but waste time and cause confusion. ...

Pretty much well understood even before I posted here... which is why no claim to professional testing standards was indicated... and which is why my original thread talks about a specific camera + lens combination and not the lens itself... and nothing was rationalized about the observed effects, a set of observations were made, similar instances were found through google, and a thread was started here to gather some more information... but thanks for your 2 cents worth of additonal wisdom anyways...

Causey... thank you for endorsing my find with personal experience... I would rather we both had great experiences with this lens... but your experience atleast gives me some comfort in knowing it's not my eyesight, nor half-minded unprofessional 3D tests that make me see what I see...

[Jasvox]

has a K10D with a Tamron 17-50. No problems at all, never had any issues and the photos I take with that body and lens combo are among the best in my portfolio. In my opinion, it's the best step-up from a kit lens being produced at the moment and the price is bang on.

Jason

[Marc Sabatella]

Well, if you followed all that I had to say, the 45 degree stuff was done with the yellow scale... and I alread posted some extracts from them... so there was nothing 3D about that... unless you have access to some such special charts (you could drop a link here for the common good then)...

It's sometimes hard to keep track of who has posted what. All I can say is that nowhere on this thread have I seen shots demonstrating a correctly performed focus test - the posted shots of the ruler are completely meaningless, and I don't understand what the test was you performed on the wall. So thus far, everything written has just been speculation. Like I said, run a test *correctly*, and all doubt is removed instantly. But right now, doubt is all we have. If you *have* run such a test (ie, one that does not suffer any of the problems I've already described), then perhaps you could post the results. If you have not already done so, the test I like to use personally is the one at focustestchart.com.

but your experience atleast gives me some comfort in knowing it's not my eyesight, nor half-minded unprofessional 3D tests that make me see what I see...

Until you perform a simle and correct test, we still don't know if the problem is with your methods or not. Could be simple coincidence that someone else has had what appears at first glance to be a simialr problem. Would take no more than a couple of minutes to find out for sure.

[rkt]

Ok, here are the results after using the test at focustestchart.com.

Now, the Tamron was used at 2.8, while the Pentax was at 4.5... so there will be a wider range in focus for the Pentax... but if you look at the Tamron results stand alone... can it still be safely concluded that it is front focusing?