[BethC]

I am having trouble with my 50 - 135 lens backfocusing on both my K10 and my K5. Had it on my K5 this morning to do some tests, then went into the AF Fine Adjustment and tried to fix it and it is still back focusing. I went all the way from +5 to -5 in the adjustments and it still back focuses 90 % of the time. Is that an issue with the SDM on that lens? Or could it be something else? I'm at a loss. Any advice?

[oxidized]

I dont think it is an SDM issue. I have never had an SDM problem, but from what I hear the lens would start to act up and sometimes would focus and sometimes it would not respond at all, until it eventually never focuses. Consistent backfocus sounds like a backfocus problem. I am not sure how it suddenly appeared, however I had a similar problem with my 50-135. I originally used it on my K-7 without any AF adjustment and focus was dead on. Several years later I bought K-5 and to use it on the K-5 i need a -9 to get accurate focus. I hope this helps.

[Docrwm]

I dont think it is an SDM issue. I have never had an SDM problem, but from what I hear the lens would start to act up and sometimes would focus and sometimes it would not respond at all, until it eventually never focuses. Consistent backfocus sounds like a backfocus problem. I am not sure how it suddenly appeared, however I had a similar problem with my 50-135. I originally used it on my K-7 without any AF adjustment and focus was dead on. Several years later I bought K-5 and to use it on the K-5 i need a -9 to get accurate focus. I hope this helps.

But this is a change from previous performance of this lens on the same camera. That does sound like a fault in the lens, as other lenses focus just fine on that camera still.

https://www.pentaxforums.com/forums/general-technical-troubleshooting/224638-...ml#post2384030

[BethC]

But this is a change from previous performance of this lens on the same camera. That does sound like a fault in the lens, as other lenses focus just fine on that camera still.

https://www.pentaxforums.com/forums/general-technical-troubleshooting/224638-...ml#post2384030

Yes, used to work great on my K5. And since I initially posted that thread, I've realized that it backfocuses on both my K10 and my K5, while all of my other lenses are fine on both bodies.

[Docrwm]

Yes, used to work great on my K5. And since I initially posted that thread, I've realized that it backfocuses on both my K10 and my K5, while all of my other lenses are fine on both bodies.

It really is sounding like a lens issue. The other possibility is that it was dropped or struck and that caused some change in its performance.

[oxidized]

It really is sounding like a lens issue. The other possibility is that it was dropped or struck and that caused some change in its performance.

thats what i was going to say next. if it had been dropped or hit some kind of mis-alignment may have happened. still though, it doesnt sound like the motor is dying.

[BethC]

thats what i was going to say next. if it had been dropped or hit some kind of mis-alignment may have happened. still though, it doesnt sound like the motor is dying.

If that's the case is it fixable? I haven;t dropped it and don't remember bumping it on anything,but can't recall anything. I'm curious if it's worth sending in. It's a year and a half old.

[oxidized]

If that's the case is it fixable? I haven;t dropped it and don't remember bumping it on anything,but can't recall anything. I'm curious if it's worth sending in. It's a year and a half old.

You said that it back focuses at -5? Have you tried going higher than that? If the back focus is consistent and the user adjustment is not enough then I would def send it in.

Before I would send it in, I would try to adjust it myself.

LinuxPhoto.org

1) I would check if the back focus is consistent. Is the AF always back focusing at the same spot (assuming the center point does not move - you would need a tripod for that)? If the AF is just all over the place then the problem maybe more complex than simple back focus.

2) Start to dial in the AF adjustment until the center point becomes in focus. If it is too severe, definitely send it in. They should be able to adjust it. Keep in mind you would also have to send in the camera body. They will want to calibrate it to the body that the lens is normally used on.

[BethC]

You said that it back focuses at -5? Have you tried going higher than that? If the back focus is consistent and the user adjustment is not enough then I would def send it in.

Before I would send it in, I would try to adjust it myself.

LinuxPhoto.org

1) I would check if the back focus is consistent. Is the AF always back focusing at the same spot (assuming the center point does not move - you would need a tripod for that)? If the AF is just all over the place then the problem maybe more complex than simple back focus.

2) Start to dial in the AF adjustment until the center point becomes in focus. If it is too severe, definitely send it in. They should be able to adjust it. Keep in mind you would also have to send in the camera body. They will want to calibrate it to the body that the lens is normally used on.

I have not tried going higher than -5. It seemed to not make a bit of difference at -5 or +5. I will try to go higher and see. I had my tripod set up this morning and used a chart that was suggested to me on the other thread. Then got 6 different items (salt shakers) put them in a row, kept all settings the same, and focused on each shaker and went down the line. Did this with that lens on both cameras, than did it with 2 different lenses on both cameras. and I did it with the K5 with the +5 adjustment and the -5 adjustment and got consistently the same results, back focus.

If I have to send the lens and my body in, can I send in the K10? Even though it's my back up? I don't think I can do with out my K5, especially this time of year!

I will check out that link you posted in a bit. I need to step away from the cameras/computer for a bit!

Thanks for the info.

[starbase218]

A while ago, I read about someone sending some of his (Canon) lenses back for servicing because the AF was off. The lenses got calibrated by Canon and when he got them back they worked much better. Maybe something similar applies to your 50-135? Although I can't imagine how this would work.

[BethC]

You said that it back focuses at -5? Have you tried going higher than that? If the back focus is consistent and the user adjustment is not enough then I would def send it in.

Before I would send it in, I would try to adjust it myself.

LinuxPhoto.org

1) I would check if the back focus is consistent. Is the AF always back focusing at the same spot (assuming the center point does not move - you would need a tripod for that)? If the AF is just all over the place then the problem maybe more complex than simple back focus.

2) Start to dial in the AF adjustment until the center point becomes in focus. If it is too severe, definitely send it in. They should be able to adjust it. Keep in mind you would also have to send in the camera body. They will want to calibrate it to the body that the lens is normally used on.

Ok, so I lied and I decided to read that article now. That's so much easier than the thing I downloaded, printed, cut, folded etc... I will not only do that with my 50 - 135 lens, but will use it before big events just to make sure all is well! I shot a 5K on Saturday and that's how I realized something was off. But this Saturday, I am shooting a wedding. I have a panic attack at the thought of not realizing something was wrong with the lens before this Saturday! That could have been really bad. My back up is the 50 - 200 mm kit lens. So I would have made due if I'd realized early enough, but I love my 50 - 135 for weddings. I already paid for a rental to be sent to me on thursday so I'll at least have that one for this weekend.

[oxidized]

Then got 6 different items (salt shakers) put them in a row

I have tried this before. Not a good idea in my opinion. For fine micro adjustments you need a scale of some kind. When I adjust AF i use a ruler and in particular i like to use the mm part and not the inches (again the more precise the better).

Also make sure you are dialing the appropriate + or - according to whether it is back focus or front focus problem.

Fixing Front and Back Focus - Introduction - PentaxForums.com

- is for front focus, + is for back focus

[BethC]

I have tried this before. Not a good idea in my opinion. For fine micro adjustments you need a scale of some kind. When I adjust AF i use a ruler and in particular i like to use the mm part and not the inches (again the more precise the better).

Also make sure you are dialing the appropriate + or - according to whether it is back focus or front focus problem.

Fixing Front and Back Focus - Introduction - PentaxForums.com

- is for front focus, + is for back focus

First test I did was in live mode in the yard with a stationary object.

Next was this test... using the charts that you download at the bottom PENTAX DSLRs: Front or Back Focusing Problems? Free test (Lens Alignment) charts for Pentax, Nikon, Canon, Sony, Olympus.

Last one was the old Scientific Salt Shaker test So it just backed up what all the others things showed....backfocusing. So it' s not the only thing I did to test the lens.

And I did the + adjustments for back focusing, then when I noticed it did nothing up to + 5 I thought, maybe I'm doing it wrong and went up to -5 and still didnt' change anything. so thanks for clearing that up.

I'm going to do the ruler test now.

[BethC]

I have tried this before. Not a good idea in my opinion. For fine micro adjustments you need a scale of some kind. When I adjust AF i use a ruler and in particular i like to use the mm part and not the inches (again the more precise the better).

Also make sure you are dialing the appropriate + or - according to whether it is back focus or front focus problem.

Fixing Front and Back Focus - Introduction - PentaxForums.com

- is for front focus, + is for back focus

Ok, so after doing the ruler test, I dialed in +9 and it seemed to front focus, then dialed it back to +7 and it seems to be focusing right now at least on the ruler. I was focusing on the line above the 16. Does that seem right now? and if it is right with that adjustment, is it stlll a good idea to send the lens back? would you trust this lens for some thing important like a wedding if it's had be adjusted this much?

[nomadkng]

your ruler should be perpendicular to the focal plane not 180 degrees across it.

you want to use the marking in front or in back of the focal point to note front of back focus.

you need a tripod with the camera at a 45 deg angle to the ruler/focus chart

ideally you want more contrast than that ruler provides as well and you need very good lighting, (I go outside midday)

a quick google search came across this:

http://www.tunerphotography.com/uploads/Instructions_for_using_the_AF_Fine_T...ocus_Chart.pdf

there are several other websites that give you instructions as well,,, pay close attention to the image on page 2, that's what a focus check image should look like

also remember that when you focus on an point, roughly 1/3 distance in FRONT and 2/3 distance BEHIND that point will be in focus. that will be the case no matter how shallow DOF you have