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02-13-2011, 06:22 PM   #1
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Focus Question - Camera, Lenses or Expecting Too Much?

Sorry for the novel size post, but I'm really perplexed, frustrated and don't know what to do. I sure could use some advice and help.

I've been thinking that I have AF problems with my K5 - not so much in low light but outdoors in bright sunlight. However, then I got to thinking that perhaps its not so much the camera as the lens(es). Then I got to thinking that perhaps I have AF alignment problems with one lens, a lens problem with another lens and perhaps a camera problem with a third lens. After yesterday I'm beginning to think that either I have a problem with the K5 or else I'm expecting way too much from 2 of the 3 lenses. I almost always use the center point for focus, and that's how the camera has been set for all of my experiences described.

DA 12-24: This lens has front focused significantly with the K7 and K5. I adjusted it using focus charts with the K7 and have been reasonably happy with it. I shot focus charts with the K5 and thought I had it adjusted correctly until I took a bunch of landscape photos in Death Valley - they looked rather blurry to me. I also took a bunch of interior photos in Scotty's Castle, which is kept very dark, the same day. They looked fairly good, some front focus, but I assumed I just didn't have the lens quite adjusted right. I changed the fine tuning, shot some focus charts and thought it looked pretty good. The next day I went out and shot a bunch of test shots at lunch, outside in good light. When the subject was 2-3 feet away, the focus looked excellent, very sharp. At about 5-7 feet away, the subject was at the front edge of the sharpest focus - a bit back-focus but not enough to do anything about. However, I took a picture of some trees about a block away and they were blurry, what was sharp was a fence in the bottom of the shot, significantly closer. So why would a lens focus perfectly close up, reasonably at mid-distance (for a wide angle), but not be able to focus to infinity on an object a half block or more away? I tried the lens on the K7 and thought that it wasn't much different - perhaps I have a faulty lens?

DA 35 macro: I took a bunch of pictures in an aquarium Birch Aquarium, Scripps Institute of Oceanography, if anyone knows it) two days before we went to Death Valley. I was quite pleased with the pictures I took there - not all were perfect, but I had a better keep rate with the combination than I had at the Monterey Aquarium with the K7 and other lenses (didn't own the 35 macro at the time). However, this lens also seemed to not want to focus to infinity - the same trees that were blurry with the 12-24 were blurry with the 35 macro. The lens looked fine when shooting focus charts, though I thought it looked a bit back-focused at mid distance. When I took the same trees with the 35 macro and the K7, there was a significant difference - the K7 pictures were much sharper. So I think I have a lens adjustment problem with the K5 - if a lens is back-focusing, will that make something at infinity blurry?

Yesterday I took only the K5 out, but I added the manual focus SMC 24mm f2.8 into the mix. I've rarely used this lens since buying it new in 1980 - I had no clue how to make use of a wide angle when shooting film. I used it occasionally with the K100 and DS as it's a nice lens and became more of a "normal" lens with digital. I quit using it with the K10 because it wouldn't meter correctly and I really haven't used it since. So it's actually in excellent condition in spite of being a 30 year old lens. When I shot some distant trees while out hiking yesterday, I found the beep came on at the same time I thought it was in focus, and at the far stop. When I got home, the DA 12-24 shots were slightly sharper than my old manual focus lens shots (something I didn't expect).

So now I'm thinking that either the K5 can't seem to focus right at infinity, or else I'm expecting too much for a wide angle lens to focus sharply on an object that's at a fairly significant distance.

FA 77: Test focus charts look great with this lens - no sign of front or back focus. Go outside and for the most part, it's fantastic - focus is fine. However, every so often, for no reason whatsoever, the AF works, the lens says it has focus but the picture comes out focused wildly in front of the target (one case I was driving in a car, aimed the camera at the edge of a cloud and had the road in front of the car in focus, that's how far off it was). Both times there was no reason for it to mis-focus, each time the subject was significantly far away, with nothing much around the focus point except the subject. What ended up being sharp was an object in the corner of the picture, significantly closer. In both cases, the "miss" shot was only 1 of about 30. I took the lens out with the K7 on another day, took 50 random shots of similar targets and didn't miss once. To be fair, when I was out taking all the shots with the wide angle lenses last week I took a few pictures with the 77 and all of them were sharp. So perhaps I shouldn't include the lens with my problems.

The only other thing I can think about that might be a factor in this could there be a difference between using the in-camera focus motor vs. SDM. I have 3 SDM lenses and they all seem to be at least consistent.

I used the Pentax Support form from Pentaximaging, but they aren't set up to try to troubleshoot a problem like this (they gave me the good suggestion to try manually focusing the lens, which is what led me to shoot yesterday with the old manual lens and suggestions about shooting focus charts).

So should I send the K5 in for evaluation/repair? Send it in with all 3 lenses that I'm having an issue with (DA 12-24, DA 35 macro and FA77, or leave the FA 77 out of the mix)? Or send the camera in with just the 12-24, asking them to evaluate the 12-24 for possible problems? Or not send anything in and just stick to using the wide angle lenses with close subjects, accepting that I'm asking too much of a wide angle?

Can anyone suggest any other test that I haven't thought of that might be conclusive to sorting out all this? The only thing I haven't done is to use the K7 and SMC 24 f2.8 or used the K100 (which I also own) for any comparison - figured the pixel differences were too big to really compare. I've begun to think that I'm incapable of taking a decent picture and it's depressing.

02-13-2011, 06:36 PM   #2
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Wow, you've certainly gone through some trouble to bring out these focusing issues.

From what I gather, you've tried the fine AF feature and still there are intermittent AF problems that are hard to reconcile. Infinity focus shouldn't be tested wide open (if that's what you tried) - it will disappoint you. ALso be cautious about the AF points - the subject could be quite contoured in depth in the one spot covering the AF point, which can make AF difficult.

I can only suggest that if the problems are reproducible, get your local repairman to evaluate it with you so that you can show the deficiencies effectively.
02-13-2011, 06:42 PM   #3

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I can't get my head around how anyone using the DA 12-24 to take landscape photos of Death Valley could get blurry photos due to any AF issue. Using the 12-24 it should be almost impossible to take a out-of-focus landscape shot.

Two things spring to mind. You have probably grossly mis-adjusted your AF, and you need to do some research on depth of field.
02-13-2011, 07:55 PM   #4
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ACtually I have heard of some 12-24's having problems focusing correctly at infinity.

02-13-2011, 08:38 PM   #5
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The problem with presenting several problems, is there is not enough detail on any one specific issue to get to the bottom of it :-)

On a general note, i wonder if in Death Valley, you aren't having problems because of air convection. I have a friend who had such good luck with a 400mm Nikon tele, that he went back and paid, about 5 years ago, about $10,000 for a 600mm tele. Had lots of problems focusing that 600 mm lens. Showed a picture one time of a blurred superstructure of tanker. Said that the problem was due to air currents passing around the superstucture. Convection flow in daylight can easily cause focusing problems over long distances or even shorter distances depending on temperature. I have a Sigma 10-20 and no problem with my K20, so am also amazed at the problems you are describing with the 12-24.

Lenses can also have problems due to "field curvature". But the rule is that if blurriness goes away with manual adjustment, that its field curvature and not focus adjustment.

If you continue to have problems, i'd send the k5 in with the 12-24 and see if they can't get to the bottom of that combo. Wide angle lenses typically don't have problems with focus, at least in my experience. something is wrong here.

best wishes,
02-13-2011, 09:08 PM   #6
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Ash - yesterday I was using f8 for the infinity focus, that's usually a pretty safe aperture. For the focus charts I mostly used f4 or f5.6, trying to limit the dof. For mid-distance and long distance subjects I used f4-f8, some f11. I find my 12-24 isn't very good at smaller than f11 apertures, and pretty soft at 12 mm regardless of aperture.

rawr - I may be completely mis-adjusting the AF, especially with the 12-24. It's just that I can't get consistent results when it comes to varying the distances. I assumed that if the focus was correct at relatively close distances, where dof is smaller, that you'd be fine at longer distances where dof becomes much less of an issue. And at infinity with a wide angle lens, anything from about 20 feet out should be in focus. That's why I asked the question that if I do have the lens adjusted for front focus too much, whether that would affect how the lens focuses on something a block away.

twitch - That's interesting, something I didn't know. That means that I might be looking at multiple problems, of which a defective 12-24 might be the answer to one. Thanks for that - I'll concentrate on solving the 35 macro as a separate issue right now, with perhaps using the manual 24mm on the K7 for comparison, and not give up.

And I was very, very surprised about the Death Valley pictures and lack of quality. The only time I've experienced anything like it was when I had an early K10, which had AF issues and why I've been thinking that my problem is the K5. I don't want it to be the camera, since the sensor has no stains (and still doesn't after a month), but I'm afraid it might be.
02-13-2011, 09:13 PM   #7
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Have you tried quick shifting the 12-24 to manually achieve focus at f/8? If you still get unsharp images then does sound like the lens is suspect. But why now?

My own copy is absolutely stunning at all apertures and I'd expect all copies to be the same. Have it also looked.
02-14-2011, 07:13 PM   #8
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Your Pentax 12-24mm should focus properly at infinity if you set AF fine tuning correct at any distance. Say you pick a target 3m away and fine tune AF. Now with the enormous DOF of the 12-24mm at 12mm you should be good even if your off by +/- 4. It could be the method your using to fine tune AF. This is the method I have found that works best for me...

Use the charts at this site as they are much better than the classic Nikon charts-

Jeffrey Friedl's Blog Jeffrey’s Autofocus Test Chart

Make sure to be at the proper distance, you should only see the middle area using live-view to set up for the test and confirm best settings.

BTW have you tried live-view contrast AF with the K-5 it will help a lot in solving your problems.

02-14-2011, 10:13 PM   #9
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I've used both charts and found Jeffrey Friedl's chart better with wide angle lenses, assuming the light is not too much where the camera starts to "see" his grey lines.

Today I went out with both the K5 and K7, 24 f2.8, 12-24 and 35. The shots across the board looked similar - i.e., the manual lens at infinity didn't look much different than the 12-24 for the most part. The K5 and K7 pictures looked similar. The 35 looked much better than it did a couple of days ago, so I think I've finally gotten that lens dialed in correctly with the K5 (there had been differences between the K5 and K7 before and I made a slight change with the setting on the K5). Then, because I wondered if the K5 didn't like anything but SDM lenses, I took the 55-300 and shot some comparison shots with both cameras. Those comparison shots looked the same between cameras, I definitely got good focus at infinity (though my furthest subject, a crane, was only barely at infinity for this lens, everything else was closer than that) so the K5 doesn't seem to object to it. I'm still not crazy about the infinity focus on the 12-24, but it's sure sharp at 2 feet. I don't think it's any worse than the manual focus 24 at infinity. Now if I can get the same results as today every day (I'm not completely convinced I will, since I haven't in the past), I'll be reasonably satisfied that the camera is NOT a problem. I still am not entirely happy with the 12-24, but I may start a new thread under the lens section with links to some full sized examples and comparison shots I took today (don't have time tonight, the drive home too several hours longer due to traffic) and ask for others who have the lens to take a look at them and tell me what they think.

If I don't get consistent results in the next few days I'll be pretty sure the problem is the camera, not the lenses. Or else me - I'm beginning to think I've suddenly lost the ability to take a decent picture (or at least one correctly focused and exposed - kept forgetting to push the green button with the manual lens today, then I'd shoot the 12-24 using M mode with totally inappropriate exposure settings. Sigh!).

Thanks for all your assistance, and hand-holding while I try to sort out this whole thing.

P.S. There is one thing, though. At one point, while using the 55-300, the K5 seemed to refuse to focus correctly. It would zoom a bit then indicate it had focus, but the focus was not even close, the frame was almost completely blurred (i.e., the distance indicator was saying 10 feet, but the subject was more like 30-40 feet away, almost at infinity). It did it several times until I manually focused it to infinity and then let it find the correct focus, since it was close. It's not that it failed to find the focus (zoom out and back then the indicator blink), the camera indicated focus lock. Thought that was very strange, because it did it 3 or 4 times (manually adjusted the focus to another point, then pushed the shutter half-way) before I got it to focus correctly.

I've tried live view a couple of times and found that when it achieves focus it does pretty well, but it's less likely to lock focus. It worked about 50% time Saturday, when I was using the DA 35 macro to shoot some pictures of lichen from a very awkward angle where I couldn't really see the viewfinder. I don't use it outside much because of the problem of seeing the LCD screen in bright sunlight. The funny thing is that my first few pictures with the K5 were taken indoors with the 77 and they front focused severely. I later tried a couple of times to re-produce the front focus in other types of dim light with the DA*50-135, but couldn't do it. I've been concentrating on getting the focus right in bright sunlight, so I don't have another disappointment like Death Valley again and haven't really tested things in low light much.

The question of atmospherics is an interesting one - one of the pictures I took several days ago with the 77 was really sharp - it was of a building a good half mile or more away, with restaurants and other businesses/roofs/roads in between. The lens caught all of the waviness of the atmospheric distortion but still the (wavy) lines of the building were sharply defined. I was very impressed.

Last edited by mtngal; 02-14-2011 at 10:32 PM.
02-14-2011, 10:36 PM   #10
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Just wondering if camera shake could be causing your problems and not focus. Did you use a tripod? Did you hand hold with a slow shutter? Was shake reduction turned on (it should not be on if using a tripod)?

Did you try focusing with Live View?

Hope you get this resolved!

I have had some focusing concerns with my K-5, but I think it was either a lack of contrast that confused the camera or user error on my part (shutter too slow).
02-14-2011, 10:49 PM   #11
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I've been trying different things - with and without tripod. With and without SR. All at reasonably good shutter speeds, some way too fast (I often get lousy pictures when shooting at super-fast shutter speeds like 1/4000, don't ask me why). So I try to keep them over 1/100 and under 1/1000. My hand-holding capability isn't the greatest when the shutter speeds get down to 1/focal length any more. It's entirely possible the problem is all me and "operator head-space and timing" (and old Army mechanic's term for user/operator error) - today I shot almost exclusively without SR and on a tripod and at least I got reasonably consistent results, something that has been missing before.
02-15-2011, 03:00 AM   #12
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QuoteOriginally posted by mtngal Quote
So why would a lens focus perfectly close up, reasonably at mid-distance (for a wide angle), but not be able to focus to infinity on an object a half block or more away? I tried the lens on the K7 and thought that it wasn't much different - perhaps I have a faulty lens?
Faulty lens, most probably a misaligned lens element. Send it back for replacement.

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