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10-06-2012, 02:00 PM   #1
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AF Fine adjustment

So, I think my Kr needs a bit of front-focus adjustment, and soon I will be checking this in earnest with one of the calibration charts. I've read the articles on using the AF "fine" adjustment to make corrections, if necessary, and I've read the manual, too. Elsewhere in threads there's been mention that some camera bodies can store these corrections for different lenses, but I've not seen any reference to this being the case with the Kr, and the manual doesn't address this question.

Anybody know if the Kr can do this -- store multiple correction/adjustment settings for different lenses?

Thanks for your expertise!

10-06-2012, 02:29 PM   #2
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K-x and K-r can only store a single correction. K-7 & K-5 can store multiple lenses. Not sure about K-30.

I don't know anything about your photography experience so don't take this wrong, but the LAST thing you do is mess with the AF fine adjust. Try everything else first. Unless you have a solid setup, well lit, on a tripod, PRECISELY aligned to the target calibration chart both vertically and horizontally and using single point focusing you are more likely to make things worse than better. In most cases the margin of error in the test exceeds the hardware error. If you are shooting wide open with very fast lenses f/1.4 or f/1.8 then yes by all means tune the lens. But with the kit lens try everything else first. It is more likely technique, lighting or the too big AF points Pentax uses than it is anything that AF Fine adjust will fix.

One way to quickly test is to setup on a tripod and focus on something very contrasty using live view, make sure the target is in the exact center. Then focus using the view finder AF. If nothing changes then you are most likely as good as you are going to get.

Remember with the K-r (if you use multiple lenses) changing the AF fine adjust to suit one lens might make it worse for another. Assuming your test is precise enough to make it better for the tested lens.

Not trying to discourage you from tuning your lens if you want to, just understand it must be done correctly or you will make things worse.
10-06-2012, 02:52 PM   #3
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Thanks. Excellent advice, I shall take it. Ironically the only really fast lens I have is an old M42 Tak, which isn't relevant to this. Working now with kit lenses from the K-r itself and my last AF film camera, plus an SMC FA 1:2.8 50mm macro. (and some other M42 legacy glass, also not relevant). No budget at the moment to invest in new glass, alas.

My photography experience is modest, although I have dabbled on and off since Asahi was making cameras (and I still have several, including Asahi Pentax and Spotmatic, as well as a later MX50). But I think I know when an image is sharp, and I'm not seeing the sharpness I would like to see in many shots. You are very probably right about lighting being an issue, as many of the shots I'm grumbling about were definitely shot at lower-than-optimum light... the camera gave me decent exposures but not great sharpness.

So I need to practice more, for sure, and knowing that the K-r won't store more than one correction is another reason not to mess with it except for some extraordinary situation.

Thank you!
10-06-2012, 04:31 PM   #4
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As a test try using Live View focusing, this bypasses the focusing screen and AF points and is considered more accurate. I use it a lot when on a tripod and doing product or food shots. It is not very fast and therefore less useful for handheld shots, IMO. See if images taken using Live View are noticeably sharper than what you are getting using the AF system. If not, then maybe you need to think about better glass when the budget allows. There are still some good values out there in F and FA glass though much less than in the past. Check out the F 35-70 it is still quite reasonable and very sharp.

One of the issues often complained about with modern Pentax cameras is that the AF points are much larger than the little red indicator squares would imply. The red square just tells you which AF point is being used, not the size of the AF box. And anything in that 'AF box' surrounding the red square can be the exact point that the camera locks onto. So just because the red square lights up that does not mean that that is the exact point that the camera focused on. I think this is the most likely reason for the many complaints about the Pentax AF system. It is fast and accurate, it is just is not hitting the exact point you think it is.

The only lens you have that I would bother fine tuning is the FA 50mm f/2.8 you should be able to get depth of field small enough to accurately tune it. If I were you I would run some tests with that lens to see how far off you are. And if it's not too bad I would leave it alone.

Another thing I forgot to mention is that when using zooms (even with cameras that store settings for multiple lenses) you can store only one point on the focal length range. So on an 18-55 you might be back focusing @18mm and front focusing @55mm. Changing the settings to correct one focal length makes the other even worse, so you just have to average it out.

10-06-2012, 07:22 PM   #5
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See this thread.

Adjusting AF is easy and the tool is free.
10-07-2012, 05:25 PM   #6
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QuoteOriginally posted by jatrax Quote

The only lens you have that I would bother fine tuning is the FA 50mm f/2.8 you should be able to get depth of field small enough to accurately tune it. If I were you I would run some tests with that lens to see how far off you are. And if it's not too bad I would leave it alone.

Another thing I forgot to mention is that when using zooms (even with cameras that store settings for multiple lenses) you can store only one point on the focal length range. So on an 18-55 you might be back focusing @18mm and front focusing @55mm. Changing the settings to correct one focal length makes the other even worse, so you just have to average it out.
@jatrax -- thank you. Yes, knowing that the K-r will store only one correction, my thought was to test the macro lens (and now, with the info that the zooms can have different corrections for different focal lengths, even more reason to be cautious with them). I do use a macro on a D80 at work, for "product" stuff, and have some experience with that rig. I'd like my K-r to be able to produce similar kinds of images...I know that 50mm Tak is a very good lens, need to do some test/practice with it. "Time" is a 4-letter word, y'know

Will try the "live view" test as you suggest. Going back through some image files, the softer images are definitely the higher-ISO ones, dim lighting and slow shutter speeds. In bright daylight, much sharper. I'm trying to learn how to cope with the AF red spot for focus, too. Long ago, in a galaxy far, far away, I could focus the Spotmatic pretty well, so I think I can get the hang of it again if I practice enough (and get the diopter set exactly right...)

@JimJ -- I've read that, thanks, and I have downloaded the charts as well. No chance to do anything with them other than print them out, but I hope to be able to check the lens soon.
10-17-2012, 03:27 PM   #7
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I have a quick-n-dirty AF fine adjustment test that gives me good results.

Grab a cereal box or anything else that's got a flat surface with small printing on it. Put the camera on a tripod some distance away from the cereal box, where you're not down toward the minimum focus distance.

Set the camera to the center AF point and take a picture. Then set the AF fine adjustment to -1, re-focus, and take another picture.

Go to review mode, and press the down arrow/flash button to bring up the review menu and choose the side-by-side comparison option. Put the two shots next to each other, and zoom in until you can see which one has the sharper text.

If the -1 adjustment one looks sharper, repeat the process with further steps out to -2, -3, etc until the pictures stop getting sharper. If the un-adjusted shot looks sharper, do the same but with positive adjustments.

Eventually you'll land on what setting gives the sharpest results. This really varies with each lens, so since the K-r only lets you set a global AF adjustment factor rather than for specific lenses, I just keep a list of AF correction factors for each of my lenses and change the AF fine adjustment when I change lenses.
10-17-2012, 05:20 PM   #8
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QuoteOriginally posted by msatlas Quote
I have a quick-n-dirty AF fine adjustment test that gives me good results.
Not arguing with what you say, but this method is faster, likely more accurate, and costs about the same:
PENTAX DSLRs: Front or Back Focusing Problems? Free test (Lens Alignment) charts for Pentax, Nikon, Canon, Sony, Olympus.

10-19-2012, 06:20 PM   #9
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Original Poster
Thanks!

@msatlas -- looks easy enough to try, I'll play with it and see what results I get. Good idea!

@JimJohnson -- thanks, I did download those charts a couple of weeks ago, played with one of them for just a little while. Unfortunately the environment wasn't optimum, but I did get a couple of quick test shots. They suggested that the lens (the macro Tak) was focusing properly. I want to try it again under better conditions (light, and less air movement, the chart on plain paper is a bit wobbly). So I'm still in "lab" mode, and appreciate all this good information.
10-21-2012, 04:05 PM   #10
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I have done a similar adjustment to what msatlas it stating above.I took 2 identical images one using LV and one using AF then compare using the side by side as stated by msatlas. LV is about as good as it gets for focus accuracy so i match my AF to my LV shots at several distances and use the most common adjustment. I found a common adjustment worked for my 18-55, 18-135 and 55-300 Pentax zooms, I had to set mine for +3. I chose 2 distances about 20' and 60' as most images I take are 20' or more. I am very happy with my results.

Hans
10-21-2012, 05:52 PM   #11
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Thanks, Hans. I'm anxious to try some of these suggestions in earnest... past couple of weeks there's been very little chance of "wasting film", unfortunately, between crazy work schedule and ugly weather. But I am definitely going to experiment with some of these ideas, starting with the macro lens. As the K-r only stores one adjustment I may have to make a little cheat card for the other lenses.
10-29-2012, 12:08 AM   #12
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AF adjustment for KR.

The AF adjustment appears to be meant for using one specific prime lens only. The method of recording settings for different lenses, and then adjusting AF settings as you change lenses seems laborious but is a work around if really necessary.

But with zoom lenses, which part of the zoom range do you adjust? Here's my dllemma - I use a Tamron 18 - 250mm zoom lens. At wide angle, the lens 'focuses' at a range that clearly exceeds the actual distance for medium close up objects - one can read the distance indicator off the lens barrel. By zooming in, I can refocus, accurately, and then I need to lock that focus and zoom out again.

The problem I presume is with my lens as it focuses accurately as I increase the focal length. Resetting the AF setting in my camera will mess up the focus accuracy for longer focal lengths. So the AF adjustment ultimately is of no value to me and anyone else who prefers zoom lenses.
10-29-2012, 07:10 AM   #13
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Thanks for your thoughts on this. I've been playing a little, when time and circumstances allow, and I've discovered that one of the kit lenses (the 18-55) does focus quite accurately under controlled conditions (tripod, "still life" subject). So possibly (likely, actually) the lack of sharpness I had seen was at least partly attributable to shooting conditions (slow shutter speed, maybe too-small aperture, etc.). At the moment the only "prime" AF lens I have is a macro, and I need to do more practice with this lens to improve my skills with it. Whether or not, ultimately, it will need any fine adjustment, remains to be seen. But I was quite pleasantly surprised at the sharpness of the AF on the short zoom -- a little chagrined to admit that maybe my perceived problem was pilot error rather than camera or lens error, but what the heck. Learn something new every day!
10-29-2012, 07:53 AM   #14
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QuoteOriginally posted by OrchidJulie Quote
a little chagrined to admit that maybe my perceived problem was pilot error rather than camera or lens error, but what the heck. Learn something new every day!
Happens to all of us at one time or another. Some of us are too old to remember it but it DID happen.
10-29-2012, 08:12 AM   #15
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Indeed. Old dogs, new tricks... one of the hardest things about this newfangled DSLR (for me) is getting used to the wee beastie's ability to change settings. OK, I set it on AV mode, select aperture, and it shifts shutter or ISO or whatever. My old Spotmatic didn't do that! I set everything, and shutter, aperture, film speed stayed put! The solution, of course, is to set everything to manual and shoot that way (and I know lots of experienced 'togs do that) but I can't quite get used to the lack of that old match-needle to give me a hint...

So it's practice, practice, practice. Now, if this weather would just cooperate... hard to shoot stuff in near-gale winds!

Thanks for the reassurance!
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