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Thread: K-5, microadjustment, and auto focus accuracy

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    K-5, microadjustment, and auto focus accuracy

    Hello fellow Pentaxians!

    I am trying to learn how to deal with front focusing and back focusing that I seem to encounter quite often with the K-5 and a variety of lenses that I've used so far. I'm not sure if inaccurate AF is a result of the camera, the lens, or both. So here are a few questions from someone that doesn't know much about cameras:

    (1) does front focusing mean that the camera is focusing closer in distance to the camera than the intended subject? And alternatively, back focusing means that the camera is focusing further away than the intended subject?

    (2) if I am having front focusing problems (and assuming the suggested definition for front focusing noted above), will I be applying " - " or " + " to the micro adjustments in the K-5?

    (3) In the K-5, the range of micro adjustment is -10 to +10. Does anyone know the equivalent in real world measurement the amount represented by each micro adjustment unit? I.E., does applying 1 micro adjustment unit equals to 1 centimeter ?

    (4) What is the best way to test whether the camera/lens is auto focusing accurately?

    Thanks for the help everyone!
    Armanius
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    Re: K-5, microadjustment, and auto focus accuracy

    1. Yes, that's correct.

    2. The way I understand it is that - corrects front focus and + back focus
    See attachment containing page 126 AF Fine Adjustment - item 4 of the manual.
    Although admittedly it seems contra of what one might expect.

    3. No idea really - might be lens and perhaps even distance-to-subject dependent.

    4. Tripod for sure to achieve consistent test results and a 'suitable' 3D subject.
    Subject could be a person: aim for the eye: if ear is sharp -> back focus, if nose is sharp -> front focus, if eye is sharp ...
    Last edited by Knorp; 28th October 2013 at 12:51.
    Bart ...

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    Re: K-5, microadjustment, and auto focus accuracy

    It is all a black art. For my 43 mm I just plonked a newspaper on the floor, put the camera on a tripod and aimed down, took a few shots at different adjustments.

    Needed +10. Much better, so much so that I will not get rid of the 43mm and K5 ...

    Lee

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    Re: K-5, microadjustment, and auto focus accuracy

    1-2 has been answered allready.
    3 I think you have to just check it out with different settings until its fine
    4 personally I use both:a) a lens checker chart and b) (and more important) I shoot subjects from an angle and also from the front side so I can see if the focus is fine or not

    In the beginning I had put it on tripod and checked in live view if the AF had focused fine but now I feel more safe to adjust and check with real world subjects at different distances.

    It has become my new hobby since I own the K5
    First find ot if the lens is sharp or if it has a problem; then adjust focus of the lens if its fine

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    Re: K-5, microadjustment, and auto focus accuracy

    There is a product from Michael Tapes called "Lens Align" which makes this process very simple. I have used it with success on both my Nikon / Zeiss lenses and now on the K-5.

    I think if you are trying to accurately use the focus adjust feature on the K-5 you need a level of precision to assure you are getting what you need.

    woody

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    Re: K-5, microadjustment, and auto focus accuracy

    Drive you crazy
    At least, drive me crazy!
    It's very much complicated by the fact that it'll focus on the thing with most contrast, and that the focus point is much bigger than the one in the viewfinder.

    This means you'll get different results with different subjects.

    I did it with a newspaper on the floor and a tripod - at about a 45 deg angle. But in the end I've just switched it all back to zero, and it seems to work fine

    Just this guy you know

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    Re: K-5, microadjustment, and auto focus accuracy

    Quote Originally Posted by jonoslack View Post
    Drive you crazy
    At least, drive me crazy!
    It's very much complicated by the fact that it'll focus on the thing with most contrast, and that the focus point is much bigger than the one in the viewfinder.

    This means you'll get different results with different subjects.

    I did it with a newspaper on the floor and a tripod - at about a 45 deg angle. But in the end I've just switched it all back to zero, and it seems to work fine
    So even when using the center point, the focus point is bigger than what the point shows in the viewfinder? Aaargh. That might explain why on smaller sized subjects, the AF is focusing on something else other than the subject itself ...
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    Re: K-5, microadjustment, and auto focus accuracy

    You need to think of it as being the same size as the central circle displayed in the VF.

    Lee

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    Re: K-5, microadjustment, and auto focus accuracy

    Quote Originally Posted by Armanius View Post
    So even when using the center point, the focus point is bigger than what the point shows in the viewfinder? Aaargh. That might explain why on smaller sized subjects, the AF is focusing on something else other than the subject itself ...
    Lee has it - but the K5 isn't alone in this, almost all cameras have the same issue to a greater or lesser extent.

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    Re: K-5, microadjustment, and auto focus accuracy

    Part of me wonders why it needs to make that much difference. OK, for close shots I agree but for mid to distant landscape shots with a reasonable aperture it shouldn't really matter but then I suppose if you are aiming for the side of a tree in the middle distance but it latches on to something with more contrast far away ... hmn. I am finding the whole K5 experience quite a good learning curve after using smaller sensor cameras for a while. "No, don't expect everything to be in focus, remember DOF?" I tell myself. Frankly, I think I have more OOF shots due to camera shake with too low shutter speeds than AF inaccuracy. And as the MegaPixels increase the worse the effect of camera shake. And the K5 (like others) has an AA filter (a good thing), so well-focused and stabilized shots need more sharpening than the LR defaults.

    The few prints I have made from the K5 and GH2, a totally unscientific experiment as they weren't even the same scenes in the same lighting etc but generally where the GH2 seemed much sharper on-screen revealed a lot to me. The K5s were total winners for me, those taken with the 43mm simply gorgeous.

    Sorry, I have drifted well off-topic (too much wine again, naughty me).

    Lee

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