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02-22-2013, 11:31 PM   #1
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Focus adjust

OK guys

im sure this has been discussed 50 million times, but has anyone come up with an easy and repeatable way to check and adjust the focus adjustment with the K-5??

I have tried a couple of times with focus charts but i have found most of them difficult to get repeatable results with - i think perhaps the focus target is just to small to get a repeatable result with?? (or maybe im doing it wrong?)

02-23-2013, 01:31 AM   #2
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QuoteOriginally posted by milesy Quote
OK guys

im sure this has been discussed 50 million times, but has anyone come up with an easy and repeatable way to check and adjust the focus adjustment with the K-5??

I have tried a couple of times with focus charts but i have found most of them difficult to get repeatable results with - i think perhaps the focus target is just to small to get a repeatable result with?? (or maybe im doing it wrong?)
The chart mentioned here https://www.pentaxforums.com/forums/pentax-dslr-discussion/208110-front-back-...arts-free.html can be printed at different sizes to suit different focal lengths and causes no AF point confusion so I found it very dependable for AF adjustment.
02-23-2013, 01:33 AM   #3
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Hi, I have not used any charts for my AF adjustment, but instead used my kids knitted snake with feathers stuck into it. The knitted pattern makes a good surface for focus and the feathers adds accuracy. Back and front focus is easy detected .

For MF lenses I use CIF. Focus on a feather and if the shutter will not fire adjust AF until it does.
02-23-2013, 01:59 AM   #4
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Keep in mind that the adjustment may be different depending on the focusing distance. You should try to calibrate for the most common distance you plan to use. Also if you are calibrating a zoom lens it will be different for the various focal lengths.

I was able to calibrate my DA 55-300 at the 300mm end, which I use for wildlife, by shooting a distant tree bark at +2 -2 intervals through the entire adjustment range (e.g. at 0 +2 -2 +4 -4, etc.) and then compare the images. For reference I used Live View which almost always nails the focus. Once I found the sharpest image (closest to the one from Live View), then I fine tuned it going +- 1 steps.

02-23-2013, 02:03 AM   #5
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This is something I need to go as well. Sure my pics are soft.
02-23-2013, 04:23 AM   #6
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I gave up trying those angled charts and use a flat target in the back yard, white cardboard with an x and some newsprint on it. Take a group of shots with different MA adjustments and pick the best. MLU, 2 sec timer, sr off. I have canon now, but it is no doubt the same. There is a new way a guy found that involves getting the best focus with live view, carefully setting the lens to MF then try different adjustments to get the most negative where you still get a focus confirmation in the viewfinder to the most positive and then split the difference. It seems pretty accurate. You can just AF and then zoom in on live view to check also. I have found a couple lenses that have changed over time too, so if you get some bad results and haven't checked a lens in a while, it may be worth it to do a quick check with live view.
02-23-2013, 07:07 AM   #7
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I tried charts and comparing shots side-by-side, but still was a little off. I now use live view as a guide.

Set your focus points to center (while using a tripod), and focus on an object through the viewfinder. Then switch to live view (contrast detect), refocus and watch which direction the focus ring turns. Adjust your focus until the ring stops moving between phase detect and contrast detect, and viola!

This helped a lot on lenses that have a thin DOF. Contrast detect in descent lighting is pretty spot on.
02-23-2013, 07:15 AM   #8
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Use wide ap and underexpose a little for this check:

Attached Images
View Picture EXIF
PENTAX *ist DS  Photo 
02-23-2013, 11:40 AM   #9
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If you want to get as good as your going to get with a specific lens at a specific focal length, those charts are in my opinion the best thing going for tweaking auto-focus. And for my money (free), this one is the best:
PENTAX DSLRs: Front or Back Focusing Problems? Free test (Lens Alignment) charts for Pentax, Nikon, Canon, Sony, Olympus.

I admit, if you aren't the type who is willing to properly set things up and otherwise follow directions, this is going to be a waste of your time.

There are still plenty of situations where I am smarter than my camera and focus manually. Virtually every auto-focus system out there uses contrast to determine focus. And sometimes my desired focus plane isn't the highest contrast part of what the sensor sees. A really good example is the eye of a grey squirrel surrounded by lots of little twigs and rough bark on an overcast day. If I can't achieve the desired focus manually, guess what? It isn't my camera's auto-focus at fault, but my choice of lens and aperture.
02-23-2013, 02:24 PM   #10
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Original Poster
thanks all for replying....well here are some results - one at -3 one at -8 and one at -10.......i would be interested to see what you guys thought gave the best result (please do not that this was printed on plain paper using a bubble jet - perhaps not the best for 100% clarity of print)

(1)




(2)



(3)

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