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04-28-2012, 06:59 PM   #1
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just bought the DA* 50-135mm and seems to have focusing issues

hi guys

after considering this lens and the sigma 50-150mm i bought this one but im really disappointed as it seems to have focusing issues.if you look at the two pics below do you see any focus issues or is this a behavior of the focal length. if this is a focus issue is this a front focus back focus issue and can it be corrected




this above image you will have to enlarge it bit more to see what i mean i was focusing on the spray bottle. but it seems out of focus when i enlarge it




thankz

04-28-2012, 07:04 PM   #2
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Can't really comment on the first - second one has quite a bit of motion blur it seems. Did you try using a tripod for these tests?
04-28-2012, 07:14 PM   #3
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Is this what you call a proper test? I look at the exif of your images on flickr and your shutter speed is very slow, especially for the second image. Before you write off the lens, please do yourself a favor and do a controlled test in bright daylight with a defined test target. Half baked efforts like this will not give a conclusive outcome.
04-28-2012, 07:14 PM   #4
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OMG, second one was taken at 1/13th shutter speed at 123mm focal length....Did you use tripod??

04-28-2012, 07:24 PM   #5
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this was not a proper test i just got this an hour back and just took some random pics. and this is how it showed up i want to use this lens mostly hand held for concerts and stuff .for the moment i will retake the shot with better lighting and then with a tripod
04-28-2012, 07:37 PM   #6
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ok guys here is a better test but still not a proper test .this was taken around the same focal length day light hiting the guitar from the side and the pic was taken from a tripod using 2 second timer to take the pic. still this looks bit out of focus to me specially the strings . not sure whether this have to do with the focal length .




thanks
04-28-2012, 08:28 PM   #7
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ok guys this another pic this is hand held and i think this pics proves my point ( if im not mistaken here ) .in this pic im focusing at the spray can but its out of focus and the hair brush behind that is more in focus




what you guys think

and this is more in the wider end
04-28-2012, 08:57 PM   #8
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NirVaan, it looks a to me like your lens/camera combo is slightly back focused. You are using a K-5, so it should be a simple matter to correct the abberation. For a quick calibration I use a ruler and take a shot at about 45deg, looking down the length of the ruler. Focus on , say, the numeral 6. If the lines and numbers behind the 6 are more in focus, you are back focused. Add positive correction on the K5, if the lines and numbers in front are more in focus you have a front focus situation, so add negative correction. If the 6 is in focus, you have no broblem at all. (if I don't have a ruler handy, I'll use the keyboard of my computer, or some small font text, You could use that hairbrush in the pic for example, but it would be difficult to remeber exactly which bristle you focussed on.)

Bear in mind that they central focus point of the K-5 is much larger than the red dot you see on the screen. Apparently it is roughly the size of the circular centre target of the standard focus screen. It is possible that the AF is actually accurate, but not focused on what you think it is focused on.

04-28-2012, 09:15 PM   #9
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thanks for the info.
this seems to be happening on the wider end ie. 50mm i dont see such a problem (to my eye) on the longer end. i.e 135mm . so will adding the correction work for the whole zoom range or will the long end start front focusing. i will try this non the less.

QuoteOriginally posted by wizofoz Quote
Bear in mind that they central focus point of the K-5 is much larger than the red dot you see on the screen. Apparently it is roughly the size of the circular centre target of the standard focus screen. It is possible that the AF is actually accurate, but not focused on what you think it is focused on.
i dont think this is the problem since i did not notice this with other lenses. even with the 55-300 zoom i had earlier.
thankz again
04-28-2012, 09:36 PM   #10
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This kind of impromptu testing isn't going to prove anything one way or the other, it's more like a test of "how can I fool the K-5's AF system", it looks like you have succeeded in doing so. The focus circle is actually a lot bigger than the red square indicates and the camera focuses by detecting contrast. Looking at the picture, the focus circle most likely encompasses both the aerosol spray and the hairbrush, and the hairbrush is definitely more contrasty than the label on the aerosol spray. Too many variables to be conclusive - you should reserve judgement until you have conducted a properly prescribed test under ideal conditions or just go out and shoot the heck out of the lens and decide whether to keep it or not after.
04-28-2012, 11:47 PM   #11
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Exactly what was said above. The reason it's happening at the wide end is cause the can looks too small to the AF point.

Bottom line: THAT GUITAR SHOT IS ALSO SHARP AS CAN BE. YOUR LENS IS OK.
04-29-2012, 12:30 AM   #12
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I would first do a lens test to make sure your lens is not defective in the first place. I believe the best practice is to do a 10x liveview manual focus shooting a test chart. Once you know your lens is technically good, then you can start calibrating your AF. Whether you can focus well with AF depends on the interaction between your cam and that particular lens. If your AF still misses after careful calibration, then you should probably look for another copy. It doesn't mean that lens or your cam is bad; it just means they are not meant to be together.

Hope this helps.
04-29-2012, 01:30 AM   #13
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thanks for all the info. i just contacted the shop (here in japan) they said to bring it to the shop and they will do a few steps and give me a different copy
04-30-2012, 12:57 AM   #14
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well went to the shop they checked it out and was correct there was a back focus issue but not with the lens but with the body. now they work perfect
04-30-2012, 03:44 AM   #15
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