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04-19-2012, 06:55 AM   #1
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DA16-50mm need advise

Hi all
I have a copy of da16-50mm which i buy it at ebay..
the problem is it not/really hard to get sharp pic. Are this is related to backfocus/frontfocus problem?. Do i need to send it to service this lens?
this is sample pic.. but this i use with CPL filter.


04-19-2012, 07:04 AM   #2
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Impossible to say from that picture. And no EXIF info so was it wide open? Do you get better pictures with the lens stopped down?
You need to do a controlled test. If it is a BF/FF problem then something will be in focus, just not what you wanted. Take a picture of a ruler from a 45 degree angle and focus on one point, then see if that point is in focus or if something else is. You MUST use a tripod to do this. That is quick and dirty, there are much better tests. Do a search for 'focus test' and you will find several methods. Some free, some with equipment you need to buy.
04-19-2012, 07:12 AM   #3
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hi jatrax
thanks
this is the exif data
ss1/125s, f2.8, ISO400
FL43mm, metering mode: spot

by the way i'll search for the "focus test"
04-19-2012, 07:17 AM   #4
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can not tell, from this small size img, it looks pretty good.
try use manual focus with live view, that way you can get accurate focus, and see if the img is sharp

04-19-2012, 07:23 AM   #5
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QuoteOriginally posted by liukaitc Quote
can not tell, from this small size img, it looks pretty good.
try use manual focus with live view, that way you can get accurate focus, and see if the img is sharp
this pic when i zoom in the middle of the flower ..it become blur.. i cannot get detail.. but when i use the humble 35mm AL.. it is easy to get a sharp flower.
04-19-2012, 07:25 AM   #6
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OK, at f/2.8 your depth of focus will be small. Check online for "depth of focus calculator" to see exactly what it is I cannot tell you without knowing the distance to subject. But it might be less than 1 inch. On fast lenses you have to watch depth of focus, it is hard to get everything you want in focus and the point of focus may be otherwhere than you thought depending on where the AF latched onto. The kit lens (or other slow lenses) mask this by having a larger depth of focus so imprecise focusing is not noticed.

Check into a focus test to understand what is happening, all is speculation until you can check under controlled conditions. Tripod, shutter delay or remote, proper focusing target.
04-19-2012, 08:42 AM   #7
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Have you set up the lens with your camera using AF adjustment? Every camera and lens is built to a +/- tolerance; some lenses will work fine out of the box, others will need adjustment.

What camera are you using? From your other posts it appears to be a K5.

From the K20D onward there's an AF adjustment facility in the Custom menu. Look in your camera manual.
04-19-2012, 10:42 AM   #8
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QuoteOriginally posted by JohnX Quote
Have you set up the lens with your camera using AF adjustment? Every camera and lens is built to a +/- tolerance; some lenses will work fine out of the box, others will need adjustment.

What camera are you using? From your other posts it appears to be a K5.

From the K20D onward there's an AF adjustment facility in the Custom menu. Look in your camera manual.

I agree with this. I have not owned this lens, but I've heard it tends to be one that needs a lot of adjustment. My DA* lens certainly did.

04-19-2012, 08:05 PM   #9
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QuoteOriginally posted by jatrax Quote
OK, at f/2.8 your depth of focus will be small. Check online for "depth of focus calculator" to see exactly what it is I cannot tell you without knowing the distance to subject. But it might be less than 1 inch. On fast lenses you have to watch depth of focus, it is hard to get everything you want in focus and the point of focus may be otherwhere than you thought depending on where the AF latched onto. The kit lens (or other slow lenses) mask this by having a larger depth of focus so imprecise focusing is not noticed.

Check into a focus test to understand what is happening, all is speculation until you can check under controlled conditions. Tripod, shutter delay or remote, proper focusing target.
ok thanks.. will check on that
04-19-2012, 08:10 PM   #10
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QuoteOriginally posted by JohnX Quote
Have you set up the lens with your camera using AF adjustment? Every camera and lens is built to a +/- tolerance; some lenses will work fine out of the box, others will need adjustment.

What camera are you using? From your other posts it appears to be a K5.

From the K20D onward there's an AF adjustment facility in the Custom menu. Look in your camera manual.
yes i'm using K5. Have play with the tolerence just now. but still cannot get sharp focus at the middle of the flower.
This is the sample..but using handheld.
EXIF:
ss 1/250s
f4
iso100
fl31mm
metering spot





any idea?
Thanks
04-19-2012, 10:02 PM   #11
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Yes, as already noted you are not doing a valid test. You cannot do that handheld, (unless you are superman). And you should not be messing with the autofocus adjustment without doing a controlled test, with a tripod. All you are going to do is keep changing things and become frustrated. It will not work. You must set up a controlled environment with a proper focus target.

Assuming a distance from sensor of 24", f/4 and FL of 31mm your depth of focus on that shot is a bit over 2". Anything closer or farther than that will be OOF. And handheld you can easily move enough when taking the shot to make part of the flower OOF. Or the autofocus can lock onto a different part of the flower than you think it did. As already mentioned try it with manual focus using liveview zoomed in. On a tripod!
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