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04-17-2010, 04:52 AM   #61
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also, do the test in daylight -- that would help your camera achieve accurate focus.

04-17-2010, 07:54 AM   #62
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I did the same subject under daylight. It was metering more than enough light. Here is F2.8 and F5.6 at 28mm 55mm 75mm
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04-17-2010, 07:55 AM   #63
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F5.6 75mm

As you can see I cropped the photos to be a relative size for comparison.
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04-17-2010, 08:57 AM   #64
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Well, it's either very very soft at f/2.8, or that's some pretty severe front focus. Have you specifically tested for the latter (eg, using a focus test chart specially designed for this purpose)?

04-17-2010, 08:59 AM   #65
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I'm not familiar with front focus or the testing of it.
04-17-2010, 09:17 AM   #66
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Front focus means that while the camera tries to focus at a given place, it missed, and focused in front instead. So a test checks to see if soemthing in front of the place where the camera tried to focus is actually in focus. Right now, you can't tell if anything in front of your subject is in focus, because there *is* nothing in front. The trick is usually to get something in front of the subejct that can be used to check where focus actually was achieved, but *without* having the AF system actually choose to focus on the thing in front instead. So most people's attempts at testing this without well-designed test charts generally fail. A popular test chart is at focustestchart.com. If you search/browse these forums, you'll see probably hundreds of posts dealing with front focus and backfocus (FF and BF) issues. Some of these reports are real, and some are not - the latter because of improperly conducted tests where in fact the camera simply *chose* to focus on the object in front. But since there is nothing in front in your case, we can rule that out right away. You either have a real focus problem that a test will reveal, or else the lens is just bad wide open.
04-17-2010, 09:36 AM   #67
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Those tests were done with manual focus so I guess it's safe to assume it's not a front-focus issue? Back to Tamron goes the lens.
04-17-2010, 10:37 AM   #68
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see if you can get it recalibrated or custom set it thru the af ajustment menu
it wont be total lost
lumpy

04-17-2010, 12:25 PM   #69
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QuoteOriginally posted by smcook99 Quote
Those tests were done with manual focus so I guess it's safe to assume it's not a front-focus issue?
No, but now we're squarely in the territory of might-be-user-error. I'd get someone *else* to try it - someone with experience manually focusing fast lenses on modern DSLR's. It's well known that the focus screen lies and shows too much in focus at wide apertures, leading to situations where you *think* you have the subject in focus but it turns out not to be. It's close to accurate at f/2.8, but could be off by enough to be fooling you. At this point, given that Tamron didn't see a problem, I'm actually think thinking this is the most likely story.

Of course, simply repeating the test using AF - after first checking for FF/BF issues - would also be in order.
04-17-2010, 01:33 PM   #70
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Here are four tests in different light and distance. On first glance it looks as though the foreground is in focus more so than the background. If this is the case is this something I can compensate for like you mentioned an AF adjustment menu?
Question 1) Can I adjust just this lens or will it affect every lens I use?
Question 2) How is it the lens can focus fine in one aperture and not another?
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04-17-2010, 06:00 PM   #71
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Strange indeed. OK, I'll ask this under the "no question is a dumb question" scapegoat: have you done similar tests with any of your other lenses to make your something didn't happen to your camera (just to rule it out)?
04-17-2010, 06:13 PM   #72
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No I have not. BUT, my other lens works perfectly.
04-17-2010, 06:44 PM   #73
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honestly, those new photos doesnt look nice at f2.8. something is wrong there.
04-17-2010, 11:00 PM   #74
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QuoteOriginally posted by smcook99 Quote
Here are four tests in different light and distance. On first glance it looks as though the foreground is in focus more so than the background.
Barely, maybe. Don't look at anything but the center line and the few lines in front and behind. Looks like the focus zone extends both in front of and behind the line, just as it should. Maybe slightly more in front than behind in some, but that's normal in tungsten light as those appear to have been. In any case nothing that would cause what you're seeing in the other shots.

QuoteQuote:
If this is the case is this something I can compensate for like you mentioned an AF adjustment menu?
Question 1) Can I adjust just this lens or will it affect every lens I use?
The answer to both those question depends on your camera; your manual should provide the answers.

QuoteQuote:
Question 2) How is it the lens can focus fine in one aperture and not another?
First, as i said, it doesn't actually look like you've got any sort of serious focus problem. But FWIW, what happens is that at f/2.8, the DOF is the smallest it will get. At smaller apertures, the DOF gets larger and larger and masks any slight discrepancy in focus point that might exist.
04-18-2010, 12:10 AM   #75
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the af focus ajustment will work on the k7andk20 you can use the global or for one lens being used at that time i had to it on a 24-60 sigma f/2.8 worked fine
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