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06-15-2007, 10:15 AM   #1
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Sigma 17-70mm/F2.8-4.5 DC MARCO

I just purchased this lens to replace my kit lens over a week... I've played around with it a lot, but I've gotten much more missed focus photos then I did with my kit lens, some photos look perfect and some look totally missed focused.

Is there any way I can test the lens b4 I return the lens other then keep shooting? I just started shooting with DSLR for 2 months, so it's hard for me to tell that it's my skills or it's the lens that missed focus the photos. (I don't think it's the camera because it's focusing great with kit lens) I am wondering if there is any testing technique that I can confirm that the lens is defective? Because I only have 2 weeks if I want to get my money back... @_@

06-15-2007, 02:01 PM   #2
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Some things to consider:

1) is the Sigma using larger apertures than possible with the Pentax kit? if so you'll have shallower DOF, which in conjunction with
2) which focus point the camera chooses may throw out what you desire further out of focus than would happen with the P kit.

I'd pay attention to which focus point is selected, the aperture... What are the symptoms precisely? Is everything fuzzy, or is the focus simply at a wrong place.

Set up some target in good light and shoot several times at different focal lengths, each time paying attention to the viewfinder focus indicators... and then look to see if the focus is actually where the camera indicated.

If the focus is off, then something's defective. If not, then you'll have to be more aware as you're shooting away...

(I've taken some crowd shots that I liked when reviewing on camera. But once large on the PC I saw the damn multi point focus picked stander-bye's closer to me as the spot to focus! the subject I tried for was well out of focus. So that's technique. But of note, there was good focus, only on the wrong thing.)
06-15-2007, 02:13 PM   #3
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Hi Teko,
Please post some of the shots that are causing you concern....there are a lot of people here that will be able to help you, but they need to see the problem in order to comment.
Grant
06-16-2007, 06:12 AM   #4
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I may have to agree with Nesster after I review my photos. Maybe some photos with wide open aperture (F2.8) is shallower, which seems softer... That makes me feel it's not perfectly focused...

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