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03-14-2009, 05:25 PM   #1
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*ist DL - Focus Problem - operator error or hardware

Hello Everyone,

I'm a total newb and photography, and DSLR's. I've recently acquired a few zoom lens and have been testing them out.

I'm having some problems with my photos and have searched the boards / internet but have not found an answer for myself.

My images when zoomed in seem to have some weird focus.

From what I know, the focus of the camera is set to center / spot, and i adjust my aperture to focus.

I'm wondering, when zoomed in should I increase the aperture value to get a better focused shot?

I've tried to get a few closeup shots of birds and flowers.

The lens I'm having issues with is a Sigma 70-300mm DG APO.

I used a tripod, and use manual shutter release and a 2second time shot to reduce any kind of shake.

For pictures of the bird, I am thinking because the subject is small I can't really get better quality? There isn't much detail and the focus seems off even though I have the bird centered.









For the closeup of the flowers, I used the macro option on the lens and tried to focus on the center (dark orange part), holding the shutter release halfway and recomposing the shot. However, the focus does not seem to stick. I can set it to try to focus on the center, but then that would mean I can't recompose any of my shots with focus on the subject that I want.






If anyone can help or direct me to some online literature I would greatly appreciate it.

My question is : is this an issue with technique (which I believe) or more of an issue with hardware?

I would like to see if there are any information on testing / adjusting the focus on my camera.

The pictures & EXIF can be found on my photostream : http://www.flickr.com/photos/28822023@N06/

-Thu

03-14-2009, 07:14 PM   #2
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It's kind of hard to tell from the posted shots, since there is nothing much in front of or behind your subject to gauge if focused simply missed or what. But, on some it seems some of the blades of grass are sharper than the bird. So it could be the camera chose to focus there. Also, at least one seems blurry from motion - either your tripod isn't as sturdy as you thought, or perhaps there was wind blowing the subject around. I'm guessing had you taken enough shots, some would have come out better. But you may also need to accept that the lens you are using isn't the sharpest lens on the planet especially at full zoom and maximum aperture.
03-14-2009, 07:14 PM   #3
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It sounds like it may be technique, but let's make sure.

For the bird shots, are the first few shots extreme crops? If so, then I think you may be looking at the limitations of the lens. If they are not crops, then something's wrong and you should definitely get better than that.

For the flower shots in the "macro" mode, if you're doing the focus/recompose method, shifting the camera may lead to slight out of focus given the narrow depth of field.

You're on the right track shooting on a tripod with mirror lockup. As much as I hate brick wall test, you might want to try focusing on a brick wall in good, outdoor light. If you can't get a good focus that way, then try a different lens. That will tell you if it's the lens or the camera.

Sounds like you've already got it set to center point focus only, but make sure it's set to that when you're doing these tests. Otherwise, you won't know for sure what the camera is focusing on and it can cause you problems while you're troubleshooting.

Good luck!
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