Focusing

[Steelo]

I've just recently got a lens to replace my kit lens on my 450d, it's a Sigma 17-70DC 2.8-4.5....and i've noticed that on a few of my photos i've taken with it, that there are certain areas out of focus/soft....

I didn't notice this on my kit lens, but then it wasn't anywhere near as sharp as this Sigma....could this be a problem with the lens, or is it more likely user issue? I am relatively new to SLR photography, so I wouldn't rule this out.

I mainly shoot landscape, and it's in these shots I find the issue, whereas shots of my car seem pretty sharp throughout....

 

[vaizki]

Well it has a maximum aperture of f/2.8 in the wide end, so I'm suspecting the "problem" is that your Depth of Field will have been shallow if the camera has chosen that aperture. In the 'tele' end it's f/4.5 only so you will have more DoF and that's why those shots may look more in focus.

Your kit lens was slower so this was not happening. It's not a bug, it's a feature.. If you want more in focus, put the camera on Av mode and select a smaller aperture (bigger number) like f/11 for your landscapes. But you will of course need more light.

 

[Steelo]

Oh dear, VERY amature mistake....i've just checked the EXIF for the photos in question, and you are indeed correct Jukka....I normally shoot in AV mode all the time and stick to around f/8-f/11, but the shots in question I was using TV mode, and it knocked the aperture to f/4....

Don't I feel the clown haha!