Focus problems with Xsi and Tokina lenses

rrcolejr

Recently got my Xsi (upgraded from my old 10D) and have noticed that I can not get sharp focus with my two Tokina lenses that I have. On my 10D they work perfectly (when I get time going to try both cameras with them again to make sure) but on my Xsi I can not get a sharp a focus. This is even with putting it on my tripod and using live view to get a sharp focus.

If I put my canon 50mm 1.8 on my Xsi it will focus perfect. Anyone have any ideas what is causing my problems? Any help will be greatly appreciated, don't want to have to replace my lenses just yet.

Thanks,
Ronnie

ziggy53

The Canon XSi/450D is one of those cameras with a "Live View" capability. One of the things you can do with live view is check manual focus.

Mount the camera on a tripod and autofocus on something with high contrast so the SF has something easy to AF against. Take an image (JPG) using the AF on.

Now switch the lens to manual focus and turn on the live view. Zoom in and set focus manually. Take another image.

Try this with a couple more scenes, just so you have a few tests to be sure of consistant performance.

Now review the images with AF on against your manual focus (which should be perfect, of course.) If the AF is not correct it should be easy to see on the computer.

It would be nice to post links to the full resolution images if you want us to comment further.

rrcolejr

Thanks for the reply Ziggy. This weekend I will try to set up a test and post the pictures up here.

ziggy53

ziggy53 wrote:

...

Now switch the lens to manual focus and turn on the live view. Zoom in and set focus manually. Take another image.

...

To be clear, the "zoom" to which I mention is the capability of the camera to magnify the live image, facilitating accurate manual focus.