I've been coming across these two terms a lot lately after checking reviews of certain Sigma Lenses and I Googled it but the stuff I found has a lot of mumbo-jumbo...

Can anyone simply explain what they mean? :)

your lens has backfocus when all your pictures come out focused somewhere at the rear of your supposed to be in-focus subject.

your lens has frontfocus when all your pictures come out focused somewhere at the front of your supposed to be in-focus subject.

hint on having a lens with these problems: you think you're doing it all wrong coz you just can't seem to get it to focus correctly. :D

i think its the photographers' error that causes backfocus and frontfocus. simply didnt care about the focus points of the camera.

@Jon - Wow, that's simple. Thanks a lot for the tip!

@Cris - Hmmm, it is possible but I think there really are some lenses that can't focus properly, read about the issues with Sigmas... Can anyone shed light on this?

Fidel,
These focus problems may also be a camera issue (with specific lenses) and as far as I know, it can be fixed by having your camera recalibrated.

Regards,
Norman

Oh okay, thanks for the input Norman. My query is answered. :)

@fidel

just in case you would like to find more about the topic and would like to test your lenses yourself.. you may check out these links regarding focus testing..

I used Tim Jackson's focus test chart in testing my EF 50mm f/1.8 and found out it had FF issues.

hope you'll find them useful :)

http://www.focustestchart.com/chart.html
http://www.photo.net/learn/focustest/

My friend loaned this Nikkor 12-24mm one time and all of his shots where out-of-focus-in-the-middle with only that lens, obviously a FF or BF problem. :D even if he locked the focus point in the middle.

focus locking and then recomposing will also lead to backfocusing.....

Thanks for the link Sandy, I'm going to test my lenses in a while, hope they're okay....

Thanks for the input too Christopher and John. :)

focus locking and then recomposing will also lead to backfocusing.....

I guess this will happen if you change your focal length or have moved slightly backward/forward during recomposition.

Back focus is the result of a mis-alignment of the sensor and its focal points.

the discussions in these links below are written using the d2x camera as an example:

AREN'T THE AF SENSORS THE SAME SIZE AS THE VIEWFINDER'S AF BRACKETS?

http://www.digitalphotographer.com.ph/forum/showthread.php?t=3786&page=4

TESTING AF SENSORS

http://www.digitalphotographer.com.ph/forum/showthread.php?t=208