Focus problem in 350D?

I bought xt 2 months ago and recently Tamron 28-75mm. I am having focus problem with this camera. I started researching other threads on this forum and found that there are a lot of front focus/back focus issues wtih xt. My theory is that xt uses other focus points which has best contrast even if you set the central focus point. Or it uses other focus points if the center focus sensor is unable to focus. To prove this I am linking to various threads which show this.

First my thread

http://forums.dpreview.com/forums/read.asp?forum=1029&message=21143451&q=tamron+focus+issues&qf=m

This thread shows that the lens chart test is working, but still focuses on the background(speaker).
http://forums.dpreview.com/forums/read.asp?forum=1029&message=20861210

Another thread indicating focus problem with 300d, but the same lens works well on xti.

http://forums.dpreview.com/forums/read.asp?forum=1029&message=21119558&q=front+focus&qf=s

Here is another thread that has a problem with 30D. The black background has more contrast against the paper. The problem goes away using 5D.
http://forums.dpreview.com/forums/read.asp?forum=1029&message=20785204

I can post many more examples that have some contrast object on the side or on other focus points that seems to be in focus.

--
-pabs

If you think it's your camera, then send it to Canon for calibration without delay now that it's under warranty.

Do not assume though that your lens is not at fault. If you get a good copy of that lens, it is out of this world. But less than stellar copies have been known to be around.

Olga

I am not sure if this is just one camera problem. I saw this happening with my brother's camera too.

If I let camera choose the focus point, those pictures are sharp where the camera indicated it focused.

Olga Johnson said:

If you think it's your camera, then send it to Canon for
calibration without delay now that it's under warranty.

Do not assume though that your lens is not at fault. If you get a
good copy of that lens, it is out of this world. But less than
stellar copies have been known to be around.

Olga

Click to expand...

--
-pabs

pabs06 said:

I bought xt 2 months ago and recently Tamron 28-75mm. I am having
focus problem with this camera. I started researching other threads
on this forum and found that there are a lot of front focus/back
focus issues wtih xt. My theory is that xt uses other focus points
which has best contrast even if you set the central focus point. Or
it uses other focus points if the center focus sensor is unable to
focus. To prove this I am linking to various threads which show
this.

First my thread

http://forums.dpreview.com/forums/read.asp?forum=1029&message=21143451&q=tamron+focus+issues&qf=m

This thread shows that the lens chart test is working, but still
focuses on the background(speaker).
http://forums.dpreview.com/forums/read.asp?forum=1029&message=20861210

Another thread indicating focus problem with 300d, but the same
lens works well on xti.

http://forums.dpreview.com/forums/read.asp?forum=1029&message=21119558&q=front+focus&qf=s

Here is another thread that has a problem with 30D. The black
background has more contrast against the paper. The problem goes
away using 5D.
http://forums.dpreview.com/forums/read.asp?forum=1029&message=20785204

I can post many more examples that have some contrast object on the
side or on other focus points that seems to be in focus.

--
-pabs

Click to expand...

Although I don't know what the camera is used, here is another example.
http://forums.dpreview.com/forums/read.asp?forum=1029&message=21247539
--
-pabs

..of cameras and lenses that may have problems and that is not surprising because those with problems post the most messages.

If you believe your camera is misfocusing, send it to Canon for calibration. If you think it's your lens, send it for calibration. Send both for calibration, if you so wish.

Referring us to messages about focusing problems does nothing to help yourself unless that was not the point of your message. If your point was something else, it has not been clear.

Olga

Hey pabs06, I tried your test of shooting through a hole in a piece of paper to force only the centre focus point.
It made no difference to my 350D with several lenses.

I have been tweaking my 350D using the mirror stop screw, and this really does show what is going on with different lenses.

I know this is not an option for you, since your 350D is still under warranty.

I have a Sigma 24-70 f/2.8 EX that is slightly forward, a 50/1.8 that is about spot on, and a 70-200 F/4L that is slightly rearward. By tweaking the mirror stop I can arrange for the Sigma to be spot on (even wide @24mm it is much better), but then the 70-200 is back-focussing enough to be a problem. I have played about with this on and off for some months, but am still not quite sure what I should do with the lenses (if anything). I am thinking of sending the 70-200 away, as I believe this is rear focussing since the others seem to be all forward of it. However I have read that the 70-200 can back-focus on a 350D but be fine on a 20D or 30D, so I am nervous about fixing it to my 350D.

Your Tammy shots look very like my Sigma before I dropped the focus back a little. I suggest you do careful focus tests with any fast lenses you can. If three or four lenses are all front focussing, then it is most likely to be your 350D that needs calibrating.
It could however be the Tammy or both!

The other point to remember is that the focus on the 350D is a little inaccurate to begin with, particularly in lower light.

Happy hunting.