20D focusing problem

[james_castagno]

My 20D is going back to Canon NJ as the focus is not spot on with any

of my lenses. It seems that if using the center focus point or the

focus points on the right side the focus is real close but not

perfect, if I use a focus point on the left side of the viewfinder the

focus is not even close. The problem seems to have gotten worse as I

originally thought that my 70-200 f4L was the problem as the problem

showed up more with that lens but now all my lenses seem to be

effected. I am curious as to whether other people who have bought this

camera have had this problem as everyone seems to have nothing but

praise for the 20D. I am not really upset, just curious.

[cwchia]

My Experience is the center point seem to be sharpest compare to the rest.

[kraig_cuddeford]

I havn't tested my kit lens but I hope there's support for this issue when I get other canon lenses. Check this long list of posts. http://forums.dpreview.com/forums/read.asp?forum=1019&message=11066731

 

It seems that it is much too common. I guess everyone needs a couple screws turned to get the carbs in sync.

[aron]

My 70-200l F/4 & my 17-40l f/4 are both soft in comparison to my cheap 18-55 kit lens. A fluke maybe, but those lenses also produce better contrast & color so they are still very effective after some sharpening. As for focus points, I focus recompose so I have never used anything but center. On the Canon survey they actually ask if numerous foucs points was a determing factor for buying the camera and I just laugh. I just need one. I realize that when on a tripod, it is helpful to have many, but the truth is once I compose a shot when tripod mounted, even with nine focus points, usually none of them line up with where I have to focus so I have to focus recompose anyway so I don't have much use for them.

[y_chen]

Well, Aron,

 

I believe multiple AF points definitely help if you use AF. You'd better use the nearest AF point to focus and then recompose a little bit. If you always use the middle one and then rotate your camera dramatically, the focus plan actually rotates as well during the recompose. That will cause problem when you have shallow depth of field and may have contribute to the softness of the subject.

[james_castagno]

Hey Aron. I use the other focusing points if I am shooting something like a portrait at a large aperture as a focus and recompose may hurt me DOF wise, but on the other hand I still shoot film with my old EOS-1 that only has a center focus point and never had a problem with portraits with that camera. In some ways I think digital may make us find problems that do not exist!

[henry_minsky1]

With the 20D, it's pretty quick to hit that tiny button and then use the joystick to select a focus point, so I tend to try to do that rather than focus and recompose, when possible.

 

BTW, I sent my 20D to Canon to have them check the auto focus, I was getting what appeared to be front-focusing on my lenses, not a lot, just enough to be oh so very irritating. I ended up sending my Sigma 18-50/2.8 lens to Sigma to check it also, as that was the one that was really hard to take, and things are much better now. sigh.

[aron]

Good points about depth of field. I do not focus and then rotate the plain. If I am shooting vertical, I compose vertical to focus.

[jon_austin]

"Good points about depth of field. I do not focus and then rotate the plain. If I am shooting vertical, I compose vertical to focus."

 

Aron: switching between vertical ("portrait") and hortizontal ("landscape") orientations is not the kind of rotation to which the other posters were referring.

 

What they're talking about is the movement of the focus plane when you recompose. When you consider that the focus plane is parallel to the face of the camera, you realize that a movement of just a few degrees during recomposure can move the plane of focus a few inches to a few feet -- relative to the distance to the subject -- depending upon the amount of movement and the distance to the subject.

 

If the amount of movement of the plane of focus exceeds the DOF, you'll lose acceptable focus on your subject, even though you focused properly and the AF function in your camera/lens combination is performing within spec.

[ren__damkot]

That means you 'rotate' the focus plane. It's explained here: url=http://visual-vacations.com/Photography/focus-recompose_sucks.htm