3/10 shots out of focus for my 350D

Questions for you pros shooting outdoor, non-posing shots. Do you only use the center focus point? I find about 3 out 10 of my photos out of focus (slightly). This is especially true if the subject is not filling up a large part of the frame, even though I made sure the center red dot is on the subject, not background and half-pressed trigger, heard beep, then recomposed. Is this because of the camera? Is 40D better?

It's probably because you recompose. The camera focuses on a flat plane, and so when you move the camera to recompose, that plane changes (in relation to the subject) making your subject out of focus. This will happen a lot more at closer distances.

Focus - lock -recompose isn't the best procedure to use. Far better to set AF points to "joystick select" and pick the point that's closest to where you need it. In recomposing, especially at wide apertures, you can let the subject distance change enough that DoF does you in.

You can either engage the focus lock option--Page 75 of your manual.

Or---

Manual focus

Or---

AF/AF lock--no AE lock---Custom function 4 option 2 Page 149 of your manual.

Any of these options will let you know if there is a problem with your XT.

Or perhaps are you shooting a fast lens wide open with a narrow DOF?

As I understand it, the focus plane is really a sphere, and all things at that distance away should be in focus. By recomposing, I only moved the angle of the camera and not the position, and hence the distance from the camera to the subject shouldn't have changed?

Chandler. wrote in post #4233823
It's probably because you recompose. The camera focuses on a flat plane, and so when you move the camera to recompose, that plane changes (in relation to the subject) making your subject out of focus. This will happen a lot more at closer distances.

Thank you. Seems you know very well about the camera even to the page no. I'm don't have the manual with me now, but by half-press and the shutter and holding it, should it archive focus lock? I'm using 1-shot mode. What do you usually use when shooting moving objects?

dave kadolph wrote in post #4234054
You can either engage the focus lock option--Page 75 of your manual.

Or---

Manual focus

Or---

AF/AF lock--no AE lock---Custom function 4 option 2 Page 149 of your manual.

Any of these options will let you know if there is a problem with your XT.

Or perhaps are you shooting a fast lens wide open with a narrow DOF?

Assuming you're using One-Shot focusing mode and that you're not very close to the subject, there are a number of possible issues:

- If the subject is too far away or too small, auto-focus could be locking onto the background. This is more likely if the subject itself doesn't have very high contrast areas and is presenting a higher contrast relative to the background. Also note that the square box around the focusing point in the viewfinder is only approximate.

- The 350D's auto-focus is not very good with low-light and fast lenses particularly when using a narrow DOF. The 400D, 30D, 40D, etc. have better auto-focus for these conditions since they include at least one high-precision f2.8 focus point. I upgraded from the 350D to the 400D for this reason.

- Your lens or camera could be front- or rear-focusing. Try the procedures and test chart at http://www.focustestch​art.com/chart.html

dr_who wrote in post #4234373
As I understand it, the focus plane is really a sphere, and all things at that distance away should be in focus. By recomposing, I only moved the angle of the camera and not the position, and hence the distance from the camera to the subject shouldn't have changed?

When you're very close to the subject, it is much more likely that recomposing will change the distance of the point you focused on from the film plane.

Give me a break

I own 3 different bodies and keep an copy of the manuals on my laptop.

And all 3 are slightly different.

And for a newbie it is easier if they have a bookmark to reference.

dr_who wrote in post #4234373
As I understand it, the focus plane is really a sphere, and all things at that distance away should be in focus. By recomposing, I only moved the angle of the camera and not the position, and hence the distance from the camera to the subject shouldn't have changed?

Lens designers go to great lengths to get the focal plane to be just that: a plane. Take the classic picture of a brick wall and see what you think.

Here's a good article on the subject:

http://visual-vacations.com …focus-recompose_sucks.htm

-js

number six wrote in post #4234809
Lens designers go to great lengths to get the focal plane to be just that: a plane. Take the classic picture of a brick wall and see what you think.

Here's a good article on the subject:

http://visual-vacations.com …focus-recompose_sucks.htm

-js

That's exactly the article I was looking for. Thanks for posting that. It does prove that the lens focuses on a flat plane.

Chandler. wrote in post #4235506
That's exactly the article I was looking for. Thanks for posting that. It does prove that the lens focuses on a flat plane.

Of course it does, focal plane is as flat as the camera sensor is!

Hermeto wrote in post #4235561
Of course it does, focal plane is as flat as the camera sensor is!

Exactly. Has to be, if my understanding of physics is correct.

Actually, we may be using wrong terms here - the focal plane is located at the sensor (or the film), inside the camera. That's why SLR shutters are usually called focal plane shutters.

What's the right word for the flat plane out there in the outside world that we've focused on? Plane of focus? Nah, I can't think of the right term...

-js