What is meant by front/back focusing?

[col4bin]

I see many posts on this topic but I am not sure what it means.

[Wilt]

You aim the focus point of the camera at an object, but the camera focuses in FRONT of that object = Front focus; you aim the focus point of the camera at an object, but the camera focuses BEHIND that object = Back focus.

[Mark_Cohran]

You aim the focus point of the camera at an object, but the camera focuses in FRONT of that object = Front focus; you aim the focus point of the camera at an object, but the camera focuses BEHIND that object = Back focus.

That's it in a nutshell, but I would add that often what people think is back for front focusing is actually mis-focusing, i.e. user error.

Mark

[BruceC]

I have been thinking about this too. How do you control front/back focusing? I have been doing some drag racing and when I focus on the car waiting to take off it's fine, but by the time the car lifts the tires (the time I want to take the picture) the car has moved 4 or more feet too far foward. Is there any thing I can do other then focus on the ground in front of the car?

[kram]

You can use AI servo or focus for a pre-determined spot and wait for the car to fill the frame.

Also, not sure how much of your problem is focus and how much is actual movement of the cars.

[BruceC]

You can use AI servo or focus for a pre-determined spot and wait for the car to fill the frame.
yeah I need to look into useing that. AI servo.

Also, not sure how much of your problem is focus and how much is actual movement of the cars.
oh you mean movements being to fast for shutter? yeah could be.

[kram]

Bruce, I was just browsing some of your shots- most of them seem to be in good sunny conditions. In which case, the movement of the cars issue is less likely.

Try AI Servo..... it does feel funny the first few times with the lens continuously focusing whenever you have the shutter (or the *) half pressed.

[BruceC]

Thanks Ill try that. how do you set it though?

[StewartR]

Bruce, I'd suggest you read the manual for your camera. DSLRs are extremely complicated things and you'll really only get the best out of them if you study how they work and what they can do.

If you've got a 350D like I have, the relevant part of the manual is page 70, where it shows you which button controls the AF Mode selection.

[BruceC]

Thanks StewartR