Former Nikon user needs help w/ AF on a 5D MK I

[stephenberk]

I bought a used 5D MK I and new EF 24-105mm f/4L, and I'm having problems with the auto focus. I shot a test subject at 16 feet from the focal plane (used a tape measure), but the center AF moved the focal point past the 20ft mark on the lens. I was shooting 50mm at f5.6 so the sharpness was ok but really soft since the subject was on the near end of the focal range. When I shoot wide open at closer distances the photos are unusable. Any thoughts on this? Do I have to send both to Canon for repair, or is this a known problem with this body model? I've shot Nikon for the last 20 years so I'm totally out of my element here; I couldn't even figure out how to use the self-timer for family holiday photos. Any help for a newbie Canon user is appreciated!

[cicopo]

You're going to need the manual to fully understand what you need to do, and if you don't have it you can download one from Canon Support.

The self timer options are found by holding down the DRIVE button & turning one of the wheels, and I think it's the rear one in this case. You cycle through single frame, burst, 2 sec timer & 10 sec timer delay & maybe another choice. 

For the AF you can set it to multiple points & use the joystick to select a specific point, or (going from memory) you can select the single center point & if you want lock that on your target & re compose as necessary, OR you can switch to AI Servo which although meant for moving targets can also do the job quite a bit of the time for stationary objects BUT it's useless for situations like a bird on a branch of a tree where there are several branches much closer. That type of situation demands that you put the active AF spot on the target rather than let the camera select what to focus on. 

[stephenberk · Accepted solution]

Thanks for the reply! I pulled the manual from the web when I got the camera and think I have everything setup correctly.

What I actually need help with is if there's a known problem with AF on the 5D1 or if I'm using the wrong settings. I'm really just trying to determine if I need to send the camera body, lens, or both to Canon for repair, or if I would be wasting my money doing so.

My test subject was 16 feet away, but the camera and lens determined she was over 20 feet away. The camera was tripod mounted with IS off, ISO 800, Av mode set to f5.6, 50mm, AF mode AI-Focus, and the center focus point square on the subjects nose. I was using ettl flash, and unfortunately I don't remember what the shutter speed was, but I can pull it from EXIF if it's important. Focus was sharp about 5 feet behind the subject.

The focus issues remain the same with or without a UV filter on the lens. AF seems pretty good for macro up to about 10 feet away, then it seems to be way off. Is this a limitation of the AF system on this camera or could it be improved spending the money to have Canon look at it? Or am I better off unloading this at KEH and getting a different camera?

[cicopo]

Both the 5D & the 24-105 have very good reputations & it's been many bodies since I had one but it had no issues what so ever. It's an excellent portrait camera but the AF is a bit slow for serious action. Other than that you may have introduced a bad variable picking AI Focus which is known to be the least reliable of the 3 AF options & isn't included on the pro bodies. Use this link to pick the most appropriate test method for your situation. 

http://photography-on-the.net/forum/showthread.php?t=857871

(note to moderators, site has been approved for referals).

[stephenberk]

Thanks, that link is what I need.

[TTMartin]

These videos are invaluable for a new Canon user or anyone who thinks their Canon camera has an auto focus issue.

Join Canon USA's Rudy Winston for a two-hour session that will remove the veil of mystery, which for many photographers, surrounds their Canon EOS camera's autofocus system.

A Look at The Canon Autofocus System Part 1

A Look at The Canon Autofocus System Part 2 

A Look at The Canon Autofocus System Part 3