AF perfect in Servo mode; searches in One Shot

I recently sold a 1D body that had been working perfectly for me. The buyer, a

nice guy who seems honest, says the AF is fine in Servo mode, but searches too

much in One Shot.

 

He's cleaned the terminals, tried three different lenses and all the focal

point settings--always with the same result.

 

Has anyone encountered this problem with the AF on a 1 Series body, or any

other Canon DSLR?

 

Also, is increased battery use the only downside to always shooting in Servo

mode?

 

Thanks for your ideas and experience.

If you can't use one shot focus, you can't focus and recompose. In servo mode if you try it the camera will simply refocus somewhere you don't want it to.

Thanks, Bob. (I knew that---really!).

"AF is fine in Servo mode, but searches too much in One Shot.

He's cleaned the terminals, tried three different lenses and all the focal point settings--

always with the same result."

 

Could it be he's using slow zooms? The 1V, 3 and 1D series require a F2.8 lens to fully

enable the center cluster of 7 cross sensors. If he used a varible aperture zoom, say an EF

28-135 IS 3.5-5.6, the camera treats it as a F5.6 optics and disables all cross sensors,

degrading them to single axis sensors. As such AF isn't nearly as effective. In fact it is

terrible in dim or low contrast situations. If he used a constant aperture F4 lens, e.g., EF

70-200 4L USM, only the center AF sensor retains cross sensitivity. The other 6 crosses

degrade to single axis sensitivity. This yields decent performance even in low light, albeit

not as good as the fully enabled high precision AF of a F2.8 or faster optic.

He probably noticed this because in AI servo, it will let him take the picture whether it is in focus or not, while in one shot, it will hunt until focus is achieved. You probably didn't notice it because you knew all about this, but the new owner may not, which could have led him to this conclusion. Did the new owner notice any difference in the pictures themselves? Were they focused accurately?

On the 1-series cameras there are some Personal Functions that fine-tune the way the AF works. It could be a good idea to make sure these are all set at the default values as a first step, since they could be responsible for unexpected behaviour. But this does sound more like user unfamiliarity than a camera problem.

"If you can't use one shot focus, you can't focus and recompose. In servo mode if you try it the camera will simply refocus somewhere you don't want it to."

 

that's true if you have the focus on the shutter button (default setting), but untrue if you put focus on the back thumb button.

Thanks for your posts to date. Here's what the buyer of the camera replied, who has been very patient with this problem, when I forwarded your thoughts to him: <p>

 

<li>1. I not only reset all personal functions to default, but I also removed the back-up battery for 1/2 hour to reset all functions.

<p>

<li>2. My Zooms are Canon L 70-200 2.8, 24-70 2.8 and 17-40 4.0 so AF sensor sensitivity should not be an issue. I have modified the custom function with regards to number of focus points (45, 11, 9) and have used the center point exclusively with no improvement.

<p>

<li>3. When the camera does focus, it acts just like I would expect. Auto focus point light, lock on target. When it is working improperly, it hunts all the way in then all the way out through to point of proper focus. If it locks at all, it is with the viewfinder completely out of focus. Not even close. If I take the shot, the end result confirms what I saw in the viewfinder. Sometimes even when it locks on target, the sensor does not light."

<p>

 

Is there anything that he and the rest of us have overlooked up to now?

<p>

 

Continued thanks for trying to help solve this problem, or at least to direct the Canon techs if the 1D has to go in for servicing.

If the lens is so severely out-of-focus that the AF system can't work out what to do next, then it will rack the lens right through its focusing range to try to lock onto something. That's normal behaviour, but becomes annoying when it happens unnecessarily (as the user thinks), as it often does with macro lenses. The 1-series cameras have a PF to switch off focus racking. If there is indeed a camera problem here, then it sounds as if racking is happening more readily than it should. If possible, a quick comparison with another 1D body with everything at default settings would provide a useful check, and if they are behaving differently then it is definitely time for a trip to a repairer.