1D Mark IIn Focus Issue

I have a problem I can find no where in forums or Canon Website. I have a ID Mark IIn that I purchase used about a year ago. I wanted to shoot raw so I purchased a 16gb Sandisk Extreme III card for it. What I noticed was approx 1500 images available on the card when set to RAW but focus or firing ratewould start to slow after about 300-400 images. This problem was consistent but only at night. In daylight there is no focus / shutter release issue. By slow I mean I would press the shutter button all the way and it would take up to 1-2 sec. to fire and in some cases not at all. I am of course assuming it is a focus issue though maybe not at all. I have tried other cards including 8gb Lexar cards with the same response. while I have used 4mb cards in the camera I have never used them consistently at night and have not observed this problem with them. Light levels are not the discerning factor as it will shoot well in very low light but become erratic once the 300-400 level is reached even in better light and contrast. I have also tried all permutations of focus from single point to automatic selection to no avail. Has anyone had this happen or heard of it. I will eventually send to CPS but I wanted to know if the problem was know or perhaps me. Any suggestions or insight is welcome.

That sounds like an odd one, alright! Only thing I can suggest, which you've likely already done, is format the card(s).

To test if it is a focus issue, you could try manual focus mode and see if you still have the problem.


Forgive me for stating something obvious, but um, the camera buffer wasn't full, was it? I mean, is the camera slow right when you turn it on, or only after shooting a bunch of shots in succession?


One more thing- are all the pictures in the same folder? If so, try no more than 100 per folder and see if that helps. (I'm really grasping at straws with this last one...)


Best of luck.

yes, I format my cards for each use.

Truly hadn't thought of using manual focus. I'll try that next time and see if it makes a difference. No the buffer was not full, that was one of my first thoughts as well though it does seem as though the more space on the card is used the slower it gets.