First try cleaning the electronic contacts on the lens.
1. Remove the lens...
2. Slightly dampen a clean, lint free rag with a few drops of isopropyl alcohol (cheap, widely availabe "rubbing alcohol" works fine)....
3. Carefully wipe the electronic contacts on the base of the lens, adjacent to the rear element and the bayonet mount. Be careful to not touch the optical elements of the lens with the cleaning rag.
This will clean off any oils that might have gotten onto those contacts, interrupting the low voltage signals between camera and lens. The "oils" might be from your fingers handling the lens, or from lubrication within the camera or the lens.
Do not use anything abrassive on those electronic contacts or the corresponding pins just inside the front of the camera. They are gold plated and you don't want to damage that (gold doesn't oxidize, so is ideal for low voltage connections such as these... if it's scratched and the base metal is revealed, oxidization can occur on that).
Some may tell you to instead use a pencil eraser to clean those contacts. Personally I don't think that's a good idea for a couple reasons. One, as I've noted often the problem is oils on the contacts... and pencil erasers are made from vegetable oil, so they're unlikely to help. Second, pencil erasers shed small particles that you don't want getting inside the camera.
4. While the lens is off the camera, also closely inspect the corresponding "pins" located just inside the front of the camera. Those are spring loaded to insure good contact. Carefully and gently press each pin to see if it's "springy", returns to it's full extension and isn't "stuck".
5. Remount the lens. Be sure it's fully rotated into it's locked position. (Yes, I have seen folks have similar problems and it was as simple as this!).
6. Now operate the MF/AF switch on the lens a dozen or so times. This type of switch is usually self-cleaning... and operating it will wipe off any oxidization that might have formed on the metal parts and be interrupting low voltages powering the lens. Reset that switch to the AF position and give it another try.
The only other things I can think of that you might try yourself are...
Go into the camera'ss menu and look up the battery detail info. It tells you the "health" of the battery. If it's showing that's low, might be a good idea to try a new battery.
Inspect the contacts on the battery and corresponding to it inside the camera. If you think it might help, clean both sets of contacts with the rag and isopropyl alcohol, as described above.
Finally, you might want to update the camera's firmware or, if it's already up to date, re-install it. Like any computer operating systems, camera firmware can become corrupted and cause problems. An update or a clean, new copy of the firmware can be downloaded from the Canon websites. Follow the instructions there carefully. It's not difficult to do, but if done wrong it can "brick" a camera... which will require professional repair.
Frankly, these are all more or less "long shots" that may or may not help... But sometimes it's a simple fix AND these are about all that's advisable for you try yourself.
If all this doesn't solve the problem, I suspect that there's something more serious wrong with the lens... not the camera. If you have another auto focus lens you can try on the camera and that works properly, it would confirm the problem is with the 24-70mm lens (which was introduced in 2002 and could be as much as 12 years older than the camera).
In the lens it may be a failed auto focus motor. Or, many lenses use a "flex cable" between the electronic contacts and the various internal mechanisms of the lens. Over time and with age, those flex cables can fail, losing connectivity. Either of these problems or some other possibile causes within a lens would require professional repair. I don't know if Canon services the EF 24-70mm first version (it was discontinued around 6 or 7 years ago). If not, a local, independent camera repair shop might be able to fix it.
Hope this helps!
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2) some other cameras, various lenses & accessories
FLICKR & ZENFOLIO
