That’s typically an indicator that the camera is not able to detect a lens. When I attach my cameras to my telescopes to do astrophotography (the telescope becomes the “lens” - and does not have any electronic communication with the camera body) the f-stop goes to “00”.
Check to make sure the contacts on the lens and camera body are not dirty (they seldom are dirty — but if you do see any obvious dirt, wipe it away with a soft cloth (don’t use a pencil eraser... the gold plating is very thin, soft, and can be scrubbed away by a pencil eraser).
On the lens side, you’ll see gold contacts. On the camera side, you’ll see tiny gold pins. Each of those pins is on a spring... if you press them with your fingers, they’ll push in... and when you release they should spring right back out. Make sure none of those pins are jammed (they all push in and spring back out).
The two above things are probably NOT the problem... but you should check them anyway.
More likely is that there’s a failure inside the lens (sometimes the wiring comes loose, etc.). Depending on the lens, it may or may not be worth repairing. Expensive “L” series lenses typically are worth repairing. Entry level (low-priced) lenses usually cost more to repair than the price of just buying a replacement lens.
Tim Campbell
5D III, 5D IV, 60Da
