Originally posted by Squirrel I cannot find focus using the optical viewfinder.
And is the same true for live view? The purpose of the question is to rule out the optical system as the source of the problem. If you can attain manual focus in live view the lens is optically capable.
Originally posted by Squirrel There are times when the camera doesn't even allow me to take the picture.
This is to be expected for AF-S. In that mode the shutter will not release until focus is attained. AF-C, on the other hand will allow shutter release even when the subject is not in focus.
To be explicit, here is the troubleshooting flow:
Able to manually attain focus at distance using live view (by visual examination)?
If no, attempt with a known good lens. If that fails there is a problem with the sensor position inside the camera.
If Yes, continue...
Able to attain far manual focus confirm using the viewfinder (PDAF)?
If No, there is problem with the PDAF system...body fault
If Yes, continue
Able to attain far AF using live view (CDAF) or viewfinder (PDAF)?
If No to both, probable failure of the in-lens focus motor or controller...lens fault
If No to CDAF only, problem with CDAF subsystem...body fault
If No to PDAF only, problem with PDAF subsystem...body fault
If Yes to both, everything is working!
I hope this helps.
Steve