Images not sharp

 

There are many factors for images not being sharp and exhibiting in many ways.

 

Camera

 

Dust on the mirror or A/F sensor
Wrong custom settings
Using the wrong focus bracket
User movement
Low light shooting conditions
Focus screen, mirror, bayonet mount or sensor out of alignment
Worn mirror box causing shutter bounce
Tough subject for the auto focus to lock on to
Camera needs to have a focal calibration
Incorrect fine tune set up
The eyesight diopter is incorrect for your eyesight making it look blurry though the eyepiece
You are too close to the subject

 

Also see lens focus issues