All of the following are reasons for cone cut except:
Cone cut:

Cause: Cone of radiation not covering the area of interest, not using film holders. Correction: Make sure that the cone is properly centered over the area of interest and the film, both vertically and horizontally.
Cause: PID not properly aligned with the periapical film holder. Correction: Position the PID carefully. If a film holder with an aiming ring is used, make sure that the PID and the aiming ring are aligned.
Cause: Top of the film not immersed in the developing solution. Correction: Maintain the level of the solution in the processing tanks and make sure that the film is completely immersed during processing.