A 30 year old male  presents with pain and swelling over the right lower back jaw region. On intraoral examination, carious #46 and #47 are seen. OPG brought by patient is very blurred. This imaging technique is influenced by all of the following except:
The image distortion is influenced by several factors, including X-ray beam angulation, X-ray source-to-object distance, path of rotational center, and position of the  object within the focal trough. These parameters vary among panoramic units and among different regions of the jaws for the same unit. They are also strongly dependent on patient anatomy and positioning of the patient in the unit. These variables make it impossible to apply preset magnification factors that can be used to make reliable measurements on panoramic radiographs.
 
Reference: ORAL RADIOLOGY PRINCIPLES AND INTERPRETATION,8th EDITION, Stuart C. White, Michael J. Pharoah
X-ray beam angulation
X-ray source-to-film distance
Path of rotational centre
Position of the object within the focal trough