Distortion Avoidance

 

The goal of clinical photography is to record a patient’s disease process or injury accurately. Unwanted perspective distortions arise from 1) poor choice of lens focal length and 2) incorrect camera position relative to the clinical finding.

 

Perspective is how the brain interprets depth within an image. Distant objects appear smaller and closer objects appear larger on the image. Subject-to-lens distances vary with the lens focal length.

 

Perspective distortion is controlled by the subject-to-lens distance: the farther away a patient is from the lens, the less distortion will be appreciated on the final image. The longest focal-length lens that is practical in the clinician’s practice setting should be used to eliminate distortions in perspective.

 

Incorrect camera position, specifically if the film plane is not parallel to the subject photographed, creates another perspective distortion. The goal is to keep the subject plane-parallel to the film plane. Distortions make interpretation of physical findings difficult. For example, is an extremity in one photograph more or less swollen than in the previous photograph? Such changes may be difficult to interpret if the extremity is not plane-parallel to the film plane. Proper positioning of the patient and camera help to minimize this perspective distortion.