Pentax 12.5-75mm Zoom Lens

 

note: drawing not to scale

To identify an unknown subject 1.6m tall, the PSDB guidelines state that the subject should fill 120% of the height of the monitor screen. Therefore the subject to vertical field of view relationship is as per the diagram above. Based upon the Pentax C31220 (C6ZAME-5) lens, which has a vertical field of view on ½" format of 3.66°, the following calculations apply:-

The 1.6m subject should fill 120% of screen. Therefore, actual field of view to be covered is 1.6 ÷ 1.2 = 1.33m

Tangent of ½ x angle of view = height of subject ÷ subject distance.

Therefore - Tangent of 1.83° = (1.33 ÷ 2) ÷ X. (Where X is the unknown subject distance).

Therefore - 0.0319503 = 0.665 ÷ X. Which implies that X = 0.665 ÷ 0.0319503

Therefore, the maximum distance at which a 1.6m person will fill 120% of the height of the monitor screen using the Pentax 7.5-75mm lens is 20.81m.

 

note: drawing not to scale

To recognise a known subject 1.6m tall, the PSDB guidelines state that the subject should fill 50% of the height of the monitor screen. Therefore the subject to vertical field of view relationship is as per the diagram above.

Based upon the Pentax C31220 (C6ZAME-5) lens, which has a vertical field of view on ½" format of 3.66°, the following calculations apply:-

Tangent of ½ x angle of view = height of subject ÷ subject distance.

Therefore - Tangent of 1.83° = 1.6 ÷ X. (Where X is the unknown subject distance).

Therefore - 0.0319503 = 1.6 ÷ X. Which implies that X = 1.6 ÷ 0.0319503.

Therefore, the maximum distance at which a 1.6m person will fill 50% of the height of the monitor screen using the Pentax 7.5-75mm lens is 50.08m.

Note: The trigonometrical function of tangent states that the tangent of an angle in a right angled triangle is equal to the length of the opposite side divided by the adjacent side.