Diopters

A diopter is a close-up lens for your camera that will enable you to take better macro video.

Screw on

Flip macro

Single-Element Diopter

Cheap

Chromatic aberration

Hoya

Tiffen????

Century

chromatic aberration

Biggest mistake is to be too near to the subject

Designed to be used at infinity focus (Tom Hardwick)

Tripod

CALCULATION

e.g. Century +3.5

100/3.5 = 28.57 maximum distance from subject to get focus (at infinity focus). Tested and it is true!

At minimum focus, closest I could get was 21cm.

Refractive index of water is 1.33 (i.e. objects appear 33% closer), so:

Maximum distance from front of port = (28.57-5)*1.33 = etc.

Nick Hope