Extension Tube Calculator — Added Magnification

Extension tubes fit between the camera body and lens, moving the lens further from the sensor. This shifts the focus range closer, increasing magnification. A 25mm extension tube on a 50mm lens adds 0.5x magnification. Tubes have no optical elements — they just add distance, preserving optical quality.

Added magnification = extension tube length / lens focal length. A 25mm tube on a 50mm lens adds 0.5x. On a 100mm lens, the same tube adds only 0.25x. Extension tubes are most effective with shorter focal length lenses.

Extension tubes reduce the amount of light reaching the sensor because the lens is further away. The effective aperture increases by: f_eff = f x (1 + M). At 1:1 magnification, you lose 2 stops of light. TTL metering compensates automatically, but you may need to increase ISO.

Yes. Stacking extension tubes adds their lengths together. A 12mm + 25mm tube gives 37mm of total extension. However, more extension means more light loss, potentially softer images (especially at the edges), and a very narrow focus range. Most macro photographers use one tube or a dedicated macro lens.