Close-Up Lens Calculator — Dioptre Magnification

A close-up lens is a simple lens that screws onto the front of your camera lens like a filter. Measured in dioptres (+1, +2, +4, etc.), they reduce the minimum focus distance, allowing closer focusing and higher magnification. Unlike extension tubes, they do not reduce light transmission.

A dioptre filter has a focal length of 1000mm / dioptre value. A +2 dioptre filter has a 500mm focal length. When attached to a lens focused at infinity, the new maximum focus distance equals the dioptre filter focal length. Higher dioptres = shorter focus distance = more magnification.

Yes, dioptre values add when stacked. A +2 and +3 together give +5 dioptres. Always place the stronger (higher dioptre) filter closest to the lens. However, stacking reduces optical quality — two-element achromatic close-up lenses give much better results than stacking single-element filters.

Extension tubes maintain optical quality and lose no light, but reduce the focus range (cannot focus to infinity). Close-up lenses are more convenient (screw on like filters), lose no light, and allow focusing from new MFD to infinity. However, cheap single-element close-up lenses reduce sharpness. Quality achromatic close-up lenses (e.g., Canon 500D) are an excellent compromise.