What is a close-up lens (dioptre filter)?

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.

How do dioptres relate to focal length?

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.

Can I stack close-up lenses?

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.

Close-up lens vs extension tube — which is better?

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.

PhotoCalcs

Close-Up Lens Calculator — Dioptre Magnification

Calculate the magnification and closest focus distance when using close-up dioptre filters.

Lens Focal Length

Your lens focal length

Dioptre Strength

Close-up filter power

Sensor Width

e.g. 36mm for full frame

How We Calculate This

Close-up lenses reduce the minimum focus distance using simple optics:

Dioptre Focal Length

Close-up FL = 1000 / dioptre value (mm)

Closest Focus (Lens at Infinity)

New MFD = 1000 / dioptre (mm)

Maximum Magnification

M = lens focal length / close-up focal length

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard optical and photographic formulas. Results may vary with specific equipment.