Close-Up Lens Diopter Calculator

A diopter is a unit of optical power. A +2 diopter close-up lens has a focal length of 500 mm (1/2 m). When mounted on a camera lens, it acts like a magnifying glass, allowing you to focus much closer than the lens normally can, which increases the subject size on your sensor. Diopter values are additive, so stacking a +2 and a +3 lens gives you a combined +5 diopter.

Choose what you want to solve for – magnification, diopter strength, or required focal length. Enter the two known values, then tap Calculate. The tool uses the standard thin‑lens formula for close‑up lenses: M = f × D / 1000, where f is the main lens focal length in millimetres, D is the diopter value, and M is the resulting magnification. Working distance is simply 1000 / D millimetres.

Minimum focusing distance – often called working distance – is how close the front of the lens can get to the subject while still achieving sharp focus. When you attach a close‑up lens, this distance becomes much shorter. Knowing it helps you plan lighting and composition, especially with timid insects or delicate objects. The calculator displays it in millimetres.

Yes, you can stack them. The total diopter is the sum of the individual diopter values. For example, a +2 stacked on a +4 gives you a +6 diopter. However, stacking too many may reduce image quality due to increased aberrations and vignetting. Our calculator works with any positive diopter value – just enter the total.

Yes, but the result applies only to the focal length you enter. A close‑up lens gives higher magnification at longer focal lengths. If you plan to use a zoom lens, set the calculator to the focal length you intend to shoot at (e.g., 70 mm or 200 mm) to see the corresponding magnification and working distance.

The formula M = f × D / 1000 is an approximation that assumes the main lens is focused at infinity and that the diopter lens is a simple thin lens. Real‑world results may vary slightly due to lens design, focus breathing, and actual diopter tolerances. However, for most close‑up photography, the estimate is within a few percent and extremely useful for planning.

Common close‑up lenses come in strengths like +1, +2, +4, and +10 diopters. A +1 gives a subtle close‑up effect, while a +10 lets you fill the frame with very small subjects. Many photographers keep a +2 or +4 in their bag for lightweight macro capability.

No, this calculator is specifically for front‑mounted close‑up diopter lenses. Extension tubes and lens reversal rely on different optical principles. For those, you need a calculator that uses bellows extension and the lens's native magnification. Check out our other macro tools for those setups.

A dedicated macro lens is designed to project a life‑size (1:1) or greater image directly onto the sensor with excellent sharpness and flat field. A close‑up lens is a supplementary accessory that screws onto the front of a regular lens. It is more affordable and portable but typically offers lower overall optical quality and less magnification, though high‑quality achromatic diopters can give impressive results.

The infinity‑focus assumption simplifies the formula and gives the maximum working distance for a given diopter. In practice, you can focus the main lens closer to increase magnification slightly, but the working distance will also decrease. The infinity‑based calculation provides a safe baseline that is accurate enough for most field estimations.