Work out the near and far focus limits your diopters give you, for every lens in your set.
If you're interested in seeing how different lens sizes and close focuses change the diopter limits, try the Explorer at the bottom of the page.
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Units control how results are displayed. You can still type any unit into any field — ' and " for feet/inches (2' 6" or 5'6), or m, cm, mm. A number typed with no symbol is read as feet in feet/inches mode, or cm in meters mode. Hover any field to see how it was interpreted.
Film plane is the default — it matches your focus marks and the ϕ mark on the camera body. The diopter gives distances measured from the diopter itself, which ignores lens length and mount measurements.
Mounting gap is the distance from the mounting point on the lens to the front face of the diopter — not the front element. Leave it blank if the diopter sits directly on the lens. It applies to every lens, so if your matte box stays at a fixed position while lenses change, re-check it when you swap.
| Strength+ or − | Glass thicknessoptional | |
|---|---|---|
The maths references the optical centre of the diopter, but the mounting gap is measured to its front face. Giving a thickness lets the app add half of it to bridge that difference, so a thick +3 is handled differently from a thin +1/2.
The effect is small — half the glass thickness, so around 7mm for a 15mm diopter — and it shifts near and far limits by the same amount. Leave thickness blank and no correction is applied.
The default values loaded here are for Schneider 138mm diopters. Replace them with your own if you're using different glass.
Add each lens with its close focus and length. Load a saved set or import a CSV.
Saved sets are stored in this browser only. Export a CSV to send your current set to someone else — they can load it with Import.
Typed with no unit: close focus reads as inches, lens length as mm.
| Lens name | Close focusno diopter, from film plane | Lens lengthfront of lens to mount | Mount | |
|---|---|---|---|---|
Close focus is the lens's close focus without any diopter fitted.
Lens length runs from the front of the lens to the lens mount. The Mount you pick then adds its flange depth to reach the film plane: PL 52mm, LPL 44mm, PV 57.15mm, or set your own with Custom.
Tip: if the numbers don't match reality, measure straight from the front of the lens to the ϕ mark on the camera. That total should equal your lens length plus the mount's flange depth.
CSV import needs columns whose headers contain name, close, and length, in any order; an optional mount column is read too. Download the template for the exact shape. Imported lenses are added to the table, not replacing what's there.
| Lens | Diopter | Near limit | Far limit | Range |
|---|
Each bar runs from the near limit to the far limit for one diopter, with the total depth of that range shown inside it. All lenses share one distance scale so you can compare them directly.
The green line on each lens row marks that lens's own close focus with no diopter fitted, labelled with its value — so you can see at a glance how much extra reach each diopter buys you.
Blue bars are negative diopters. They're open-ended, with an arrow at the right edge, because a negative diopter's far limit is infinity — it shifts the whole focus range outward.
Drag the lens, the diopter, or the green CF mark — or use the sliders — and watch the limits react. Metric readouts here are in cm.
Same formulas as the worked example above. Diopter strength is defined per metre, so DS is used in metres inside the bracket.