Macro Photography Calculator
This macro photography calculator works out the magnification you'll get from a macro lens, extension tubes or a close-up filter, along with the working distance, effective aperture, light loss and the wafer-thin depth of field — and how many frames a focus stack needs.
Combine a lens with extension tubes or a close-up filter and see the magnification, depth of field and exposure you'll get.
At macro magnifications the sharp zone is a fraction of a millimetre. Work out how many frames a stack needs and how far to move between them.
See what every combination of your extension tubes does on a particular lens.
How to Use the Macro Photography Calculator
Magnification
- Choose your sensor and lens focal length
- Enter the lens's own magnification where you have it focused — 1 for a macro lens at its closest, 0 at infinity
- Add any extension tubes or close-up filter
- Set the aperture marked on the lens and read the magnification, frame size, depth of field, effective aperture and light loss
Focus stacking
- Enter the magnification and aperture you'll shoot at
- Enter how deep the subject is and the overlap between frames
- Read the frame count and rail step, then shoot from front to back on a focusing rail
Extension tube table
- Enter your lens and the tubes you own
- Compare every combination: magnification, frame size and how close the subject must be
How to Calculate Macro Magnification
Magnification is the size of the subject on the sensor divided by its real size. A macro lens gives it directly on its focus scale; extension tubes and close-up filters add to whatever the lens already gives.
Macro photography formulas
Extension tubes: m = m₀ + E / f
Close-up filter: m = m₀ + f × D / 1000
Effective aperture = N × (1 + m)
Depth of field = 2 × N × c × (1 + m) / m²
m₀ is the lens's own magnification, E the tube length and f the focal length in millimetres, D the filter strength in dioptres, N the f-number and c the circle of confusion. These are thin-lens estimates: internal-focus macro lenses shorten their focal length up close, so real figures vary a little.
Worked example: a 50mm lens on a 25mm extension tube
- Magnification with the lens at infinity: 25 / 50 = 0.5× (1:2)
- Frame covers on full frame: 36 / 0.5 × 24 / 0.5 = 72 × 48 mm
- Subject about 150 mm from the lens; f/8 behaves like f/12
Extension tube magnification chart
Magnification from common tube lengths with the lens focused at infinity. Focusing the lens closer adds its own magnification on top.
| Lens | 12mm of tubes | 20mm of tubes | 36mm of tubes | 68mm of tubes |
|---|---|---|---|---|
| 35mm lens | 0.34× (1:2.9) | 0.57× (1:1.8) | 1.03× (1.03:1) | 1.94× (1.94:1) |
| 50mm lens | 0.24× (1:4.2) | 0.4× (1:2.5) | 0.72× (1:1.4) | 1.36× (1.36:1) |
| 60mm lens | 0.2× (1:5) | 0.33× (1:3) | 0.6× (1:1.7) | 1.13× (1.13:1) |
| 85mm lens | 0.14× (1:7.1) | 0.24× (1:4.3) | 0.42× (1:2.4) | 0.8× (1:1.3) |
| 100mm lens | 0.12× (1:8.3) | 0.2× (1:5) | 0.36× (1:2.8) | 0.68× (1:1.5) |
Macro depth of field chart
Total depth of field on a full-frame camera at 1:2, 1:1 and 2:1, and the effective aperture at 1:1. The sharp zone is measured in fractions of a millimetre — which is why macro photographers focus stack.
| Aperture on lens | At 1:2 (0.5×) | At 1:1 | At 2:1 | Effective aperture at 1:1 |
|---|---|---|---|---|
| f/2.8 | 0.97 mm | 0.32 mm | 0.12 mm | f/5.6 |
| f/4 | 1.39 mm | 0.46 mm | 0.17 mm | f/8 |
| f/5.6 | 1.95 mm | 0.65 mm | 0.24 mm | f/11.2 |
| f/8 | 2.78 mm | 0.93 mm | 0.35 mm | f/16 |
| f/11 | 3.83 mm | 1.28 mm | 0.48 mm | f/22 |
| f/16 | 5.57 mm | 1.86 mm | 0.7 mm | f/32 |
Understanding Macro Photography
Close-up work bends the usual rules of exposure and depth of field. These are the ideas behind the numbers.
Magnification
The size of the subject on the sensor compared with its real size. "True macro" traditionally starts at 1:1 (life size).
Example: at 1:1 on full frame a 36mm-wide coin fills the frame edge to edge.
Extension Tubes
Hollow spacers between lens and camera that let the lens focus closer. Magnification rises by the tube length divided by the focal length, so they work best on short lenses.
A 25mm tube adds 0.5× to a 50mm lens but only 0.125× to a 200mm.
Close-up Filters
Magnifying lenses that screw onto the front of the lens, rated in dioptres. Their effect grows with focal length, so they suit telephoto and zoom lenses.
A +2 filter adds 0.2× to a 100mm lens and 0.4× to a 200mm.
Effective Aperture
Up close, the lens projects a larger image, so less light reaches each point of the sensor. The aperture behaves as N × (1 + magnification).
Example: f/8 at 1:1 exposes and diffracts like f/16 — two stops less light.
Depth of Field Up Close
At macro distances depth of field depends almost only on magnification and aperture, not focal length. It shrinks with the square of magnification.
At 1:1 and f/8 on full frame the sharp zone is under a millimetre deep.
Diffraction
Stopping down to gain depth eventually softens everything, as light spreads through the small opening. The limit is reached sooner up close, because the effective aperture is smaller.
The answer: shoot at the sharpest aperture and focus stack for depth.
Macro Photography Calculator FAQs
What does 1:1 magnification mean?
The subject is recorded on the sensor at life size: a 10mm insect covers 10mm of the sensor. At 1:2 it covers half its real size. On a full-frame camera, 1:1 fills the frame with an area 36 × 24mm.
Why does my camera say f/8 when the lens is behaving like f/16?
At high magnification the light is spread over a larger image, so less reaches each part of the sensor. The effective aperture is N × (1 + magnification): f/8 at 1:1 behaves like f/16 for exposure and diffraction. Through-the-lens metering corrects the exposure automatically, but diffraction still applies.
How many photos do I need for a macro focus stack?
Divide the depth of the subject by the depth of field per frame, allowing some overlap. A 10mm-deep subject at 1:1 and f/8 on full frame, where each frame is sharp over about 0.93mm, needs around 14 frames with 20% overlap. The Focus stacking tab works it out for your setup.
Extension tubes or a close-up filter?
Tubes contain no glass, so they don't lower image quality, but they cost light and move the focus closer. Close-up filters keep the light but add glass; a good two-element (achromatic) filter is much sharper than a single-element one. Tubes work best on shorter lenses, filters on longer ones.
What is the sharpest aperture for macro?
Usually around f/5.6 to f/8 on the lens at 1:1 on full frame. Beyond an effective aperture of about f/22, diffraction softens the whole image. The calculator shows the limit for your sensor and magnification.