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Macro magnification calculator
Extension tubes on any lens: the magnification and reproduction ratio you reach, the effective aperture and light loss, working distance and the focus-stacking step.
All tools- Magnification
- 0.65×1:1.54 reproduction ratio
- Frame covers
- 55.4 × 36.9 mm of subject
- Effective aperture
- f/13Meter TTL, or open up 1.44 stops for flash
- Working distance
- 13 cmThin-lens estimate from the lens's centre
- Total depth of field
- 1.8 mmStep a stack by about two thirds of this
How it works
The method behind the numbers.
An extension tube moves the whole lens further from the sensor, so the lens focuses closer and projects a bigger image. The formula assumes the lens sits at its closest focus, where it already reaches its own maximum magnification; tubes then add their share on top.
m = m(native) + extension ÷ f
N_eff = N × (1 + m)
s = f × (1 + 1 ÷ m)
DoF = 2cN(1 + m) ÷ m²- Magnification. m is the size of the image on the sensor relative to the subject: 0.5× is a 1:2 reproduction ratio, 1× is life size, and beyond that the image is larger than the subject. Short focal lengths gain more magnification from the same tube, but they also shorten the working distance.
- Light. Extension costs light even though the f-number on the barrel does not change: the effective aperture is N × (1 + m), a two-stop loss at life size. Through-the-lens metering sees it automatically; with flash or a handheld meter, open up by the compensation figure.
- Working distance. The thin-lens figure is measured from the lens's optical centre. A real macro lens focusing internally keeps more distance than the formula suggests, and its focal length shortens as it focuses closer, so treat the number as a floor, not a promise.
- Stacking. The depth of field here is the total sharp zone, in front of and behind focus together. For a focus stack, step the rail or the focus ring by about two thirds of it, so frames always overlap.