How do you calculate magnification when stacking one lens on another for macro photography?
Asked 1/3/2012
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In a lens-stacking macro setup—such as mounting a reversed normal or wide-angle lens on the front of a telephoto—what determines the maximum reproduction ratio or magnification of the combination? Is there a simple way to calculate it from the lenses' focal lengths?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
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$$ M = {F_p \over F_r} $$
where
- \$M\$ = magnification
- \$F_p\$ = Focal length of the prime lens
- \$F_r\$ = Focal length of the reversed lens
Source: Peter Forsell's great page about Math for macro photographers.
Originally by user507. Source · Licensed CC BY-SA 4.0
user507
14y ago
0
Generated from our catalog & community — verify before relying on it.
Yes. For a stacked-lens macro setup, magnification is approximately:
M = Fp / Fr
where:
- Fp is the focal length of the primary lens mounted on the camera
- Fr is the focal length of the reversed lens mounted on the front
So the reproduction ratio is mainly determined by the ratio of the two focal lengths. A longer primary lens and a shorter reversed lens give higher magnification.
Examples:
- 200mm primary with 50mm reversed ≈ 4× magnification
- 100mm primary with 50mm reversed ≈ 2× magnification
In practice, actual results can vary a bit with lens design and focus settings, but the focal-length ratio is the standard rule of thumb for stacked-lens magnification.
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