I have a 50mm prime lens and a 18-55mm standard lens at my disposal. How do I measure the magnification of a reversed lens when used with a reverse mount. What are the factors that come into play to calculate the magnification?


1 Answer 1


Photograph a normal ruler, mm scale preferred. Then if your sensor is 24 mm wide (camera specs should say), and if the image shows say 20mm of that ruler, then the magnification is 24/20 or 1.2x (larger than 1:1 life size).

Normally lenses show smaller than life size, like showing 40 mm on a 24mm sensor would be 24/40 = 0.6x magnification.

  • \$\begingroup\$ Note that the ruler photo has to be taken at the smallest possible focal distance from the ruler. \$\endgroup\$ Commented Dec 7, 2015 at 17:14
  • \$\begingroup\$ Ruler will show actual magnification at any distance you choose to use (if macro setup offers any choice of focus distance). Only the Maximum magnification needs to be at closest distance. \$\endgroup\$
    – WayneF
    Commented Dec 7, 2015 at 21:08
  • \$\begingroup\$ This seems to be a great explanation. Thanks for the answer! \$\endgroup\$
    – MnZ
    Commented Dec 8, 2015 at 14:04

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