How is the Magnification of a Macro Lens Rated with Digital SLR’s?
A macro lens is rated or measured by how large the subject is in real life compared to its size on the actual 35mm (36mm x 24mm) size sensor or negative. When a 4”x6” (150mm x 100mm) standard size print is made it will be about 4 times bigger then the image was on the sensor.
Examples of macro magnification:
1:4 macro magnification means the insect (or flower!) is 1/4 its normal size on a 35mm size sensor. This could also be known as “1/4X”. So a 4”X6” photo (102x152mm) enlargement will show the image near life size. Some companies advertise this as "macro photography" but it is actually "close up photography".
1:2 macro magnification will have the same insect 1/2 (1/2X) size on a 35mm size sensor as it is in actual life.
1:1 or 1X macro magnification has the insect the same size in real life as it is on the actual 35mm size sensor. This is the standard magnification for a macro lens. Now if a 4x6 photograph is made off of the image then the insect would be about 4 times larger then in real life. The image would be about 9 times bigger then real life on a 19” computer monitor!
2:1 or 2X macro magnification has that same insect twice the size on your sensor as the actual insect. 2X would fit an entire full length portrait of a mosquito on a 35mm size sensor. This mosquito would be about 8 times larger on a 4x6 print and about 20 times bigger on a 19” computer monitor than in real life! 20 times bigger or 20X is approaching the life size of some mosquitoes that have attacked me on some back packing trips.
4:1 or 4X would just fit a portrait of a mosquito's face and be 4 times bigger on the sensor as it is in real life. 4X is very difficult in macro photography field work. I don't take photographs of mosquitoes much but used them as an example since most of us know about how big mosquitoes are. I usually take macro photographs of other things!