Macro Photography Magnification Calculator
Enter focal length, minimum focus distance, and extension tube length to get reproduction ratio, working distance, effective aperture, exposure compensation, and depth of field. Nothing uploaded.
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Learn more: macro magnification and photography metrics
Reproduction ratio and magnification in macro photography
Reproduction ratio (magnification) is the ratio of image size to subject size on the sensor. 1:1 (life size) means a 1cm subject creates a 1cm image on the sensor. 2:1 means the image is twice the size of the subject - extreme macro. Most dedicated macro lenses achieve 1:1 at their minimum focus distance. Understanding this metric is critical for planning a macro shoot: a 1:1 magnification lens shows far more detail than a standard telephoto.
Working distance and practical shooting
Working distance is the physical space between the front of the lens and your subject at minimum focus distance. A 100mm macro at 1:1 has a working distance of about 10-15 cm - allowing you to place lights or reflectors. A 50mm macro at 1:1 has only 5 cm of working distance, making lighting difficult. Extension tubes push the lens further from the sensor, increasing magnification but reducing working distance even more, making subjects even harder to light and focus.
Effective aperture and exposure correction
At macro distances, the lens is extended far from the sensor, which reduces the light reaching the sensor. The effective f-stop is: N_eff = N_set × (1 + magnification). At 1:1 magnification with f/8, the effective aperture is f/16 - requiring 2 extra stops of exposure or flash power. This is why macro shots need significantly more light than normal photography and why depth of field is so thin.
FAQ
What is reproduction ratio in macro photography?
Reproduction ratio (magnification) is the ratio of image size to subject size on the sensor. 1:1 (life size) means a 1cm subject creates a 1cm image on the sensor. 2:1 means the image is twice the size of the subject - extreme macro. Most dedicated macro lenses achieve 1:1 at their minimum focus distance.
Why does effective aperture matter in macro photography?
At macro distances, the lens is extended far from the sensor, which reduces the light reaching the sensor. The effective f-stop is: N_eff = N_set × (1 + magnification). At 1:1 magnification with f/8, the effective aperture is f/16 - requiring 2 extra stops of exposure or flash power. This is why macro shots need more light than normal.
How do extension tubes increase magnification?
Extension tubes add physical distance between the lens and sensor, moving the minimum focus distance closer and increasing magnification. Adding 25mm of extension to a 100mm macro already at 1:1 can push magnification to approximately 1.25:1. The calculator shows the effect of any extension tube length on reproduction ratio and working distance.