Macro — What is 1:1?

The world of macro photography is challenging and filled with terminology.  First, what does it mean when a photo is taken at 1:1?  Most important to understand is that this is NOT related to print size.  It simply means that the object size is the same as its image size on the sensor; in other words it is a reproduction ratio.  For example, a micro four thirds sensor is about 17.3 mm wide.  So this picture, using a Lumix G85 with a Micro Four Thirds sensor, set around 2 inches from the subject, showing 17 mm on a ruler is captured at a 1:1 ratio:

Think of this as a fraction (sensor size/object size).  I can print this out any size I want, and obviously the resulting image on screen or on paper can be at any ratio I want.  Now look at the following image using the same image, same camera, but pulled back to around 3.5 inches from the subject:

This shows approximately 35 mm of the ruler on 17.3 of sensor.  So, this is a 1:2 capture.  Now let’s try an experiment.  Here is a crop of the 1:2 capture, down to the field of view of the 1:1 capture:


Ignore for now the lighting difference, dust, and camera to subject distance.  It is apparent that the cropped 1:2 image and the native 1:1 capture are identical in the field of view.  So what does mean for your shooting?  Get what you want in the picture, and ignore the ratios.

--© Robert Rose 2018