Introduction To Underwater Macro Photography

The classical definition of macro photography is when the image projected on your sensor is actually life size, often referred to as 1:1 (“one to one”).

If you don’t have an interest in the basic technical explanation, skip to the next section, it’s not going to make you a better photographer to understand this right now. But for those who wish to understand more about what it means to reproduce at 1:1, read on.

In order to understand what 1:1 means, it is important to understand the concept of image magnification and reproduction ratio, which is determined by dividing the image height or width on your sensor, by the subject’s height or width. Here is the calculation: 

Magnification = (image height) / (subject height)  X
or expressed as a reproduction ratio:
Reproduction ratio =  image height:subject height

For example, when using a full frame sensor (36mm width x 24mm height), filling the frame with a 24mm tall subject corresponds to 1X magnification, or 1:1 reproduction ratio, since: 

magnification = 24mm / 24mm = 1X


reproduction ratio = 24mm:24mm = 1∶1

Similarly, filling the same frame with a 12mm tall subject would correspond to 2X magnification, or a 2:1 reproduction ratio. To continue the example, filling the frame with a 48mm tall subject would be 0.5x magnification, or a 1:2 reproduction ratio.

Technically macro photography is accomplished with lenses that can achieve a 1:1 or greater reproduction ratio. Close up photography is often defined as an image with a reproduction ratio between 1:4 and 1:10. However, the terms “macro” and “close-up” are often used interchangeably for practicality reasons. No one is going to measure your subject and then compare it to your sensor size to see if it’s actually a close-up or macro image. Even in competitions it does not really matter.  Additionally, any image with a reproduction ratio greater than 1:1 is said to be supermacro , as it’s greater than life size. To learn more about super macro, visit our guide to

Underwater Super Macro Photography.