The term macro photography is one used loosely in today’s world. Many people and companies in the industry use it to convey a meaning although it does not fit the true definition of the term. In popular culture it has taken on that same sense, to convey something small being photographed to look large. If you have a close-up of an insect or plant it is usually called a macro shot. Part of the confusion may come from the origin of the word itself. Macro comes from the Greek word Makros, meaning large.
Macro photography is a photo having a reproduction ratio of 1:1 or greater. 1:1 means the size of the subject on the sensor or film plane is the same as in real life. When the reproduction ratio is 2:1 then the subject in the images is twice its real size. Conversely if the subject has reproduction ratio of 1:2 then it is half its actual size. Many photos called macro are actually close-ups. Close-up photos have subjects with a reproduction from 1:10 up to 1:1.
There are several different camera sensor sizes on the market today. The full frame sensor is a 24x36mm sensor, having the same dimension as 35mm film. Unless otherwise noted with 35mm camera systems this is the size sensor camera lenses are designed to match up with. Then there are the Canon APS-H sensor giving you a .3 increase in focal length, the APS-C for cameras other than Canon which give you .5 increase in focal length and finally there is the Canon APS-C giving you a .6 increase in focal length.
These differences can get a little confusing. Let’s take a look at the standard 24×36 sensor most lenses are designed to work with. Think about what the lens is designed to do. The lens gathers the light as it passes through the glass and redirects it to a specific point at a specific size. The point is the sensor or film plane and the size in this case is 24x36mm. When the sensor is smaller than 24x36mm, some of the light projected by the lens will hit the inside of the camera where there is no sensor to record it. If the sensor only records part of the light being projected you get the same effect as increasing the focal length of the lens. For the Canon APS-C it gives the effect of a 30% increase in magnification, for the Nikon DX and other non Canon APS-C you get 50% and for the Canon APS-C you get a 60% increase in focal length. In each case the smaller sensor only records part of the image projected by the lens.
Now lets take a look at magnification. Magnification is the size of the subject on the sensor or film plane compared to actuality. Like the reproduction ratio we talked about above, magnification is another way of expressing the same thing. 1:1 would be a magnification of 1, 2:1 would be a magnification of 2x and 1:2 would be magnification of .5. These terms can be used interchangeably in the context of photographic conversations.
Magnification is independent of sensor size. Therefore if you shoot an image at 1:1 with a macro lens what you are seeing on the sensor is 1:1 regardless of the sensor size. This is because the lens is projecting a 1:1 image and the reduced size sensor only picks up part of the image. Reduced size sensors can be an advantage when you have a subject that even at 1:1 does not fill the frame.
A lens can achieve greater magnification by increasing the distance between the glass elements in the lens and the sensor. 1:1 images are created this way. There are several different ways to accomplish an increase in distance. Macro lenses are able to create 1:1 images without accessories because they have the distance required built into them as a part of their design. You can use extension tubes to add some distance. Their distance is fixed but you can stack them to create a number of different combinations. You can also use a bellows to add distance. A nice feature with the bellows is the ability to change the distance, as you desire. They are, however, not the easiest tool to use in the field. With both extension tubes and bellows you will have some light loss.
If you want to know the magnification you are shooting at you will have to manually focus ahead of time. Set your macro lens at 1:1 manually on the focusing scale and then move the camera and lens until your subject comes into focus. The best way to do this is with a tripod and a focusing rail.
Understanding magnification or reproduction ratio is essential to understanding how macro and close-up photography works. We will have a tutorial on how to calculate magnification coming soon. Take the time to learn the basic math behind macro photography. By understanding how different techniques are achieved you can increase your skill set and create even better photos.