Understanding Magnification in Macro Photography
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- If your 50mm macro lens is focused at infinity, that means that glass is 50mm away from your film plane because the glass is as far back as it can be and that’s usually the focal length of your lens.
- So, if you have a 100mm lens on, you focus at infinity, your glass is approximately 100mm away from the film plane.
- If your 50mm macro lens is focused at infinity, that means that glass is 50mm away from your film plane because the glass is as far back as it can be and that’s usually the focal length of your lens.
When people look at your photos and ask, “Is that a 2:1 ratio, 1:1 ratio?” Do you know how to answer? Do you care?
If magnification ratios aren't important to you, does that mean you're not that invested in macro photography? You don't need to have scientific knowledge of magnification ratios as a macro photographer, but it is good to know some basics.
The truth is, there is some sense in magnification ratios. I'll explain them in a way that is easy to understand:
Magnification Ratio: the ratio of the real size of the object on the film or sensor to the real size of the object in real life.
1:1 Ratio — means it is exactly the same size.
1:2 Ratio — the image on the sensor is half the size of the real thing.
Here’s an example: if you were to photograph a quarter and the actual quarter, if you overlaid it on your sensor, was exactly the same size as the image, that would be 1:1. It’s the same size in real life as it is on your sensor or film. If the quarter is half as big on the film as it is in real life, that’s a 1:2 ratio. The real life size is always the 1, and that’s the first one.
If the image on the sensor/film is ½ as big as the size of the real subject, the / is changed to a :, turning it into a ratio. So, ½ now becomes 1:2.
Magnification Ratios and Macro Lenses
It’s important to know about magnification ratios when choosing a lens. A true macro lens will go to a 1:1 magnification. Camera manufacturers, however, will try to trick us by saying their lens is macro when it’s really not.
For example, they could say that their 70-300mm lens has a macro function, but all that really means is that lens will focus a little bit closer than another one, that’s it. It isn't really macro. A true macro lens is not going to be a zoom of any kind, instead it will be a 50, 60, 100, 200, and some in between.
If you're working with extension tubes or macro lenses, having an idea of what the magnification ratio does help. For example, if you have a 50mm lens on your camera and you're shooting just normal photography, you're working at a magnification ratio of about 1:10. If you take that 50mm lens and add a 50mm extension, you are now working at a 1:1 magnification ratio. How does this work?
Basically, if you want to use extension tubes, you need to know a little bit about how they affect magnification ratios. If you add more extension onto your existing 50mm lens, like say, two extension tubes equalling 68mm, you're getting more magnification. But add that same stack of 68mm extension onto a 70-200mm lens set to 70mm and you’re almost back to 1:1, just off by 2mm.
Understanding how this works can really help to improve your macro photography, making it easier for you to capture the sharpest up-close images possible.