This will be a short post explaining what a lens maximum magnification means.
With lenses in general, but especially in macro options, magnification will be one of the most promonently displayed and advertised features of the lens, along with maximum aperture and focal lenght. It will be given as a ratio: 1:1, 1:2 or 2:1. With ‘regular’ lenses the number will be shown as a decimal fraction like 0.50x or 0.25x. Both of those representations refer to the same phenomenon and theoretically could be used interchangably, so that 1:1 would correspond to 1x, 1:2 to 0.5x, 2:1 to 2x and so on.
As you probably figured out yourself the number is used to describe the relationship between the object you are photographing and the image you get, but how exactly? The RAW or JPEG files you get from the camera of course can be resized to fit your needs so clearly this is not what we are talking about.
The canvas those numbers are referring to of course is not your display, but rather your camera’s sensor
The maximum magnification describes how large can an image on your sensor be relative to the object you are photographing.
If maximum magnification of your lens is 1:1 (or 1x), this means that if your object is 1cm long, it can ‘burn’ a 1cm long image on your sensor
For 1:2 magnification a 1cm object produces a 50mm image, and analogously for a 4:1 magnification it is a 4cm image of a 1cm object.
This of course is some quick easy math, but what does it mean in practice? How do those tumbers correspond to what I see in my files? I mean, surely I can bump an image of a bee to fit a whole wall and it will still be sharp and detailed.
When it comes to the files you actually get from your sensor, the number describes the proportion of the frame you can fill with your object, and it is dependant on the size of your sensor. As and example let’s look at APS-C.
Classic APS-C sensor is 25mm, or 2,5cm wide. For our example let’s say we have a fruitfly that is 5mm long and we are shooting it at 1:1 magnification. In practice it means that a fruitfly that is 5mm long can fill up 1/5th of the frame lenghtwise (5mm is 1/5th of 25mm). With a 2:1 lens, a 5mm fruitfly would be 10mm on your sensor and it would fill 40% of the frame (10/25 = 0,4).
Here of course you might ask, does that mean that actually the smaller the sensor, the larger image you can get? Does it mean that, given the same lens, an image of a bug made with an APS-C camera will appear larger than that made with Full Frame? The short answer is yes. And no.
Let us ignore here all the issues with focal length equivalence – it does not matter here because whatever we are doing we are aiming for 1:1 magnification, meaning that although with different crop factors we would physically be at a different distance from the object to get 1:1, a fly that is 5mm long would still prduce a 5mm long image on a sensor.
Comming back to our previous calculation, a 5mm object fills 20% of the 25mm wide APS-C sensor. But a Full Frame sensor is 35mm wide, which means that a 5mm object would only fill 14% of the frame.
In practice, if you printed both images uncropped on a sheet of paper that is 10cm wide, you will get a 20cm bug from an APS-C camera and a 14cm bug from Full Frame.
Images above are not actual 1:1 magnification photos but rather crops to illustrate the principle.
Now, is the image magnified to a greater degree on an APS-C? No it is not. it is still 1:1. But is the image effectively larger? Yes, yes it is. This last piece of information is very critical if you are talking to a macro photographer, otherwise it doesn’t make any difference.