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These two expressions describe one and the same thing – how close we are to the subject – and are interchangeable. The only difference between the two is the way they’re written. Magnification is represented by a number (for example 2x) and the reproduction ratio – as a relation (2:1).

The term “magnification” is unitless quantity, giving the relation between the actual size of the subject and the size of its projection on the camera’s sensor:

If, for example, we photograph a subject that is 36 mm in length (with a fullframe camera – sensor size – 36×24 mm), and its projection on the sensor is only 18 mm (fills half the frame), we have magnification 0.5x (i.e. reproduction ratio 1:2).

If we get closer to our subject, so it becomes projected as 36 mm (filling the whole frame horizontally), we get magnification 1x (i.e. reproduction ratio 1:1 – lifesize)

If we get even closer, so only half of our subject (18 mm) fills the entire frame, we get magnification 2x (i.e. reproduction ratio 2:1) – 18 mm of the subject get projected as 36 mm on the camera sensor.

From the definition for magnification, it is clearly seen that it’s a property only of the lens. It doesn’t matter if we use a fullframe camera or an APS-C/APS-H camera. If we shoot one and the same scene first with the fullframe camera and then with the APS-C, at the same object distance, there will be less of the scene in the frame from the second camera.

This doesn’t mean that we gain more magnification – as you can see, the eyes of the spider are the same size in both projections. The smaller size of the second sensor just uses less of the lens’ angle of view, so there’s a smaller part of the scene in the frame.

If we draw back with the APS-C camera, so we get the same frame as from the fullframe camera, we will gain deeper depth of field. That’s the main advantage of the APS-C/APS-H cameras over the fullframe ones – that with the same frame, the depth of field is deeper.

The easiest way to figure out the magnification of a system is to measure it. For this purpose, we take a picture of a ruler and then divide the sensor width by the mm count in the frame. If your camera’s viewfinder has 100% coverage of the frame, you don’t need to shoot the ruler, but most of the entry class DSLRs have only 90-95% coverage. In these cases, you can use the live-view mode and count the millimeters in the frame on the camera’s diplay.

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