1:1 magnification, what is it?

Started Oct 21, 2009 | Discussions thread
D Knisely Senior Member • Posts: 2,053
Re: 1:1 magnification, what is it?

1:1 means that the size of the subject in the plane of focus is identical to the image sensor size in the camera. For example, if you take a 1:1 image with a full-frame (FX) camera, at the focus distance of the lens, the recorded subject dimensions would be 24x36 mm. On a Nikon 1.5x crop sensor (DX), the recorded subject dimensions would be 16x24 mm (because the image sensor is smaller, the effective magnification is larger, just like a cropped sensor makes a telephoto lens seem to focus at a longer effective focal length).

1:2 means that the subject size is TWICE the size of the camera's sensor (48x72mm for FX; 32x48mm for DX). Magnifications of about 1:2 to 1:10 would generally be considered to be "closeups" and not truly macro images. This would roughly correspond to typical small to large flowers that fill the frame.

A lens that is "1:1" can close-focus down to a true macro 1:1 magnification, while a lens that is "1:2" can only focus closely enough to reach a subject image size that is twice as large. Any lens that is a true macro lens must focus to a magnification of 1:1 or larger.

1:1 is typically considered to be the lowest magnification for true "macro" photography. If you go to higher magnifications, the subject image size recorded gets smaller. For example, a magnification of 2:1 would mean the subject images size is 1/2 of the camera's sensor size (12x18mm for FX; 8x12 mm for DX).

Magnification is a very useful concept for macro and closeup photographers because it tells you what subject image size you're going to be recording independently from the focal length of the lens. For example, a 105mm macro lens focused for 1:1 magnification will be much closer to the subject than a 200mm macro lens focused for 1:1, but the recorded subject size will be identical (given the same camera with the same sensor size is being used).

Depth of Field (DoF) and the need for steadiness are basically functions of magnification. So notice that, for example, if you take a picture of a flower than is 2" across with an FX DSLR, the magnification would be 1:1 (roughly 24mm in diameter, the height of the FX DSLR sensor). On the other hand, if you shoot the same 2" flower on a P&S with a very tiny sensor, the magnification will be more like 1:5 or even higher. Since DoF for the same aperture is a function of magnification, the P&S will have much greater DoF for the same subject image size! (The P&S will also close-focus using a very wide angle of view and a very close working distance. This also accounts for the greater DoF at the same magnification.) That's why flower macros with P&S cameras are so much "easier" to take (assuming you are looking for DoF to cover the whole flower).

I hope this helps. You might want to get a copy of John Shaw's oustanding macro and closeup book Closeups in Nature if you're interested in the subject.


 D Knisely's gear list:D Knisely's gear list
Olympus E-M5 II Nikon AF Micro-Nikkor 200mm f/4D ED-IF Olympus M.Zuiko Digital 45mm F1.8 Olympus M.Zuiko Digital ED 12mm 1:2 Olympus M.Zuiko Digital ED 60mm 1:2.8 Macro +3 more
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