In our latest photography cheat sheet we answer the question 'What is a macro lens?'. In our infographic we explain some of the finer points of using macro lenses and illustrate the effects different magnifications can produce with your subjects.
The official definition of a macro lens is that it should be able to reproduce a life-sized image of an object on the recording medium - in this case the image sensor.
True macro lenses offer a magnification factor of 1.0x or 1:1 at its closest focus setting. Fit one of these lenses to a DSLR like the Canon EOS 60D, and a standard UK postage stamp will fill the whole frame.
That might not sound particularly impressive, but when you consider that the 18Mp sensor in cameras like enable very large format prints, the potential for creating massive enlargements from shots of tiny objects is really quite astonishing.
What's more, you can get still get very impressive enlargements of small objects using a macro lens that only offers 0.5x (or 1:2) maximum magnification.
In our latest photography cheat sheet we've illustrated the effects produced by macro lenses at different levels of magnification and how your subject will appear.
Simply click on the infographic to see the larger version of this cheat sheet, or drag and drop it to your desktop.
'Flat field' lenses
One feature that's shared by all macro lenses is that they're 'flat field' lenses. General-purpose lenses typically suffer from field curvature, so the point of focus will be at a slightly different distance towards the corners of the frame compared to the centre.
For example, the Canon EF 24-70mm f/2.8L-series zoom lens is quite notorious for this. In macro lenses, field curvature must be minimised as much as possible, so if you photograph a small flat object square on, such as the postage stamp we mentioned, the centre and corners of the stamp should all be sharp and in focus.
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