21 March, 2015

It's all about the f-number

400 blog posts later, and here I am trying to talk technical about photography. Can you tell I've run out of ideas after 7 years of blogging?

Like most weird people, there's nothing I enjoy seeing more than a macro image with some good 'bokah' - a completely blurred background behind a nicely focused insect or flower. This isolation effect of the foreground against the background is accomplished simply by using a small f-number on your camera's aperture settings (typically around f/2.8), and can really make a subject stand-out nicely. Small f-numbers work perfectly for singling out little bits of detail along one imaginary focal 'line', but when it comes to photographing moths in artificial situations (i.e. on a leaf or rock), bigger is often better.

Most moths aren't totally flat, which means that when you take a photo using a small f-number, the proportion of the insect that will remain in focus is limited to areas of the body along the same imaginary focal line of the original point of focus. This is called having a 'shallow' depth-of-field, and is not a fantastic thing when you want to show the whole moth in all it's sharpened glory.

The larger the f-number (f/8-f/11 is often the sweet spot) the broader the depth-of-field will be, and as such the greater the proportion of the moth that will remain in focus. Voila!

A Twin-spotted Quaker, snapped using an large f-number of 10 (left) and a small f-number of 2.8 (right)

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