Spirals, Ratios, Cropping and Composition

From the research I've been doing into composition has sprung a world of Fibonacci spirals. The size and ratios of images is are  important considerations when framing the shot in camera. The Fibonacci spiral fits into the GoldenSection of 1:1.6, if we remove a square (equal to the length of the short short side) from the rectangle formed by this ratio we are left with a rectangle which retains the original ratio of 1:1.6

Nikon D90 with Tamron AF 90mm Macro lens at 90mm

f/18. 1/4sec. ISO250. Tripod and self timer.

Looking further I decided to work out the ratios of common film sizes and cameras.

4 x 6 in = 1 : 1.6

5 x 7 in = 1 : 1.4

8 x 10 in = 1 : 1.25

30 x 40cm = 1 : 133

A4   210 x 297mm = 1 : 41    This is also special because it folds in half and gives 2 rectangles with the same ratio.

40 x 50cm = 1 : 1.25    This maximum size of mount for our competition photography.

10 x 12in = 1 : 1.2

35mm gauge film neg  35 x 24mm = 1 : 1.45  with 8 sprocket holes per frame

Nikon D90 on Large image size (and for NEF)   4288 x 2848 pixels = 1 : 1.5

I've found it useful to use transparent overlay of the spiral over the screen as an aid to composition, usually placing the tight part of the spiral over the centre of interest. To me the 1 ; 1.6 rectangle often looks a little long, but can work well in portrait mode.

This isn't the be all and end all by any means, it's just another useful tool. It has helped my 'photographic eye' as I'm weighing up shot options and for post production work.

The tight part of the spiral is not far off a third so this must be part of the reason it works.