articles/Digital/onmattersofresolution-page2

On Matters of Resolution! - part 2 of 1 2 3 4 5

by Mike McNamee Published 01/02/2009

Nature photographers are caught between a rock and a hard place (sometimes literally). The telephoto situations require fast shutters and wide apertures with whatever light is available. However, (and this is the point of this little article), the insect photographers are always strapped for depth of field, while at the same time demanding sharpness above many other features of an image - you may get away with a slightly soft image of a bride, it may even be better for it - try that with a dragonfly!

Let us look specifically at pixel count, and more particularly at pixel pitch (the distance between two pixel sites on the chip).

The pixel count is calculated by multiplying the number of pixels across by the number of pixels going down. So a chip with 3,000 x 2,000 pixels would have 6,000,000 pixel sites in total. This big number is shortened by calling it a mega pixel (mega equals 1 million (roughly), if we ignore binary theory). The camera software assigns a colour number to each pixel site in the red, green and blue channels which boosts the file size by three, making our six mega pixel camera create an 18 megabyte file.

So far then we have looked at how many pixels there are and how many are contained in a certain area. So, assuming the pixels are square (not always true, Nikon's are rectangular, FujiFilms are polygonal) then if you divide the run along the chip by the pixel count you get the pixel pitch. This does not tell you anything about the area of a pixel site. In order to operate, pixels need space all around them to separate them from their neighbours.

This is to prevent them from shorting electrically, allow data to run down the chip for collection and finally to prevent the electrons from one pixel squabbling with their neighbours. Nature shooters should think of this like gannets' nests in a colony, each is just out of pecking range from their neighbour. When electrons squabble with each other it produces blooming in the image at a very fine level, manifested as a loss in contrast.

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• On Matters of Resolution! page 5
  

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