Lenses

Working distance depends on the magnification required and the focal length of the chosen lens. At a given magnification, the longer the focal length of the lens the greater the distance between camera and subject. Focal length of the lens also affects background coverage as longer lenses have a narrower field of view.

Focal Length	Angle of View	Image Plane to Subject	Lens to Subject
200mm	12º	0.50m	0.26m
105mm	23º	0.31m
24mm	84º

Please see diagram for a clearer indication of the effect of angle of view on background coverage.

Depth of field

Depth of Field is dictated by the magnification required and the f-stop chosen. (Image resolution and degree of enlargement will also affect the sharpness of the final picture). At ½-lifesize (magnification ratio 1:2) stopping the lens down to f16 gives approximately 6mm depth of field – regardless of the focal length of the lens. At ¼-lifesize (magnification ratio 1:4) f16 gives approximately 21mm depth of field.
Where it’s an option, reducing magnification is the easiest way to increase available depth of field. When working in the field with very small subjects this may be the only way to obtain adequate depth of field. Under controlled conditions image stacking becomes an alternative option.

Backgrounds

The background can make or break a picture. For insect photography the use of a longer focal length lens can help by reducing background coverage. Choice of f-stop is also a major factor in controlling how distracting elements in the background are in the final image. Choosing an aperture of f8 rather than f16 will improve the appearance of the background but obviously reduces the available depth of field. In order to make maximum use of depth of field it is essential to ensure that the camera back is parallel to the main plane of interest of the subject – for a butterfly this clearly going to be the wings- top to bottom and left to right. If the camera is lined up correctly it should be possible to use f8 or f5.6, if necessary, to produce a distraction-free background whilst only sacrificing sharpness at the tips of the insect’s antennae. Deciding how to line up the camera when photographing dragonflies can be more difficult and, despite being generally larger than butterflies and therefore requiring less magnification to produce a good sized image, it is difficult to achieve adequate sharpness without stopping down to at least f8. This means having more ‘problem’ backgrounds with dragonfly photographs.