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With macro photography you can get pictures of many interesting and beautiful subjects, such as these frozen air bubbles in ice...

Introduction

Macro photography is photography of subjects that are very small, but not so small as to require a microscope. There are many applications for macro photography: flowers, plants, insects, minerals, snowflakes, rime, raindrops, hailstones, icicles and such. You can photograph anything a few millimeters in size and larger.

Equipment

To do macro photography, you need bellows or extension rings that fit your particular camera and lens mount. These rings or bellows are mounted between your camera lens and the camera body; therefore you need a camera that can have the lens detached. An SLR camera generally works best.

Apart from the bellows, you need a sturdy tripod and a cable release. Since you will be photographing small objects at some magnification, any small vibrations of the camera will most certainly blur the exposure.

...or the internal structure of a hailstone.

It is best to use lenses ranging from 50mm (standard) to 85mm (portrait) on the bellows. Lenses outside this focal length range are either impractical or not very suitable.

Magnification and effective f/ratio

The bellows effectively lengthen the focal length behind the lens (the effective focal length) while the distance of the lens to the object is drastically reduced. Typically, the subject to photograph is only a few centimeters in front of the lens, while the bellows or extension rings can add more than 10 cm to the focal length.

Assuming the lens will be used with focus at infinity, the magnification is L/F where L is the length of bellows and F is the focal length of the lens (e.g. for a 50mm lens, F = 50mm).1 Thus, with bellows or extension rings that are 150mm in length, the magnification factor would be 3. Without bellows, L=0 and the magnification is 0.

The magnification says how big an object of some dimensions will be imaged on the film (or sensor) plane of the camera. E.g. photographing an ice crystal 1mm in size with a magnification of 4 will yield an image of the crystal 4mm in size on the frame.

For macro photography you need a camera with bellows and lens, mounted on a tripod with a cable release.

In addition to the magnification, the f/ratio changes as well, because the focal length is effectively increased while the lens aperture is the same. The factor by which the f/ratio number changes is M+1 where M is the magnification. If you set your lens to f/8 and you use a magnification of 3, you effectively have f/32, so a magnification of 3 adds 4 stops to the lens aperture.2

When photographing subjects very close to the lens, any slight variations in depth will have a major effect on the focusing of the image on the film, because the subject distance to the lens is now much smaller than the image distance to the lens, so small variations in subject distance give large variations in image distance (normally this is the other way around). You will need to set the lens at high f/ratio numbers such as f/16 or higher to have enough depth of focus.

Other than these differences, macro photography is not any different from normal photography. But since there is generally not much available light due to the large f/ratio, you are bound to long exposure times, usually several seconds. It is very important that the camera setup (and the subject!) does not move at all during the exposure.

Suitable lenses

Because bellows and extension rings usually only reach up to about 15cm in length, you will need lenses with a short focal length if you require higher magnifications. Typically a standard (50mm) lens is best to use.

Reversing the lens

The photos will have better sharpness if the lens is mounted backward on the bellows. There are special adapters available for this purpose.

Since you are using the lens in a manner that it wasn't designed for, you can expect bad lens errors to show up, such as color fringes (chromatic aberration), coma, vignetting, unsharpness due to diffraction and such. To partly overcome this, there are adapters available to mount a lens backward. Mounting a lens backward significantly improves image quality, since with macro photography the image distance is longer than the object distance to the lens, while the lens has been designed to have the image distance much shorter. Reversing the lens overcomes this.

Focusing

You can set the lens at infinity or any other distance; this doesn't matter much since the lens will move very slightly in comparison to the long length added by the bellows. You will focus by adjusting either the length of the bellows (there are adjustment screws on it for that purpose), or by adjusting the distance to the subject to photograph. Since the latter adjustment is very hard to do properly, bellows are much better than extension rings, since those cannot be adjusted in length.


1. This formula can be derived from the law of focal lengths: 1/a + 1/b = 1/F where a is the object distance to the lens, b the image distance, and F the focal length. The magnification M = b/a = b * 1/a = b * (1/F - 1/b) = b/F - 1. The image distance b = F+L where L is the length of bellows used, so the magnification M = (F+L)/F - 1 = L/F.

2. This formula can be derived as follows. Suppose the f/ratio of the lens is n, thus the actual lens aperture is F/n. (n could be 2.8, 4 or whatever for f/2.8, f/4 and such.) The effective focal length of the lens with bellows is F+L = F + F*L/F = F * (1+M). Thus, F/n = F*(1+M) / (n*(1+M)), so the effective f/ratio is n*(1+M). In other words, n is multiplied by a factor of 1+M.