Reversed 50mm - a dedicated Macro lens

Close-range or macro-photography of small objects, flowers, insects, coins, stamps and the like seems to be gaining great popularity amongst many photographers with especially photographs of insects being seen with increasing frequency. Most digital cameras with their very short focal length lenses allow the photographer to approach a subject much closer than was ever possible with the traditional 35 mm camera. Many digitals in addition also have a close-range facility usually (incorrectly) referred to as a “Macro” mode and designated by a tulip icon that allows the photographer to focus up to about 10 or 15 cm from the subject. None of them, however, allow for true macro photographs.

Bona fide macrophotography, also often called photomacrography refers to photographs taken at life size or greater magnifications. The Focal Encyclopedia of Photography puts it as follows “Macrophotography is the process of taking larger-than-life photographs with ordinary camera lenses. Macrophotography ends and photomicrography (with microscope lenses) begins, at about 10x diameters.”

The difference between the actual size of the subject and the image size is designated by their relation to each other, for example, a 1:1 ratio would refer to a life size image, 1:2 would be one half life size and 2:1 would be double life size. There are various ways of achieving these degrees of magnification such as by using dedicated macro lenses designed for this specific purpose, or extension tubes or bellows which are placed between lens and film plane. Both these methods, however, require relatively costly and specialised equipment. True macro lenses, due to their optical complexity are notoriously expensive and will usually only be found in the arsenal of the professional. Extension tubes/bellows on the other hand, although less expensive can only be fitted to an SLR camera.

Few aspiring macro photographers realise that they probably have lying about in the back of some cupboard a highly sophisticated, highly corrected macro lens just waiting to be used. What I'm talking about is the standard 50mm lens from a (now obsolete?) 35 mm SLR film camera. These lenses are also readily available from 2^nd hand dealers or swop shops at next to nothing. I recently purchased two at under R50 each. The standard 50 mm lens has been designed for long lens to subject distances (infinity) and a short lens to film distance (focal length). This principal is illustrated in the sketch below.

In macro photography, however, these conditions are reversed and the lens to subject distance needs to be less than the lens to film distance in order to attain the desired degree of magnification of the subject. It only makes good sense therefore to reverse the lens to achieve this.

The shorter the focal length of the lens the greater is the magnification that can be achieved. A 28 mm lens for instance will allow you to get considerably closer than a 50mm. The shorter focal length lenses, however, do present other problems such as vignetting (darkening of the edges of the image) so we'll stick with the 50 mm lens for the moment.

A reversed lens can be fitted directly onto the front of virtually any fixed or zoom lens, this is known as stacking or when a SLR camera with a removable lens is being used the reversed lens can also be used with a bellows unit or extension tubes only. When lenses are stacked the resulting increase in glass and air surfaces does cause a slight degrading of image quality, thus if your equipment allows it the latter method will produce better definition. On the other hand the quality loss through stacking is relatively small and this method offers many other advantages. When stacking all the functions of your fixed lens such as exposure control and auto focus can still be fully utilised, these functions will of course fall away when the lens is used with extension tubes only. Even if you are using dedicated extension tubes they won't be operative on the reversed lens.

A 50 mm lens fitted to a Canon Powershot G3 which has a fixed (non-interchangeable) zoom lens

Fitting the reversed lens is actually a very simple operation. Although reversal rings are made by some manufactures they are difficult to obtain and anyway the chances are great that the lens to be reversed will differ from the lens on your camera (if you are stacking) and you probably won't find a ring that fits both lenses. In fact, it is probably easier making your own from the outset. You are going to need two filter rings or step-up or step-down rings, one to fit the front of your fixed lens (or bellows/extension tubes) and one to fit the front of the supplementary lens that is to be reversed. These rings now need to be glued together back-to-back, superglue works fine although I find that two-part resin glue or paste gives a firmer bond. When gluing be sure that the two rings are accurately centred. Now all that is needed is to screw the two lenses together front to front.

Two filter rings can be glued together to form a very functional reversal adaptor for a 50 mm lens.

Keep in mind that only the optics of the supplementary lens are needed when the lenses are stacked. The aperture of the supplementary lens must thus be fully opened and the lens focused on infinity. Exposure and focus are controlled by the master (fixed) lens.

Reversed lens fitted to a DSLR via extension tubes. When extension tubes are used exposure is controlled by the aperture on the reversed lens. The usual exposure compensation applies.

When a reversed lens is attached to extension tubes or bellows the aperture of the reversed lens is used for exposure while movement of the bellows focuses the lens or when using fixed extension tubes focus is obtained by moving the camera backwards or forwards. The focusing mechanism on the lens itself will have almost no effect and for best results should be left on infinity.

Reversed lens stacked on a 100 mm macro lens.

When lenses are stacked the focal length of the master lens needs to be long enough to accommodate the supplementary lens, that is, it's field of view needs to be narrow enough so as not to record an area larger than the maximum aperture opening of the supplementary lens or vignetting will occur. If the camera's fixed lens has zooming capabilities, zoom in at least to the point where no darkening of the edges can be seen. With a 50 mm reversed supplementary lens a 100 mm lens (or a lens zoomed to the equivalent of 100 mm) works perfectly. If a lens with a shorter focal length than 50 mm is used as the supplementary a correspondingly longer master lens is needed. While on the question of lenses it is worth noting that prime lenses (lenses of a fixed focal length) deliver considerably better results when used as master lenses than do zoom lenses.

The possible degree of magnification using stacked lenses is also quite straightforward to determine. In our example above where a 100 mm lens is used in conjunction with a reversed 50 mm lens you would get a magnification of 100 divided by 50. That is x2 or put another way 2:1. In the same way a 200 mm master lens combined with a 28 mm supplementary will give you a 7:1 magnification.

The author using a stacked 100 mm macro and a reversed 50 mm in the field

Unless you are using specialist equipment especially designed for macrophotography be prepared to experiment. Accessories for adapting standard cameras for macro purposes are both scarce and highly priced, however you'll be surprised what can be achieved by various makeshift methods using an assortment of lenses, masking tape, presstick and glue. One of my favourite supplementary lenses which I use very often in conjunction with a 100 mm macro lens and which gives excellent results, is the front part of a pair of old binoculars.

It can be done!

Article and photographs copyright Lambert Smith, 2006

 Top of Page