Notes by Peter Flower
These notes are a follow-up to the brief comments made at a meeting of Reigate Photographic Society on Monday 30 March 2009. They are not intended as a comprehensive explanation of this topic, but to act as a pointer to the principal considerations in the choice of equipment, and some guidance on achieving the best results in close-up photography.
Before going into the technical details it should be explained that these notes refer to exchangeable lenses for SLR or DSLR cameras. Users of compact and 'bridge' digital cameras will be aware of the amazing close-up capabilities of lenses on these cameras, and these require no further comment.
The term 'macro' is used fairly loosely in relation to photographic lenses. However, the term on which it is based, 'photomacrography', is really applicable to captured images bearing about a 1:1 ratio with the subject. A good-quality fixed focal length macro lens will normally provide this capability. Some zoom lenses with so-called macro settings will often be limited to a 1:4 ratio.
Options for close-up photography
There are, broadly, four options available (although they can be used in combination, if you are really wild!)
1. Macro lens
2. Close-up 'filter' ( a dioptre lens that attaches to the filter ring)
3. Zoom lens with macro facility
4. Lens use with extension ring(s) or bellows
Macro lens – With 35mm film cameras, fixed focal length macro lenses of 50mm, 80mm and 100mm were popular options. With the increasing popularity of digital cameras, having a 1.5 or 1.6 factor relative to 35mm frame size, 60mm provides the equivalent of about 90mm. (An example of this is a newly-announced Tamron 60mm f/2 lens which will be available in Canon, Nikon and Sony mounts) The big advantage of these lenses are that their optical performance is optimised for close-up work. At the same time they provide the capability to focus out to infinity, whilst providing adequate image quality. They tend to have a wider maximum aperture than zoom lenses, and retain that capability at all times. The result is a bright image in the viewfinder which aids accurate focusing.
The minus points are that image size is reliant on focal length and distance from the subject (lacking the flexibility of zoom), and the cost.
Close-up filter – This is the simplest, and cheapest, option. A simple dioptre lens is attached to the filter ring of the existing lens. These are available in different strengths that will govern just how close the subject can be. The effect is similar to the use of a magnifying glass. The principal shortcoming is that optical quality is likely to be compromised. Just how significant this may be will depend upon the type of subject being photographed. A close-up of a flower head with slight softening or vignetting around the edges may, in fact, be quite attractive. But, an image of a detailed document with barrel distortion and soft edges might be totally unacceptable. It should also be remembered that the furthest focus point will also be limited whilst the 'filter' is attached.
Zoom lens with macro facility – This is a very versatile option, within the limitations provided by the available macro ratio. It is unlikely to match the close-up capability of a true macro lens. It does provide a great deal of flexibility in the camera-to-subject distance whilst retaining the desired image size. The principal disadvantage is that the maximum aperture size is likely to be lower than that of the fixed focal length lens, and this will further decrease as the telephoto end of the range is reached (unless a very expensive zoom lens is purchased!). This will have an affect on exposure times, and result in a dimmer image in the viewfinder (making accurate focusing more difficult).
Extension rings (or bellows) – Used in combination with any lens these enable closer focus to be achieved by moving the lens further away from the plane of the film or electronic sensor. There are no optical elements involved, so in theory there is no detriment to optical performance. Purists will no doubt point out the technical flaws in this theory but these are unlikely to trouble most people! The most significant practical consideration is that moving the lens away from the sensor plane will affect image brightness. The effective focal length of the lens has been changed. Because the f-stop is calculated using focal length and iris diameter the true values no longer equate to that of the lens alone. This factor, combined with the limited maximum aperture of the zoom lens, will result in a dimmer viewfinder image making accurate focusing more difficult. Having said this, the problem should not be over-stressed, and is certainly not a reason to reject this option unless your eyesight is particularly poor. The important factor with this option is to ensure that the extension rings retain full exposure automation by having electrical contacts (mechanical controls on older equipment). Trying to use manual exposure settings allied to hand-held meter readings is an exercise recommended only for mathematics wizards or the very brave!
Extension rings are available in different depths, and in the past when they were simply metal 'spacers', or with mechanical levers to control the lens aperture, they were sometimes available in sets (e.g. 5mm, 10mm, and 25mm) that could be used singly or in any combination to give varying total spacing of the lens from the camera body.
Bellows are available, and give a significant amount of flexibility (sorry about the pun!) in obtaining the required image size. There are models available that allow control signals to be passed from camera to lens, to allow exposure automation, but these tend to be extremely expensive. The variability of actual extension length presents even more problems in calculating exposure on a manual basis. Bellows excepted, this is a reasonably priced option.
Practical considerations
The choice of equipment is likely to be governed by financial considerations and the amount of equipment that you want to want to carry (or store!). If the use is for indoors and static subjects the choice is much easier. A sturdy tripod is really the only additional item of kit required.
If the requirement is for photography of live subjects, such as butterflies, bees and other insects, small mammals and lizards, then the choice is more complex. Faster shutter speeds may be required (necessitating wider apertures) and the distance from camera to subject may be important (to avoid spooking the subject). A tripod may be a practicality, but the use of a monopod, or even hand-holding, may need to be resorted to. There are, obviously, endless permutations to the various photo-taking scenarios, and only the reader can decide the priorities.
In the case of static subjects there are four important factors for success -
1. Use a sturdy tripod.
2. Focus manually – auto-focus may not choose the desired focal point.
3. Use aperture priority (or manual settings of aperture and shutter speed). Choose your aperture carefully to achieve the desired depth of field (which will be very shallow). If your camera has it, use the depth-of-field preview function.
4. Minimise the possibility of camera shake when activating the shutter. If possible use the self-timer function, mirror lock-up, or at least a remote release.
With mobile or potentially moving subjects the available modes of operation are obviously more limited. The chances are that the smallest possible aperture will be needed in order to compensate for any error of focus. The self-timer and mirror lock-up options are no longer practical.
In the final analysis, success is only likely to be achieved by a great deal of trial and error. The comforting thought is that experimentation using a digital camera, with sizeable memory card, is virtually a cost-free exercise!
The following images were taken using -
Canon 350D DSLR fitted either with a Sigma 18-125 zoom lens, plus 25mm Canon EF extender, or a Canon 100mm f/2.8 macro lens. (One taken with 300mm zoom)
They illustrate some of the capabilities, and factors that need to be considered. The distances quoted are from the focus point on the subject to focal plane in the camera. (This is indicated on the camera body by a mark on the top plate) This is quoted to give consistency to the information. For obvious reasons the length of the lens, measured from the lens-mounting flange, may vary according to the focal length chosen and the focus setting. Many lenses have an internal focusing mechanism but zoom lenses usually extend considerably when moving from normal to telephoto ends of their range.
Sigma 18-125 zoom at 70mm with 25mm extension tube. Distance 12 inches f/8
*Sigma 18-125 zoom at 125mm with 25mm extension tube. Distance 21 inches f/5.6 (Card box at an angle)
Sigma 18-125 zoom at 125mm with 25mm extension tube. Distance 21 inches f/11. (Note difference in depth of field).
Sigma 18-125 zoom at 125mm with 25mm extension tube. Distance 30 inches f/11
Canon 100mm macro lens. Distance 30 inches (Note how much larger the image is at an identical distance)
Canon 75-300mm zoom lens at 300mm with 25mm extension tube. Distance 47 inches f/11.
(Shows ability to obtain reasonable image size at distance from the subject)
General view of the oil lamp, to show position of the rim and wick adjustment control.
Canon 100mm macro lens. Distance 23 inches f/11.
Canon 100mm macro lens. Distance 23 inches f/2.8. (Note limited depth of field in comparison, with control wheel well out of focus)
Canon 100mm macro lens. Distance 12 inches (closest focusing distance) f/8.
Sigma 18-125mm zoom lens at 50mm with 25mm extension tube. Distance 8.5 inches f/8.
Sigma 18-125mm zoom lens at 125mm with 25mm extension tube. Distance 13.5 inches f/8.
Sigma 18-125mm zoom lens at 125mm with 25mm extension tube. Distance not measured, but lens very close to subject. f/8
Sigma 18-125mm zoom lens at 38mm with 25mm extension tube. Distance - lens touching the lamp rim on the left. f/8
