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Macro Photography
Macro photography can be thought of as close-up photography and for much of the time this definition will suffice. However, for the formal definition, read the box below.
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Real definition of macro photography
Although most people think of macro photography as just another name for close-up photography, this is not technically correct. I could get 20cm from a flower with an ultra-wide angle lens on the camera and it would not be macro - however I could be 50cm away with a 180mm macro lens, and this would be true macro.
The term macro relates to the magnification of the image as it appears on the sensor. For example, if you have a small metal ball 10mm in diameter and the image cast onto the image sensor is 10mm as well, then this is called 1:1 magnification (life size). If it is 5mm on the sensor it is 1:2 (half magnification), and if it more than fills the sensor such that it would be 50mm across it is 5:1 (5x magnification).
Traditionally, macro meant anything that was 1:1 or higher, although it is widely accepted that 1:2 (0.5 magnification) is still considered macro.
In the world of compact cameras, the term macro has come to mean a camera's ability to focus very closely on an object.
Of course you can increase the magnification when you print the image onto paper. One definition I've seen for macro is being able to get a life-size image when printed at 6x4". This is not really macro at all as with a crop sensor camera such as on most Canon or Nikon DSLRs, this would only require a magnification of less than 1:6. |
What do I need?
What you need for macro photography depends on whether you have a compact or a DSLR camera.
Macro on Compact Cameras
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Compact camera users don't need any extra equipment as most compacts allow you to focus very closely on an object. All you need to do is put the camera into macro mode (usually this mode is represented by a small flower icon). |
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Photo by Colin. Picture taken with a Fuji S9600 superzoom/bridge camera. This
camera had the ability to focus as close as 1cm from the object. This British two
pence coin is 1inch (2.5cm) in diameter. With the lens this close, getting light to
the object can be a problem so a tiny LED torch was used.
If you do need to get closer, then some bridge/superzoom cameras have a filter screw thread on the lens and so you can add close-up attachments.
Macro on DSLR Cameras
The standard lens that most DSLRs come with usually lets you focus down to a distance of about 20-30cm - certainly not as close as compact cameras. Therefore, to take good macro photography, you are going to need to get out your Visa card and purchase some extra kit. Luckily it is not as expensive as you might think and there are different options available:
- close-up filters (sometimes called dioptres)
- reversing ring
- extension tubes
- some zoom lenses have macro capability
- dedicated prime macro lenses
Close up filters are a bit like the glass in spectacles worn by a long-sighted person - they change the direction of the rays of light to allow you to focus closer than you normally would. These are often the only option available to users of bridge cameras, but for DSLR users, we would not recommend them as it is adding additional glass elements into the light path and this affects image quality. If you do buy one, try to get one that consists of two glass elements rather than one otherwise you would suffer reduced image sharpness and increased chromatic distortion.
Extension tubes are a much better cost-effective option. They are attached between the camera body and the lens and their purpose is to move the lens further away from the camera body. This has the effect of moving the closest focusing point much nearer to the front of the lens. As they contain no glass, there should not be any noticeable drop in image quality, although you do lose some light which you (or the camera) will need to compensate for.
They often come in sets of three - each one able to move the lens a different distance from the camera body. They can also be used in combination.
Make sure you buy a set with the electrical contacts so the camera body and lens can still 'talk' to each other. If you don't, you will lose the ability to auto focus, and the camera will not be able to control the lens aperture. These cheap ones are very common on eBay so beware.
The slight downside of extension tubes is that you lose the ability to focus at infinity so you can't leave them on the lens once you've finished taking your macro shots.
Reversing rings allow you to attach the lens in reverse on to your camera (the attachment screws on to the filter thread and this attaches to the body of your camera). We'll be honest and say we've never used these so can't comment too much, but the results are apparently very good. For obvious reasons, all electronic contacts with the camera are lost so you'll be working in full manual mode.
There is also a technique (again we've not tried this) where you join two lenses together using a coupler on the filter ring of both lenses. One attaches to the camera as normal, and the other reversed one (which much be of a shorter focal length) in front of that. This method allows the camera to continue to control the aperture on the normal lens. Autofocus must be turned off though or you risk damaging the normal mounted lens.
The magnification is the focal length of the normal mounted lens divided by the focal length of the reversed lens. For example, a 200mm lens which has a reversed 20mm lens on the front will give a magnification of 10:1.
Zoom lenses with a macro mode are an excellent way to get into macro photography as, although they are more expensive than extension tubes, you are generally buying the lens for its normal zoom focal range, so the macro is an added bonus. Often the macro feature only works at the longer end of the zoom range. For example - on a Sigma 70-300mm lens, the macro can only be engaged while the lens is within the 200-300mm range. The normal minimum focusing distance of this lens is about 1.45 metres (giving a maximum magnification of 0.24x, however if you switch to macro mode, this lens will focus to 0.95m giving 0.5x (1:2) magnification.
Compact camera users may think that only being able to focus down to 0.95 metres is pretty poor, but remember we are talking about a 300mm lens here. The picture below is of a flower no bigger than two inches (5cm) across and taken from about a metre away.
photo by Colin. Sigma 70-300mm lens at 300mm macro mode, 1.6s f/8, 100 ISO
This shows you don't need to be very close to the subject. In fact if I was trying to get a close up of a deadly snake, I think I would prefer to be some distance away.
photo by Phil
Dedicated Macro Lenses (Nikon call them micro lenses) provide the ultimate in quality for this type of photography. Although these lenses can be used for general photography as they focus from close range to infinity, they are generally designed to offer optimum image quality at 1:1 magnification (generally at its closest focusing distance).
Nearly all dedicated macro lenses offer 1:1 magnification, although you can get lenses with even greater magnification (Canon's MP-E 65mm f/2.8 is a 5:1 macro lens).
Most manufacturers will make a range of macro lenses at different focal lengths. For example, Canon make a 50, 60, 100 and 180mm macro lenses ; Nikon offer 60, 105 and 200mm. With the shorter focal lengths you often need to be very close to the subject to achieve 1:1 magnification and this can cause problems with illumination of the subject. Therefore many photographers prefer the longer lenses.
Take the Canon 60mm macro lens - its closest focusing distance is 200mm (this is from the subject to the focal plane where the image sensor is, not the front of the lens). The lens is 70mm long, the focal plane, probably another 30mm behind that. Therefore, the front of your lens is only about 100mm (four inches) from the subject. It is going to be more difficult to get even illumination with the lens so close, and potentially casting a shadow. The 180mm lens has a minimum focus of 480mm and the lens is 186mm long. Therefore the front of your lens is around 264mm (about 10.4 inches) from the subject.
Problems with Macro
The two main problems with macro photography are:
- getting even illumination of the subject when very close to it
- getting the image in sharp focus as the depth-of-field is so shallow
Getting Even Illumination
As mentioned in the caption for the coin picture above, the illumination problem comes from the camera being so close to the subject that it blocks the ambient light.
A lot of macro photography is done indoors where there is going to be less light to start with so you might think a flash is the easy option. Most on-camera flash, however, is designed to work no closer than about one metre. The camera's lens will most likely cast a shadow over the image if the flash is your main source of illumination. DSLR users with a lens hood on the camera will suffer even more.
Photo by Amanda. The shadow cast by the lens hood is clearly visible.
To get around this problem, there are various external flashguns designed specifically for close-up photography. These often use either multiple smaller lights positioned level with the front of the lens, or a ring flash that goes around the lens. I've even seen accessories that channel light from an external flash gun into a ring diffuser that fits around the lens.
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above left: Sigma EM140 Macro Flash
above right: Nikon Speedlight Commander Kit.
left: an LED-based light designed to fit around the lens of compact cameras. |
A cheap alternative (and the method used for the coin picture above) is to use some form of torch (flashlight). Modern LED lights are excellent for this as they are small (and therefore easy to throw in your camera bag) and very bright. I use a 19 LED headlight (shown below) as I can control how many LEDs are turned on at a time (1,7 or 19).
Photo by Colin - one of the most useful camera accessories for macro work
Focus and Depth-of-Field in Macro Photography
With macro photography (especially with a DSLR camera) the depth of field can be incredibly shallow. It is feasible for the DoF to be less than 1mm (really!).
Here are some examples (based on a crop sensor APS-C DSLR camera):
300mm lens - aperture f/5.6 - subject at 1m - DoF = less than 2mm
300mm lens - aperture f/16 - subject at 1m - DoF = about 5mm
180mm lens - aperture f/5.6 - subject at 0.5m - DoF = 1.1mm
180mm lens - aperture f/16 - subject at 0.5m - DoF = 3.2mm
50mm lens - aperture f/5.6 - subject at 10cm - DoF = less than 0.5mm
50mm lens - aperture f/16 - subject at 10cm - DoF = 1.3mm
In the examples above the 300mm and 180mm lens could easily focus down to that distance if they have macro capability. To get a 50mm lens to focus to 10cm would probably require the use of extension tubes.
As you can see, the depth of field is so shallow that it is best to follow these basic rules.
- If your subject can't move, use a tripod. If it is moving (a flower in the wind for example) you are probably not going to get a brilliant macro shot. Take loads and hope you get one where the subject isn't moving.
- Use manual focus - it's much more accurate (though see nerd box below).
- When dealing with very tiny DoFs, focus by moving the camera slightly. If you are hand holding the camera, this is especially true as the act of turning the focus dial with probably move the camera's position.
- If you have it, use live view with the focus part of the image enlarged on the display allowing you to carefully check focus.
- Use focus bracketing (either automatic or manual) - you can always be clever and merge them in Photoshop afterwards to get a bigger depth of field in your final image.
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Manual Focusing - What You See Is Not What You Get (WYSINWYG!)
Manual focusing on DSLRs is not that easy compared to the old manual focus film cameras. This is mainly because modern cameras do not always give you a true impression of the actual depth of field of your image.
The image in the viewfinder can have a greater depth of field than the end result picture due to the nature of modern focusing screens. This extra depth of field makes it harder to see what is genuinely in or out of focus.
When cameras were manual focus the set up was quite simple: light coming into the lens would be reflected by the mirror onto the focusing screen. The focusing screen is a piece of glass beneath the pentaprism where the light can be focused in order for it to make a visible image in the viewfinder.
When autofocus was invented things became more complicated. The mirror inside the camera became a semi-transparent mirror sending some light to the focusing screen and some through the mirror, onto a sub-mirror and down onto the autofocus sensors. If left alone this would make the viewfinder image darker and this would not be desirable. Combined with the increasingly common use of slow zoom lenses that have a widest aperture of say f/3.5 - f/5.6, you could end up with a dark image to try to compose with.
In order to rectify this, work was done to brighten up the viewfinder image. This involves the use of micro-lenses within the focusing screen, used to focus light into the pentamirror. Most of this light is coming from the centre of the lens. With faster lenses this gives the impression of a greater depth of field.
Viewing an image through an f/2 lens, for example, will show a greater depth of field in the viewfinder than you will get in your image if shot at the widest aperture. This makes manual focusing harder as you are seeing more in focus than is really going to be in focus. This can be a problem when focusing on a particular part of the image is critical.
In macro photography you have very limited depth of field to play with even at narrow apertures such as f/22. Focusing to the millimetre can be critical and this is not easy with a DSLR. Some DSLRs have optional focusing screens designed for manual focusing but if you have live view, this can often be used to zoom into the live image while you are composing. This is very useful for precise manual focusing as the image is unaffected by the false depth of field created by the focusing screen micro lenses. |
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