This is a quick-ish guide to macro photography with DSLRs and similar. I am no expert by any means, and this is not a definitive guide, but this is a collection of what I've come across so far and hope it is of help to others. I expect to update it from time to time.
Sample images are linked through the thumbnails. They are jpegs straight from the camera without any further processing.
What is it?
A traditional definition is that the image of the subject is projected onto the film or sensor at 1:1 magnification or bigger. In other words, life size or bigger. The meaning seems to be blurred somewhat, but loosely speaking, it is the taking of photos of small subjects or areas of subjects such that they appear big in the final image. It does not necessarily require you to get super close to the subject, although depending on the method that is often required. It is also not the taking of a regular picture and enlarging a small portion of it, as often you will not get the same level of detail if you do that.
Magnification and impact of focal length
Macro lenses are specified for their maximum magnification. Lower effective magnification can of course be achieved by moving further away or reducing the focal length on zooms.
The maximum magnification is usually at the minimum focusing distance. In the case of a zoom lens, it is usually at maximum focal length. For camera lenses, the maximum magnification may be stated either as a ratio of sensor to subject size, or as a numerical magnification.
2:1 = 2x magnification
1:1 = 1x magnification
1:4 = 0.25 (1/4) magnification
Note this is regardless of the focal length. The impact of the focal length is how far away the subject is in order to get the maximum magnification. A longer focal length lens will allow you to be further away. e.g. a 50mm 1:1 macro lens will give the same subject size as a 100mm 1:1 macro lens. However, on the 100mm, you could be further away from the subject. Note the distance is measured from the sensor plane, and not the front of the lens. So physically longer lenses will have an impact on the perceived separation from camera to subject.
What to use?
Prime 1:1 macro lenses
These generally give the best results as they are dedicated to the function. Typically available in focal lengths of 50mm and higher with fairly big apertures of f/2.8. As with most lenses, they tend to increase in price as the focal length increases. They are also useful as a general prime lens.
Example: Tamron 90mm f/2.8 1:1 macro
Damselfly - 3.7MB - Sony A350, Tamron 90mm macro, 1/160s, f/7.1, ISO250
Zoom 1:X macro lenses
These are generally zoom lenses which also have the ability to focus quite close, therefore allowing you to get big images of close subjects. In general, the magnification is less than 1, and the quality is not as good as a prime, and apertures may not be as big. However they are more versatile.
Example: Olympus Zuiko 70-300 f/4-5.6
, maximum magnification 1:2.
Dragonfly - 6.1MB - Olympus E510, Olympus Zuiko 70-300 at 300mm, 1/500s, f/11, ISO800
Close up lenses
These are lenses in the optical sense and not photographic sense. They are usually a single element although more expensive ones may have multiple elements. They screw into the filter thread at the front of a photographic lens. These provide a degree of magnification and reduces the minimum and maximum focusing distance of the photographic lens. By allowing you to get closer, you therefore get bigger images. However, you generally lose the ability to focus on infinity so you can not leave the close up lens fitted if you want the whole range. These lenses can be found at very low cost, but you get what you pay for in optical quality. In general they will be made of unremarkable glass and not coated. Therefore there is increased opportunity for chromatic aberrations and other unwanted light reflections degrading the image quality. It is possible to find higher grade close up lenses, but of course the price will increase also.
They are rated in strength and are typically available in ratings from +1 to +10 where a bigger number is a stronger effect. The +10 may also be called a "macro lens". They can be stacked where the effect is added, although with more elements there is more chance for image quality degradation.
See also here
These are literally tubes which fit between the camera lens and body, and have no optical elements. Therefore the optical quality of the lens is preserved. By moving the lens out, it reduces the minimum and maximum focusing distance, allowing you to get closer and therefore a bigger image.
Basic ones only provide a mechanical extension, and the electrical contact between camera body and lens is lost. More advanced ones will provide the electrical connection as well as any other mechanical connections that may be present, therefore allowing auto-focusing.
These generally cost more than a basic close up lens, but still far less than a dedicated photographic macro lens.
Under construction. For now click here
for my quick play with this method.
Focusing and Depth of Field
At the combinations of settings useful for macro, you will tend to operate in an area of very shallow DoF. The subjects may be small, but the DoF tends to be smaller!
Therefore accurate focusing is essential to get a sharp image. In this case, manual focus is usually preferred over autofocus. If the camera has zoom in live view mode, that can help fine tune focus.
The DoF can also be increased by reducing the aperture size (higher f-number). The usual problems with using small apertures apply. e.g. diffraction softening, low light transmission and increased visibility of any dust on the sensor.
Focus stacking is an advanced technique for getting around the shallow DoF. This is achieved by taking multiple images and moving the focus in each one, such that the desired 'in focus' range is covered. Using software, the images can be later combined to give a single in focus image. Obviously this technique works best when the subject and camera does not move between shots.
Dandilion Clock - 3.1MB - Sony A350, Tamron 90mm macro, 1/400s, f/2.8, ISO100
The shallow DoF when wide open was used to see "through" the near seed tops to the further seeds side on.
As with general photography, light is a key consideration. Brighter lenses can be used wide open in poor light. But if you want to have deeper DoF, then more light is the primary answer.
Dedicated macro flashes and ring flashes/lights fit close to the front of the lens for illumination, but tend to have a relatively high cost. A standard add-on flash with diffuser can be used with care. Any built in flash with or without diffuser can do in a pinch.
A more advanced composition skill is balancing the light of the subject to that of the background. Depending on the subject, the lightness levels between subject and background can vary significantly. In these cases fill flash can be used to supplement the subject.
Generally speaking, most 1:1 fixed focal length lenses do not feature any form of image stabilisation. Therefore those cameras which feature in body stabilisation have a potential advantage here.
The usual considerations on image stabilisation apply here - specifically that it helps gives a sharp shot of a static subject, but does not help if the subject is moving.
Sensor size and pixel density
The sensor size does not directly impact the optical magnification. At a given magnification, the projected image will be the same physical size on a full frame sensor as for a cropped sensor. The difference is the full frame will show a bigger area of it. So like any other lenses, the crop factor can be used to determine the equivalent field of view between different sensor sizes. The note to take here is that as a cropped sensor shows a smaller area, when compared to a full frame image displayed at the same overall size, the cropped sensor will appear to give more magnification.
In addition to the crop factor is the pixel density. Under good conditions, packing more pixels into the same area means that you will get more detail. When viewed at 1:1 pixel level, a higher pixel density sensor output will effectively give more magnification.
As an indication, the linear magnification of a 15 MP sensor would be 1.22x that of a 10MP sensor, assuming the sensors are the same size. Note that more size does not always equal more quality.
Wasp - 4.2MB - Sony A350, Tamron 90mm macro, 1/100s, f/8, ISO400