There are several ways of doing macro photography but I will be dealing with the use of extension tubes.
These are light-tight tubes without any optical elements (they're just tubes) which fit between the camera body and the lens and allow the lens to focus more closely and increase the magnification as you are projecting a smaller area of the image onto the camera's sensor.
The tubes I have came in a set of three and have the electrical contacts that allow the autofocus and metering to work. They can be used individually or together in any combination. The bigger the distance between the lens and the camera, the higher the magnification.
The first problem I encountered was that I got in my own light, the lens is so close to the subject that I had to take the pictures with the sun at 90 degrees. Using more tubes brings the subject closer to the lens - about 2cm if all three are used - which makes this even more difficult.
The next thing was focusing which is extremely critical, I was using my standard 18-55mm lens and zooming didn't seem to have any effect except to make things more or less fuzzy. I ended up setting the lens on 55mm and moving back and forth until the camera focussed. This gets even more difficult when using more tubes and I found myself swaying gently back and forth with my finger firmly pressed on the shutter release until the camera decided to take the shot.
Depth of field is also affected by the tubes, if the lens is wide open anything that's not in the plain of focus is out of focus so I had to close down to F20 or smaller to give a few millimetres of depth to the shots. This means that I have to use a slow shutter speed but luckily with a DSLR, I can up the ISO to help with that. All of the following pictures were taken at ISO 400 using my Nikon D5100 and an 18-55mm Nikkor lens.
The following pictures where shot in my garden and illustrate the use of single and combinations of extension tubes. These are all full frame images with no cropping.
@18mm, no extension tubes - minimum focus - with ruler for scale.
@55mm, no extension tubes - minimum focus
@55mm, 12mm extension tube
@55mm, 20mm extension tube
@55mm, 36mm extension tube
@55mm, 12mm extension tube + 20mm extension tube
No example as this is almost the same as using the 36mm tube alone.
@55mm, 12mm extension tube + 36mm extension tube
@55mm, 20mm extension tube + 36mm extension tube
@55mm, 12mm extension tube + 20mm extension tube + 36mm extension tube
Finally, a 1:1 crop of the last image to show how close in you can get.
Pros and cons of extension tubes.
Pros :-
Relatively inexpensive compared to macro lenses.
Can be used on any lens.
No extra optics to degrade image quality.
Cons :-
Cheaper products may be poor quality and may not work with your camera's metering and autofocus - read the reviews before buying, some of them are horror stories!
Little or no depth of field which leads to use of small apertures and low shutter speeds.
Easy to get in your own light.
Difficult to focus.
Have to remove the lens to change tubes which increases the chance of dust on the sensor.
There are other ways of getting close-ups, these are the usual ones :-
1. Macro lens. A lens which has been designed to focus more closely than the typical lenses supplied with a camera.
2. Close-up lenses. These are lenses that screw on to the end of your lens like a filter and allow closer focusing.
3. Other methods. There are adapters which allow lenses to be mounted backwards onto the camera and others which allow a second lens to be screwed onto the filter screw on the end of your lens.
Has anyone had any experience with these other methods?
(and many others 
