The idea of Macro Photography is to create a close up images. The traditional definition of Macro Photography relates to the size of an image in respect to the film. The photographed images size that is projected on the film or CCD should be close to real life. (one to one ratio)
There are dedicated lenses for Macro Photography but when you are getting started many basic lenses have a form of macro capability. This is a great place to start for the beginner. I would recommend using a 70-200 or 300 mm zoom lens to give the best results. The actual image that you shoot will be the same as if you were using a dedicated 100mm Macro lens but there are some issues.
In my opinion the main drawback to using the zoom lens option is that you have to be as much as 6 feet away from the subject to use your lenses minimal focal range. (the closest the lens will focus) It will work but practice is important. The other drawback is that the focal depth is greater and harder to control. This is the range of focus within the photo. (what you can see clearly in the shot) Even with the issues outlined they are a great way to get started.
You can also buy filters that magnify the image to allow you to shoot macro with standard lenses. This looks like a standard filter but it magnifies the subject when attached.
A solid tripod and a time release is almost a must for this type of work. When shooting small things any camera shake is magnified and frustrating. The force required to pushing the shutter button can cause enough shake to cause problems. It is better to not touch the camera when shooting. If you do not have an off camera release, (remote) use the timer feature on your camera.
You can use a point and shoot camera to create some very interesting macro TYPE images with the auto setting plant close-up. Look for the setting with a flower, or something that is close-up. It is actually the macro setting on many point and shoot cameras. Focusing is the challenge for most of these cameras.
On the SLR cameras you can use the auto setting discussed above to get started but you want to move to the manual settings as soon as you feel comfortable with the advanced operations, because it will give you so much more in the way of control.
In most cases I use manual focus because it gives me greater control as to the area that is in focus. When I photograph without a tripod, the hand motion alone will change the distance from the camera to the subject enough to cause the auto focus drive system to go crazy. My trick when hand holding is to do basic focus and then focus the image by moving the camera.
How to control the Depth of Field? There are 2 answers to that.
Remember that the aperture controls how much is in focus. An f2.8 will have a shallow depth of field where an f8 or f22 will have a greater depth of field. What that means is the amount of area in front and behind the subject that will be in focus. You start out by selecting the specific part that you want in sharp focus. Then select the F Stop to give you the amount of area around that you want in focus.
2. The Distance from the subject
Everything that was said in part one still applies, the only change is your distance from the subject. When you back up from the subject and zoom in using a zoom lens, (same image in the picture as before with the same settings) your depth of field increases. Where before the area in focus could have been 2mm in front and behind what was in focus, the new area of focus when you backed off could be 20mm in front and behind. Creating 40 mm of in focus area compared to the 4mm in the earlier example.
Get close and have fun. Try some macro and let me know how it went.
PS: The images in this blog were shot with a zoom 70-300 mm lens.