Macro shot of a slightly rotten strawberry.
Here’s a shot of a strawberry I took using my Aunt’s macro lens. I was lucky enough to get to borrow it for a weekend. Take a look at the settings, there’s a 10 second exposure! Obviously I had to do this with a tripod. Why such a long exposure time? Well, here’s the issue with macro. As you get very close to the subject, your depth of field gets extremely shallow. Normally, that effect can look nice (for example a portrait). However, with macro shots, it gets to be a bother as a few milimetres will start getting blurry. Notice the blur towards the bottom of the strawberry.
The fix for this is to stop down the aperture (ie use a larger f number). That will help you get most of the subject in focus. Since the aperture is so narrow here, you’ll need a long shutter speed and plenty of light. Sometimes this isn’t enough. There is a problem with using extremely high aperture values. The problem is that past a certain aperture value, the light will start to diffract and lower the resolution of your shot. This is the case no matter how many megapixels your camera might have. In addition to that, it’s possible that there is too much depth variation in the subject itself, and no matter what aperture value one uses, it is impossible to get everything satisfactorily in focus.
There’s an option for this issue as well, but it requires post-processing. The idea is to use the sharpest aperture value, (usually f/8 or so), and then focus on different areas of the subject. Obviously this only works on still objects. After taking different shots, one can combine the sharpest parts of each image by using photoshop or another post-processing tool. This is called focus-stacking and it’s a high-level technique.