Being curious about how digital cameras can capture macro so easily I investigated the subject. Here are my findings, gained by chatting to the tech expert at a major camera company.
Engage macro mode on a digicam and the system adjusts the lens elements to re-arrange them into an array that best suits close focusing. Quite a feat, as even simple camera lenses have a surprising number of lens elements to juggle.
Unfortunately, by engaging macro mode with the vast majority of cameras you lose control of both the lens aperture (f-stop) and shutter speed.
Why is this so important?
The best macro photography — regardless of camera — requires that you use the smallest lens aperture to gain optimum image sharpness and depth of field. Using a small lens aperture means you need more light, so you need to extend the exposure time to make a correctly exposed photograph.
So you can’t reduce the lens aperture to a smaller, more favourable setting; nor can you slow the shutter speed to permit the use of a smaller lens aperture.
For the keen macro makers I’ve discovered a few digicams that do allow the use of macro mode and lens and shutter speed adjustment (see Chosen Few).
With DSLR cameras the macro operation is somewhat different. Select macro and you activate a different chain of events: with any lens fixed to the camera, engaging macro mode on the camera commands the lens aperture to close to its minimum, so extending the depth of field and allowing you to move closer to the subject.
Shooting macro with a compact digicam is easy but you have to forgo a fair bit of control and you need to understand that the demands of an amateur as far as resolution and colour quality are less stringent than the pros.
The pro approach would be to use a purpose-built macro lens on a DSLR. Dedicated macro lenses are not cheap but they are optimised to operate at closer than normal distances. With macro lenses you are unlikely to experience problems such as colour fringing and optical distortion; many macro lenses also compensate for the additional exposure necessary when racking out the lens to distances very different to those used in normal photography.
Source : digital-photography-school.com