How Do I use My Auto Focus? Part-1

There is a lot to cover when explaining auto focus, so it will take 2 installments to cover it all.

Auto Focus From The Beginning

The first auto focus SLR for general sale was released in 1978. That camera, the Polaroid SX-70 Sonar OneStep, used an active auto focusing system that sent out sound waves. Today's digital SLR's use a passive system that takes advantage of light coming in through the lens.

So, auto focus sure isn't anything new, having been around for 30+ years now.

How Does My Digital SLR Auto Focus?

It’s called SIR TTL passive phase detection - (Secondary Image Registration - SIR, Through The Lens - TTL).

It’s a pretty simple system actually. It’s used by most dSLR cameras today for that reason.

Wikipedia - GNU Free Documentation License

Here is how it works:

Light enters the lens and is reflected by the main mirror, but the main mirror (1.) is only 50% reflective.

Half of the light goes up through the pentaprism/pentamirror (4.) and to the viewfinder eyepiece (5.).

How to Get Sharply Focused Images

If the subjects in your pictures aren't sharply focused they won't look very good. They'll be missing one of the qualities that makes a photo an image and not just a snapshot.

Here are some things you can do to get tack sharp images. It's a combination of technique and equipment use, rather than just one thing.

It's the Photographer

You'll hear many people say it's not the equipment, it's the photographer. Well, yes and no. Photography is one of the few pursuits where equipment can make a pretty big difference and we'll look at equipment first.
There are some aspects of photography that if you want to get pro results, you have to use the same equipment the pros use. You can always rent instead of buying if your need is short term, or your photography equipment budget is tight.