How Do I Use My Digital SLR's Auto Focus? Part-2

Most digital SLR's will offer some auto focus mode options, like single focus, continuous focus, and that trusty old stand-by - manual focus.

They also offer some focus area modes that use just the one focus point you have selected or some other focus area mode that help keep things in focus in your photos.

Auto Focus Modes

Single Servo Focus
The most commonly used focus mode is Single focus. (Nikon - AF-S, Canon - One Shot AF)
Use single focus when you are making photographs of subjects that aren't moving.
When the shutter is pressed halfway the camera focuses, turns on an in-focus indicator in the viewfinder, and then locks the focus until the shutter is released, or until the shutter button is returned to it's normal position.
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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.

LENS INFO

Lens Lingo

One of the things new photographers grapple with is lens lingo.
What do all those numbers and abbreviations mean?
We’ll start with the kind of lens, or lenses, that likely came with your dSLR.
Note: Each camera maker has their own lens mount design. Nikon lenses (F-mount) cannot be directly mounted on Pentax cameras (K- mount). However, someone may make an adapter that allows such a mash up.

Two Lens Types

There are 2 lens types:

Digital SLR Camera Settings

More people than ever before are using digital SLR cameras.

When film was the primary medium people used to make photos, you didn't get to see your photos until they were printed. If you didn't do your own darkroom processing, you relied on the photo lab to develop the negatives and make the prints for you.

Now, dSLR photographers can see a small version of their photo right on the camera, but if they want those photos to display nicely on a computer monitor, somewhere online, on some other digital device or have it printed, there are choices about camera settings that need to be made. Those choices can have a big impact on how sweet your photos look and how much editing you can do to them and still have them look nice.

Each camera has many settings, and most are covered in each camera's users manual, but 2 of the more important, somewhat esoteric settings, are worth taking a closer look at.

Recommended Reading - Technical

The technical aspects of photography seem daunting to a lot of new photographers. From a technical viewpoint the basics are really rather simple and can be conveyed without much muss or fuss.

One of the best at doing that is Bryan Peterson. Bryan is a successful professional photographer that also has a gift for explaining technical aspects of photography in easy to understand ways. I recommend three of Bryan's inexpensive, yet information packed books:

Recommended Reading - Composition

I have a couple of book shelves filled with various books I have read on the many different aspects of photography.

A lot of new photographers aren't aware of many of those books so I decided it would be helpful to let people know about them.

My book collection covers several different aspects of photography:

The In-Camera Light Meter

Since we rely so heavily on the in-camera light meter it's very helpful to have a good understanding of how it works and how you can configure it so it provides you the most reliable information.

Reflected Light and Algorithms, oh my!

Your in-camera meter measures how much light is reflecting off the scene it is metering. If everything reflected the same amount of light we would be home free. Obviously, a nice polished piece of chrome on a motorcycle will reflect more light than the skin of a pretty girl sitting on the bike.

Since the amount of light being reflected from different parts of the scene varies, in-camera meters measure the light intensity in different parts of image and uses an algorithm to determine the most suitable exposure for the final picture. We get to tell the meter which algorithm to use. Well, the camera manufacturer gives us the chance to select from several metering modes that each represent a different algorithm.