It's not expensive gear or fancy software that separates great photographers from ordinary ones. After all, even $200 pocket-sized digital cameras are more advanced than the contraptions that Ansel Adams used to take his famous photos 50 years ago.

No, it's not equipment: Knowledge is what makes a great photographer. As any photographer will tell you, there are a million little rules of thumb that can come in handy at the most unexpected moments. This week I've got four gems that you can store away for the right moment.

Calculate Print Size

You might wonder how big you can safely print a digital photo. This is where a little long division goes a long way. Just take the pixel dimensions of your photo and divide by 200. The result is the size, in inches, you can print on a typical inkjet printer.

Freeze the Action

Last week, I wrote about controlling motion blur and its mean-spirited cousin, camera shake. To reduce blur from camera shake, I recommended that you use a tripod or set your camera to a fast shutter speed. But what shutter speed?

As a general rule, the slowest speed that you can use reliably while hand-holding your camera is equal to the reciprocal of your focal length. If you're using a 100mm lens, for instance, you'll need to shoot at 1/100 second or faster. 50mm? You can probably get away with a rather slow 1/50 second.

Read Capturing Subjects on the Move for more on using ISO.

Get the Most Out of Your Flash

You probably know that your camera's built-in flash is not especially powerful; it can throw light only about 10 feet or so (check your camera manual for the exact range). But you might not realize that increasing the camera's ISO can extend the flash's range.

ISO is a measure of the camera sensor's sensitivity to light, and most cameras let you dial up the ISO for taking better pictures in low light--with the trade-off being more digital noise in your shots.

Here's the secret: To double the range of your flash, quadruple the ISO. So if your flash has a 10-foot range, but you're shooting across a 20-foot room, change the ISO from 100 to 400.

Read Take Better Flash Photos for more tricks.

Use Depth of Field Strategically

You are probably familiar with the concept of depth of field. When you pick a point in your photo to be in sharp focus, there's a region in front and behind that location that's still sharp.

The depth of field size varies depending upon the focal length of the lens and the distance from the camera to the subject, but one thing always remains true: There's always about twice as much depth of field behind the point of focus as there is in front.

You can put this handy knowledge to good use when photographing long subjects the extend deep into the scene--especially close ups and macro photos. To maximize the focus in your scene, focus about one third of the way from the front, since you'll automatically have more sharp focus behind than in front.

For more tips, read Master Your Camera's Depth of Field.

Hot Pic of the Week

Get published, get famous! Each week, we select our favorite reader-submitted photo based on creativity, originality, and technique. Every month, the best of the weekly winners gets a prize valued at between $15 and $50.

Here's how to enter: Send us your photograph in JPEG format, at a resolution no higher than 640 by 480 pixels. Entries at higher resolutions will be immediately disqualified. If necessary, use an image editing program to reduce the file size of your image before e-mailing it to us. Include the title of your photo along with a short description and how you photographed it. Don't forget to send your name, e-mail address, and postal address. Before entering, please read the full description of the contest rules and regulations.

This week's Hot Pic: "Dangling Feet," by Bob Gaffney, West Whately, Massachusetts

Bob writes: "I took this photo on a trip to Negril, Jamaica--it's a great way to get away from the New England winter. I used my Konica Minolta Dimage A2."

This Week's Runner-Up: "Spicebush Swallowtail," by Richard Mudd, Brooksville, Florida

Richard writes: "I saw this butterfly from my kitchen window and hurried outdoors to to capture an image with my Canon Powershot S3. I did some editing with Photoshop Elements, including the Out of Bounds procedure."

See all the Hot Pic of the Week photos online.

Have a digital photo question? Send me your comments, questions, and suggestions about the newsletter itself. And be sure to sign up to have the Digital Focus Newsletter e-mailed to you each week.