The Basics01 The Wide-Angle Function (Wide Field of View)02 The Zoom Function03 The Macro Function04 White Balance05 ISO
02 The Zoom Function

The Zoom Function

Zoom Specifications

Compact cameras currently available on the market feature zoom lenses with a wide range of specifications. Let's revisit some of the checkpoints that we discussed in the "Wide-Angle Function" article.

Product manuals and catalogs contain entries like this:

Ex.) CX2

"The CX2 lens is a zoom lens that covers focal lengths from 28 mm to 300 mm"
*Equivalent for 35 mm film cameras

However, the actual focal length value shown on the lens, such as f=4.9 – 52.5 mm, is much smaller than the catalog value. You might be wondering why this smaller number is equivalent to 35 mm or 105 mm.

Actually, all of the film used by conventional 35 mm film cameras is standardized. That means that the image size (aspect ratio) for any 35 mm camera (even when there are slight differences) is 2:3 = 24 mm x 36 mm, and focal length displays are the same.

Instead of using film, however, digital cameras use image sensors (CCD, CMOS) that vary according to camera model and/or manufacturer. The focal length is based on the CCD, CMOS size (much smaller than regular 35 mm film). Focal lengths for the CX2, for instance, are wide-angle: 28 mm = 4.9 mm, and tele: 300 mm = 52.5 mm.

Another important factor is zoom ratio. A larger zoom ratio gives you more focal length options during shooting. You can look at both ends of the focal length to tell if the zoom places more weight on the wide-angle end or focuses primarily on the tele end.

The CX2, for example, has a zoom ratio of 10.7 and uses a 10.7x zoom that covers the entire range from wide-angle to tele (300 mm telephoto).

The GX200 has a zoom ratio of 3x (5.1 – 15.3 mm, equivalent to 24 – 72 mm), but uses a mid-range tele zoom that focuses on the 24 mm wide-angle end, giving it a focus range that makes taking snapshots and portraits with a compact digital camera easier than ever before. Attach a wide conversion lens, and you can even get into 19 mm super wide-angle territory.

[Picture 1] Using a 28mm with wide-angle lens, I was able to capture the ambience of the sunset over the sea.
Photo: Nao Nishitsuji ●CX2 ●1/6 ●F3.5 ●ISO100 ●EV-0.7

[Picture 2] Here, I took a picture of the moon using a 300mm zoom lens from the same location as picture 1. The zoom function highlights the moon, which fades into the background of picture 1, giving the image an entirely different feel.
Photo: Nao Nishitsuji ●CX2 ●1/5 ●F5.6 ●ISO100 ●EV-1.3

Photography Using Zoom

By allowing you to freely choose a focal length from wide-angle to tele, the zoom lens helps you take better photos. However, you can get even more out of the zoom lens by having a good understanding of "subject and focal length," "shooting distance," and "the effects of aperture."

Checkpoints for Using the Zoom Lens
1.Subject and Focal Length
As focal length moves toward the long tele side, the in-focus "focus range" (depth of field) becomes shallower.
2.Shooting Distance
At the same shooting distance from a subject, a longer focal length makes the image shallower.
3.The Effects of Aperture
A longer focal length makes the depth shallower, even at the same aperture.

With the tele end's out-of-focus blurring effect, you can put more emphasis on the main subject by creating separation from the background or foreground. Basically, as you push the zoom further toward the tele end, the blurriness (the out-of-focus area) of the image becomes more and more prominent. As shown in the "Wide-Angle Function" article, the wide-angle end, which is great for pan-focus shots, gives you a completely different representation. If you want to frame your image with a focus on a middle- or long-distance view, though, tele will deliver sharp results in the entire range, much like wide-angle.

The best way to learn more about how blurriness affects images is to go out and shoot plenty of pictures in a variety of situations. Digital cameras store shooting information for each picture, so it's be a good idea to review your data when you print your photos.

The zoom gradates the background and lets you accentuate the main focus of the image.
Photo: Nao Nishitsuji ●CX1 ●1/310 ●F5.2 ●ISO100 ●EV+0.3 ●WB: Outdoors

1.The Zoom Function 2.Zoom Image Samples