The Lowdown On Zooms

Digital And Optical Zooms • How Many Clicks Do You Get? • The Color Of sRGB And Adobe RGB (1998) • Film Vs. Digital Vs. Sensor Size...Again

This Article Features Photo Zoom

tech tips
The young alligator was photographed at the Tennessee Aquarium in Chattanooga using a Canon G10 compact point-and-shoot camera. I used the zoom at its maximum optical setting of 30.5mm (140mm 35mm equivalent). The camera is capable of a digital zoom of 560mm (35mm equivalent), but the image quality would have suffered greatly.

Digital And Optical Zooms
Q My son has a digital point-and-shoot camera with an 18x zoom, but when you zoom to the extreme end, the viewfinder displays a message that it’s a digital zoom, and the resulting quality isn’t very good. Is it also true that zoom lenses on D-SLRs don’t work well at their maximum ends? My 200mm zoom telephoto has a 1.6x factor. How does this relate to the digital vs. optical zoom on my son’s point-and-shoot?
D. LaKing
Via the Internet

A The issues you raise point out common confusions about the differences between true optical zoom and the “crop factor” of some digital sensors.

Digital sensors, the devices within digital cameras that receive image information and record it, are packed with pixels; each pixel collects a dot of information. A 10-megapixel sensor holds 10 million pixels. The size of a sensor is expressed in terms relative to 35mm film, a 36x24mm frame (864 square millimeters). A full-frame sensor, available in some professional D-SLRs, is the same size as 35mm film; these have either more pixels for resolution or larger pixels for light-gathering capability. The APS-sized sensors available in some D-SLRs are smaller (they range from 329 to 548 square millimeters). A point-and-shoot camera has a very small sensor (as small as 43 square millimeters), so the pixels on it are very small and crammed together.

Your “1.6x factor” has to do with your camera’s sensor, not your lens. It means that your APS-sized sensor has an angle of view that’s narrower than a full-frame sensor or 35mm film. The effect is a crop of your image—making the subject seem larger in the frame—that uses all of the megapixels on your sensor and gathers maximum information.

Optical zoom is a lens-oriented term. It refers to the range of optical magnification of which the lens is capable when using the entire imaging sensor in the camera. D-SLRs have only optical zooms—that is, the zoom happens in the lens, not the camera. In most lenses, you can expect a small amount of drop-off in quality when the lens is extended to the lower and upper extremes of its range and used at its widest aperture. But this is a different phenomenon and not nearly as image-degrading as the “digital zoom” option found on some compact point-and-shoots.

At the end of a point-and-shoot’s particular optical zoom range, many cameras offer “digital zoom.” With digital zoom, the image is cropped on the sensor in the same way you might crop it on your computer. Remember that the sensor is where your pixels reside. More pixels means more detail in your image. Digital zoom crops the image at the sensor to effectively enlarge your subject. The result is that your larger image is created with a smaller portion of the sensor, using fewer pixels, offering less resolution and yielding a poor-quality image.

How Many Clicks Do You Get?
Q I wonder about the longevity of the shutter mechanisms on recent-model, video-capable D-SLRs. Most shutters are advertised to be capable of 500,000 or so cycles, so if you’re shooting at 24 or 30 fps, you wouldn’t get far before reaching the lifespan of the shutter. Is there something I’m missing?
S. Wolpert
Via the Internet

A Pro cameras such as the Canon EOS-1Ds Mark III and Nikon D3X are rated at approximately 300,000 cycles (shutter clicks). The two D-SLRs that offer video (Canon EOS 5D Mark II and Nikon D90) are actually rated at approximately 150,000 cycles. If we do the math, that would give us less than 1.5 hours of video before the shutter would be worn out. Actually, the shutter doesn’t fire for every frame of video. It simply opens the lens, and each video frame is controlled electronically. Each video segment is only one click (cycle) of the shutter. That’s why it doesn’t sound like a machine gun when the camera is capturing video.

I’d be more concerned about wearing out shutters when frequently using techniques such as time-lapse (one of my personal favorites), where I typically shoot over 1,000 images (and as many as 4,000 or more) for each finished segment. In this case, each frame does represent a cycle of the shutter. With this said, even if you do wear out a shutter mechanism, it’s not a terminal condition for the camera; it’s easily replaced for about $300.

The Color Of sRGB And Adobe RGB (1998)
Q I recently sent some files for printing to a printing house I hadn’t used before and was disappointed with the very unsaturated and washed-out results. I shoot in Adobe RGB (1998) and process in Photoshop CS2. Would you please clarify the debate between sRGB and Adobe RGB (1998), both in capture and the preferred format for image printing?
L. Caine
Golden, Colorado

A Adobe RGB (1998) and sRGB each refers to a defined portion of the range of colors visible to the human eye. The defined spaces are established standards by which cameras, monitors and printers are calibrated. The sRGB space is smaller (shows fewer colors), but it’s more representative of what some applications, particularly the Internet and lower-quality magazines and newspapers, are capable of displaying. Adobe RGB (1998) is more representative of what today’s photo printers can do. It seems pretty obvious to me that you’d want to capture, process and print your photographs with the most extensive color space available. So most of us set our cameras, calibrate our monitors and print our files in Adobe RGB (1998).

It’s possible that your new printing lab took your Adobe RGB (1998) image and printed it with sRGB. In that case, the printed results would tend to be less colorful than those you see on your monitor. Always check the lab’s guidelines for preferred file formats before you send your images. Some labs prefer to print from sRGB even though it has a smaller color space.

Another standard, Pro Photo RGB, has significantly more colors than Adobe RGB (1998). Unfortunately, most devices we photographers use aren’t yet capable of that color space. It may become a standard in the future.

Film Vs. Digital Vs. Sensor Size…Again
Q Can you tell me if the new Canon EOS 5D Mark II is equal in image quality to 35mm film or better than the quality of the 50D or Rebel with the smaller sensors? I’m ready to upgrade, but don’t know in which direction to proceed.
Via the Internet

A At the risk of receiving yet another rude letter from that avid film shooter (you know who you are) who keeps writing to me about film’s superior quality, I’ll say again that we surpassed the quality of film at 8 megapixels. Today’s 21- and 24-megapixel full-frame D-SLRs, in my opinion, are equivalent to a scan from a 6×9 medium-format film camera. I base my opinion on the quality of the prints I’m able to produce from 35mm film scans, medium-format film scans and digital files produced by D-SLRs from 3 to 21 megapixels. So if image quality is your biggest concern, choose a camera with a full-frame sensor and more megapixels.

There are other reasons for choosing a D-SLR with a smaller sensor or fewer megapixels. If you need a very fast camera to capture action, you might choose a D-SLR such as the Canon EOS-1D Mark III that can capture at 10.5 fps but has a slightly smaller sensor with only 10 megapixels, or the Nikon D3 at 12.1 megapixels and 9 fps. If your primary concern is extending your zoom range, choose a D-SLR with a smaller sensor to take advantage of the crop factor.

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One of North America’s best-known contemporary outdoor and nature photographers and a leader in the field of digital imaging and photographic education, Lepp is the author of many books and the field editor of Outdoor Photographer magazine. One of Canon’s original Explorers of Light, Lepp finds inspiration in advancing technology that fuels creative innovation and expression of his life-long fascination with the natural world.