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Olympus C-720 Ultra Zoom Olympus packs an 8x zoom lens into an amazingly small body, for an amazingly low price. Select a topic Reference: Datasheet C720 Sample Images --------------------------------- 1. Intro and Highlights 2. Executive Overview 3. Design 4. Viewfinder 5. Optics 6. Exposure & Flash 7. Shutter Lag & Cycle Time Tests 8. Operation & User Interface 9. Camera Modes & Menus 10. Image Storage & Interface 11. Video, Power, Software 12. Test Results & Conclusion --------------------------------- Print-Friendly Review Version Additional Resources and Other Links Reader Comments on C720 Review --------------------------------- Digital Camera Comparometer (TM) --------------------------------- <-- Digital Cameras (Home) <-- Digital Camera Reviews Index <<Viewfinder :(Previous) | (Next): Exposure & Flash>> Page 5:Optics Review First Posted: 7/1/2002

Optics
The Olympus C-720 is equipped with an all-glass lens, with 10 elements in seven groups. The 8x, 6.4-51.2mm lens provides a focal length range equivalent to a 40-320mm zoom on a 35mm film SLR. (That's a slight wide angle to a long telephoto. Most 3x zoom lenses have a wide angle limit of 35mm, a bit more than 10% wider than the C-720's 40mm figure.) Apertures range from f/2.8 to f/7.1, with the maximum aperture setting dependent on the lens zoom position. Normal focusing distance extends from 24.5 inches (60cm) to infinity, while the macro focus range is 4.1 - 81.6 inches (10 to 200 cm). The Macro / Spot button on the back panel adjusts the focus range for closeup subjects, and includes an option for spot metering in Macro mode. Autofocus is determined through the lens, using a contrast detection method. This means that the autofocus will work properly with auxiliary lenses, as long although it should be noted that add-on lenses will usually affect a camera's focusing limits. A green circle lights solid in the viewfinder display whenever focus is set, and flashes if the camera is having trouble adjusting focus.

I don't (yet) do formal autofocus low-light testing, because there's such a wide variation of performance depending on the particular subject and lighting involved. (Sharp-edged, high-contrast subjects are much easier for cameras to focus on than low-contrast, fuzzy ones.) -Thus, any number I might come up with may be only marginally representative of what my readers might experience. That said, I do recognize the need for at least some sort of indication of low-light focusing capability. So, with a big YMMV (your mileage may vary) warning, I'll report that I found the C-720's autofocus worked fairly reliably at light levels of 1 foot-candle (about as bright as a typical city night scene, under normal street lighting), quite well at levels of 2 foot-candles, and hardly at all at levels of a half foot-candle and below. - A shame, since the C-720 is perfectly capable of acquiring images all the way down to the 1/16 foot-candle limit of my low-light test setup. - I'd really like to see a manual-focus option on the C-720 for use in low light situations.

The C-720's lens barrel incorporates body-mounted filter accessory threads that couple to Olympus' range of accessory lens kits, which extend the camera's telephoto, wide-angle, and Macro shooting capabilities. (An adapter barrel is required though, to permit mounting the auxiliary lenses beyond the furthest extension of the 720's telescoping lens assembly.)

While the C-720's lens provides up to 8x optical zoom, the camera's 3x Digital Zoom increases that magnification to a maximum 24x (albeit with noticeable quality degradations in the resulting image). Digital zoom is activated through the Record menu and controlled by the Zoom Lever on top of the camera. Since so-called "digital zoom" just crops out and enlarges the central pixels from the CCD's image, it directly trades resolution for magnification. This will result in very soft images if you're working at the camera's maximum 3 megapixel file size, but can be useful if you're only shooting at 640x480 anyway. (For web or email use.)

Geometric distortion on the C-720 was better than average at the wide-angle end, as I measured an 0.46 percent barrel distortion. The telephoto end fared better still, as I could only find about four pixels of barrel distortion, about 0.20 percent. The 720's images are quite sharp across the frame, but the corners get soft -- Quite soft at the telephoto end of the zoom range, moderately soft at the wide angle end. Chromatic aberration was also moderate, showing about five or six pixels of light coloration on either side of the target lines. The corner softness at the telephoto end (technically, "coma," I think) made the chromatic aberration much more apparent there. (Chromatic aberration is visible as a slight colored fringe around the objects at the edges of the field of view on the resolution target shots.) Like the C-700 before it (and some other long-zoom cameras as well), the C-720's combination of corner softness and chromatic aberration can lead to rather visible purple fringes around the edges of distant, dark objects against bright backgrounds.

Confused by Apertures and Depth of Field? - Do you know how to use "Front Focus" or "Back Focus" to get *all* your subject in focus? Visit our free Photo Lessons area and click on the lessons "Focusing Up Close" and "Selective Focusing Outside!"