Using a Zoom Lens

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Go out and look at the moon one night. Note how small it appears. Try to get a picture of the moon and you will see how small it is in an image. The moon is only a half a degree in apparent size (there are 360 degrees in a circle, 180 degrees in a half circle thus you could fit 360 moons side by side across the sky from West to East through the Zenith).

The moonChances are you are going to want to use a zoom or telephoto lens to get a closer look. The picture of the crescent moon at right was taken using a 300mm telephoto lens coupled to a standard film camera. A telephoto lens is like having binoculars or a small telescope for your camera. You can get a closer view and see more details.

There are two basic types of telephoto lens - fixed and zoom. A fixed lens has one focal length. A zoom telephoto lens has a range of focal lengths you can use.

Some cameras come with a zoom lens built into the camera. Film cameras of the SLR type (Single Lens Reflex) use interchangeable lenses with varied focal lengths, which may be fixed or zoom types. As you increase the focal length of the lens the magnification of the resulting image size increases as well. Thus a 200mm lens provides a closer view than a 50mm lens. The closer view comes at a cost. The 200mm lens will be four times larger than the 50mm lens and be heavier too. A mount or tripod to help support the camera and lens becomes essential. See Zoom accessories for more information about the types of things you need to bring along when using a Zoom lens of any type.

Basic digital cameras provide two kinds of zoom options, optical and digital. When shooting the eclipse event it is best to avoid digital zoom in the camera and strictly work with the optical zoom. In fact the best way to treat digital cameras is to turn off all the extra digital enhancements (with the exception of image stabilization) when obtaining the images. There will be plenty of time for image enhancement work after the eclipse using the computer.

Cameras that claim to have a 200x digital zoom are fooling you. A general rule of thumb in telescopes and astronomy is not to exceed 60x per inch of objective lens. For a 200x camera you'd want a lens 3 to 4 inches across and that is as big as some of the new cameras! Shut down the digital zoom and stick to the optical zoom. Even that is pushing the limits of the small optics involved - experiment on the moon to see what kind of results you can get. If the maximum zoom looks bad, try reducing the magnification factor until you get an image where the moon appears sharp.

More Zoom Lens information >

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