The ideal focal length for telephoto photography of solar eclipses ranges from 500 to 2000 mm, depending on whether you are concentrating on the corona or on the prominences. For the Sun and corona together, their image size increases to 18 mm. Their folded light path allows a long focal length to fit within a short portable tube, making small catadioptric telescopes easily portable-ideal for most eclipse photography.Ĭoupling a 2x tele-converter with a 500 mm lens will produce a 1000 mm focal length, which doubles the Sun's size to 9.1 mm. Catadioptric telescopes use a combination of mirrors and lenses to focus the light into your eye or onto film. The least expensive 500 mm telephoto lens is a catadioptric telescope. You can calculate the Moon's or Sun's image diameter on your film (in millimeters) for any camera system by dividing the focal length (in millimeters) by 110. Allowing for one solar radius of corona on either side of the Sun, an image of the total eclipse covers about 9 mm on the film. A 500 mm focal length yields a solar image of 4.5 mm on a standard 35 mm negative. For eclipse close-ups, a telephoto lens or telescope with a focal length of 500 mm or greater is recommended. The size of the Sun's image on your film is determined solely by your lens's focal length. Focal Length Graphic ©1999 by Fred Espenak Super Telephotos and Telescopes Although zoom lenses usually have smaller apertures and are slower than fixed lenses, they work fine for photographing eclipses if they are of good optical quality. An instant later, the shutter closes and the mirror returns to its original position. When you press the shutter button, the mirror flips up and the shutter curtain opens, permitting the image to reach the film. The viewfinder of an single lens reflex camera uses a prism and mirror system that allows you to look directly through the same lens that takes the actual photograph. Tele-converters fit between the camera body and the lens to increase the lens's focal length by 1.4 to 2 times, thus increasing magnification. Additional magnification can be obtained with tele-converters. Zoom lenses provide adjustable magnification and new designs cover a wide range of focal lengths. Telephoto (high-magnification) lenses begin at 105 mm and go to 500 mm or 1000 mm. Wide-angle lenses have focal lengths of 35 mm or less, while normal lenses fall within the range of 45 mm to 70 mm. No decision affects your eclipse photography more than the choice of a lens. SLRs come in several film-size formats, but this chapter will concentrate on the 35 mm SLR. But older SLRs are also fine for eclipse photography. The modern SLR is an electronic marvel that features auto-focus, programmed auto-exposure, and a built-in motor drive to advance the film. You can even remove the lens and hook the camera body up to a telescope so that the telescope provides the optics. SLRs also feature interchangeable lenses, from extreme wide-angle to high-power telephoto. (click for more photos) The Right Cameras and LensesĬlose-ups of the eclipsed crescent Sun and detailed portraits of the solar corona require the use of a single-lens reflex (SLR) camera. Preparing for the 1991 Total Solar Eclipse Fred Espenak checks on his telescopes during the 1991eclipse in Baja, Mexico. Checklist for Solar Eclipse Photography.Field of View and Size of the Sun for Various Focal Lengths.The Global Positioning System and Time Signals.Telescope Clock Drives and Polar Alignment.
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