|
|
| The `speed' of a telescope's optics, found by dividing the focal length by the aperture. The smaller the f/number, the lower the magnification, the wider the field, and the brighter the image with any given eyepiece or camera. Fast f/4 to f/5 focal ratios are generally best for wide field observing and deep space photography. Slow f/11 to f/15 focal ratios are usually better suited to lunar, planetary, and binary star observing and high power photography. Medium f/6 to f/10 focal ratios work well with either. An f/5 system can photograph a nebula or other faint extended deep space object in one-fourth the time of an f/10 system, but the image will be only one-half as large. Point sources, such as stars, are recorded based on the aperture, however, rather than the focal ratio - so that the larger the aperture, the fainter the star you can see or photograph, no matter what the focal ratio. |
How To Pick A Telescope . . . | Telescopes | Eyepieces | Microscopes | Binoculars | Accessories | Terms | FAQ |
Terms of Sale | Privacy Policy | Fine Print
Toll-Free Telephone: 800-422-7876
Alternate Telephone: 405-364-0858 24 Hour Fax Line: 405-447-3337
Telephone Hours: Monday-Friday 8 AM - 9 PM CST
Saturday Noon - 5 PM CST
Store Hours: Monday-Friday 9 AM - 5 PM CST
Saturday Noon - 5 PM CST
First Telescope
680 S.W. 24th Ave.
Norman, OK, 73069
© 2008 by Ad-Libs Advertising, Inc. All rights reserved
 |
|
Printer friendly version
Email page link to a friend