what is the difference between an f/6 and an f/7?
f question
Started by tom0011, 08/26/2002 02:58PM
Posted 08/26/2002 02:58PM
Opening Post
Posted 08/27/2002 12:39AM
#1
In layman terms...
After hitting the first mirror or lens, it's the length the light has to travel to come to a point. The number is not in inches or millimeters, but rather compaired to the diameter of the lens or primary mirror.
Example: an 8" telescope that is F5 takes 40" for the light to reflect off the mirror and come to a point. 8x5=40.
Works for metric too: a 100mm refractor that is f8 takes 800mm for the light to come to a point after passing through the front 100mm lens. 100x8=800.
Just be careful not to mix inches and millimeters. BTW, 25.4 millimeters equal one inch if you need to convert.
Hope this helps.
After hitting the first mirror or lens, it's the length the light has to travel to come to a point. The number is not in inches or millimeters, but rather compaired to the diameter of the lens or primary mirror.
Example: an 8" telescope that is F5 takes 40" for the light to reflect off the mirror and come to a point. 8x5=40.
Works for metric too: a 100mm refractor that is f8 takes 800mm for the light to come to a point after passing through the front 100mm lens. 100x8=800.
Just be careful not to mix inches and millimeters. BTW, 25.4 millimeters equal one inch if you need to convert.
Hope this helps.
Mark Hansen
http://public.fotki.com/mhansen/
Funding Member
