Back to Home

ATM Forum Message

Forums: Atm · Astrophotography · Blackholes · Blackholes2 · CCD · Celestron · Domes · Education
Eyepieces · Meade · Misc. · God and Science · SETI · Software · UFO · XEphem
RSS Button

Home | Discussion Forums | Amateur Telescope Making | Post
Login

Be the first pioneers to continue the Astronomy Discussions at our new Astronomy meeting place...
The Space and Astronomy Agora
Focal Length

Forum List | Follow Ups | Post Message | Back to Thread Topics | In Response To
Posted by Daniel Johnson on October 29, 2002 00:30:35 UTC

The focal length is half the radius of curvature (a paraboloidal mirror is nearly spherical, so I refer to the curve of the sphere). I haven't been following your progress, so I don't know what equipment you have. The formulas given by the previous writer is good. If by experimenting you can move a pinpoint light source so that your mirror focuses an image of the pinpoint exactly back on the pinpoint (or, more practically, on a white card that moves with the pinpoint at the same distance from the mirror), then you are at the radius of curvature, since a sphere focuses a point source at its center exactly back to the center. Divide by two, and that's your focal length. Or use the formula given by the previous correspondent.
--Dan Johnson

Follow Ups:

Login to Post
Additional Information
Google
 
Web www.astronomy.net
DayNightLine
About Astronomy Net | Advertise on Astronomy Net | Contact & Comments | Privacy Policy
Unless otherwise specified, web site content Copyright 1994-2021 John Huggins All Rights Reserved
Forum posts are Copyright their authors as specified in the heading above the post.
"dbHTML," "AstroGuide," "ASTRONOMY.NET" & "VA.NET"
are trademarks of John Huggins