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

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

Forum List | Follow Ups | Post Message | Back to Thread Topics | In Response To
Posted by Robert May on February 23, 2000 18:48:26 UTC

You can find the negative focal length of a negative lens by placing a positive lens of equal or stronger focal length and seeing what the resultant focal length is. If the focal lengths are the same, then the lenses will effectively become a 0 power piece of glass. The focal length is this formula: 1/(fl of neg. lens) = 1/(fl of sum of both lenses) - 1/(fl of pos. lens). Thus you see that if the FL of both of the lenses together is infinite then the value of the pos. lens is the value of the negative lens with the opposite sign. Needless to say, if the pos. lens isn't at least as strong as the negative lens then the formula doesn't work nor can you get a focus of the source. It is also assumed for the best results that the lenses are close to each other for this test.

Follow Ups:

    Login to Post
    Additional Information
    About Astronomy Net | Advertise on Astronomy Net | Contact & Comments | Privacy Policy
    Unless otherwise specified, web site content Copyright 1994-2023 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