Back to Home

Astrophotography 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 | Astrophotography | Post
Login

Be the first pioneers to continue the Astronomy Discussions at our new Astronomy meeting place...
The Space and Astronomy Agora
Magnification At Prime Focus

Forum List | Follow Ups | Post Message | Back to Thread Topics | In Response To
Posted by John Huggins on March 30, 2001 12:58:13 UTC

Magnification is an undefined concept at Prime focus.

You should think of this in just like the lenses for your camera.

In 35mm, the lens that most approaches a similar field of view as your eye has a focal length of 55mm. With 120 film, this "normal" lens is 80mm.

I suppose we can call this "normal" lens a power of 1x. A 110mm FL lens would have a power of 2x for 35mm and (110/80) = 1.375x for 120 film.

Figure out the effective focal length of your telescope in mm to provide a comparison to the above normal lens.

My 10inch f/6 telescope has a FL of 60 inches = 1524mm. So with 35mm film, I can get away with this:

(EFL Telescope)/(FL of normal lens for 35mm film),

(1524mm)/(55mm) = 27.71x

The larger 120 film takes in "more sky" from the same scope:

(1524mm)/(80mm) = 19.05x

Additinal references:

http://www.connecti.com/~rreeves/allclass.htm

http://www.philipstripling.com/astro.html#pm
This site assumes you are using 35mm film and the normal lens is 50mm.

And if these links die with time try this:

http://www.google.com/search?hl=en&lr=&safe=off&q=Magnification+at+Prime+Focus

I hope this helps.

John

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 1994-2019 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