Telescope Express - Calculating Magnification & Eyepieces

Calculating magnifications:

M=fo/fe; M=f(objective)/f(eyepiece)  fo - Focal length telescope  fe - Eyepiece focal

-Maximum magnification:

Mmax = 2 * Φ

-Minimum magnification:

Mmin = 2 * Φ / 10

-Best result Eyepiece (best magnification):

Er = fo / Φ

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In my case, a Celestron NexStar 127SLT:

fo = 1500mm  Φ = 127mm (D, diameter) f/12

9mm Eyepiece -> M=166x 12mm Eyepiece -> M=125x 25mm Eyepiece -> M=60x

Mmax = 2 * Φ = 254, then 254x Mmin = 2 * Φ / 10 = 25.4, then 25.4x   Er = 1500mm / 127mm = 11.8mm, then f/12 (12mm eyepiece)

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More information at:
http://espacio846.blogspot.com.es/2011/08/como-calcular-los-aumentos-de-mi.html
http://www.astropractica.org/tab/config.htm
http://astrum.astrosabadell-labs.org/astrum/astrumpr-279ene17/html5/index.html