Thread: Low Mag / High Mag
View Single Post
  #9  
Old 12-09-2017, 02:40 PM
Merlin66's Avatar
Merlin66 (Ken)
Registered User

Merlin66 is offline 		 
Join Date: Oct 2005
Location: Junortoun Vic
Posts: 8,904
Col,
If it's 100mm f5 then the focal length is 500mm.
To get x20 the eyepiece fl needs to be 1/20 of 500 = 25mm
Reply With Quote