Primary Focus


The Primary Focus frame allows the computation of primary focus image projection from a telescope to the camera or CCD. Enter any two of the three inputs Focal Length-F, Aperture-D both in mm and/or Effective Focal Ratio EFR. Press “Calculate” to figure the Magnification and Image Scale. Press “Clear” to clear the variables to try new ones. This section uses formulas from “Astrophotography for the Amateur”. See bibliography for more information.


The Star Brightness allows the computation of stellar magnitude difference to Brightness ratio and also the Combination of Combined or Determination of Singular from combined and one absolute magnitude.  Enter either the Star Magnitude difference or the Brightness ration and press “Calculate” to compute the other. For the other calculation enter either the two separate star brightness entries or one star brightness and the combined star brightness and it will calculate the missing component.