This post shows how to determine the amount of dithering (using
By way of introduction, dithering is accomplished by shifting the aiming point of the telescope in random directions between exposures. The maximum distance the dithering is allowed to move away from the original aiming point is the Maximum Dither Distance, or, MDD. With that in mind let us now determine the amount of dithering to expect for your system.
First calculate the constant K for your system using the equation below.
K = 2 x (FLi / FLg) x (Pg /
where:
FLi = imaging telescope focal length (mm)
FLg = guide telescope focal length (mm)
Pg = size of guide camera pixel (microns)
Second, set Scale in the PHD2 Dither Settings (Global tab in Advanced settings) to 1.
Third, the Maximum Dither Distance (MDD) in image pixels is calculated from:
MDD = K x [Dithering Distance]. [Equation 2]
Dithering Distance is set in
EXAMPLE:
For my new system (about to order ASI1600MM camera package with filter wheel and filters):
FLi = 348 mm
FLg = 160 mm
Pg = 5.2 microns
Using equation [1]: K = 2 x (348 / 160) x (5.2 /3.78) = 5.98 (let's call this 6).
Using equation [2]:
If Dithering Distance = 1 the MDD = 6 x 1 = 6 image pixels
If Dithering Distance = 2 the MDD = 6 x 2 = 12 image pixels
If Dithering Distance = 3 the MDD 6 x 3 = 18 image pixels
etc.
I hope you find this useful.
Comments/questions welcome.
Steve