Comment 1 for bug 604975

Addition :

a) If you take a picture behind an ocular, the formula is given by replacing the focal length of the telescope above by Feq, the equivalent focal length of the telescope + ocular :

Feq = equivalent focal length for telescope + ocular (mm)
Ftel = telescope focal length (mm)
D = distance between ocular and CCD (mm)
Foc = ocular focal length (mm)

Feq = Ftel * ( ( D / Foc ) - 1 )

b) If you take a picture behind an ocular with a DSLR equiped with a lens, the equivalent focal length of the assembly is :

Feq = equivalent focal length for telescope + ocular + DSLR (mm)
Flens= DSLR focal length (mm)
Ftel = telescope focal length (mm)
Foc = ocular focal length (mm)

Feq = Ftel * Flens / Foc