Пожалуй, приведу некую табличку:
D = diameter of aperture in mm
Minimum useful magnification .................... 0.13*D 0.2*D for better сontrast
Best visual acuity .............................. 0.25*D
Wide views ...................................... 0.4*D
Lowest power to see all detail (resolution of eye
matches resolution of telescope) ............. 0.5*D
Planets, Messier objects, general viewing ....... 0.8*D
Normal high power, double stars ................. 1.2*D to 1.6*D
Maximum useful magnification .................... 2.0*D
Close doubles ................................... 2.35*D
Sometimes useful for double stars ............... 4.0*D
Limit imposed by atmospheric turbulance ......... 500
Прошу прощения, что по-аглицки, но лень переводить
