A 'working out the magnification' question
I've bought a dinky little 4" mirror scope, (the Skywatcher Heritage 100), which I've been having lots of fun with. I looked at Saturn the other day with the widefield eyepiece, and it was tiny. So I started to work out the magnification.
At 400mm focal length, with a 25mm eyepiece, I've got a 16 times magnification. Is that right? (400/25 = 16). Which would explain the apparent smallness of the planet. The 10mm eyepiece gives me 40X, and yes, I could see more detail, (and nice and sharp to
That diagram is missing an arc from eyepiece focal length and focal ratio to exit pupil. Most owners know the focal ratio of their scope from memory and thus can quickly calculate it just by dividing the eyepiece focal length by the focal ratio. In this case, 20mm/6=3.33mm. That's much quicker and easier than the computation shown.