Quote:
Originally Posted by janoskiss
@Wavytone sorry to be blunt but your advice on EP selection (3 EPs, abc) is terrible. I can't be bothered explaining why (it's late and I'm out of energy) but maybe others can chip in. Or just think about it for a minute.
|
Well you've motivated me to explain. Having been a visual observer for 40+ years using scopes from f/3.7 to f/18, I well know the temptation to acquire a box full of eyepieces, having owned upwards of a dozen at times, the rationale being to have all bases covered. Which is bullcrap.
1. Some years ago three friends who were very active DSO observers ran an experiment to determine the optimal run for selecting eyepieces to observe smallish DSO's - mainly galaxies and planetary nebulae. They came up with X1 magnification per mm of aperture.
There is also a good basis for this from optometry - this correlates with a magnification such that the resolution of the scope (the Airy disk) on the retina is similar to the spacing of the rods in your retina used for low light vision. When you do the maths for the average eye this does indeed work out very close to a magnification of X1 per mm of aperture.
On bright objects (the planets) where some colour is visible more extreme magnification is desirable - and useful - due to the spacing of the colour-sensors in your retina (cones) being quite different to that of the rods.
2. Then there is a little matter called "seeing". On most nights at average locations seeing is rather better than 1 second of arc. You can figure for yourself what that means in terms of magnification, but again it leads to a very different result for dim objects where you're relying on your rods, vs the bright objects (planets) where colour is visible, and the cones come into play.
3. Most visual observers have a scope that handles a range of magnifications from lowest to highest around 1:4, this is a consequence of using very fast newtonians. Using factors of 2 you can cover that easily in just 3 eyepieces.
Even a range of 1:10 can be accomplished in just 4 or 5 eyepieces easily. But do you really need them all ?
4. I'll say NO. from a purely practical perspective I have no problems switching from a very low power wide field eyepiece (42 or 50mm) to say 13mm or even 8mm in one step.
Presumably you find this a bit hard and want to swap rather more eyepieces.
I don't, and I suggest you take a hard look at those you actually use often. My guess is there are just 3, and the rest don't matter.