Not all EPs are created equal. The cheap plossls supplied with scopes are acceptable at low power and usually rubbish at higher powers.
The factors that effect eyepiece decisions are:
- The size of the scope, both aperture and focal length
- Your budget
- Targets you are interested in
- Seeing conditions where you are
- Do you wear glasses?
The way these affect you are
1) Size of your scope. There is an oft quoted rule of 50x per inch of aperture as a "theoretical" maximum power. In reality it is more like 20x. So for an 8" scope 160x is about it except on those really exceptional nights.
2) Your budget. Spending more money on EPs gives you more scope. In my scope the supplied plossls were completely useless at focal lengths below 15mm, which only gave me 100x. The 12mm, 9mm and 6mm plossls were never used. I now have a 10mm Ethos and a 6mm Delos, both of which are used regularly. So if you can afford good wide field EPs, you will find more flexibility with choices. That said, a 6mm Delos still requires pretty good seeing to be any real use, just that a plossl is almost never usable.
3) If you are primarily after DSOs, most of the targets that are reachable with an 8" are not ones that need much power. The exception is the smaller planetaries. On the other hand if you are a solar system observer, power is your friend, but again you must be very patient for good conditions.
4) Following on from points above, if good seeing is rare where you are, you are better off going for DSOs and concentrating on low power.
5) If wearing glasses when observing, cheap, high power EPs are a waste as the eyerelief is usually poor.
My recommendation would be get a couple of high quality EPS, one low power and one moderate power. I am a Televue user can only give opinions on them. The 24mm Pan is a great economical EP with gives 50x in your scope and will give years of pleasure. For moderate power a 13mm Nagler(92x) or 14mm Delos(86x) are also good choices.
Others have opinions on EPs and their favoured brands, but only knowing
much about TV, I cannot comment on other brands. Good EPs are a lifetime investment.
Malcolm
Quote:
Originally Posted by Nab
Is there a general rule of thumb when considering eyepiece size selection? Going beyond low-medium-high.. It is wise (for example ) to not quite double your magnification between each eyepiece? 20mm/10mm being the Skywatcher supplied kit seeming to suggest this - although it does seem (observationally) a large jump from 60x to 120x..
Using my 8" dob scope, and playing around in Stellarium with top shelf eyepieces…
Would (again for example) a 24 (50x), 13 (92x), 7 (171x), 5 (240x) seem like a good combination? - which the Stellarium simulation seems to suggest it is.
I'm also assuming that practically 240x is going to be about the maximum usable accounting for tracking if nothing else.
Looking forward to your views..
Thanks.
Darren.
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