Quote:
Originally Posted by ausastronomer
Several people have advised you on a 4mm to 6mm eyepiece at the high power end.
I am assuming your scope is a 10"/F4.7 with a 1200mm focal length?
I would advise you in the first instance to go with a 7mm or an 8mm eye piece as opposed to a 4mm to 6mm eyepiece. An 8mm eyepiece will give 150X and a 7mm eyepiece 172X in that scope. This compares to a 6mm eyepiece giving 200X, a 5mm eyepiece giving 240X and a 4mm eyepiece giving 300X.
Depending on the area you observe and its prevailing weather conditions and topography there are many nights where you cannot get to 200X in a 10" Newtonian, but can get to 150X to 180X. This would mean that a 7mm or an 8mm eyepiece would see a lot more use than a 4mm to 6mm eyepiece. With a non tracking scope the slightly longer focal length eyepiece is a also a bit easier for a newcomer to use and keep the target well within the FOV.
When you expand your eyepiece collection past 3, most definitely get your self a 5mm, or 6mm eyepiece as it will certainly get used on nights of good seeing and you will appreciate the extra power on those nights. It's just not where I think you need to go considering you don't have something to give you around 150X, which can quite often be your upper limit with a 10" scope under less than ideal seeing, or if your optics have not thermally stabilised.
There are plenty of choices out there and it all comes back to budget and personal preference. You usually get what you pay for. There are certainly some good second hand bargains that come up from time to time and that will often get you a premium 2nd hand eyepiece for the price of a mediocre new one in the $200 to $300 price range. Used Televue Radians are good choice on the 2nd hand market, as are Pentax XW's and Vixen LVW's. These have a medium wide field and long eye relief combined with excellent optical performance. Whilst good orthoscopics and plossls are good eyepieces optically they aren't any better optically than the eyepieces I have mentioned and they aren't as easy for a beginner to use in a non tracking dobsonian.
At the longer focal length end a 27mm Panoptic is about as good a low power finder eyepiece as you will find for a 10" dobsonian, without breaking the bank.
Cheers
John B
|
Thanks John
Another great response and more to think about. A few people have advised a quality Barlow (2x) Televue that I am eyeing off (second hand) to go with my 13mm Nagler TV...which would give me that high magnification aspect that my 10" would probably just manage (as you mentioned). Still debating whether a separate piece at say 7mm or the 2X Barlow which would give about 6.5mm...what do you think on this issue? A dedicated piece at about the 7mm or a Barlow? I can get the TV Barlow 2x at about $130 which is not bad.
Your profile mentions you are in the Hunter Valley region of NSW? How is the viewing down there?
Thanks for any advice, this site has been excellent and I am really enjoying getting to learn all this new knowledge, there seems to be a bit to learn!
Andrew H
