Choosing Eyepieces

[pitts11]

I'm just having some confusion over what eyepiece to buy with all the information about exit pupils, field of view, etc. I'm planning on buying a 12" Lightbridge or maybe a Sky-Watcher and I think that buying another eyepiece with it is a good idea, since the included piece probably wont be the best and I'll want a different magnification. I know that I should stay under 600x with a 12" aperture, but I don't know whats sizes would be good for viewing things from nebulas to planets. I'm also worried about getting a coma around the image. My question is What 1 or 2 eyepieces would be suitable for viewing DSO's or planets with a Dob? What do you use?

[John]

I've owned a 12" Lightbridge but have recently downsized to a 10" Orion Optics - the Lightbridge was a great scope was too heavy for me to use frequently. 12" dobs are big beasts !.

The standard eyepiece with the Lightbridge is a 26mm Meade QX which is mediocre to be kind to it. F/5 scopes need decent quality eyepieces to perform at their best.

With a 12" F/5 scope (Meade or otherwise) I found the most useful eyepiece focal lengths to be:

30mm (ish - I used a 31mm Nagler)

20mm

13mm

9mm

7mm

5mm (occasionally)

All fast newtonians produce some coma - it's a feature of the design. I did not find it a problem personally though. You can get a coma corrector if it bothers you.

Unless you spend big bucks on eyepieces you will get some astigmatism (slightly mishappen stars) in the outer 20% of the field of view in a fast scope but again that's not a big issue as long as you don't let it bother you.

For DSO's use low or medium power - the longer focal length eyepieces. For planets use 9mm, 7mm or even 5mm as conditions allow. Forget 600x though, it's really not possible with our viewing conditions in the UK and also tracking an object manually (as you have to do with a dob) will be almost impossible at that power.

Hope that helps a bit.

[michael.h.f.wilkinson]

I think six EPs is a bit much (OK I have more but that is only because three are in theprocess of being sold to a colleague). To start with I would go with the 30 mm (Nagler if you can afford it, but consider the TMB Paragon 30mm if the Nagler is beyond your budget), Next up I would go for about 14-17 mm (here there is more choice, the Nagler 17T4 gets a great press, I quite like my Meade Series 5000 14mm UWA), and then an 8 and a 5 mm (or there abouts)

[John]

I think six EPs is a bit much ...

My wife agrees with you Michael

[michael.h.f.wilkinson]

My wife agrees with you Michael

Aren't wives all the same:rolleyes:.

However, I can always say: "look at the number of shoes YOU have":evil6:

[pvaz]

John gave you an excellent set of EPs to work on your scope. However that's probably not the answer you ware looking for, having to get a 6 EP set off the start.

I'll give you a suggestion of my own. This is a set built for top quality (needed on a f5 scope) but trying to keep costs as low as possible, without sacrificing the quality.

1st of a good quality barlow, to double any EPs effect:

- Antares 2" 1.6x Barlow (Is used successfully with top quality EPs without noticeable drop in quality. So are the Televue ones but those cost 3/4x more.)

1 good quality 2" EP:

- 28mm Skywatcher Nirvana (reviews say it competes with the 31mm Nagler for about 75% of the price). Used with the Barlow it becomes a 17.5mm EP.

- 13mm Nagler (can be replaced with another brand, maybe a baader hyperion, though edge sharpness may suffer a bit). Will become a 8.125mm when used with the barlow. For the small dsos and planets when used with the barlow.

- 7mm ortho (either University optics or baader models). Used for planets and double stars. With the barlow it becomes 4.38mm. If you use glasses you'll need to replace this one for another 7mm ep design with more eye relief. (Maybe a 7mm Nirvana or 7mm Nagler)

So you got you 6 different magnifications. There is a bit of a hole, a 10mm would be nice for planets on bad seeing conditions, but the 13mm and 8.1mm(13mm+barlow) aren't so far so they'll probably do.

In this set the most used mags won't require a barlow, the 2nd most used ones use the barlow+EP. The cost is a bit high, you can buy cheap EPs with same focal lenght to see if astronomy is your thing or not, then move on for something better, and there is no need to rush, you won't need or even appreciate all this if you get them on day one, since you don't have previous experience with lower quality EPs to know the difference. The idea of my post is just to show you another possibility and make you know your options.

If you do decide to buy quality EPs try the 2nd hand market. I got 2 top quality EPs recently one for about 60% of the price the other for 75%, both in mint condition.

[PeterW]

Go for fewer and quality! I got a cheap 25mm ep a few years back and it failed to deliver on my f5 scopes, so I have just got me a 28mm UWAN to fill the 'low power ep hole. I also have a 13mm and 5mm naglers and the Baader 8-24mm zoom, which is very well regarded, but the field of view does get a 'bit small' beyond about 18mm! It sort of covers the middle ground. Eyepieces are your telescope foundations, they will continue to be useful whatever scope you end up with. Have a look through as many as you can and see how wide field you feel you 'need'. I have purposely never looked through an Ethos to avoid the 'green envy' kicking in.

All the best, with a few (carefully selected and not necessarily the cheapest) eyepieces you ought to be able to observe whatever you want to. I would also save up a few pennies for some good filters (UHC or OIII)(unless you are one of the handful of lucky people not to suffer from light pollution in the UK!!).

PEterW