6mm or 10mm eye piece

[risingmoon (Sandra)]

I want to make sure I don't waste my money on an eye piece I may or may not use. Can anyone suggest which would be the most practical one to get. My scope is a SE8 and I want to get good magnification from the stars and moon. I have a plossl 25mm one on my scope already and a 6mm one in my cart on a site but have not yet paid for it so can change it if needed.
A few have told me a 6 or 10 would be good but want to be sure.

[erick (Eric)]

Hi Sandra

Your telescope is an f10 focal ratio with an equivalent focal length around 2m (2,032mm according to the specifications). The magnification you will get is calculated by dividing the focal length of the telescope by the focal length of the eyepiece.

So your 26mm eyepiece gives you a magnification of 2032/26 = 78 times. A 10mm eyepiece will give a magnification of 203 times. This is already quite a high magnification and your views will start to be limited by the "seeing" conditions of the sky. I think a 6mm (339 times magnification) will just be too much for all but exceptional conditions. I think you should not go shorter than 10mm and maybe look at designs which give you a wider field of view. The plossl design is around 50 deg apparent field of view (AFOV). There are designs, that won't be too expensive, that will give you 68-70 deg AFOV, and maybe 80 deg AFOV. Above these AFOV values, the eyepieces become much more expensive.

You also want to look at the "eye relief" figure.

I had a quick scan of this article and it looks quite good as well as being very detailed, if you want that:-

http://observers.org/beginner/eyepieces.freeman.html

At some stage, you might want to be thinking about a longer focal length eyepiece, up around 40mm, to give you less magnification and a better view therefore, of rich star fields and large nebula.

[Suzy]

Eric, that's a great link!
Bookmarked, and nicking it for future use to throw at beginners.

Hi Sandra,
I find that a 7mm (either in my 6" or 10" scopes) hits the sweet spot beautifully for planets. And a 30mm nice for low power widefield scanning.

I'm actually selling very soon a complete beginners start up kit (the lot- telrad, barlows, finders, eyepieces - phew everything!) A Meade 6.7mm eyepiece will be amongst it as well as a 30mm. Pm me if you're interested.

[risingmoon (Sandra)]

The link explains it all in good clear English so thanks a heap Eric. Sometimes it is hard to look for the right info if you don''t know where to start looking for in the first place.

[risingmoon (Sandra)]

Thank you Suzy. I probably would be interested in the set in the future but at the moment I am just sticking with one at a time mainly for financial reasons. I have a much better understanding of everything even after reading the info on the link Eric gave. You would be doing justice on giving it to other newbees as it is easy and clear to understand.

[Poita (Peter)]

I'd either grab a 10mm or a 8mm-24mm zoom eyepiece to get started.

A 6mm won't get much use as the atmosphere isn't often clear enough to make use of it. At high magnifications the atmosphere shimmers like the heat shimmers you see on a hot day, so it takes a particular type of night to be able to use the highest magnifications.

A 10mm or a 12mm would be a great addition to your 25mm.

If you get a 10mm or 12mm try to get one with a wide field of view.

What is your budget for it?

[dannat (Daniel)]

I agree with peter a 11-13mm will d well in your scope, giving 150-190x which is usable on most nights, depending on seeing light pollution

[psyche101]

Just a thought, I am by no means an expert, but what about a 10mm and a barlow? That would give you a 10 and a 5 pretty much, and turn your 25 into a 12.5? Double the collection in one hit!