Did I buy the wrong eyepiece?

[szymon]

I have a 900mm long 80mm aperture reflector, f/11.  I just bought a new eyepiece, a 6mm Celestron Omni Plossl.  Doing the maths, 900x6=150x and 2x80=160, so this seems like the right "high powered" eyepiece with a 50 degree field of view.

But I'm now wondering, would I have been better off buying the 12mm version of the same eyepiece instead.  The telescope came with a 12mm eyepiece and it's pretty poor (I don't know telescopes but I do know cameras and lenses, and it's far from good).  I have a Celestron Deluxe 2x Barlow on its way, which would effectively turn the 12mm into a 6mm.  I'm likely not going to be able to usefully use the 6mm with the barlow (3mm would be 300x magnification, which I'm sure will be way beyond the capability of the scope).

The lens is coming via Amazon prime, so I could still change my mind in the next few hours and get the 12 instead.  It's £10 more expensive (the 6mm is £20, the 12mm is £30, including next day delivery).  So, would I be better off just getting a better 12mm?

-simon

[Lowjiber]

Generally, you'll find that your maximum useable magnification (in clear skies) is attained with an eyepiece with a focal length approximately equal to your scope's focal ratio expressed in millimeters.  In this case, the 6mm is overdriving the scope.

Since you're just starting your eyepiece collection, I'd advise getting a good 12mm eyepiece to replace the "not so good" one that you have, and then go from there.

Clear Skies

[happy-kat]

I use my 16mm in my 750mm scope the most. My 6mm requires good seeing conditiins to get the best from it.

What other eyepeices do you have?

Does your barlow work well?

[szymon]

I cancelled the 6mm, probably the right thing to do. Now I'll consider the 12mm. Perhaps I'd be better off buying a higher end 12mm instead of the omni - buy well, buy once.

The only eyepieces I have are a 25mm and a 12mm which both came with the scope. I haven't received the Barlow yet, it'll be arriving tomorrow.

[Reeny]

Try the 12mm with the barlow first.

I have a 3-inch travel scope at 700mm focal length.

25mm is great for wide views, 12mm and 9mm both give a clear sharp image, but 6mm is stretching the scope to the absolute max at 116x mag.

A 7mm or 8mm would work best for me.

Maybe a good quality zoom is the way foreward.

[szymon]

I would love to buy a good quality zoom, but they are double the price of the scope :-)

I dropped a mail to Sky's the limit, who do a "try and buy" thing where they send you a number of eyepieces and you can choose the one you want to buy. If they can get them to me before I leave, I'll be able to make a good decision by actually testing them out myself :-)

[Reeny]

The 60 degree BST starguiders come highly recommended.

http://stores.ebay.co.uk/Skys-the-Limit-Astro-and-Optical/BST-Starguider-ED-/_i.html?_fsub=2568750014&_sid=53377064&_trksid=p4634.c0.m322

An 18mm and 8mm would test the barlow.

I'm guessing that the 8mm at 112x will give a better view without all that extra glass in the way.

And if the Barlow work OK with your scope, the 18mm BST would give you a very nice 50x and 100x magnification.

Whichever combination you decide to try, Christmas isn't too far away if you wanted to keep two of them.

I stopped using a barlow on the little scope because a dedicated eyepiece of the correct size works much better

[szymon]

No email from Sky's the Limit and they're not answering the phone, so I guess I won't be testing the BST Starguiders :-|.  Maybe they're on holiday, it's the time of year for it.

Never mind, tonight is going to be nice clear weather with no clouds, visibility is more important than eyepieces! :-)

[szymon]

Oooh, spoke too soon -- got an email from Alan at Sky's the Limit, now organising to have the following "on loan" for my holiday:

Series 500 1.25'' 6.5mm Plossl Eyepiece
Series 500 1.25" 12.5mm Plossl Eyepiece
Series 500 1.25" 30mm Plossl Eyepiece
1.25" 8mm BST Explorer Dual ED eyepiece Branded "Starguider"
1.25'' 12mm BST Explorer Dual ED eyepiece Branded ''Starguider’'
1.25'' 25mm BST Explorer Dual ED eyepiece Branded ''Starguider’'
1.25" 12mm 60 Degree Flat Field Eyepiece
 

I can compare them all and choose which one(s) I want to keep.  What a wonderful service!

-simon

[happy-kat]

My stock 25mm does it's job OK, the 12mm looks a good size in that lot the BSTs are quite popular but I have not tried one. Looks like fun to try :-)

My other useful eyepiece is a 32mm giving me the maximum low powered view my telescope can give.

[szymon]

Looking at the skies yesterday, through the (very few) breaks in the clouds, I've decided that my 25mm is probably "ok" as a wider lens.  I guess the f/11 scope is quite forgiving?  I had a very good view of the moon through it, with clear visibility of craters.  So my goal is now to get a better "closer" eyepiece.

With that in mind, I changed the list slightly -- now have the following coming for Saturday:

Series 500 1.25'' 6.5mm Plossl Eyepiece
Series 500 1.25" 12.5mm Plossl Eyepiece
Series 500 1.25" 30mm Plossl Eyepiece

1.25'' 5mm BST Explorer Dual ED eyepiece Branded ''Starguider’'

1.25" 8mm BST Explorer Dual ED eyepiece Branded "Starguider"
1.25'' 12mm BST Explorer Dual ED eyepiece Branded ''Starguider’'
1.25'' 12.5mm 50 degree Premium Plossl eyepiece

Three different 12's to compare, a range of shorter eyepieces to see what the scope can do with them, and one 30mm which might be "a bit better" than my current 25.  I'll probably end up keeping the 12mm BST Explorer and the 30mm Plossl, we'll see.