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Need Eyepiece advice Orion 8" Dob


AstroJosh

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Hey everybody

I recently purchased the Orion SkyQuest XT8 and tried it out. It came with the default standard 25mm 1.25" eyepiece and I was wondering if anyone had any suggestions as to which eyepieces I might also purchase. I was a bit disappointed at the lack of detail and magnification the 25mm offered.

Note: the scope also accepts 2' eyepieces.

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If you only have the 25mm eyepiece then you need something for higher powers. I've always found 7mm eyepieces a very useful higher power option so maybe a 7mm plossl would be a good choice ?.

You usually need a range of 3-4 eyepieces to get the best out of a scope and the XT8 has loads of potential.

For low power, wide field you could invest in something like a 32mm Panaview (Skywatcher) which is a 2" eyepiece.

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I would suggest a 12-15mm Plossl, and a decent 2x Barlow. This will give you a maximum power of 160-200, which is a good start for a dob beginner. As your tracking ability improves, you may want to go to higher magnifications, but that would be a good start. The 25mm ep will still be a great search ep. If you can afford a little more, you may want to go for a long eye relief ep in 6mm. In that case, get an 18mm plossl and a2x Barlow as well, but not all at once if you can't afford it.

Check the "Eyepieces, the very least you need" sticky in Beginners help.

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Thanks jahmanson. I already suspected Plossl were the best in the business.

So any number of eyepieces in the 7-32mm range would be my bets bet?

Well they are not "the best" but they are good all round, value for money eyepieces.

I was suggesting a 7mm plossl (in the 1.25" fitting) and a 32mm Panaview (not a plossl design) which is a 2" eyepiece.

If you have a bigger budget then other options are available of course ...... :)

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I have the same scope and I observe both DSOs and planetary.

I find I only really need 4 EPs:

- 1 in the 30 to 35mm range (got a 32) widfield for observing those big DSOs such as the Orion Nebula, Veil Nebula, Andromeda...

- 1 in the 12 to 16 mm range (got a 15) also wide field for the smaller DSOs and closer looks inside the big ones.

- 1 for planetary and really tiny DSOs (clown nebula, blue snowball, ring neb) around 8-10 (got a 9 ortho and a 10 plossl)

- the last optional one is a 4 to 7mm (got a 5) to have bigger images of planets/moon on decent seeing nights and to split doubles.

Others to fill the gaps rarely get used.

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Paulo,

that's a very good selection, and probably what I'd choose. It's interesting how the 25mm range doesn't get used too much.

I'd just add if your budget is constrained go for a narrower field of view more quality eyepiece rather than the cheaper variety of wide field eyepiece, some of which don't work very well in faster telescopes.

http://stargazerslounge.com/equipment-help/95404-6mm-uwa-ep-good-bad.html

The paradigms seem to be getting good reviews and they are not too expensive either (I haven't have a look through one yet).

cheers

Alan

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Thanks everyone, I've gotten some good advice.

And sorry if I'm new to this, but just for confirmation:

Smaller eyepieces allow for greater magnification/smaller field of view?

Hope that isn't too bleeding obvious...

The shorter the focal length of the eyepiece, the higher magnification it delivers with a given scope and the smaller the field of view will be.

magnification = scope focal length divided by eyepiece focal length

true field of view in degrees (approx) = eyepiece apparent field divided by magnification

I hope I've got those right !.

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Yeah that's it!

You just divide the scope's focal length by EP's focal lenght to get magnification. Then, to know the width of the field of view(FOV) you divide the EP's FOV by the magnification.

Example: If you have a 30mm EP with a FOV of 70 degrees. When you use it on your scope (that haves a 1200mm focal lenght) you'll get:

Magnification = 1200/30 = 40x

(True) Field of View = 70/40 = 1.75 degrees (means the area of the sky you see is a circle with 1.75 degrees diameter, enough to fit most large DSOs)

EDIT: Same time post as John! Are we telepathic or what?! :)

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Paulo,

that's a very good selection, and probably what I'd choose. It's interesting how the 25mm range doesn't get used too much.

cheers

Alan

I think the Plossl 25 mm are the default for two reasons:

- They offer a very easy eye relief of about 20 mm, which makes them very easy to use for novices.

- They are actually very useful if you have a slower scope (F/8 - F/10) which were much more common in the past. I just replaced my 26mm Plossl for a 22mm Nagler, and it is very handy for more extended sources. In "Dob" terms, they are 13mm and 11 mm equivalents, respectively, which get a lot of use in fast scopes, I hear.

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