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Old 18-11-2020, 04:07 PM
a5tarman
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If you could only own one eyepiece

Hi everyone,

If you could only own one eyepiece which one would you go for? I'm planning on getting a 10 inch dobsonian soon (GSO), mainly used in bortle 5-6 skies. I will probably want to get at least one very nice eyepiece. I'm leaning to a superwidefield (televue or similar). I'm interested in everyone's opinions. What have you had the best time with? Is there a brand/FOV you go to 90% of the time?
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Old 18-11-2020, 04:32 PM
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Atmos (Colin)
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If I was only going to have ONE eye piece I’d be aiming for a magnification around 120x. With your 10” it gives a high enough Mag to do some planetary viewing but still wide enough for scanning star clusters.

The closest would be a 9mm Nagler or maybe a 10mm Ethos if looking at TV as a brand. I’d go for the Nagler myself, half the price and the 100 FOV is possibly a bit large for my eyes.
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Old 18-11-2020, 05:44 PM
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The Mekon (John Briggs)
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Without doubt a 13mm Nagler type 6. And that is with any scope you care to mention. In your scope it will give around 90x to 100x
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Old 18-11-2020, 06:04 PM
JA
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For one only ..... use a ZOOM. Yes there are compromises to consider: cost v range v portability v optical performance v FOV, etc....

Best
JA
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Old 18-11-2020, 06:30 PM
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peter_4059 (Peter)
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Vixen LVW13mm
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Old 18-11-2020, 06:42 PM
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Max Vondel (Peter)
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13mm Ethos or 14mm Explore Scientific 100 degree
Depending on budget restaints
Giving you around 100X

The GSO 10" is a great scope
Lots of light gathering without becoming too difficult to handle
And with a few tweaks can be made fantastic
(focuser, finders, handles)

Last edited by Max Vondel; 18-11-2020 at 06:53 PM.
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Old 18-11-2020, 07:05 PM
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Outcast (Carlton)
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Have you considered perhaps a high quality zoom eyepiece to provide you with greater flexibility?

From all accounts, Pentax & Baader have zoom eyepieces of exceptional quality.

I haven't used either of these; I do have a cheapy Celestron zoom which I find useful if just having a quick grab & go look, see at what's about...

Cheers
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Old 18-11-2020, 08:29 PM
a5tarman
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I still plan to use a variety of eyepieces, namely the standard GSO 9mm, 15mm, 25mm, and 30mm superview. But I'm thinking it would be nice to invest in at least one high quality eyepiece. As they can be expensive I'd like to think it would be a piece that realistically gets the most use and gives the most pleasure. I'm interested to know what FOV specifically everyone enjoys most often.
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Old 19-11-2020, 12:34 AM
Hemi
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A very nice question to think about. For most people its theoretical as they will have more than one.
But I think this link to an old article gives an interesting perspective, and one that makes sense to me...

https://stargazerslounge.com/topic/2...he-exit-pupil/

With your scope and moderate light pollution and assuming average seeing, Id aim for the best EP that gives you a 2-3mm exit pupil. Assuming your 10in (250mm) GSO is f5, yielding a focal length of 1250. A 10-15mm ep will result in a nice and satisfyingly comfortable exit pupil and give an all night, every night usable magnification of about x100-125.
The cost/quality/aFOV is then down to you.

Happy decision making.

Hemi
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Old 19-11-2020, 06:23 AM
N1 (Mirko)
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Like John, I say 13mm Nagler Type 6 (then change scopes for diffenent magnifications )
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Old 19-11-2020, 09:34 AM
a5tarman
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Thanks for the considered responses so far.

haha so it seems I should get one 13mm nagler and 3-4 scopes with different focal lengths
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Old 19-11-2020, 11:34 AM
astro744
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Quote:
Originally Posted by a5tarman View Post
Thanks for the considered responses so far.

haha so it seems I should get one 13mm nagler and 3-4 scopes with different focal lengths
Owning multiple 'scopes is a given as no one 'scope does it all. However you can certainly resist the temptation and use one telescope for a lifetime.
If you start investing in quality eyepieces though you will find they work in any telescope you ever are likely to get. I have always liked the following three eyepiece set:

Tele Vue 24mm Panoptic. (Widest true field in 1.25" format at 68 deg. apparent field).
Tele Vue 13mm Type 6 Nagler. (Compact 'spacewalk' eyepiece at good mid power and exit pupil on most 'scopes)
Tele Vue 9mm Type 6 Nagler. (Same as 13mm but high enough jump in mag and reduced exit pupil to be noticeable).

The above was a common choice pre-Ethos/Delos era. There are many more choices now especially long eye relief alternatives. Lower power and larger true fields requires 2" and higher power simply requires shorter focal length. You could easily complement the 9mm Nagler with a 7 and 5mm to suit different focal length 'scopes and/or get higher powers when seeing permits.
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Old 19-11-2020, 12:31 PM
N1 (Mirko)
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I might add that my ES8211 does a pretty good job at replacing the 13T6 when that one can't or shouldn't be used (i.e. anything done at home by the beach), to avoid unnecessary risk. Much cheaper too. Should be quite nice in the 10" GSO, of which I have the 8" version.
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Old 19-11-2020, 01:10 PM
a5tarman
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Do you guys find that you can do without a coma corrector if you have high quality eyepieces?
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Old 19-11-2020, 03:35 PM
astro744
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Quote:
Originally Posted by a5tarman View Post
Do you guys find that you can do without a coma corrector if you have high quality eyepieces?
Absolutely! Primary mirror coma is a tiny aberration (increasing in a linear fashion from centre to edge) and only a high quality eyepiece will show it in its purest form. In fact the first time I saw pure coma I thought it was quite beautiful. I only use a Paracorr when I try and get my Newtonian views to look similar to my TV-101 but most of the time coma does not bother me even at f4.5.
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Old 19-11-2020, 10:03 PM
SkyWatch (Dean)
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I agree with the Nagler T6 13mm that others have endorsed. It is my most used eyepiece across a range of scopes, unless I want high power: and even then it barlows very well. I find the FOV is as big as I want to go: I have tried the 100-degree ones, and keep going back to the Nagler.

For the best low-power and best FOV, I can't go past the TV32mm plossl for a 1 1/4" focuser (maximum possible TFOV), and for a 2" focuser my favourite is a Panoptic 27mm. I love the 68 degree AFOV: for me it really works.

I also find I don't need a coma corrector for any of these in my f5 scope.

If you are patient these eyepieces come up on this site in the Used section (that is where I got my Panoptic), generally for around 60-65% of the new price. (I also picked up an ES82 11mm there a while back.)

Good luck!

Dean
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Old 20-11-2020, 02:46 AM
astro744
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There is a lot of good information on the Tele Vue site.

See https://www.televue.com/engine/TV3b_page.asp?id=154
Specifically https://www.televue.com/engine/TV3b_...n=Advice&id=96

Eyepiece specifications at https://www.televue.com/engine/TV3b_page.asp?id=214

The field stop (mm) column is an indicator of true field. You can see that the 40mm Plossl, 32mm Plossl and 24mm Panoptic all have a 27mm field stop diameter and therefore give the same true field.

True field of view (deg.) = field stop diameter (mm) x 57.3 / focal length of telescope (mm)

For the above three eyepieces you will get the same true field but at different magnifications and apparent fields and exit pupils. The 40mm has a 43 deg apparent field, 32mm is 50 deg and 24mm is 68 deg. I find the 68 deg a very pleasing wide field to look at and still be able to take in the entire view without having to move your eye side. The exit pupil determines image brightness and it is calculated as follows:

Exit pupil (mm) = eyepiece focal length / telescope focal ratio

Also Exit pupil (mm) = telescope aperture / magnification

Of the above the 40mm gives the largest exit pupil and the 24mm gives the smallest. However even at f10 the 2.4mm exit pupil of the 24mm Panoptic provides for ample light and better contrast as the background is darker than the 40mm which gives a 4mm exit pupil. In an f5 telescope dont even contemplate the 40mm as your exit pupil will be too large but in any case the 40mm is like looking through a tunnel because of its narrow apparent field.

Of the three eyepieces I have recommended, if you had to choose one I say go the 13mm Type 6 Nagler but only after youve looked through a few eyepieces first at a star party through a telescope similar to what you are contemplating. You may actually like something completely different.
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Old 24-11-2020, 09:24 AM
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Tulloch (Andrew)
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This one
http://www.astroanarchy.com.au/Acces..._Zoom_Mk4.html

Together with a focal reducer and 2x Barlow, you have everything covered
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Old 24-11-2020, 01:15 PM
Renato1 (Renato)
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It depends on what you want to look at with your 10" dob.

If you can access dark skies and like galaxies and other faint stuff - the eyepiece to get is an ultrawide angle (82 degree) eyepiece that delivers a 2mm exit pupil - just multiply the telescope's focal ratio by 2, to get the eyepiece focal length.

If you live somewhere bright and want to look at bigger brighter deep sky objects, then get an ultrawide angle eyepiece delivering 4mm or 5mm exit pupil.

You could compromise and get an eyepiece in between, with a 3mm exit pupil, but apart from use on very faint open clusters, I've never found much use for it in a dob, and think you'd be viewing sub-optimally on nearly everything.

One eyepiece is never going to be ideal for all types of objects one may wish to observe, unless there exists somewhere a very expensive zoom eyepiece that doesn't have a narrow field of view at low power (in which case, that's the one to get).
Cheers,
Renato
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Old 25-11-2020, 01:26 PM
AG Hybrid (Adrian)
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Only 1 Eyepiece? Easy. Baader Hyperion. 8mm-24mm Zoom. Goes good in my 12" F5 newt, 8"F4 newt, Mak 150mm and AR 102 f 6.5.

If it haaaaassss to be a super/ultra wide. For a 10" F5 something between 9-14 mm. A mid power.
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