20 replies to this topic

[iceman]

Hi all.

I'm getting my 10" Dob in about 2-3 weeks, and it's a GS brand, comes with a 2" focusser with a 1.25" adapter, so I can use both size EP's.

What's the difference between 2" and 1.25" eyepieces?

I've heard from knowledgeable sources that there's generally no difference, and that the quality of the 1.25" EP's are actually better than the 2"s.

He said the only real benefit of the 2" EP's are the comfort of viewing, as you don't need your eye directly over the eyepiece as you do with a 1.25".

The conondrum i've got, is whether to buy the accessories in 2" or 1.25" sizes.. Eg: barlow lens, moon filter, OIII filter etc.. They're much more readily available in the 1.25" size, plus they're cheaper than in the 2" size.

Your thoughts and suggestions are most appreciated

[iceman]

Oh and just to add a bit more info, i'm not looking at gettnig TeleVue naglers or anything like that.. I'm starting with simple Plossl's.

[erik]

2" ep's are nice for viewing large extended dso's, or starfields. they're not totally necessary though and you'll do fine with some good 1 1/4" plossls to start out with. 2" ep's aren't generally poorer in quality than 1 1/4" ep's as you mentioned, but they do tend to show abberations in your scope, especially with a fast dob such as yours. coma will probably be seen near the edges with even the best 2" ep's. but they're still useful and the coma isn't really noticeable unless you look for it...

[jrcrilly]

Below about 20mm focal length very widefield eyepieces will have a field stop smaller than 1.25". Eyepieces with about 50 degrees AFOV (such as Plossls) below 35mm or so will also - thus there's no optical reason for going with a 2" barrel. On the other hand, better widefield EP's tend to be large and heavy, and the 2" format is more stable and secure for those. Widefield views with EP focal lengths longer than 20mm do benefit from the larger field stop possible with the 2" format.

[lighttrap]

Mike,
You really only need one 2" eyepiece. And you don't really "NEED" even that. Eventually, you'll probably want to get a 30 or 32mm 2" eyepiece for low power wide scanning views, but that can wait. The bulk of your eyepiece collection and accessories should be built around the 1.25" format.

[jrcrilly]

The bulk of your eyepiece collection and accessories should be built around the 1.25" format.

...unless you prefer the comfort and convenience of larger, heavier eyepieces. Or you use balance-sensitive instruments and want all your most commonly-used EP's to be within a narrower weight range.

[Scott Beith]

12:4 ratio right now. 1 1/4":2"
I really like the views in the 2" EP's.

[BluewaterObserva]

I'm a 2" convert....

If you buy a 2" Barlow, you can use all 2" accessories with all your eye peices. I sure wish I had more 2" nebula filters. I think I observed all Saturday night without pulling out even one 1.25" eye piece. The 2" barlow makes this totally possible.

[David Knisely]

Hi all.

I'm getting my 10" Dob in about 2-3 weeks, and it's a GS brand, comes with a 2" focusser with a 1.25" adapter, so I can use both size EP's.

What's the difference between 2" and 1.25" eyepieces?

I've heard from knowledgeable sources that there's generally no difference, and that the quality of the 1.25" EP's are actually better than the 2"s.

He said the only real benefit of the 2" EP's are the comfort of viewing, as you don't need your eye directly over the eyepiece as you do with a 1.25".

The conondrum i've got, is whether to buy the accessories in 2" or 1.25" sizes.. Eg: barlow lens, moon filter, OIII filter etc.. They're much more readily available in the 1.25" size, plus they're cheaper than in the 2" size.

Your thoughts and suggestions are most appreciated

Well, to disagree with some who have posted, a 2 inch eyepiece is *not* necessarily of "lower quality" than a 1.25 inch barrel eyepiece. Its the execution of the design which counts, and for 2 inch eyepieces, this means a *lot* of money if you want halfway decent performance. 2 inch eyepieces are generally used when larger fields of view are needed and can't be supplied by 1.25 inch barrel eyepieces. The limit to field of view is the eyepiece field stop, which is often the opening at the front of the eye lens (not always at that location in some wider-field designs). As such, it is the "bottleneck" which can cut off the light coming from wider angles. The true field of view in a telescope is: TFOV = 57.296*efsd/Fl, where "efsd" is the eyepiece field stop diameter and "Fl" is the focal length of the telescope. With 1.25 inch eyepieces, the maximum field stop diameter is about 27mm, so you can see what your maximum field would be here. With 2 inch eyepieces, the field stop can get as large as 44mm, so you could get quite a bit more field of view if you wanted to. The use of 2 inch eyepieces is especially common with the larger Newtonians, as they almost have to have at least a few 2 inch barrel eyepieces to just get a low enough power and a wide enough field to see a some the larger objects in their entirety (which a smaller telescope might easily fit in its lower power field with an 1.25 inch barrel). With a 10 inch, you are kind of on the dividing line between needing a 2 inch and not needing one, so you can probably get away with not having one right now. For the maximum field of view, you might benefit from a larger 2 inch eyepiece, but many of the less expensive ones (under $250) do not perform well at shorter f/ratios. If you really want good performance in a 2 inch eyepiece, I would recommend that you save your money for a while and then buy a TeleVue Nagler or Panoptic. Clear skies to you.

[erik]

i don't think anyone actually stated that 2" ep's were lower in quality than 1 1/4" ep's, except for the original poster. i said that 2" ep's tend to show the *scope's* abberations more because you're viewing the light all the way to the edge of the primary and secondary mirrors. i also don't think that you need to spend $250 or more for a decent 2" ep. the 40mm orion optiluxe at $139 shows hardly any coma in my f/6 scope, and i've tried it in several f/5 scopes and had great views in those as well. while i haven't personally tried the GSO 2" ep's yet, a lot of people seem to like them, and they're dirt cheap. while all of us would want an ep case full of naglers and panoptics if we had an unlimited supply of money, in my opinion, there are plenty of good 2" ep's available at reaonable prices that will satisfy most observers (and i don't *want* to spend that much on one ep, i'd rather save my $$ for something that justifies it's cost a bit better!).

[iceman]

Thanks for the responses guys, there's so much to learn when you're fairly new to astronomy and astro-equipment..

For now, i'm going to start with 4 Plossl's (9, 15, 26, 40mm) and a 2x Barlow, all at 1.25" size.

I'll look at getting a 2" EP in the future when more money is there to be spent on astro-gear, but even then, there's other things (such as OIII filter, Telrad finder) that are higher on the shopping list

I want my kids to be able to look easily through the EP and not get the blackout effect etc, and I have grand visions of taking the scope to my kids pre-school (and later, primary school) and giving some tutelage on astronomy and showing them some cool stuff (when I save for a solar filter too!
Is it true that the 2" EP's would be easier/more comfortable for kids to look through?

[erik]

2" ep's can be easier for kids to look through, if they don't suffer from blacking out, like many ep's with long eye relief do. also, 2" ep's are generally used for low power, so they wouldn't be able to get in close on the planets unless you got a 2" barlow. but that's expensive and unnecessary. in my experience, kids are sometimes easier to teach how to look into the ep than many adults. i'd recommend teaching them how to view through a 1 1/4" ep. start with a low power ep (like your 25mm) on the moon. if they can see that, then move to the higher power views...

[Tom L]

The UO Ortho 9mm and 12.5mm eyepieces are very good eyepieces and you might consider changing out the 9 and 15mm plossls with these 2 orthos. I consider my 12.5 and 9mm orthos my favorites right now. Just a thought...

[ErnieM]

I own a Hardin 8" dob.I do have a Scopetronix 2" 2xbarlow with a 1 1/4" adapter.I use my 32mm 2" EP to find objects.Once found I go to my 1 1/14" EPs.The views are far better with the 1 1/4" EPs(Meade super plossl and Parks ocular are my favorites).All my filters are 1 1/4".Stay with this size.

[David Knisely]

i don't think anyone actually stated that 2" ep's were lower in quality than 1 1/4" ep's, except for the original poster. i said that 2" ep's tend to show the *scope's* abberations more because you're viewing the light all the way to the edge of the primary and secondary mirrors. i also don't think that you need to spend $250 or more for a decent 2" ep. the 40mm orion optiluxe at $139 shows hardly any coma in my f/6 scope, and i've tried it in several f/5 scopes and had great views in those as well. while i haven't personally tried the GSO 2" ep's yet, a lot of people seem to like them, and they're dirt cheap. while all of us would want an ep case full of naglers and panoptics if we had an unlimited supply of money, in my opinion, there are plenty of good 2" ep's available at reaonable prices that will satisfy most observers (and i don't *want* to spend that much on one ep, i'd rather save my $$ for something that justifies it's cost a bit better!).

Nope, erik, I didn't mean to imply that you said that (it just seems to get said a lot about 2" eyepieces). As for coma, you should see *no* coma in an eyepiece (if you really do, then there is something seriously wrong with the eyepiece). Most eyepieces show varying amounts of astigmatism (the most common aberration seen), lateral color, distortion (usually pin-cushion), and field curvature. Coma is fairly rare in an eyepiece, and many of the people who say that they actually see it are mostly observing the astigmatism generated by the eyepiece (tends to cover up much of the coma of many Newtonians). I have to use my 24mm Panopic or my 14mm Ultrawide before I can detect the coma in my 10 inch f/5.6 Newtonian. As for the Orion Optiluxe, it might be better than some, but at short f/ratios, it will probably also show astigmatism towards the edge of the field. I use my 30mm Widescan III eyepiece on my 100mm f/6 Newtonian, but the star images in the outer third of the field show noticable astigmatism, so these simple 5-element 2-inch eyepieces should only be used at moderate to long f/ratios (works pretty well in my f/10 SCT). Clear skies to you.

[lighttrap]

3 things:
Iceman,
Are you sure that you really want a 40mm 1.25" plossl? I had a Televue 40mm plossl that had such excessive eyerelief that it was extremely hard to get the head position right so as not to experience blackout. In general, there's not much reason to go above 32mm in the 1.25" size, since the field stop in 1.25" is the barrel, and therefore the 40mm will not show any wider AFOV. (The exception, and the reason for some of the really long focal length 1.25" ep.s is for use in really long focal length scopes, such as some SCTs and MCTs where super long focal length ep.s are needed simply to get the magnification down far enough.) I'm assuming that the scope you're getting has a 1250mm focal length. If so, a 40mm ep will give you 31.25x and a 32mm will give 39x. Either way, both of these lower powers are where an inexpensive 2" ep would come in handy. In a 2", you actually would gain AFOV by going above 30mm.

That brings me to Erik's excellent point that you really don't have to spend megabucks to get a 2" eyepiece that will give satisfying views. I'm pretty picky about what I see at the eyepiece, yet I'm quite happy with a $69 Burgess 32mm 2". Likewise, there are growing legions of folks that are quite pleased with their GSO 2" eyepieces for around the same amount, (or maybe even a little less).

Finally, there is the third point. Speaking of being picky about what I see at the eyepiece, I agree wholeheartedly with TomL about considering the UO orthos for your shorter focal lengths. I've got several small plossls including 12.4mm and 10mm and 9mm and 6.7mm that I no longer use simply because the views in the inexpensive UO orthos are so much better. My opinion, and this is strictly my opinion, is that good quality plossls are great in the 32mm to 15mm range, but below that (or thereabouts), the UO orthos generally give crisper, cleaner images. In your area the UO orthos may be marketed under different names. Some possibilities might be Circle T, KK, or perhaps something altogether different. Maybe somebody else can help out with that.

Just some thoughts.

[erik]

david, yes, ep's themselves don't show coma. what i meant to say was that the coma from the scope itself may become visible in a 2" ep. several cheaper 2" ep's do show optical defects (as you mentioned), but the optiluxe is one of the best i've seen for the money. 3 element 2" ep's, such as my orion deep view, show many other problems in fast scopes (that particular ep has severe field curvature), but all i was saying is that most observers probably wouldn't notice the abberations in a quality 2" ep since they are usually near the edge of the fov. i agree that someone who wants perfection should save their money for a TV, but i use the optiluxe and like it quite a bit. although i could afford to buy a nagler if i wanted, i don't feel that the increase in performance justifies the price, but that's just me...

[rboe]

My 2" Optilux has been a wonderful surprise. It ain't no nagler, but it covers the bill quite well indeed. I got to try a Widescan III (in a slow scope) and it was very nice too. Don't recall the size though. 32-40mm or so.

However; I have a very fast dob in my stable so I see naglers in my future.

Thanks for the heads up on coma. These discussions always teach me something. Keep it up. What is the seagull effect I see in my fast dob in the cheap eye pieces then?

I second the UO comments. I have a 12.5 and consider it one of my better investments. I have a 8mm radian that does not get used nearly enough for what I paid for it.

[Jarad]

Seagulls are astigmatism - happens with cheap EP's in fast scopes. That's why you're going to end up with nagler's, Pan's, or Pentaxes for your fast dob.

Jarad

[Scott Beith]

Hi Guys,
I have been noting an interesting series of reports from users of the Orion 40mm Optiluxe. Some users report that it loses edge sharpness at the very edge of the FOV, but in my Stellarvue Nighthawk - it is sharp to the edge. I have checked many times, but the stars at the very edge of the FOV are just as sharp as the stars in the center of the FOV. I think I know why there are differing reports - 2" EP's seem to show flaws in a fast scope at the edge of the FOV. A fast reflector has coma, that is known. The Stellarvue Nighthawk has an exceptionally flat field (as tested by Sky and Telescope magazine). S&T stated it is flat right to the edge of it's 5 degree FOV. Therefore, I think that the Optiluxe isn't to blame for loss of sharpness at the edge of the FOV - it is simply a wide enough EP to show the inherent optical design characteristics of a fast newt or generic fast refractor.
No ill intent to owners of Chinese refractors as my Yard Cannon is a CR150 that I really like !!!
I just mean to bring up a point about scope design and the Optiluxe EP.

Does anyone have information that would change my point of veiw? Am I off base with my deductions? If so, let me know...

[iceman]

Excellent advice there from everyone, thanks heaps. I'll definitely go for the 32mm instead of the 40mm.. As for Ortho's instead of Plossl's for the higher power EP's, I don't have that option initially unfortunately, without spending more money, as the 9, 15 and 25mm Plossl EP's come WITH the scope.

I'll have to save up for those, and i'll try some out at the local astro club before purchasing any new EP gear.

Thanks for replies.