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Are 2-inch eyepieces all that?

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#1 LeubDier

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Posted 11 September 2013 - 11:46 PM

I have a used Nexstar 8i with a few nice 1.25-inch eyepieces (a 28mm, a 9.5mm, and a 5mm and two Barlows (a 2x, and a 2.5x).
I read something the other day that someone really thought the 2-inch eyepieces was the way to go for a scope like mine.
I'm a little skeptical about it because the 2-inchers are soooooo expensive, and I have a pretty good array of 1.25-inch eyepieces.
Also I've heard that the rear of the scope is 1.5-inches, so you don't really get full benefit of the 2-inch eyepieces.
Anyone out there with an opinion about the 1.25" vs 2" eyepieces?

#2 StrangeDejavu

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Posted 12 September 2013 - 12:08 AM

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#3 dpwoos

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Posted 12 September 2013 - 12:32 AM

Whether an eyepieces is 2" or 1.25" has nothing to do with eye relief. A 2" eyepiece does allow for a larger field stop and so wider field, but once the field stop diameter is 27mm or less a 1.25" barrel works just as well. Note that every Ethos 13mm and less uses a 1.25" barrel, as well as every Nagler 16mm and less, and every Delos, etc. So, the only time one needs a 2" eyepiece is when a field stop greater than 27mm is desired.

#4 starcrafter

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Posted 12 September 2013 - 12:34 AM

Yes.

#5 GlennLeDrew

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Posted 12 September 2013 - 12:42 AM

I've used a TeleVue 55mm Plossl on a C8 to very good effect. This was with a 2" visual back and full aperture 2" diagonal, which introduces not at all noticeable vignetting. The 2" thread-on SCT diagonals have a needlessly small aperture somewhat closer to the focus, which results in more prominent vignetting.

The reason a 48mm field stop behind a 38mm rear port can result in not notable vignetting is because of the separation between the two apertures. This throws the vignetting source well out of focus.

For the kind-to-eyepiece f/10 telescope, even a very low cost eyepiece performs well. My recommendation? A 30mm 80 degree eyepiece, which can be had for about $75, will be a very enjoyable experience. It has a 46mm field stop for essentially maximal true field, yet delivers a more versatile 3mm exit pupil that is both reasonably bright under a dark sky and not too bright under light pollution. And it will go deeper and deliver more detail than will an eyepiece putting up a larger exit pupil.

#6 lamplight

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Posted 12 September 2013 - 07:15 AM

Hi there.

This all assuming you want the largest field of view you can get. Which may or may not fit into your viewing preferences. I find I don't use mine that often since im usually starhopping faint fuzzies. But that may change. Like mentioned above, you'd really want to upgrade the visual back and diagonal to 2" as well to get the most out of the field of view. If you like wide binocular views you might like the views of a nice 30mm+ . If you have any opportunity to look through some good wide field 2" EPs that will decide it for you :)

#7 mich_al

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Posted 12 September 2013 - 07:41 AM

If you where to go to a 2" visual back you can still use your existing 1.25" eyepieces, just use a 2" to 1.25" adapter. I don't think short focal length eyepieces come in 2" anyway.

#8 Joe Aguiar

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Posted 12 September 2013 - 08:20 AM

yes and a 2" EP doesnt have to costs hundreds, you can get one of the Skywatchers 28mm, 35mm, 42mm EP for about $50 to $60 about new. It will give you low power and wide field as MICH Al says keep your current 1.25" EP for the higher power and use a 2" for low power large objects.

What i do is the low powers since its not hig mag the ep doesnt have to be as great or expensive as a high power ep where you are looking at fine detail close up, so you dont have to buy an ethos at $700 a decent 2" up to $100 will be fine for low powers.
joe

#9 brianb11213

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Posted 12 September 2013 - 08:46 AM

yes and a 2" EP doesnt have to costs hundreds, you can get one of the Skywatchers 28mm, 35mm, 42mm EP for about $50 to $60 about new. It will give you low power and wide field as MICH Al says keep your current 1.25" EP for the higher power and use a 2" for low power large objects.

Agreed.

What i do is the low powers since its not hig mag the ep doesnt have to be as great or expensive as a high power ep where you are looking at fine detail close up

Actually the demands on a low power EP are greater than those of a high power EP as it needs to be corrected over a much wider area. I don't advocate spending huge amounts of money on individual EPs (unless you have a huge shedload of cash just begging to be frittered away) but many really basic 2" EPs are somewhat disappointing. There is a bit of a link between the EP and the type of scope you are using it in, especially with short focus Newtonian/Dobsonian scopes where low power EPs need to be very well corrected to be worthwhile.

#10 REC

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Posted 12 September 2013 - 08:49 AM

Yes, good way to go. You can find a good 2" for about $100 and gives you a more secure way to mount to the scope.

As for 1.25" EP..the widest FOV you can get with a 32mm EP id about .8*. With my 34mm SWA I get a 1.2* FOV and can fit the entire Double Star cluster in it and most of the Pleiades ...that alone is worth it!

#11 REC

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Posted 12 September 2013 - 08:59 AM

BTW....I just checked the classifieds and found a few good ones around $100 and below.

Also, if you want I have a new Apetura 2" 30mm 68* fov that I can sell you for $45. It is the same as the GSO superview and had great reviews.

#12 Joe Aguiar

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Posted 12 September 2013 - 09:43 AM

There is a bit of a link between the EP and the type of scope you are using it in, especially with short focus Newtonian/Dobsonian scopes where low power EPs need to be very well corrected to be worthwhile.

yes agreed with you on this with fast scope ep need to be well corrected but i said about those 3 eps as the poster is using a 8" F/10 sct so it doesnt have to be super well corrected in a f/10 scope
joe

#13 obin robinson

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Posted 12 September 2013 - 09:45 AM

I have one 2" eyepiece: a Galileo 32mm. It's all I need and it works very well. I really like the wide-field views when searching for a well hidden object. After I find it with the 2" I swap out for some high powered 1.25" eyepieces.

obin :cool:

#14 Kevdog

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Posted 12 September 2013 - 09:55 AM

I have a used Nexstar 8i with a few nice 1.25-inch eyepieces (a 28mm, a 9.5mm, and a 5mm and two Barlows (a 2x, and a 2.5x).
I read something the other day that someone really thought the 2-inch eyepieces was the way to go for a scope like mine.
I'm a little skeptical about it because the 2-inchers are soooooo expensive, and I have a pretty good array of 1.25-inch eyepieces.
Also I've heard that the rear of the scope is 1.5-inches, so you don't really get full benefit of the 2-inch eyepieces.
Anyone out there with an opinion about the 1.25" vs 2" eyepieces?


I wasn't sure what to do either on my C11. But I did upgrade to a 2" diagonal (Williams Optic SCT threaded one) and the Williams Optic 40mm SWAN. It made a HUGE difference in how much I could see in the extended objects (like the Orion Nebula, Andromeda Galaxy, Pleadies, etc). Also I really like the light gathering of the lower magnification, so many objects got brighter and easier to see, even though they got smaller. And I was moving from a 32mm Orion Sirius.

I'm now selling the WO 40mm, only because I got an 18" Obsession and the fast optics aren't as forgiving, so I've upgraded to the 30mm ES82, so I no longer use the WO 40mm, but it's great in a slower scope f/6 or slower (like any SCT).

#15 BigC

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Posted 12 September 2013 - 04:25 PM

If you want to get the widest possible field of view at modest cost then get a 2" visual back ,2" diagonal (with 1.25 reducer insert to use when needed) and ,yes, a Galileo 2" 32mm eyepiece. As another says the inexpensive 2" 32mm does very well for those big views (I have several of them) ;unless you find a great deal on a widefield 2" ,your higher power views will be done using a 1.25" eyepiece.

#16 Bob Griffiths

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Posted 13 September 2013 - 08:00 AM

ALL of my 26 mm and lower power eyepieces are 2 inch eyepieces.... and all of my higher power are 1.25 inch eyepieces that I use in ALL my scopes including
my C8 as well as C11 and my 4 and 5 inch refractors...

So put me in the YES you should category

Bob G

#17 csrlice12

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Posted 13 September 2013 - 09:03 AM

Yes, and with a long f/l scope, they're you only option for wide field DSO viewing...not to mention if you get a focal reducer in he future..you'll. Want well corrected eyepieces.

#18 Jon Isaacs

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Posted 13 September 2013 - 09:26 AM

I have one 2" eyepiece: a Galileo 32mm. It's all I need and it works very well. I really like the wide-field views when searching for a well hidden object. After I find it with the 2" I swap out for some high powered 1.25" eyepieces.

obin :cool:


Obin:

I see that you have a 10 inch Starfinder, those were F/4.5 if I am not mistaken. Does it have a 2 inch focuser? If so, how sharp are the stars at the edge of the field? What exactly does "working very well mean?"

Having owned a number of 2 inch eyepieces around 30mm in focal length and owning telescopes of a variety of focal ratios, it has been my experience that most of them are quite sharp in the center of the field of view but most exhibit astigmatism away from the center, particularly at faster focal ratios. At F/10, an eyepiece has a much easier job of it than at F/5 but off-axis astigmatism is still an issue with simpler designs. Good edge performance at F/5 is expensive, less so at F/10.

Jon Isaacs

#19 obin robinson

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Posted 13 September 2013 - 10:20 AM

Obin:

I see that you have a 10 inch Starfinder, those were F/4.5 if I am not mistaken. Does it have a 2 inch focuser? If so, how sharp are the stars at the edge of the field? What exactly does "working very well mean?"

Jon Isaacs


Jon,

I have 2" Crayford focusers on all of my telescopes including the Starfinder 10" F/4.5. the 32mm 2" Galileo does have a bit of astigmatism away from the center. I use the 2" eyepiece as a wide-field finder and then I drop the 1.25" higher powered eyepieces in. When I use the 2" on the 4.5" telescope it works pretty well. I also only saw astigmatism towards the edge of the ED80.

I may get another 2" eyepiece in the future but for now the one I have does the job. It actually works really well in the ST80 when I am looking for satellites. The fast optics and wide field of view really grab a lot of light. Because I am looking for a moving object I don't really mind the astigmatism. It is particularly useful for finding geostationary birds. I really like the Galileo 32mm and would recommend it to anyone looking for a bargain 2" wide-field eyepiece.

obin :)

#20 Jon Isaacs

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Posted 13 September 2013 - 10:46 AM

I really like the Galileo 32mm and would recommend it to anyone looking for a bargain 2" wide-field eyepiece.



Obin:

How much did you pay for it? I see offered at a variety of prices. Have you compared it to other similar cost eyepieces?

My recommendation first timers is to try to get some looks through a variety of eyepieces if at all possible. Obin refers to a "bit of astigmatism" but what "a bit" means depends on the individual.

Jon

#21 simagic

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Posted 13 September 2013 - 11:16 AM

Mr novice here. I'm getting a Explore Scientific - AR102 f/6.5. With it is coming a 2" Explore Scientific 82°/18mm eyepiece . It comes with a two-inch dielectric diagonal and included is a 1.25" eyepiece holder adapter. So, upon reading this thread, it leads me to the belief that 'if' I choose to get a stronger eyepiece for closer views (for example a 10mm or a 6mm), that instead of getting a 2" eyepiece, I should get an 1.25 eyepiece (such as the Orion Sirius Plossl eyepieces that seem to "show up" a lot when looking). An "EP" is often mentioned here but I don't know what that is (yes, a novice). If i do get a 10mm or 6mm 1.25" eyepiece is the Orion Sirius Plossl a good choice or maybe something better with a better field of view. This is what "I think" that I determined from this thread. Thanks.

#22 Jon Isaacs

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Posted 13 September 2013 - 11:32 AM

Somatic:

Plossls are good eyepieces but in the shorter focal lengths they have very little eye relief so I would recommend something with more eye relief..

Jon

#23 Pharquart

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Posted 13 September 2013 - 11:46 AM

So, upon reading this thread, it leads me to the belief that 'if' I choose to get a stronger eyepiece for closer views (for example a 10mm or a 6mm), that instead of getting a 2" eyepiece, I should get an 1.25 eyepiece.


I don't think this will be much of a choice. You probably won't find 6mm eyepieces (or maybe even 10mm) in a 2" format because it's not needed, unless they are very wide fields of view.

The 2" format is required when the combination of long focal length and apparent field of view cross a magic line. Wide fields and long focal lengths require a larger "field stop" diameter in the eyepiece barrel. You can only get so big in a 1.25" format. If you want a longer focal length or a wider field than is supported by the maximum diameter field stop in a 1.25" eyepiece, you need a 2" eyepiece. The two measurements are both important. You can fit a 14mm/82 degree field into a 1.25" eyepiece. 18mm/82 degrees won't fit. Similarly, 14mm/100 degrees won't fit.

2" eyepieces are more expensive to manufacture (more glass and metal), so if you don't need the size for the large field stop, there's no real advantage to making one. That's why there are essentially no 2" eyepieces with short focal length.

Some eyepieces have a barrel that's designed to fit in either a 1.25" or 2" focuser, but they're not really 2" eyepieces. They still have the smaller field stop limitation.

Brian

#24 simagic

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Posted 13 September 2013 - 11:52 AM

Sooooooo, would the 10mm or 6mm Orion Sirius Plossl (52 degree)be a good choice or Orion Expanse Wide-Field (66 degree) ORRRRR is there one better such as ??_ _ _ _?? or _ _ _??. After spending the money on the scope I want to get a 'decent' eyepiece for close up even if it costs another 20-30 dollars. I saw this article about Expanse ...AGAIN, I am a novice so some of the vocabulary was not known but it lead me to believe the expanse had an issue. It mentions a "black mark" against it in the article http://telescopespac...-6mm-orion-e... So, what should I get for closer viewing?? Thanks

#25 Gert K A

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Posted 13 September 2013 - 12:24 PM

How about an 8mm Paradigm? it is a well respected eyepiece ;)








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