EP size basics

[starwonder]

Although I am aware you can get EP's in either 1.25" or 2" sizes what is the fundamental viewing difference between the two?

I mean do you get a wider view through the EP with the 2" than the 1.25"?  

Any help greatly appreciated, thanks.

[michael.h.f.wilkinson]

The wider barrel simply allows wider views.

[starwonder]

Thanks Michael.  So if the 2" give a wider view why do the 1.25" EP's seem more popular?  Is this purely because they'll be cheaper? 

[Charic]

starwonder.......Eyepieces for telescopes are  changed to increase or decrease the magnification of the telescope, a standard barrel size makes  changing the lenses an easier task.  the 1¼ inch 1.25" 31.75mm (all the same) are the most popular telescope eyepiece barrel diameters of to date. The size of the barrel is primarily to support the longer focal lengths of the eyepieces. The practical upper limit on focal lengths for eyepieces with 1¼ inch barrels is about 32 mm.The larger barrel size of the  2 inch eyepiece holder helps alleviate the limit on  that focal length. The upper limit of focal length with 2 inch eyepieces is about 55 mm.  The 2" lenses are normally heavier so may un-balance a scope unless you lock down tighter, or counter balance with weights, and  they cost more? You will still get wide views from a 1.25" lense, depending on the lens ie ES 14mm gives an 82 degree view.
 

[starwonder]

Cool, thanks for that Charic.     I feel I'm starting to understand the technicalities of EP choice but know I've still a long way to go yet.  

Much appreciated.

[michael.h.f.wilkinson]

Focal length is only part of the equation. The real issue is the size of the field stop. This is the circular aperture at the bottom of many EPs which delimits the part of the prime-focus image plane actually seen through the EP. The maximum field stop is 27.5mm in a 1.25" EP, and 47mm in a 2". The required diameter depends on a combination of focal length and apparent field of view. For 1.25", the maximum field stop is reached by a 32mm Plössl (50°), or a 24mm super-wide (68°), or a 16mm Nagler (82°). My 31mm Nagler could never fit into a 1.25" barrel.

[Charic]

michael.hf.wilkinson......... too true,  There`s so much to learn with this hobby.

[Tinker1947]

So the prevoius post have outlined "why" there are 2 sizes, in practice its easier to change 1 type either the 1.25" or the 2" viewing in the dark means a lot of pockets if your outside in the garden or a rack to hold them in a obby, what doesn't help is also needing a adapter as well as  pockets with EP's in (only one item per pocket) i find the 2" better for changing than going from 2" to 1.25 by the time you have taken out a 2" EP then put the dust caps on, then find the adapter then the right size 1.25" EP, removed the dust caps placed it in the adapter this then in the focusor, refocused all this with gloves on or fingers that are going blue in the cold, my obby has a rack and i still tend to stick to one size when viewing.......

This has since been moved to the rear wall due to changing from Newt to a C11 these scopes have focusers  at different ends of the tube....

[starwonder]

May as well just get 2"' ones then?

[Moonshane]

May as well just get 2"' ones then?

It's not possible (or worth it) to get / make short focal length eyepieces (maybe anything below about 15mm) in a 2" fitting. I have just one 2" eyepiece in a set of 14.

[Tinker1947]

It's not possible (or worth it) to get / make short focal length eyepieces (maybe anything below about 15mm) in a 2" fitting. I have just one 2" eyepiece in a set of 14.

  Hyperion make a full range, there may be other i have a few and find them very good in my C11......

http://www.firstlightoptics.com/baader-planetarium/baader-hyperion-68-degree-eyepiece.html

[Moonshane]

  Hyperion make a full range, there may be other i have a few and find them very good in my C11......

http://www.firstlightoptics.com/baader-planetarium/baader-hyperion-68-degree-eyepiece.html

Hyperions are 1.25" eyepieces surely with a 2" skirt?

[michael.h.f.wilkinson]

I predominantly use 2" EPs (the 12, 17, 22, and 31 mm Naglers) for DSO work, and 1.25" for planetary work (XW7, Delos 8, XF8.5, and XW10). The 12 mm fits both 1.25 and 2" barrels.

[helicalwave]

It's not possible (or worth it) to get / make short focal length eyepieces (maybe anything below about 15mm) in a 2" fitting. I have just one 2" eyepiece in a set of 14.

You can get Baader Hyperion eyepieces in short focal lengths with 2" barrels, although the eyepiece itself is optically 1.25", the wider barrel is used when attaching a camera to the EP for digiscoping, to give it a more rigid mount.

[Tinker1947]

Hyperions are 1.25" eyepieces surely with a 2" skirt?

They fit a 2" focuser as standard with a 1.25" supplied adapter if required.....

[starwonder]

Doesn't that kind of defeat the object of getting a 2" with the wider view if it's actually a 1.25"?

[Tinker1947]

Doesn't that kind of defeat the object of getting a 2" with the wider view if it's actually a 1.25"?

For me it would mean one less attachment  in a pocket if there all 2" they go from 5mm to 24mm in 7 EP's plus the 31/36mm Aspherics

[starwonder]

Yes, you have a point there Tinker1947 but isn't there a significant cost difference?  I must admit though I think I'd rather get all 2" than mess about with so many different sizes.  

I'm looking at buying my first set of EP's and don't want to waste my money or subsequently buy both sizes if it's unnecessary.  I'll get a 25mm with my new scope thrown in (don't know whether it's a 1.25" or 2") and I'll be looking for probably a 7mm at first for the planets and then a 15mm later on.  

Have also be tempted to get a zoom EP but don't know if the quality of optics is as good as a fixed lens, like it is with camera lenses.

[Moonshane]

really the combination eyepieces like Hyperions, most Ethos and some Naglers are just 1.25" eyepieces with the 'convenience' of  2" fitting. if you are talking about 2" eyepiece in terms of fitting they are 2" eyepieces. if you are talking about the advantages of 2" eyepieces in terms of field of view, they are 1.25" eyepieces.

[Naemeth]

First and foremost, a larger barrel size is there for increasing the AFOV. You could make a 3" orthoscopic, but what would be the point? Traditional Abbe-Orthoscopic designs have about 40 degrees, this means that you can fit the whole field into a 1.25" barrel right up to a 40mm eyepiece.

I wouldn't rule out any EP sizes, it's not really that much of a hassle to change over compared to the advantages you'd be gaining of having both (2", say 30mm ish as a nice widefield eyepiece, and 1.25" for reduced weight and less need to counterbalance).

[John]

2" eyepieces require 2" filters which is worth remembering. Fortunately, with a suitable adapter, it's possible to use 1.25" in eyepieces with a 2" filter so you don't need 2 sets of filters.

As Shane says, the Hyperions and others which offer a 2" barrel option are still, optically, 1,25" eyepieces. The 2" barrel is provided to allow (or maybe encourage !) the use of a 2" drawtube / diagonal for holding the eyepiece. Some of these eyepieces are pretty heavy so thats a sensible move as the 2" fittings are more secure for heavy eyepieces.

You can use these eyepieces with hybrid barrels in a 1.25" fitting of course but the result can be a little comical - here is my 13mm Ethos in a Celestron C5 for example:

[John]

I wouldn't rule out any EP sizes, it's not really that much of a hassle to change over compared to the advantages you'd be gaining of having both (2", say 30mm ish as a nice widefield eyepiece, and 1.25" for reduced weight and less need to counterbalance).

Thats good advice. When starting out in the hobby I think we all make little resolutions for ourselves such as not being interesting in ultra wide eyepieces, not ever wanting 2" eyepieces, never spending more than £100 for an eyepiece etc, etc, but most of these seem to get bent / broken later on as your experience grows and your needs change   

[Naemeth]

Thats good advice. When starting out in the hobby I think we all make little resolutions for ourselves such as not being interesting in ultra wide eyepieces, not ever wanting 2" eyepieces, never spending more than £100 for an eyepiece etc, etc, but most of these seem to get bent / broken later on as your experience grows and your needs change 

I learned that the hard way . This was me, a mere 6 months ago:

Okay, I haven't bought any green and black yet. But I've come to an important realization: I will save a lot of money if I go for TeleVue eyepieces straight away, no point in going for the middle ground really. Fortunately at the moment, at least, the scope (or at least, focuser) limits weight of an eyepiece to probably around 150g (most I'd be comfortable with putting on it), so this rules out: Ethos / Nagler / Delos / Panoptic (just, these may be okay) / Radian (difficult to get anyway).

Now, this is fortunate for me, all the high quality eyepieces at this level are around 50 degree, so I won't get the ultra-wide bug.

Here's my plan:

Save and get 3-6mm Nagler Zoom (Sell 4mm, Supplied MAs, TAL x2 Barlow) and keep the Vixen LV 7mm.

Get TeleVue Plössls, 15mm, 11mm, 20mm, 8mm, 26mm (then sell current 26mm), 32mm.

Relax, until I get a Sumerian Dob ~16" in quite a few years, then panic about ultra-wide eyepieces.

I was right about the Nagler Zoom and Plossls, but totally wrong on the lack of ultra-wides. I've just got myself a Panoptic, and am planning to add a 12mm Delos pretty soon.

(http://stargazerslounge.com/topic/181461-made-a-decision-down-the-slippery-slope/#entry1879899)

[AlexB67]

It would be even more comical to see that eyepiece and adapter attached to the Sky-watcher Heritage 76mm mini Dob, it'll be getting to the point where newcomers would wonder which bit is the scope :0)

[Andrew*]

Thats good advice. When starting out in the hobby I think we all make little resolutions for ourselves such as not being interesting in ultra wide eyepieces, not ever wanting 2" eyepieces, never spending more than £100 for an eyepiece etc, etc, but most of these seem to get bent / broken later on as your experience grows and your needs change 

But usually these resolutions are broken when you realise WHY you are breaking them and the benefits to your observing.