2" Eye Piece

[Bino Pete]

Just having a look at various suppliers for 2" eyepieces and noticed that the majority are 20mm focal lengths and higher. Is there a reason why a lot of the higher power (7, 9, 12 etc) are only stocked in 1.25".

Thanks

[Riemann]

A combination of longer focal length and wider apparent field of view gives rise to the need for 2" eyepieces because 1.25" eyepieces have a physical limit as to the steepness of the angles that the light can take.    With short focal lengths you don't hit that physical limit even with very wide AFOVs.   As it is much cheaper to make a 1.25" eyepiece than a 2" eyepiece, manufacturers stick to that unless they have to move up to 2".

[John]

The benefit of the 2" format is that it can offer a larger field of view. Up to around 18mm-20mm the 1.25" barrel can accomodate an ultra wide field but if you want that in longer focal lengths, you need the 2" format. The field of view is defined by the diameter of the field stop which is a type of aperture stop built into the barrel of the eyepiece.

 

[Bino Pete]

20 minutes ago, John said:

The benefit of the 2" format is that it can offer a larger field of view. Up to around 18mm-20mm the 1.25" barrel can accomodate an ultra wide field but if you want that in longer focal lengths, you need the 2" format. The field of view is defined by the diameter of the field stop which is a type of aperture stop built into the barrel of the eyepiece.

 

At present I have the Celestron X-cel LX eyepieces in 7, 9, 12 and 18mm with a 30 and a 42mm in 2". I will be using these with my new scope (CPC800) that will have a 2" diagonal with 1.25" adapter. 

I've been looking at the Baader Hyperion Mark III Zoom eyepiece. Will I get better views with this eyepiece in comparison to my X-cel's as the baader has a 2"adapter or is the baader still technically a 1.25" eyepiece?

Sorry if it's a stupid question!

[John]

The Baader Hyperions and the Hyperion zoom are all 1.25" eyepieces in terms of optical design but they do come with a 2" barrel section which some like to use. Using them in a 2" eyepiece holder does not make them 2" eyepieces though !

The Hyperion zoom is convenient in that it covers a range of focal lengths but from 24mm to around 12mm the field of view is actually smaller than the Celestron X-Cel LX's and it only gets a little larger at 8mm. The X-Cel LX's are going to perform at least as well as the zoom in pure optical terms.

 

 

[Louis D]

It all has to do with the maximum field stop you can fit inside, or just above, a 1.25" barrel.  It's right about 27mm inside the barrel, slightly more but vignetted if above (as in the 35mm Celestron Ultrascopic).  This translates to a 32mm 50 degree eyepiece, a 24mm 68 degree eyepiece, an 18mm 82 degree eyepiece, a 13mm/14mm 100 degree eyepiece, and a 140 degree 9mm eyepiece.  Thus, to go wider than each of these in a similar focal length requires moving up to a 2 inch barrel.  Sometimes, the particular design requires a larger barrel to accommodate the large field lens as in the 17mm Nagler T4 or the 14m ES-100.  Sometimes, it's the sheer weight and bulk of an eyepiece that necessitates the larger barrel, as in the case of the 9mm ES-120 and 12mm ES-92.  My 140 degree data point comes from reports from the owners of the first 10 pieces of that eyepiece that were missing the field stop.  They reported that the true field of view was just about equal to the 13mm Ethos which is longest 100 degree eyepiece in a 1.25" barrel.

[Bino Pete]

On 4/18/2016 at 17:35, John said:

The Baader Hyperions and the Hyperion zoom are all 1.25" eyepieces in terms of optical design but they do come with a 2" barrel section which some like to use. Using them in a 2" eyepiece holder does not make them 2" eyepieces though !

The Hyperion zoom is convenient in that it covers a range of focal lengths but from 24mm to around 12mm the field of view is actually smaller than the Celestron X-Cel LX's and it only gets a little larger at 8mm. The X-Cel LX's are going to perform at least as well as the zoom in pure optical terms.

 

 

Is the ' Baader Hyperion Mark III Zoom eyepiece' suitable for spectacle wearers - Everyone's thoughts please?

[YKSE]

It works for me with glaases on. It's my alignment, PST viewing and family outreach EP, jsut as indicated here: