1.25" to 2" Adapter

[LDW1]

Does / has anyone used a 1.25" to 2" eyepiece adapter in their 1.25" telescope so that they can utilize their 2" eyepieces ?

[RT65CB-SWL]

I have one and use it with the SkyWatcher 2"/28mm LET|LER [the only 2" eyepiece I have] with my TeleVue Ranger. 

Edited November 24, 2022 by Philip R

[LDW1]

I want to try it with my Vixen A62SS refractor using my 36mm Hyperion and a couple of others.

[Don Pensack]

Bear in mind that 2 things will happen:

1) you will need about 2" more in travel of the focuser to focus the eyepiece.

2) you will have horrible and significant vignetting, turning the 36mm Hyperion into a 53° eyepiece.

I strongly urge you to invest in some full-field 1.25" eyepieces like APM 24mm UFF, ES 24x68°, TeleVue Panoptic, 24mm Hyperion, 32mm Plössl, ES 26x62° etc.

and skip the idea of using a 2" eyepiece in a 1.25" focuser.

[LDW1]

18 minutes ago, Don Pensack said:

Bear in mind that 2 things will happen:

1) you will need about 2" more in travel of the focuser to focus the eyepiece.

2) you will have horrible and significant vignetting, turning the 36mm Hyperion into a 53° eyepiece.

I strongly urge you to invest in some full-field 1.25" eyepieces like APM 24mm UFF, ES 24x68°, TeleVue Panoptic, 24mm Hyperion, 32mm Plössl, ES 26x62° etc.

and skip the idea of using a 2" eyepiece in a 1.25" focuser.

I hear you, I already have a 40mm, 32mm Omni, a 24mm Pan and a 24mm Hyperion but I just like to experiment as I have said in the past. It isn't very expensive ie $24 C.

[Louis D]

Didn't your 36mm Hyperion Aspheric come with a 1.25" screw-on adapter to allow you to experiment?  It's that small piece shown between the box and the eyepiece in the image below:

The only way I've found to avoid hard vignetting and in-focus issues with 2" eyepieces in a 1.25" focuser is to hold the eyepiece's 2" barrel over and around the 1.25" insertion barrel being careful not to scratch the 2" barrel's internal blackening or the field lens.  My 27mm Panoptic works really well in this mode.  Wider field stop eyepieces like the 36mm BHA, probably not so much.  You'll need to completely remove the tightening screw from the 1.25" eyepiece holder to make this work at all.

[LDW1]

1 minute ago, Louis D said:

Didn't your 36mm Hyperion Aspheric come with a 1.25" screw-on adapter to allow you to experiment?  It's that small piece shown between the box and the eyepiece in the image below:

The only way I've found to avoid hard vignetting and in-focus issues with 2" eyepieces in a 1.25" focuser is to hold the eyepiece's 2" barrel over and around the 1.25" insertion barrel being careful not to scratch the 2" barrel's internal blackening or the field lens.  My 27mm Panoptic works really well in this mode.  Wider field stop eyepieces like the 36mm BHA, probably not so much.  You'll need to completely remove the tightening screw from the 1.25" eyepiece holder to make this work at all.

I have several other non Hyperion eps that I want to play with, they are 2". They are in the 30-50mm range, as I said it is not a lot of money lost vs some enjoyment. Plus I want to try it in my WL and Ha solar scopes.

[Louis D]

Another option might be to unscrew the 1.25" eyepiece holder from the diagonal entirely and hold the 2" eyepiece over the open hole to minimize vignetting and in-focus requirements.

Ideally you would want to use a 2" diagonal with a 1.25" nosepiece adapted to the front end (SCT (GSO) or 48mm (WO/Synta) to T-thread (42mm x 0.75) step down ring and T-mounted 1.25" nosepiece needed).  That would push the constriction pretty far forward of the eyepiece field stop to substitute soft vignetting for hard vignetting.

That's sort of what I've got going with my 127 Mak with a 2" visual back attached to a 27mm diameter rear baffle.  It's a very gradual vignetting that is hardly noticeable visually.  See the lower image when using an eyepiece with a 46mm field stop in a 127 Mak:

Edited November 24, 2022 by Louis D