Attaching A 1.25" Nose Piece To A 2" eyepiece Question

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Refractordude
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Attaching A 1.25" Nose Piece To A 2" eyepiece Question

#1

Post by Refractordude »


What percentage of the field of view is lost when attaching a 1.25" inch nose piece to a 2" eyepiece.
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notFritzArgelander
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Re: Attaching A 1.25" Nose Piece To A 2" eyepiece Question

#2

Post by notFritzArgelander »


It depends on the size of the field stop of the 2" eyepiece. I estimate that the Baader Hyperion 36mm aspheric has a 43.1mm field stop. Assuming that the nosepiece reduces that to (1.25x25.4) 31.75mm I'd estimate 31.75/43.1 = ~74% is the field remaining for a ~26% loss.

The estimate of the field stop comes from = focal length * AFOV(degrees) / 57.3 (degrees per radian).
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: Attaching A 1.25" Nose Piece To A 2" eyepiece Question

#3

Post by Lady Fraktor »


It is a bit of a reversal as most adapter eyepieces are 1.25" with a extra 2" barrel, more a convenience than anything.
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Re: Attaching A 1.25" Nose Piece To A 2" eyepiece Question

#4

Post by Bigzmey »


notFritzArgelander wrote: Sat Dec 05, 2020 4:04 am It depends on the size of the field stop of the 2" eyepiece. I estimate that the Baader Hyperion 36mm aspheric has a 43.1mm field stop. Assuming that the nosepiece reduces that to (1.25x25.4) 31.75mm I'd estimate 31.75/43.1 = ~74% is the field remaining for a ~26% loss.

The estimate of the field stop comes from = focal length * AFOV(degrees) / 57.3 (degrees per radian).
My calculations are somewhat different. According to Baader 36mm Aspheric EP field stop is 45mm. Max stop field for 1.25" format is 27mm. This reduces FOV from 72 deg to 43.2 deg (40% loss) with 64% loss in viewed area.

In a way the 1.25" adapter turns it into a 36mm Plossl right in between 32mm Plossl (49 deg FOV) and 40mm Plossl (39 deg FOV).
Last edited by Bigzmey on Mon Dec 07, 2020 6:15 pm, edited 2 times in total.
Scopes: Stellarvue: SV102ED; Celestron: 9.25" EdgeHD, 8" SCT, 150ST, Onyx 80ED; iOptron: Hankmeister 6" Mak; SW: 7" Mak; Meade: 80ST.
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EPs: Pentax: XWs & XFs; TeleVue: Delites, Panoptic & Plossls; ES: 68, 62; Vixen: SLVs; Baader: BCOs, Aspherics, Mark IV.
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Re: Attaching A 1.25" Nose Piece To A 2" eyepiece Question

#5

Post by notFritzArgelander »


Bigzmey wrote: Mon Dec 07, 2020 6:09 pm
notFritzArgelander wrote: Sat Dec 05, 2020 4:04 am It depends on the size of the field stop of the 2" eyepiece. I estimate that the Baader Hyperion 36mm aspheric has a 43.1mm field stop. Assuming that the nosepiece reduces that to (1.25x25.4) 31.75mm I'd estimate 31.75/43.1 = ~74% is the field remaining for a ~26% loss.

The estimate of the field stop comes from = focal length * AFOV(degrees) / 57.3 (degrees per radian).
My calculations are somewhat different. According to Baader 36mm Aspheric EP field stop is 45mm. Max stop field for 1.25" format is 27mm. This reduces FOV from 72 deg to 43.2 deg (40% loss) with 64% loss in viewed area.

In a way the 1.25" adapter turns it into a 36mm Plossl right in between 32mm Plossl (49 deg FOV) and 40mm Plossl (39 deg FOV).
Yours is a better estimate.
1) You used an actual field stop spec rather than my use of a formula.
2) My taking the 31.75mm as the field stop is optimistic.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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