The Effects Of A Step-Down Adapter For 2" EPs

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JayTee
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The Effects Of A Step-Down Adapter For 2" EPs

#1

Post by JayTee »


I am awaiting delivery of a step-down adapter for my 2" eyepieces. It will allow me to use my 2" eyepieces in a 1.25" focuser. The 2" eyepieces I would like to use in my 8" f/7.5 Newt are my ES 20mm/100° and my ES 30mm/82°

My question is, will there be visible effects created by this adapter? If so, what might they be?

Thanks

PS. I have a 2" R&P focuser that I could install on my Newt, but I'm not ready to do major surgery on that scope, yet.
JT
∞ Scopes: Celestron CPC1100 #2 Scope: 8" f/7.5 Dob AP Scopes: TPO 6" f/9 RC, ES 80mm f/6 APO G&G Scopes: Meade 102mm f/7.8, Bresser 102mm f/4.5 Guide Scopes: 70 & 80mm fracs
∞ Mounts: iOptron CEM70AG, Celestron AVX, SLT & GT (Alt-Az), Meade DS2000
∞ Cameras: Canon T3i (x2), ZWO ASI294MC Pro & 120MC, Orion SSAG, WYZE Cam3 (x2)
∞ Binos: 10X50,10.5X70,15X70², 25X100
∞ EPs: ES: 21 100°, 30 82° X-Cels: 9, 12, 18, 25 GSO:15,20
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I never met a scope I didn't want to keep. "My God, it's full of stars." Searching the skies since 1966!
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notFritzArgelander
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Re: The Effects Of A Step-Down Adapter For 2" EPs

#2

Post by notFritzArgelander »


You can expect some vignetting for 2" eyepieces with field stops larger than the inner diameter of the adapter.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: 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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JayTee
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Re: The Effects Of A Step-Down Adapter For 2" EPs

#3

Post by JayTee »


The adapter arrived today, but guess what... it's cloudy!
JT
∞ Scopes: Celestron CPC1100 #2 Scope: 8" f/7.5 Dob AP Scopes: TPO 6" f/9 RC, ES 80mm f/6 APO G&G Scopes: Meade 102mm f/7.8, Bresser 102mm f/4.5 Guide Scopes: 70 & 80mm fracs
∞ Mounts: iOptron CEM70AG, Celestron AVX, SLT & GT (Alt-Az), Meade DS2000
∞ Cameras: Canon T3i (x2), ZWO ASI294MC Pro & 120MC, Orion SSAG, WYZE Cam3 (x2)
∞ Binos: 10X50,10.5X70,15X70², 25X100
∞ EPs: ES: 21 100°, 30 82° X-Cels: 9, 12, 18, 25 GSO:15,20
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I never met a scope I didn't want to keep. "My God, it's full of stars." Searching the skies since 1966!
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Re: The Effects Of A Step-Down Adapter For 2" EPs

#4

Post by Bigzmey »


With 1.25" adaptor ES100 20mm will have FOV just under 80 deg and ES82 30mm around 50 deg.
Scopes: Stellarvue: SV102ED; Celestron: 9.25" EdgeHD, 8" SCT, 150ST, Onyx 80ED; iOptron: Hankmeister 6" Mak; SW: 7" Mak; Meade: 80ST.
Mounts: SW: SkyTee2, AzGTi; iOptron: AZMP; ES: Twilight I; Bresser: EXOS2; UA: MicroStar.
Binos: APM: 100-90 APO; Canon: IS 15x50; Celestron/Vixen Giant 20x80; Orion: Binoviewer, LG II 15x70, WV 10x50, Nikon: AE 16x50 & 8x40.
EPs: Pentax: XWs & XFs; TeleVue: Delites, Panoptic & Plossls; ES: 68, 62; Vixen: SLVs; Baader: BCOs, Aspherics, Mark IV; Meade: UWA, SWA.
Diagonals: Baader: BBHS mirror, Zeiss Spec T2 prism, Clicklock dielectric; TeleVue: Evebrite dielectric; AltairAstro: 2" prism.
Filters: Lumicon: DeepSky, UHC, OIII, H-beta; Baader: Moon & SkyGlow, Contrast Booster, UHC-S, 6-color set; Astronomik: UHC.

Observing: DSOs: 2706 (Completed: Messier, Herschel 1, 2, 3. In progress: H2,500: 2101, S110: 77). Doubles: 1863, Comets: 26, Asteroids: 149
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Re: The Effects Of A Step-Down Adapter For 2" EPs

#5

Post by JayTee »


Hi Andrey,

Did you use 1.25" as a new field stop of sorts to get those numbers?
JT
∞ Scopes: Celestron CPC1100 #2 Scope: 8" f/7.5 Dob AP Scopes: TPO 6" f/9 RC, ES 80mm f/6 APO G&G Scopes: Meade 102mm f/7.8, Bresser 102mm f/4.5 Guide Scopes: 70 & 80mm fracs
∞ Mounts: iOptron CEM70AG, Celestron AVX, SLT & GT (Alt-Az), Meade DS2000
∞ Cameras: Canon T3i (x2), ZWO ASI294MC Pro & 120MC, Orion SSAG, WYZE Cam3 (x2)
∞ Binos: 10X50,10.5X70,15X70², 25X100
∞ EPs: ES: 21 100°, 30 82° X-Cels: 9, 12, 18, 25 GSO:15,20
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I never met a scope I didn't want to keep. "My God, it's full of stars." Searching the skies since 1966!
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Re: The Effects Of A Step-Down Adapter For 2" EPs

#6

Post by Bigzmey »


JayTee wrote: Fri Mar 25, 2022 7:42 pm Hi Andrey,

Did you use 1.25" as a new field stop of sorts to get those numbers?
I have used 27mm - max field stop for 1.25" EPs. I know it is not as simple as that since you will see the FOV gradually loosing brightness at the edge instead of sharp field stop.
Scopes: Stellarvue: SV102ED; Celestron: 9.25" EdgeHD, 8" SCT, 150ST, Onyx 80ED; iOptron: Hankmeister 6" Mak; SW: 7" Mak; Meade: 80ST.
Mounts: SW: SkyTee2, AzGTi; iOptron: AZMP; ES: Twilight I; Bresser: EXOS2; UA: MicroStar.
Binos: APM: 100-90 APO; Canon: IS 15x50; Celestron/Vixen Giant 20x80; Orion: Binoviewer, LG II 15x70, WV 10x50, Nikon: AE 16x50 & 8x40.
EPs: Pentax: XWs & XFs; TeleVue: Delites, Panoptic & Plossls; ES: 68, 62; Vixen: SLVs; Baader: BCOs, Aspherics, Mark IV; Meade: UWA, SWA.
Diagonals: Baader: BBHS mirror, Zeiss Spec T2 prism, Clicklock dielectric; TeleVue: Evebrite dielectric; AltairAstro: 2" prism.
Filters: Lumicon: DeepSky, UHC, OIII, H-beta; Baader: Moon & SkyGlow, Contrast Booster, UHC-S, 6-color set; Astronomik: UHC.

Observing: DSOs: 2706 (Completed: Messier, Herschel 1, 2, 3. In progress: H2,500: 2101, S110: 77). Doubles: 1863, Comets: 26, Asteroids: 149
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Re: The Effects Of A Step-Down Adapter For 2" EPs

#7

Post by OzEclipse »


Hi Jay Tee

You might also get some internal reflections from the eyepiece barrel and some UW eyepiece designs are negative eyepieces, the field stop is not in front of the front element. Use of an adaptor will force the eyepiece to sit high off the tube wall. You will need a high focal point above the focusser to be able to reach focus.

The only light loss IMO will be vignetting.
Joe
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Amateur astronomer since 1978...................Web site : http://joe-cali.com/
Scopes: ATM 18" Dob, Vixen VC200L, ATM 6"f7, Saxon ED80, WO M70 ED, Orion 102 Maksutov, ST80.
Mounts: Takahashi EM-200, iOptron iEQ45, Push dobsonian with Nexus DSC, three homemade EQ's.
Eyepieces: TV Naglers 31, 17, 12, 7; Denkmeier D21 & D14; Pentax XW10, XW5, Unitron 40mm Kellner, Meade Or 25,12
Cameras : Pentax K1, K5, K01, K10D / VIDEO CAMS : TacosBD, Lihmsec.
Cam/guider/controllers: Lacerta MGEN 3, SW Synguider, Simulation Curriculum SkyFi 3+Sky safari
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Re: The Effects Of A Step-Down Adapter For 2" EPs

#8

Post by Don Pensack »


I suspect you won't be able to achieve focus because the eyepieces will be pulled out of the focuser too far.
Astronomer since 1963
Currently using a 12.5" dob and a 4" apo refractor
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