So what am I missing, between large aperture reflector versus smaller refractor?
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So what am I missing, between large aperture reflector versus smaller refractor?
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Re: So what am I missing, between large aperture reflector versus smaller refractor?
∞ AP Scopes: #1: TPO 6" f/9 RC #2: ES 102 f/7 APO #3: ES 80mm f/6 APO
∞ G&G Scopes: #1: Meade 102mm f/7.8 #2: Bresser 102mm f/4.5
∞ Guide Scopes: 70 & 80mm fracs -- The El Cheapo Bros.
∞ Mounts: iOptron CEM70AG, SW EQ6R, Celestron AVX, SLT & GT (Alt-Az), Meade DS2000
∞ Cameras: #1: ZWO ASI294MC Pro #2: 662MC #3: 120MC, Canon T3i, Orion SSAG, WYZE Cam3
∞ Binos: 10X50,11X70,15X70, 25X100 ∞ AP Gear: ZWO EAF and mini EFW and the Optolong L-eXteme filter
∞ EPs: ES 2": 21mm 100° & 30mm 82° Pentax XW: 7, 10, 14, & 20mm 70°
Searching the skies since 1966. "I never met a scope I didn't want to keep."
- cumbrianwolf
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Re: So what am I missing, between large aperture reflector versus smaller refractor?
How wide-field are we referring to, as I thought my scope was wide atJayTee wrote: ↑Fri Jan 14, 2022 6:17 pm Not only do we consider the f/number, to me the more important number is the focal length. The focal length determines your image scale (based on which imaging camera you use) and your guide scope suitability. A small ish refractor with a short focal length is going to show a bigger chunk of sky than your Newtonian. We like these because the smaller refractors are great for the bigger nighttime objects, like Andromeda, the Pleiades, and other large astro features.
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Re: So what am I missing, between large aperture reflector versus smaller refractor?
∞ AP Scopes: #1: TPO 6" f/9 RC #2: ES 102 f/7 APO #3: ES 80mm f/6 APO
∞ G&G Scopes: #1: Meade 102mm f/7.8 #2: Bresser 102mm f/4.5
∞ Guide Scopes: 70 & 80mm fracs -- The El Cheapo Bros.
∞ Mounts: iOptron CEM70AG, SW EQ6R, Celestron AVX, SLT & GT (Alt-Az), Meade DS2000
∞ Cameras: #1: ZWO ASI294MC Pro #2: 662MC #3: 120MC, Canon T3i, Orion SSAG, WYZE Cam3
∞ Binos: 10X50,11X70,15X70, 25X100 ∞ AP Gear: ZWO EAF and mini EFW and the Optolong L-eXteme filter
∞ EPs: ES 2": 21mm 100° & 30mm 82° Pentax XW: 7, 10, 14, & 20mm 70°
Searching the skies since 1966. "I never met a scope I didn't want to keep."
- Lady Fraktor
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Re: So what am I missing, between large aperture reflector versus smaller refractor?
My 80mm
The maximum
See Far Sticks: Elita 103/1575, AOM FLT 105/1000, Bresser 127/1200 BV, Nočný stopár 152/1200, Vyrobené doma 70/700, Stellarvue NHNG DX 80/552, TAL RS 100/1000, Vixen SD115s/885
EQ: TAL MT-1, Vixen SXP, SXP2, AXJ, AXD
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Tripods: Berlebach Planet (2), Uni 28 Astro, Report 372, TAL factory maple, Vixen ASG-CB90, Vixen AXD-TR102
Diagonals: Astro-Physics, Baader Amici, Baader Herschel, iStar Blue, Stellarvue DX, Tak prism, TAL, Vixen
Eyepieces: Antares to Zeiss (1000101)
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- cumbrianwolf
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Re: So what am I missing, between large aperture reflector versus smaller refractor?
I am starting to grasp it once again, something I need to look into more.Lady Fraktor wrote: ↑Fri Jan 14, 2022 6:34 pm Quite significant actually, a 254mm f/4 with a 25mm eyepiece has a TFOV of 1.34°
My 80mm f/6.9 using a 25mm eyepiece has a TFOV of 2.5°
The maximum FOV of your 254mm is 2.69°, my 80mm is 4.9°
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Re: So what am I missing, between large aperture reflector versus smaller refractor?
https://astronomy.tools/calculators/field_of_view/
∞ AP Scopes: #1: TPO 6" f/9 RC #2: ES 102 f/7 APO #3: ES 80mm f/6 APO
∞ G&G Scopes: #1: Meade 102mm f/7.8 #2: Bresser 102mm f/4.5
∞ Guide Scopes: 70 & 80mm fracs -- The El Cheapo Bros.
∞ Mounts: iOptron CEM70AG, SW EQ6R, Celestron AVX, SLT & GT (Alt-Az), Meade DS2000
∞ Cameras: #1: ZWO ASI294MC Pro #2: 662MC #3: 120MC, Canon T3i, Orion SSAG, WYZE Cam3
∞ Binos: 10X50,11X70,15X70, 25X100 ∞ AP Gear: ZWO EAF and mini EFW and the Optolong L-eXteme filter
∞ EPs: ES 2": 21mm 100° & 30mm 82° Pentax XW: 7, 10, 14, & 20mm 70°
Searching the skies since 1966. "I never met a scope I didn't want to keep."
- cumbrianwolf
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Re: So what am I missing, between large aperture reflector versus smaller refractor?
- JayTee
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Re: So what am I missing, between large aperture reflector versus smaller refractor?
You could easily use your TS 80 as an imaging scope. Go on craigslist and find an "El Cheap" 50 - 70mm frac as your new guide scope. Now you have short
∞ AP Scopes: #1: TPO 6" f/9 RC #2: ES 102 f/7 APO #3: ES 80mm f/6 APO
∞ G&G Scopes: #1: Meade 102mm f/7.8 #2: Bresser 102mm f/4.5
∞ Guide Scopes: 70 & 80mm fracs -- The El Cheapo Bros.
∞ Mounts: iOptron CEM70AG, SW EQ6R, Celestron AVX, SLT & GT (Alt-Az), Meade DS2000
∞ Cameras: #1: ZWO ASI294MC Pro #2: 662MC #3: 120MC, Canon T3i, Orion SSAG, WYZE Cam3
∞ Binos: 10X50,11X70,15X70, 25X100 ∞ AP Gear: ZWO EAF and mini EFW and the Optolong L-eXteme filter
∞ EPs: ES 2": 21mm 100° & 30mm 82° Pentax XW: 7, 10, 14, & 20mm 70°
Searching the skies since 1966. "I never met a scope I didn't want to keep."
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Re: So what am I missing, between large aperture reflector versus smaller refractor?
F = focal length of objective
f = focal length of eyepiece
d = sensor diameter (
D = objective diameter
with everything in mm, then
Magnification M =
TFOV (in radians) = 2*atan(0.5d/F) or, approximately, d/F
Dawes limit (arc seconds) = 116/D
degrees = (180/
The light flux is inversely proportional to the F ratio squared, the exposure time is proportional to the F ratio squared so a
Generally for a 10" Newt compared to an average refractor, it has an advantage of F ratio, resolution based on Dawes limit and magnification. The resolution is deteriorated by the secondary obstruction and bumps in the mirror surfaces. Aside from that, the improved resolution according to Dawes maxes out at about 8"
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