Difference between SkyWatcher Explorer 130 RA and 130M?
- flord.lord
- Earth Ambassador
- Articles: 0
- Posts: 49
- Joined: Thu Jun 04, 2020 1:59 pm
- 3
- Location: UK
- Status:
Offline
Difference between SkyWatcher Explorer 130 RA and 130M?
Hi,
The two scopes in the title are:
https://www.rothervalleyoptics.co.uk/sk ... drive.html
And
https://www.rothervalleyoptics.co.uk/sk ... scope.html
I was a bit confused by this:
- Is the only difference the multi-speed handset, and DC power/battery? How useful is the multi-speed handset?
-Do I need motorised tracking at all on this scope, let's say at 160x magnification (as without it is significantly cheaper)
Thanks!
The two scopes in the title are:
https://www.rothervalleyoptics.co.uk/sk ... drive.html
And
https://www.rothervalleyoptics.co.uk/sk ... scope.html
I was a bit confused by this:
- Is the only difference the multi-speed handset, and DC power/battery? How useful is the multi-speed handset?
-Do I need motorised tracking at all on this scope, let's say at 160x magnification (as without it is significantly cheaper)
Thanks!
---------------
5.1" SkyWatcher Explorer 130M EQ-2
4" SkyWatcher Heritage 100P Mini Dob
Greater London - Bortle 8
5.1" SkyWatcher Explorer 130M EQ-2
4" SkyWatcher Heritage 100P Mini Dob
Greater London - Bortle 8
- Refractordude
- Interdicted
- Articles: 0
- Posts: 1493
- Joined: Sun May 12, 2019 1:05 am
- 4
- Status:
Offline
-
TSS Awards Badges
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
At 166 magnification I would say a tracker is not needed. If I wanted a reflector around your price range I would get this https://www.firstlightoptics.com/beginn ... onian.html, and upgrade with a red dot finder if the stock finder is difficult to use. The 150mm aperture dob has a much better/very easier to use mount. Being a f/ 8 it will knock the planets and moon out the park.
- Refractordude
- Interdicted
- Articles: 0
- Posts: 1493
- Joined: Sun May 12, 2019 1:05 am
- 4
- Status:
Offline
-
TSS Awards Badges
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
Just recalled I have a review of a 6" f/ 8 dob . Right click the image.
- Lady Fraktor
- Universal Ambassador
- Articles: 0
- Posts: 9961
- Joined: Mon Apr 29, 2019 9:14 pm
- 4
- Location: Slovakia
- Status:
Offline
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
Tracking would be up to you, at higher magnifications for lunar and planetary it is a handy thing to have.flord.lord wrote: ↑Tue Jul 21, 2020 10:28 pm Hi,
The two scopes in the title are:
https://www.rothervalleyoptics.co.uk/sk ... drive.html
And
https://www.rothervalleyoptics.co.uk/sk ... scope.html
I was a bit confused by this:
- Is the only difference the multi-speed handset, and DC power/battery? How useful is the multi-speed handset?
-Do I need motorised tracking at all on this scope, let's say at 160x magnification (as without it is significantly cheaper)
Thanks!
The motor with hand control should give multiple speeds and some more convenience over a simple
Gabrielle
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
Az/Alt: AYO Digi II, Stellarvue M2C, Argo Navis encoders on both
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 (1011110)
The only culture I have is from yogurt
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
Az/Alt: AYO Digi II, Stellarvue M2C, Argo Navis encoders on both
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 (1011110)
The only culture I have is from yogurt
- flord.lord
- Earth Ambassador
- Articles: 0
- Posts: 49
- Joined: Thu Jun 04, 2020 1:59 pm
- 3
- Location: UK
- Status:
Offline
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
A 6"Refractordude wrote: ↑Wed Jul 22, 2020 12:06 am At 166 magnification I would say a tracker is not needed. If I wanted a reflector around your price range I would get this https://www.firstlightoptics.com/beginn ... onian.html, and upgrade with a red dot finder if the stock finder is difficult to use. The 150mm aperture dob has a much better/very easier to use mount. Being a f/8 it will knock the planets and moon out the park.
I ordered this : https://www.rothervalleyoptics.co.uk/sk ... scope.html but it's out of stock everywhere imaginable, so the ones in my original post are my other options, along with the non-motor driven: https://www.rothervalleyoptics.co.uk/sk ... scope.html.
I have considered the Explorer 130P, but it is more expensive and an
So I just have to decide on motor drive or no.
---------------
5.1" SkyWatcher Explorer 130M EQ-2
4" SkyWatcher Heritage 100P Mini Dob
Greater London - Bortle 8
5.1" SkyWatcher Explorer 130M EQ-2
4" SkyWatcher Heritage 100P Mini Dob
Greater London - Bortle 8
- Lady Fraktor
- Universal Ambassador
- Articles: 0
- Posts: 9961
- Joined: Mon Apr 29, 2019 9:14 pm
- 4
- Location: Slovakia
- Status:
Offline
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
An interesting looking new version of a EQ -2, it will be interesting to hear how stable it is.
The tripod can be stiffened up quite easily for less shake as well.
If thef/ 7 telescope has a corrector and spherical mirror they are not great for mid high powers and up without a lot of rework.
Spherical do work well whenf/ 10 or slower.
The tripod can be stiffened up quite easily for less shake as well.
If the
Spherical do work well when
Gabrielle
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
Az/Alt: AYO Digi II, Stellarvue M2C, Argo Navis encoders on both
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 (1011110)
The only culture I have is from yogurt
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
Az/Alt: AYO Digi II, Stellarvue M2C, Argo Navis encoders on both
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 (1011110)
The only culture I have is from yogurt
- flord.lord
- Earth Ambassador
- Articles: 0
- Posts: 49
- Joined: Thu Jun 04, 2020 1:59 pm
- 3
- Location: UK
- Status:
Offline
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
Do all spherical mirrors have correctors? Also, the spherical mirror focuses less light - does this mean I get less effectiveLady Fraktor wrote: ↑Wed Jul 22, 2020 5:57 pm An interesting looking new version of a EQ-2, it will be interesting to hear how stable it is.
The tripod can be stiffened up quite easily for less shake as well.
If the f/7 telescope has a corrector and spherical mirror they are not great for mid high powers and up without a lot of rework.
Spherical do work well when f/10 or slower.
---------------
5.1" SkyWatcher Explorer 130M EQ-2
4" SkyWatcher Heritage 100P Mini Dob
Greater London - Bortle 8
5.1" SkyWatcher Explorer 130M EQ-2
4" SkyWatcher Heritage 100P Mini Dob
Greater London - Bortle 8
- Lady Fraktor
- Universal Ambassador
- Articles: 0
- Posts: 9961
- Joined: Mon Apr 29, 2019 9:14 pm
- 4
- Location: Slovakia
- Status:
Offline
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
No they do not install correctors on all models of spherical mirrored reflectors.
Normally a Newtonian with a spherical mirror will have a long focal length to deal with the larger light cone produced.
They also will have a larger secondary mirror because of this compared to a same sized telescope with a parabolic mirror.
The first two you listed are the correct tube length to be a naturalf/ 6.92 and the Skywatcher website states they have a parabolic primary.
Normally a Newtonian with a spherical mirror will have a long focal length to deal with the larger light cone produced.
They also will have a larger secondary mirror because of this compared to a same sized telescope with a parabolic mirror.
The first two you listed are the correct tube length to be a natural
Gabrielle
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
Az/Alt: AYO Digi II, Stellarvue M2C, Argo Navis encoders on both
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 (1011110)
The only culture I have is from yogurt
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
Az/Alt: AYO Digi II, Stellarvue M2C, Argo Navis encoders on both
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 (1011110)
The only culture I have is from yogurt
- flord.lord
- Earth Ambassador
- Articles: 0
- Posts: 49
- Joined: Thu Jun 04, 2020 1:59 pm
- 3
- Location: UK
- Status:
Offline
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
I'm confused...the first two I listed (Explorer 130M and Explorer 130RA) 100% both have spherical mirrors. Also they have the standardLady Fraktor wrote: ↑Thu Jul 23, 2020 5:17 pm No they do not install correctors on all models of spherical mirrored reflectors.
Normally a Newtonian with a spherical mirror will have a long focal length to deal with the larger light cone produced.
They also will have a larger secondary mirror because of this compared to a same sized telescope with a parabolic mirror.
The first two you listed are the correct tube length to be a natural f/6.92 and the Skywatcher website states they have a parabolic primary.
---------------
5.1" SkyWatcher Explorer 130M EQ-2
4" SkyWatcher Heritage 100P Mini Dob
Greater London - Bortle 8
5.1" SkyWatcher Explorer 130M EQ-2
4" SkyWatcher Heritage 100P Mini Dob
Greater London - Bortle 8
- Lady Fraktor
- Universal Ambassador
- Articles: 0
- Posts: 9961
- Joined: Mon Apr 29, 2019 9:14 pm
- 4
- Location: Slovakia
- Status:
Offline
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
I did some digging around and the f/ 6.92 are a spherical mirror.
These telescopes are good for low and mid power sweeping/ viewing but do not do higher powers well nor are they suited forAP if you are thinking of doing that.
If built correctly (long focal length) spherical mirrors will lose some contrast and resolution due to the oversized secondary that is required.
These I doubt will have a larger secondary so the light cone will be clipped off.
Personally the Newtonian with a parabolic mirror are better all round telescopes.
These telescopes are good for low and mid power sweeping/ viewing but do not do higher powers well nor are they suited for
If built correctly (long focal length) spherical mirrors will lose some contrast and resolution due to the oversized secondary that is required.
These I doubt will have a larger secondary so the light cone will be clipped off.
Personally the Newtonian with a parabolic mirror are better all round telescopes.
Gabrielle
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
Az/Alt: AYO Digi II, Stellarvue M2C, Argo Navis encoders on both
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 (1011110)
The only culture I have is from yogurt
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
Az/Alt: AYO Digi II, Stellarvue M2C, Argo Navis encoders on both
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 (1011110)
The only culture I have is from yogurt
- terrynak
- Orion Spur Ambassador
- Articles: 0
- Posts: 808
- Joined: Sat Jun 08, 2019 3:58 am
- 4
- Location: Los Angeles
- Status:
Offline
-
TSS Awards Badges
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
I totally agree with Gabrielle - views with the 130/w spherical mirror will get soft at higher powers compared to the Explorer 130P, which has the parabolic mirror. A friend of mine had both types of 130mm Newts (spherical F/ 6.92 vs. parabolic F/ 5.0) and he was able to confirm this.
Phil Harrington (Star Ware) also recommended against this scope (reviewing the Orion SpaceProbe 130 version of it) because of the above and the weak EQ2 mount for this scope (130/900mmOTA ).
Phil Harrington (Star Ware) also recommended against this scope (reviewing the Orion SpaceProbe 130 version of it) because of the above and the weak EQ2 mount for this scope (130/900mm
Scopes: Reflectors, refractors, and 1 catadioptric. Ranging in aperture from 50mm to 150mm.
- notFritzArgelander
- In Memory
- Articles: 0
- Posts: 14925
- Joined: Fri May 10, 2019 4:13 pm
- 4
- Location: Idaho US
- Status:
Offline
-
TSS Awards Badges
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
One can ask the question in a different way. As the focal length increases the spherical mirror is a better approximation to a parabola. So one could ask "when, for a 5" scope, is a sphere as good as a parabola"?
For a 5" scope the focal ratio would have to be greater thanf/ D = 7.8. At f/ D = 6.92 these scopes will not be as good as parabola and should be avoided.
For a 5" scope the focal ratio would have to be greater than
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
- helicon
- Co-Administrator
- Articles: 592
- Posts: 12355
- Joined: Mon May 06, 2019 1:35 pm
- 4
- Location: Washington
- Status:
Online
-
TSS Awards Badges
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
I had an f/ 10 reflector on an EQ mount with a spherical mirror which worked just fine.
However, as others have stated a parabolic is highly recommended in shorter focal lengths.
However, as others have stated a parabolic is highly recommended in shorter focal lengths.
-Michael
Refractors: ES AR152 f/6.5 Achromat on Twilight II, Celestron 102mm XLT f/9.8 on Celestron Heavy Duty Alt Az mount, KOWA 90mm spotting scope
Binoculars: Celestron SkyMaster 15x70, Bushnell 10x50
Eyepieces: Various, GSO Superview, 9mm Plossl, Celestron 25mm Plossl
Camera: ZWO ASI 120
Naked Eye: Two Eyeballs
Latitude: 48.7229° N
Refractors: ES AR152 f/6.5 Achromat on Twilight II, Celestron 102mm XLT f/9.8 on Celestron Heavy Duty Alt Az mount, KOWA 90mm spotting scope
Binoculars: Celestron SkyMaster 15x70, Bushnell 10x50
Eyepieces: Various, GSO Superview, 9mm Plossl, Celestron 25mm Plossl
Camera: ZWO ASI 120
Naked Eye: Two Eyeballs
Latitude: 48.7229° N
- terrynak
- Orion Spur Ambassador
- Articles: 0
- Posts: 808
- Joined: Sat Jun 08, 2019 3:58 am
- 4
- Location: Los Angeles
- Status:
Offline
-
TSS Awards Badges
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
Michael, I'm thinking you're referring to the Edmund Palomar Jr. - the 4.25",
The famous Criterion RV-6 Dynascope (6") had a reputation for excellent performance despite its spherically shaped mirror at
Scopes: Reflectors, refractors, and 1 catadioptric. Ranging in aperture from 50mm to 150mm.
- notFritzArgelander
- In Memory
- Articles: 0
- Posts: 14925
- Joined: Fri May 10, 2019 4:13 pm
- 4
- Location: Idaho US
- Status:
Offline
-
TSS Awards Badges
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
The technical detail is whether a spherical mirror deviates from a parabolic mirror in a way that satisfies the Rayleigh criterion that a defect in the shape of a mirror should produce no more than a 1/4 wave error in the wave front.terrynak wrote: ↑Fri Jul 24, 2020 10:19 pm
Michael, I'm thinking you're referring to the Edmund Palomar Jr. - the 4.25",F/ 10 scope. Nice long focal length, given theaperture .
The famous Criterion RV-6 Dynascope (6") had a reputation for excellent performance despite its spherically shaped mirror atF/ 8.
In Jean Texereau's How to Make a Telescope the application of this is discussed in detail. On pp. 16-17 there are formulas and a table:
Measuring f and D in cm: f^3 = 34.9D^3.
Measuring in inches one gets: f^3 = 88.6D^3.
The table has
Both the examples you cite are "close enough" to parabolic so that within the Rayleigh criterion I wouldn't care about the difference between parabola and sphere. If the difference is smaller than what is required to have perfect optics, there is no functional difference. I wouldn't care whether the Edmund Palomar Jr or RV-6 Dynascope was advertised as a parabola or a sphere. Rayleigh has them as being equivalent.
I built an 8" f9 with a mirror that was spherical with only slight parabolizing. The table gives
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
- notFritzArgelander
- In Memory
- Articles: 0
- Posts: 14925
- Joined: Fri May 10, 2019 4:13 pm
- 4
- Location: Idaho US
- Status:
Offline
-
TSS Awards Badges
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
In the bolded quote I made a stupid typo. I apologize.notFritzArgelander wrote: ↑Fri Jul 24, 2020 10:45 pm
The technical detail is whether a spherical mirror deviates from a parabolic mirror in a way that satisfies the Rayleigh criterion that a defect in the shape of a mirror should produce no more than a 1/4 wave error in the wave front.
In Jean Texereau's How to Make a Telescope the application of this is discussed in detail. On pp. 16-17 there are formulas and a table:
Measuring f and D in cm: f^3 = 34.9D^3.
Measuring in inches one gets: f^3 = 88.6D^3.
The table has f/D = 7.0 for a 4" and f/D = 8.2 for a 6".
Both the examples you cite are "close enough" to parabolic so that within the Rayleigh criterion I wouldn't care about the difference between parabola and sphere. If the difference is smaller than what is required to have perfect optics, there is no functional difference. I wouldn't care whether the Edmund Palomar Jr or RV-6 Dynascope was advertised as a parabola or a sphere. Rayleigh has them as being equivalent.
I built an 8" f9 with a mirror that was spherical with only slight parabolizing. The table gives f/D = 9.6 for a 10".... So a REALLY long tube.
It should be:
Measuring f and D in cm: f^3 = 34.9D^4.
Measuring in inches one gets: f^3 = 88.6D^4.
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
- terrynak
- Orion Spur Ambassador
- Articles: 0
- Posts: 808
- Joined: Sat Jun 08, 2019 3:58 am
- 4
- Location: Los Angeles
- Status:
Offline
-
TSS Awards Badges
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
An 8" F9 Newt means a scope 1803mm long or almost 6 ft. in focal length!notFritzArgelander wrote: ↑Fri Jul 24, 2020 10:45 pm
The technical detail is whether a spherical mirror deviates from a parabolic mirror in a way that satisfies the Rayleigh criterion that a defect in the shape of a mirror should produce no more than a 1/4 wave error in the wave front.
In Jean Texereau's How to Make a Telescope the application of this is discussed in detail. On pp. 16-17 there are formulas and a table:
Measuring f and D in cm: f^3 = 34.9D^3.
Measuring in inches one gets: f^3 = 88.6D^3.
The table has f/D = 7.0 for a 4" and f/D = 8.2 for a 6".
Both the examples you cite are "close enough" to parabolic so that within the Rayleigh criterion I wouldn't care about the difference between parabola and sphere. If the difference is smaller than what is required to have perfect optics, there is no functional difference. I wouldn't care whether the Edmund Palomar Jr or RV-6 Dynascope was advertised as a parabola or a sphere. Rayleigh has them as being equivalent.
I built an 8" f9 with a mirror that was spherical with only slight parabolizing. The table gives f/D = 9.6 for a 10".... So a REALLY long tube.
I was lucky enough to find a 5"
Bresser currently markets a 130/1000mm or
Flord.lord, if you still want a long focal length 5" Newtonian, the Bresser scope is the one to get. Here's the link:
https://www.bresser.de/en/Astronomy/Tel ... scope.html
Scopes: Reflectors, refractors, and 1 catadioptric. Ranging in aperture from 50mm to 150mm.
- notFritzArgelander
- In Memory
- Articles: 0
- Posts: 14925
- Joined: Fri May 10, 2019 4:13 pm
- 4
- Location: Idaho US
- Status:
Offline
-
TSS Awards Badges
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
Yes, and the mount I built for it was a beast. :sigh:terrynak wrote: ↑Sat Jul 25, 2020 1:19 amAn 8" F9 Newt means a scope 1803mm long or almost 6 ft. in focal length!notFritzArgelander wrote: ↑Fri Jul 24, 2020 10:45 pm
The technical detail is whether a spherical mirror deviates from a parabolic mirror in a way that satisfies the Rayleigh criterion that a defect in the shape of a mirror should produce no more than a 1/4 wave error in the wave front.
In Jean Texereau's How to Make a Telescope the application of this is discussed in detail. On pp. 16-17 there are formulas and a table:
Measuring f and D in cm: f^3 = 34.9D^3.
Measuring in inches one gets: f^3 = 88.6D^3.
The table has f/D = 7.0 for a 4" and f/D = 8.2 for a 6".
Both the examples you cite are "close enough" to parabolic so that within the Rayleigh criterion I wouldn't care about the difference between parabola and sphere. If the difference is smaller than what is required to have perfect optics, there is no functional difference. I wouldn't care whether the Edmund Palomar Jr or RV-6 Dynascope was advertised as a parabola or a sphere. Rayleigh has them as being equivalent.
I built an 8" f9 with a mirror that was spherical with only slight parabolizing. The table gives f/D = 9.6 for a 10".... So a REALLY long tube.
Yes, that would be a good performer.I was lucky enough to find a 5" F/8 Newt (127/1020mm) - the Meade 127NT, which was available only in '97/'98 before it was discontinued. Fits the Rayleigh criterion for a spherical, but someone mentioned that it has a parabolic mirror as well. Came with a LXD 500A mount, with a payload capacity of 15 lbs (according to manual). Very sturdy mount for an OTA this size.
Bresser currently markets a 130/1000mm or F/7.7 Newt in Europe (Messier NT-130/1000 EXOS-1) - like the Meade above, it may even have a parabolic mirror as well (may not make a noticeable difference with a spherical at high magnifications, but still nice to have); the EXOS-1 mount also has a payload of 15 lbs.
Flord.lord, if you still want a long focal length 5" Newtonian, the Bresser scope is the one to get. Here's the link:
https://www.bresser.de/en/Astronomy/Tel ... scope.html
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
- terrynak
- Orion Spur Ambassador
- Articles: 0
- Posts: 808
- Joined: Sat Jun 08, 2019 3:58 am
- 4
- Location: Los Angeles
- Status:
Offline
-
TSS Awards Badges
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
notFritzArgelander wrote: ↑Sat Jul 25, 2020 1:55 amAn 8" F9 Newt means a scope 1803mm long or almost 6 ft. in focal length!I built an 8" f9 with a mirror that was spherical with only slight parabolizing. The table gives f/D = 9.6 for a 10".... So a REALLY long tube.
Yes, and the mount I built for it was a beast. :sigh:
I was going to ask about the mount (and whether it was anYes, that would be a good performer.
I was able to pick up a Bresser 150/1200mm
Scopes: Reflectors, refractors, and 1 catadioptric. Ranging in aperture from 50mm to 150mm.
- notFritzArgelander
- In Memory
- Articles: 0
- Posts: 14925
- Joined: Fri May 10, 2019 4:13 pm
- 4
- Location: Idaho US
- Status:
Offline
-
TSS Awards Badges
Re: Difference between SkyWatcher Explorer 130 RA and 130M?
This was in the mid 1960s before the "Dobsonian revolution" rebranded altazimuth mounts. The original mount was a crude equatorial mount made from pipe fittings with no provision for latitude adjustment...... One had to be careful to not screw theterrynak wrote: ↑Sat Jul 25, 2020 2:26 amnotFritzArgelander wrote: ↑Sat Jul 25, 2020 1:55 amAn 8" F9 Newt means a scope 1803mm long or almost 6 ft. in focal length!I built an 8" f9 with a mirror that was spherical with only slight parabolizing. The table gives f/D = 9.6 for a 10".... So a REALLY long tube.Yes, and the mount I built for it was a beast. :sigh:I was going to ask about the mount (and whether it was anYes, that would be a good performer.
EQ orDob ) on my previous post but decided to hold back...
I was able to pick up a Bresser 150/1200mmOTA new from a seller who managed to get a hold of a few of these, as well as a few 130/1000 OTAs. Should have snapped up a Bresser 130/1000OTA as well, even though I already had the older Meade 127NT. Seriously thought about it, but never managed to pull the trigger.
I'm sure you would have been pleased with those views. The designs are sound.
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
Create an account or sign in to join the discussion
You need to be a member in order to post a reply
Create an account
Not a member? register to join our community
Members can start their own topics & subscribe to topics
It’s free and only takes a minute