Difference between SkyWatcher Explorer 130 RA and 130M?

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terrynak
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Re: Difference between SkyWatcher Explorer 130 RA and 130M?

#21

Post by terrynak »


Heh Heh, I would love to have looked through that scope! Never seen an 8" F/9 Newtonian before...
Scopes: Reflectors, refractors, and 1 catadioptric. Ranging in aperture from 50mm to 150mm.
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Re: Difference between SkyWatcher Explorer 130 RA and 130M?

#22

Post by notFritzArgelander »


terrynak wrote: Sat Jul 25, 2020 4:53 am Heh Heh, I would love to have looked through that scope! Never seen an 8" F/9 Newtonian before...
It was a planet killer and great on globs. BTW Gary Seronik has built a 6" f9. At the time I made my own optics.

https://garyseronik.com/the-big-red-one ... /#more-141
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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terrynak
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Re: Difference between SkyWatcher Explorer 130 RA and 130M?

#23

Post by terrynak »


notFritzArgelander wrote: Sat Jul 25, 2020 5:42 am
terrynak wrote: Sat Jul 25, 2020 4:53 am Heh Heh, I would love to have looked through that scope! Never seen an 8" F/9 Newtonian before...
It was a planet killer and great on globs. BTW Gary Seronik has built a 6" f9. At the time I made my own optics.

https://garyseronik.com/the-big-red-one ... /#more-141

Re: planet and glob killer - I bet! Thanks for the Seronik article - now I know what a 6" F/9 Newt looks like. Of course, yours would have been slightly bigger.

Tim, the guy who I used to get a lift with to the RTMC (Riverside Telescope Makers Conference) still makes scopes - as well as collecting older classic scopes. There were old timer scope-makers still putting up scopes in the DIY competition - its too bad the RTMC is no more (ended last year). I remember seeing Gary Seronik there one year.

The longest focal length Newtonian (relative to the aperture) that I've seen is the 4.25" Edmunds Palomar Jr. (F/10), that someone was selling at the RTMC.
Scopes: Reflectors, refractors, and 1 catadioptric. Ranging in aperture from 50mm to 150mm.
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Re: Difference between SkyWatcher Explorer 130 RA and 130M?

#24

Post by flord.lord »


terrynak wrote: Sat Jul 25, 2020 1:19 am
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.
An 8" F9 Newt means a scope 1803mm long or almost 6 ft. in focal length!

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
Thanks for the suggestion, but I ended up pulling the trigger on the Explorer 130M due to the BBC Sky at Night magazine and customer reviews. It's been cloudy across the pond but have tested it on some distant objects and the view through the 25mm (the "good" modified achromat) is nice and crisp. I think I might replace the 52° Super MA 10mm with a Svbony 62° "goldline" eyepiece, which I've heard have a nice price:quality ratio. The biggest hurdle for me has been the mounting: I am pretty proficient in RA and Dec. axes but need to learn the slo mo controls. Balancing was a big one too.

I need to improve on polar alignment and moving the scope when you can't actually see the controls.

Another thing is the portability and the weight; I got a bit carried away while purchasing! Has to be completely assembled and reassembled when I move it between floors and is a challenge for a small sportswagon boot (trunk?)

I hope to target planets/DSOs tonight!
---------------
5.1" SkyWatcher Explorer 130M EQ-2
4" SkyWatcher Heritage 100P Mini Dob

Greater London - Bortle 8
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Re: Difference between SkyWatcher Explorer 130 RA and 130M?

#25

Post by terrynak »


flord.lord wrote: Sat Jul 25, 2020 11:16 am Thanks for the suggestion, but I ended up pulling the trigger on the Explorer 130M due to the BBC Sky at Night magazine and customer reviews. It's been cloudy across the pond but have tested it on some distant objects and the view through the 25mm (the "good" modified achromat) is nice and crisp. I think I might replace the 52° Super MA 10mm with a Svbony 62° "goldline" eyepiece, which I've heard have a nice price:quality ratio. The biggest hurdle for me has been the mounting: I am pretty proficient in RA and Dec. axes but need to learn the slo mo controls. Balancing was a big one too.

I need to improve on polar alignment and moving the scope when you can't actually see the controls.
Another thing is the portability and the weight; I got a bit carried away while purchasing! Has to be completely assembled and reassembled when I move it between floors and is a challenge for a small sportswagon boot (trunk?)

I hope to target planets/DSOs tonight!
Congrats on your new scope F.L (despite all the comments you've seen on this thread)!

You should see a difference in the brightness in the DSOs targeted previously - as well as seeing stars in the globulars that were previously just fuzzy balls.

I used the Orion Sky Scanner/Skywatcher Heritage 100P for about two and a half years before I eventually got to a 114/900mm Newt - same focal length as your new scope and spherical mirror as well, but with a smaller 114mm aperture (4.5"), a focal ratio of F/7.9 (compared to your F/6.9). We won't get into the pros/cons of that! Only a 14mm increase in aperture compared to your 30mm increase, but still a marked improvement.

It was great to reach higher magnifications with this scope compared to the Sky Scanner without having to use a Barlow. Easier to pick up smaller/fainter galaxies which requires higher magnifications than with the previous scope as well.

If you can get a soft-carry bag/case for it, which can hold tripod, scope, and counterweight - that would be ideal. Orion has a telescope bag that was made to fit your scope - its for the Orion Spaceprobe 130 which is exactly identical to the SW Explorer 130M in both tube and EQ mount (made by the same manufacturer). Here's the link:

https://www.telescope.com/catalog/produ ... sembleId=5

I used my 114/900mm scope on a alt-az mount for about a year until I switched over to the EQ mount. Took a while before I learned how to use an EQ.

I also have a 127/1020mm Newtonian as well - 3mm shorter in aperture to yours, but an increased focal length (F/8).

I still have my Orion SkyScanner - use it occasionally at home, but mainly used as a travel scope. Took it to Australia with me last December and used it to pick up galaxies not visible from our Hemisphere.

Again, enjoy your new scope!
Scopes: Reflectors, refractors, and 1 catadioptric. Ranging in aperture from 50mm to 150mm.
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Re: Difference between SkyWatcher Explorer 130 RA and 130M?

#26

Post by flord.lord »


terrynak wrote: Sat Jul 25, 2020 10:10 pm
switched over to the EQ mount. Took a while before I learned how to use an EQ.
This basically summarises last night :? !

Got rough polar alignment (I think) by putting Dec. at 90° and "sighting" down the RA axis at Polaris.

Let me just say (as I'm sure you're aware) going from a tabletop base to an EQ (skipping an altaz!) is daunting!

I was so near M13 when...the slow motion control cable fell off the tripod!! :flame: How do I stop that?

Some other bugbears include:
The telescope hitting the tripod
The telescope hitting the cables
Not being able to move it in *that* place in an altaz direction
The altaz base lock not staying and having to re-polar align

Anyway...it's obviously a learning curve. I'm interested in how long it took you/takes people to learn?

Apologies for the rant...
---------------
5.1" SkyWatcher Explorer 130M EQ-2
4" SkyWatcher Heritage 100P Mini Dob

Greater London - Bortle 8
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Re: Difference between SkyWatcher Explorer 130 RA and 130M?

#27

Post by terrynak »


flord.lord wrote: Sun Jul 26, 2020 8:02 am
terrynak wrote: Sat Jul 25, 2020 10:10 pm
switched over to the EQ mount. Took a while before I learned how to use an EQ.
This basically summarises last night :? !

Got rough polar alignment (I think) by putting Dec. at 90° and "sighting" down the RA axis at Polaris.

Let me just say (as I'm sure you're aware) going from a tabletop base to an EQ (skipping an altaz!) is daunting!

I was so near M13 when...the slow motion control cable fell off the tripod!! :flame: How do I stop that?

Some other bugbears include:
The telescope hitting the tripod
The telescope hitting the cables
Not being able to move it in *that* place in an altaz direction
The altaz base lock not staying and having to re-polar align

Anyway...it's obviously a learning curve. I'm interested in how long it took you/takes people to learn?

Apologies for the rant...

I didn't use my EQ mounts for about a year - used alt-azimuth mounts on my Newtonians instead.

Later I came across this excellent training video from Eyes in the Sky:



This video demonstrates how to slew your telescope to the desired target using an EQ.

Once I watched the video, I was able to get the hang of using an EQ fairly quickly. Shortened the learning curve immensely!

To avoid the cables getting in the way of the telescope, I replaced them with radio/control knobs - available at any electronics or hardware store. As for your cable falling off the tripod, it was probably because the screw on the cable wasn't tightened enough to the shaft.

Hope this helps.
Scopes: Reflectors, refractors, and 1 catadioptric. Ranging in aperture from 50mm to 150mm.
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