Better Telescope?

Dec 21, 2020
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Does anyone have any thoughts on the Orion Starblast 4.5 vs. the Gskyer 600x90 AZ as a first telescope? Any information on the differences between the two or advantages or one over the other would be appreciated. Price isn’t a factor as the cost of the 4.5 with kit made them about equal.
 
Aug 29, 2020
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In 1970 I designed 9* C.A. telescope for MSS Multi-Spectral-Scanner (depicted) that took 1st compleat photos of planet Earth (Photos in every Atlas, 30m res)

1st the Orion 4.5"C.A. is 114.3 mm (10,261mm*2) vs 90mm C.A. (6,362mm*2) for greater photon gathering Clear Aperture by factor of 1.61 or 61% more light but Larger dia (C.A.=Clear Aperture) also means higher RESOLUTION & that counts IF U want to see sharp edges of moon craters, saturn rings, etc

2nd Orion Starburst uses a Reflective Mirror that's also PARABOLIC so U don't get purrfect reflection to focus of distant objects, one step better than a spherical optic> A mirror has no color aberations whereas a Refractor glass lens will have some dispersion of different colors & color distortion> A Refractor lens is like a stack of prisms that bend light as if it were a rainbow to steer light onto focus, but slight differences in angle for eash "rainbow" light color leads to image distortion by smearing different colors off of point> A Reflecting Mirror has no such issues

That's why MSS was a reflecting telescope w/a parabolic primary but a shpherical secondary b/c its secret was the Semi-Kinematic Truss aimed its CENTROID at the center of radius of 2nd mirror> U could strike it w/a ball peen hammer and the 'scope would NOT DEFOCUS> Perkin Elmer Corp built the MSS telescope & told me it was the BEST they'd ever built b/c of that feature (PE built Hubble too)

Also noticed Orion has a 2X Barlow lens> sorta' a supercharger for amplyfying the IMAGE U will observe from your basic F/4 telescope> F/4 means Focal length is 4 times C.A. or only 18" to keep scope length short b/c the image produced by the primary has to be in a position where your eyepiece can observe it> The MSS had a 4 foot (48") focal length so F/# was 48"/9"=F/5.3> Orion F./4 is a bit faster When they say "Fast" they mean the photons collected by C.A. R brought into focus quickly (shortened so U can get a compact tlescope, but NOT too fast b/c U still want sharp resolution and that's another reason for a Reflector, it can be fast

So in closing, I'd take the ORION Reflector telescope that I surmise is a Newtonian design wherein primary reflects a sharp image up to a flat mirror that folds the image beam out towards the eyepiece for viewing>

I built a Dobson Side Walk Astronomer telescope in 1994 w/a 69" focal length U can measure F.L. by shining a flashlight into your scope from a distance & holding a piece of white paper next to the flashlight & move towards telescope until flashlight IMAGE on paper exactly matches REAL flashlight & then U R at twice the focal length> U can measure it w/in a fraction of an inch if U nudge it

In 1979 I published a paper in Machine Design on Simplified Optics wherein I used dimensional analysis to combine Paraxial Equations of Optics into only 2 equations> Image location & Magnification> It shows 1 to 1 magnification at 2 focal lengths> Gave it to "Bible of Optics" by Melles Griot, they loved it & used it to expand into laser beams> Give me an email address & I'll send a copy
Cordially,
Roger E Carmichael, BSME
Man, the MSS design was 50yrs ago> Never told anyone its secret 'till now b/c during the Cole War we had to keep the lid on it lest Commies get ahold of it
 
Dec 29, 2020
11
3
15
Does anyone have any thoughts on the Orion Starblast 4.5 vs. the Gskyer 600x90 AZ as a first telescope? Any information on the differences between the two or advantages or one over the other would be appreciated. Price isn’t a factor as the cost of the 4.5 with kit made them about equal.
My only suggestion would be to go for the largest diameter you can get. Everything else can be added on later.

Put all of the available money into getting a scope with the largest diameter mirror you can get.

Definitely do not choose a 90 mm (3.5-inch) over a 4.5-inch.

If you can afford a 4.5-inch then you can probably afford a 6-inch. And an 8-inch is only a little more. And so is a 10-inch which is so much better.

A rule of thumb for magnification versus diameter (for reflectors, I think) is 50x per inch of diameter. You can insert eyepieces that will make if magnify more, but then you get a dimmer image with changed colors that is difficult to focus.

I would shop around a little more, first. There must be larger scopes for almost the same price.

Cheers,

Tom Gootee
 
Aug 29, 2020
18
10
15
In 1970 I designed 9* C.A. telescope for MSS Multi-Spectral-Scanner (depicted) that took 1st compleat photos of planet Earth (Photos in every Atlas, 30m res)

1st the Orion 4.5"C.A. is 114.3 mm (10,261mm*2) vs 90mm C.A. (6,362mm*2) for greater photon gathering Clear Aperture by factor of 1.61 or 61% more light but Larger dia (C.A.=Clear Aperture) also means higher RESOLUTION & that counts IF U want to see sharp edges of moon craters, saturn rings, etc

2nd Orion Starburst uses a Reflective Mirror that's also PARABOLIC so U get purrfect reflection to focus of distant objects, one step better than a spherical optic> A mirror has no color aberations whereas a Refractor glass lens will have some dispersion of different colors & color distortion> A Refractor lens is like a stack of prisms that bend light as if it were a rainbow to steer light onto focus, but slight differences in angle for eash "rainbow" light color leads to image distortion by smearing different colors off of point> A Reflecting Mirror has no such issues

That's why MSS was a reflecting telescope w/a parabolic primary but a shpherical secondary b/c its SECRET was the Semi-Kinematic Truss aimed its CENTROID at the center of radius of 2nd mirror> U could strike it w/a ball peen hammer and the 'scope would NOT DEFOCUS> Perkin Elmer Corp built the MSS telescope & told me it was the BEST they'd ever built b/c of that feature (PE built Hubble too)

Also noticed Orion has a 2X Barlow lens> sorta' a supercharger for amplifying the IMAGE U will observe from your basic F/4 telescope> F/4 means Focal length is 4 times C.A. or only 18" to keep scope length short b/c the image produced by the primary has to be in a position where your eyepiece can observe it> The MSS had a 4 foot (48") focal length so F/# was 48"/9"=F/5.3> Orion F./4 is a bit faster When they say "Fast" they mean the photons collected by C.A. R brought into focus quickly (shortened so U can get a compact telescope, but NOT too fast b/c U still want sharp resolution and that's another reason for a Reflector, it can be fast

So in closing, I'd take the ORION Reflector telescope that I surmise is a Newtonian design wherein primary reflects a sharp image up to a flat mirror that folds the image beam out towards the eyepiece for viewing>

I built a Dobsonian 10"C.A. Side Walk Astronomer telescope in 1994 w/a 69" focal length that I later "Stopped Down" to 8"dia. by laying an auto air clnr on top of primary> (For backyard astronomy 10" C.A. is cost-effective size limit) Used a Sona-Tube concreate tube for main hsg and in pollishing the mirror the SECRET is in final stages of fine grit, put a 4" FOAM slab over polishing tool & lay a 7.5 lb weight on top of the foam for PURRFECT pressure on to do polish

U can measure F.L. by shining a flashlight into your scope from a distance & holding a piece of white paper next to the flashlight & move towards telescope until flashlight IMAGE on paper exactly matches REAL flashlight & then U R at twice the focal length> U can measure it w/in a fraction of an inch if U nudge it

In 1979 I published a paper in Machine Design on Simplified Optics wherein I used dimensional analysis to combine Paraxial Equations of Optics into only 2 equations> Image location & Magnification> It shows 1 to 1 magnification at 2 focal lengths> Gave it to "Bible of Optics" by Melles Griot, they loved it & used it to expand into laser beams> Give me an email address & I'll send a copy
Cordially,
Roger E Carmichael, BSME
Man, the MSS design was 50yrs ago> Never told anyone its secret 'till now b/c during the Cole War we had to keep the lid on it lest Commies get ahold of it
 

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