Orion Astroview 90 vs. 6” f/8 Newtonian

Orion Astroview 90 vs. Homebuilt 6” f/8 Newtonian w/Parks Optics

OK, here’s the comparison I promised, right on schedule (the weatherman finally called it right days in advance!)

First of all, a few comments and report on seeing conditions. Thursday was a great night to do this test since both Saturn and Jupiter were well placed in the sky and seeing was excellent.

It would be unfair not to preface this with a comment on the optics in the reflector. Parks makes excellent production mirrors, better than most. If one is to make a decision between an Orion and similar 6 inch Dob and the AstroView, I don’t think the comparison would be quite the same. I wouldn’t expect the same quality from Orion that I expect from Parks. That being said…

To begin, I used a 12.5mm Ortho in the Newt and a 9mm Ortho in the AstroView and aimed at Saturn. This yielded powers of 98 and 101 respectively. Seeing was steadier in the AstroView, although both were above acceptable. There were LENGTHY periods of steady seeing in the smaller aperture scope, and this provided more opportunity to view detail. Not a surprise. Steady moments were rarer in the Newt, and the glare from sheer brightness washed out some detail.

The South Polar Region yielded more detail in the 90, it was just easier to see. A neutral density, colored, or polarizer filter would fix the obscuring brightness for larger apertures such as 6 inch but for this test I used no filters. Cassini was sharp and clear in the 90, and the same was true of the 6 but only during moments of steady seeing. The shadow of the globe on the back of the ring system was easier in the AstroView as well. But in those good moments, detail was a bit sharper in the 6. The South Equatorial Belt was obvious in both scopes. The view in the 6 was pretty bad in rare moments when the seeing acted up. The 90 had no such problems.

Then I switched the 9mm to the 6 incher, and put a 7mm Ortho in the AstroView, yielding 135x in the Newt and 130 in the 90mm. Now the Newtonian started to do its stuff due to the reduced brightness. Still, seeing was a factor but no problem for the AstroView. At this point it was a very close contest, in fact, pretty much strictly a matter of taste. The brighter image in the 6-inch was now at a more comfortable level than the AstroView, which was a bit dim. Still, no problem making out lots of detail in either. I’d say I preferred the brighter image in the 6 at higher powers, but preferred the steadiness of the image in the 90. I could see the same amount of detail in either, both provided excellent views.


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Both scopes also showed a faint shroud of light around the planet. Neither was objectionable to me. The refractor, of course, had its due share of violet, and the Newt, even though recently cleaned, showed glare from the inside of the tube and diffracted light from the secondary obstruction. For me, that settles that debate… both types have extra light floating around if you look for it.

OK, on to Jupiter. I still had the 130x – 135x EP’s in the scopes. Jupiter was awesome in the Newt during steady moments. Red Spot, bright pink (anyone notice nice coloring in GRS this year?) A paler section to the east. Nice contrast! Festoon city! Detailed voids in the SEB and NEB. Knots, spots, a feast! Too bad there were no transits last night.

In the refractor, almost the same, but not quite. The dimmer image cost a very small amount of detail, but with patience I could see everything I could see in the 6. I think this is amazing performance for a scope just over half the size! And, as mentioned above, I’m comparing a Chinese objective to a Parks mirror. Another round of Kudos for Chinese refractors. I’d have to say if this was my first scope, and I eventually learned to see well as would be necessary with ANY scope, I’d be absolutely thrilled with the views.

Unfortunately, clouds set in before I could push the power. But the views were so excellent I have no regrets.

I like the refractor. Again, as I have said before in the forum, I like to sit down. I adjusted the refractor tube a little forward from balance to make the height of the EP just right for sitting with my elbows comfortably on my knees, supporting my chin. Very relaxing. The Newt, yes, brighter, but I had to stand in a crooked position to look into the EP and I’d call it a night earlier than I would with a refractor, especially considering the sometimes wavier image in the larger aperture. The larger reflector didn’t reveal any more detail than the 90, but the detail was a little sharper.

If you prefer to be comfortable while viewing, or have small kids around, and enjoy steadier seeing, and have a primary interest in lunar/planetary, the refractor would be the way to go. You will certainly see more planetary detail in a refractor than in a less-than-perfectly collimated reflector. And I remind you, this comparison was done with a Parks mirror with probably a 1/10 wave surface error or less with a two-vane spider and reduced secondary obstruction (1-inch). You won’t get this performance in the average Dob. To mention a 90mm in the same breath as this scope is a credit to the AstroView.

However, I will not claim equality in any way on DSO’s between a 90mm aperture and a six-inch aperture. You makes your choices and you lays your money down. If you want deep-sky performance, and don’t mind learning to collimate WELL, and you don’t mind sometimes awkward viewing positions, then a 6-inch Dob with excellent optics would be a better choice.

Update... I shot some pics with the AstroView 90 last night, here they are or those of you who wonder what you can do with a small scope. Keep in mind I'm not the world's greatest astrophotographer!

Note the detail in Saturn's rings and polar region. I think this is pretty good for 90mm.

Bob

Attached Image:

>>If one is to make a decision between an Orion and similar 6 inch Dob and the AstroView, I don’t think the comparison would be quite the same. I wouldn’t expect the same quality from Orion that I expect from Parks. That being said…

Maybe not, but these days the Chinese seem to be making some excellent mirrors. Gary Hand reported that the 10 inch F5 mirrors he tested were all 10th wave or better. Given the ease of making a 6 inch F8 mirror vs. a 10 inch F5 mirror, I would expect the Orion scope to do just fine.

Jon

I would not call a night with moments of steady seeing at 100x "great seeing."

I just can't imagine recommending a 90mm achromat (even if it is f/10) over a 6 inch Newtonian for viewing planets. I have a very nice 102mm ED refractor that I put on my C14 and I routinely get to check the refractor's performance. When you start pushing the 4" refractor into good observing territory, 130x and over, it gets too dim.

I also think that views of planets at 100x don't tell us much. That's what I get with a 40mm in my C14. At that power it shows more than the 102mm at the same power, but "nothin' to write home about."

The view in my 5" refractor of Jupiter etc. is quite good and shows enough detail to maintain interest. It doesn't show the color and festoon detail that the 14" does but it is enough to maintain interest. I have seen here and there people say "get a 90mm refractor" for planet viewing over an 8 inch Newt etc but gosh 'n' golly a 90mm scope on a cheap EQ mount is not what I would nominate for a newbie. I see however that there are some very positive user reviews posted. One person said it was a lot better than his dept store scope. That, I can believe.

regards
Greg N