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Something for nothing: Celestron C90

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#151 pdxmoon

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Posted 17 July 2013 - 12:09 PM

I have mine mounted on a Meade AZ3 mount. I suspect any similar mount would work fine. Even pointing at vertical it holds position well.

Here's a link that shows the mount:
http://www.meade.com.../az_series.html


Do you use the clamshell with that Meade mount, or have you reconfigured the head?

#152 jrbarnett

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Posted 17 July 2013 - 01:13 PM

http://ts2.mm.bing.n...897169&pid=15.1

I'd guess "neither". It looks like that mount comes standatd with a 1/4-20 stud threaded up through the saddle. The tappings on the bottom of the C90's dovetail will let you thread the OTA directly onto the mount.

Regards,

Jim

#153 caheaton

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Posted 17 July 2013 - 01:35 PM

The mount comes with a dovetail saddle, so I just clamp the mount to the dovetail on the C90.

Here's a photo of the same mount with my 80ED mounted on it. It shows the short dovetail saddle clamped to the scope. (The 80 is a bit heavy for that mount, but it works as long as I don't point the scope anywhere near vertical...I've since moved the scope to a different mount and use the AZ3 for the C90).

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  • 5976133-az3.jpg


#154 pdxmoon

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Posted 17 July 2013 - 03:39 PM

Friends, does this have a regular threaded tripod female side so I could find a goodwill tripod for grab and go?

#155 PeterR280

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Posted 17 July 2013 - 04:42 PM

It has a regular camera type thread for a photo tripod.

#156 tnakazon

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Posted 17 July 2013 - 08:48 PM

... Regarding right angle brackets, if you are handy its not to difficult to make your own, or get the one from Orion ($30) that fits the various marks of the Versago, buy the Vixen unit and its close to $100, way over priced for what it is,DA.


Yes, the Vixen Porta Multi-Plate is way overpriced. Regarding the Orion L-bracket, the 1/4-20 mounting stud doesn't look like it will securely hold the C90 in place via the bottom of the fixed dovetail, either on my Vixen Mini-Porta or the VersaGo II. I'd rather have the C90 on a mount with a dovetail saddle. So I'll try it on my Astromaster CG2 & CG3 mounts, despite being not so grab-and-go-able GEMs.

#157 Binojunky

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Posted 18 July 2013 - 10:35 AM

It holds my C90 fine and I have mounted my Apex 127 Mak with it with no issues other than a bit of the jiggles when focusing and that was the aluminum legs on the tripod,DA.

#158 SantanuRoy

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Posted 18 July 2013 - 05:48 PM

Hi Jim,

I am new to astronomy and astrophotography. I have some novice sort of queries.

I own a Skywatcher 15012 Reflector telescope (i.e., 150 mm aperture and 1200 mm FL) on a EQ3-2 mount. I do AP with that using my Nikon D90 DSLR. I have attached an image of the Jupiter taken on 13-Oct-2011 at 23:56 hrs.

The problem with the Skywatcher 15012 is that it is huge in size, hence not very easy to transport.

From this discussion thread I have learnt a lot about the Celestron C90 MAK Spotting Scope. My questions are:

1. If I bye this C90 MAK Spotting Scope since it is handy and easily transportable, how much satisfied will I be with its images (through naked eye, as well as camera) as compared to the Skywatcher Reflector mentioned?
2. Also, how much AP will be possible with it (i.e., I am talking about the image quality with the C90 MAK)? I chiefly do planetary imaging but plan to photograph DSOs also in future.

Thanks in advance.

Santanu

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#159 tnakazon

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Posted 18 July 2013 - 09:48 PM

It holds my C90 fine and I have mounted my Apex 127 Mak with it with no issues other than a bit of the jiggles when focusing and that was the aluminum legs on the tripod,DA.

Re: Orion dovetail L-bracket, that's good to know, thanks. Still, I'll try the C90 on my Astromaster CG2 and/or CG3 mounts first.

#160 jrbarnett

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Posted 19 July 2013 - 04:03 PM

Hi Santanu.

I'm not much of an imager, so take my opinions with a grain of salt, but I think that the tiny rear baffle diameter and long focal length for its modest aperture make this a less than optimal night time imaging platform. On the other hand, I've seen some very nice daylight nature images taken using the scope.

My use for the C90 has been 100%visual to this point, though I may try some daylight imaging next month on vacation.

Regards,

Jim

#161 jrbarnett

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Posted 19 July 2013 - 04:16 PM

I use a dual saddled DSV-1.

http://www.desertsky....com/DSV-1.html

Regards,

Jim

#162 314Sprout

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Posted 19 July 2013 - 04:59 PM

A dual saddle DSV-1 is ideal for this telescope. Throw an AT-72 (Green, pink, doesn't matter!) on the other side as a finder, and the orientation of the C-90's finder mount is irrelevant.

#163 jag767

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Posted 19 July 2013 - 10:31 PM

So I have just been comparing this scope to my 102mm f10 refractor. It goes without saying there are definite differences, but out of curiousity I put both on the Cat's eye nebula. Considering I am in an extremely light polluted area, and what I can see isnt all that amazing to begin with, this little guy came very very close to the refractor.

#164 tnakazon

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Posted 20 July 2013 - 02:44 PM

Interesting finding - I need to dig out my C90 which I haven't used in almost a year and do some shootouts with my other scopes having a similar aperture as this Mak.

#165 Starman81

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Posted 04 December 2013 - 05:28 PM

I stumbled onto this scope while perusing OpticsPlanet's website. They have a site-wide 10% off sale, bringing this package down from $164.99 to $148.49--great deal! Then I saw this thread... I had to bite!

I already have an L-bracket to use it with on the AT Voyager mount and will try it out with the same on the SLT Mount. It could be a match made in heaven for lightweight grab'n'go setup with the option to have tracking & GoTo or not, depending on the mount used. I am well aware that cooling issues will have to make a more 'pre-planned' grab'n'go but I am okay with that. I will use it on the Moon, planets and double stars mainly.

#166 wcstarguy

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Posted 06 December 2013 - 11:12 PM

Here is my C90 and the Orion L Bracket on my pipe mount with my Orion GoScope 80. Works very well. Sometimes I mount my Apex 127 on one side with the GoScope 80 on the angle bracket. I have since added the dovetail bracket from the GoScope tabletop mount (which I don't use) to the L Bracket for a little more stability. I have thought of getting one of the AT72 scopes but not sure it would give me much more in this particular combination.

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  • 6238306-Dual-Pipe-Mount-small.jpg


#167 jrbarnett

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Posted 06 December 2013 - 11:39 PM

Mabruk!

Great scope, especially for such a low price.

Enjoy it. And be sure to use it by day, too.

Regards,

Jim

#168 Starman81

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Posted 07 December 2013 - 01:30 AM

Mabruk!

Great scope, especially for such a low price.

Enjoy it. And be sure to use it by day, too.

Regards,

Jim


Thanks Jim! Definitely going to replace the diagonal it came with and I already replaced the finder with an 8x50. A 6x30 would suffice and be more fitting but I don't have one on hand at the moment.

Here it is on the AT Voyager; only realized afterwards I hadn't removed the tag.

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  • 6238427-C90 on AT Voyager.jpg


#169 Starman81

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Posted 07 December 2013 - 01:39 AM

Other notes:

- 32 and 12.5 Plossls were a little rough in condition, rubber eyeguards were a little chewed up looking and field stops a little ragged (32mm moreso). At this price, I am not complaining, just thought I should mention it.

- Included erect image diagonal vignettes the 32mm Plossl pretty badly and even my XW 20. Another reason that it should be dispensed with in all haste! *Edit*: Hmmm... I hope it's an issue with the diagonal as that can be replaced and not the rear port diameter. I'll have to measure it.

Here is a shot of it on the Nexstar SLT mount (using an L-bracket on both setups).

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  • 6238435-C90 on SLT.jpg


#170 PowellAstro

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Posted 07 December 2013 - 02:04 AM

If you guys have an interest in improving your C90, look at this thread.

C90 Contrast Boost
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#171 CollinofAlabama

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Posted 08 December 2013 - 11:16 PM

it achieves higher magnifications using more comfortable, longer focal length eyepieces without the need for a Barlow. In terms of light grasp and resolving power it exceeds the capabilities of an 80mm refractor on both scores (the effective clear-aperture light grasp of a C90 once you account for transmission losses and obstruction, is 85mm). Most importantly, at under $200, it's cheaper than a refractor.


First, Jim, thanks for this post. I'm seriously considering getting one of these for travel purposes (and public star parties under a moon-blighted sky when there are no conjunctions that might require a 1.5 degree plus field). You've clarified this post already, in pointing out that the C90 is about like your AT72ED minus the gigantic field, which I would agree completely. I would also agree that, for Deep Sky, this little Mak will indeed perform like an 85mm clear aperture scope.

But still, I think for full disclosure to the masses, one should consider a few characteristics of the C90. First, it does NOT have an oversized primary, as Meade touted about its Maks. I realize that Ed Ting (and many others) still rate the Synta Maks as superior to their Meade counterparts, but just because Meade has put out, perhaps, an inferior product doesn't invalidate the claim their making regarding primary mirror size.

It's important to consider the aspherical corrector plate as demonstrated here. The drawing is exaggerated for effect, but the defocusing effect of the corrector plate means the primary mirror, in order to operate at the size of the corrector plate optically, must be oversized relative to the corrector plate. The Synta's are not, as Gary Seronik wrote about in his S&T review of the Orion Mak 127 soon after the Apex line came out (2001?) Seronik wrote that the 127's actual functioning aperture was really 121mm, and not 127mm, due to this lack of an oversized primary. Proportionally scaling his figures to the 90mm model, one gets 85.75mm as the functioning full aperture of the Synta 90mm. When one subtracts the Pi-R-Squared of this 85.75mm and the Pi-R-Squared of the 31mm painted secondary, one ends up with the photon equivalency of an 80.7mm unobstructed aperture instrument. Of course, on planets, it can't possibly perform at this level, since it's an obstructed view, so the 72mm ED or long tube 60mm achromat scope sounds about right. OTOH, for DSOs, in my experience at least, obstructed aperture instruments tend to produce results of the effective aperture of the primary, almost regardless of the CO size (at least when it's below 40%, which it is well below on all the longer focal ratio Synta Maksutovs).

And speaking of focal ratio, using my calculations above, I put the C90 as operating at F/14.58, so pretty slow indeed. But I also concur with your findings, Jim, that the maximum TFOV you'll get out of one of these is about 1.3 degrees. That won't frame the Pleiades, and can't help with conjunctions or when a planet cruises near the Pleiades, Beehive, etc. But of course, it will easily put any planet well inside the field, including every moon you might be able to see for Jupiter and Saturn. But the TFOV issue does make me wonder about this. Something else for less than nothing! Decisions, decisions.

And kudos to 314Sprout finding Enceladus. Man, you and Jon Isaacs sure have it good in San Diego! You've GOT to live in the best place in North America for clarity of skies. Mine aren't bad, and I'm not complaining at all here in West Texas when I consider my eastern origins (Alabama and Iowa), but South California sounds like the best -- and the climate ain't half bad, neither! Since we're in the ice box that's gripped the central US, you indeed have it good.

Don't underestimate the 90mm Mak.

#172 Starman81

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Posted 09 December 2013 - 03:43 PM

I'm having a lot of fun with daytime testing with this nifty little scope, but only a masochist could do something like this! Not that I kept that combination on the scope very long but I still gotta give credit to that prism diagonal/visual back combination--it held up decently with no deep gouges in the nose of the diagonal, if you can believe it.

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  • 6242944-C90 with Binoviewer XW20s.jpg


#173 rmollise

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Posted 09 December 2013 - 04:41 PM


But still, I think for full disclosure to the masses, one should consider a few characteristics of the C90. First, it does NOT have an oversized primary, as Meade touted about its Maks.


Meade's oversized primary mirrors (barely) amounted to absolutely no visible improvement. ;)

#174 CollinofAlabama

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Posted 09 December 2013 - 09:28 PM

Agreed, but because Meade built an inferior product to Synta in no way distracts from the optical facts concerning the requirement of a Gregorian Maksutov to have an oversized primary relative to the corrector plate to operate at the full aperture of the corrector plate.

Don't know if you have the article, Rod, but it's a good read, and even Seronik, tho pronouncing the Orion 127mm as only operating as a 121mm aperture writes that any user would be hard pressed to complain with the view it throws up. Having owned ALL the the original Apex models in the day, I have to say I agree. They are, at least my three random samples of 90, 127, and 102mm models, very sharp and nice, optically. But they operate at 121, 85.75, and 97mm apertures. And then one must factor in the obstruction.

I agree with Seronik (and most everyone posting here, apparently), that these little Syntas, be they Orion Apex, Celestrons, or SkyWatcher labels, put up views that would be hard for anyone to complain about. They're quite good, and the current price of the C90 from people like B&H Photo and others, is just one fantastic buy, thus Jim's title for this thread.

I only posted this because before you put down your money, you might want to know all the facts. Just a matter of disclosure. Look, the Celestron 102GTs that sold for under $100, and are still only $120, are one fantastic deal, but they are really 97mm clear aperture scopes, too, due to the lens cell blocking light. Just the facts.

Of course, this may also have some bearing on the stray light issue addressed above. Probably does. Doesn't mean this scope is garbage, by any stretch of the imagination. Folks complain about TeleVue refractors not having metal baffles, only cloth ones, and that's a reasonable thing for a person to be aware of before purchase. Doesn't mean any of these products are junk, only that no telescope made by man is perfect, like its creator. Don't you guys wish women would start building telescopes? I'm sure my wife would make a perfect one!

#175 rmollise

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Posted 10 December 2013 - 08:58 AM

Thanks for recommending the article, and, yes, it's a good idea in theory...the Meade implementation just made on observable difference. ;)
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