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Something for nothing: Celestron C90

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#201 CollinofAlabama

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Posted 06 January 2014 - 03:33 PM

The C90 is a beautiful instrument, and I may yet get one, but ... It's limited to a 1.3* field :-( Dude, there's nothing you can do about that. It's a pinhole instrument if ever there was one. I know it's mighty compact. One of the most compact scopes a person can buy, but I'm still thinking a C70 Travelscope would be the better ultra-light.

As for adding a C-70, or anything larger than a 6x30 RA finder, why? The whole point of owning one is portability. It's way not the primary scope. It's a grab 'n go if ever there was one. Even the 9x50 RA, admittedly a much better astronomical finder, is already disturbing the balance of this instrument and requires counterweights and mount sturdiness that invalidates the purpose of ownership. So why? Yes, one can water ski behind the Battleship, pray tell why? It's like a 2" focuser. Well, one can add it to the C90, but what good can it do optically? Why take a perfectly portable grab 'n go and saddle a huge finderscope to it? Makes no sense. Keep it easy, simple to mount. This thread demonstrates the foolish over engineering so common on CN. Keep things practical, folks, not ridiculous, just because they can be made so.

#202 Sarkikos

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Posted 06 January 2014 - 05:32 PM

The C90 is a beautiful instrument, and I may yet get one, but ... It's limited to a 1.3* field :-( Dude, there's nothing you can do about that. It's a pinhole instrument if ever there was one. I know it's mighty compact. One of the most compact scopes a person can buy, but I'm still thinking a C70 Travelscope would be the better ultra-light.


I don't believe in a Jack-of-All-Trades telescope. I don't use any of my Cats for wide-field views. I don't have a focal reducer for my Cats and don't intend to buy one.

Cats - even the little C90 - are best used for planets, the Moon, double stars, maybe the moderate-to-small-sized open clusters and such. But I don't expect a Cat to give me the best view of Milky Way vistas and rich-field objects. Not gonna happin'.

I have a C70 travelscope. It's a little 70mm f/5.7 achromat. Yes, it is better than the C90 for big DSO like the Double Cluster or IC 4665. But I'd take out my C90 Mak any night for planet/lunar over the C70. The C90 has no chroma, has bigger aperture and reaches higher magnification easier than the C70. A big expansive field is not so important for planets and the Moon.

Always use the best tool you have for the job at hand.

Mike

#203 t.r.

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Posted 07 January 2014 - 07:28 AM

Why take a perfectly portable grab 'n go and saddle a huge finderscope to it? Because I can. :sumo:Makes no sense. To you. :slap:Keep it easy, simple to mount. Mounts on the same mount as before and still grab'n go portable. :pThis thread demonstrates the foolish over engineering so common on CN.Really Collin, you are gonna go there? :smirk: Keep things practical, folks, not ridiculous, just because they can be made so. Says you, people who can't think outside the box and folks confined by self-imposed rules to conform to some ideal. :grin:


Look, it is simple...The C90 has a tight fov and a *BLEEP* finder scope as supplied. Why not replace the finder with a widefield mini refractor to compliment the capability of the Mak C90 setup? No harm, no foul to anyone...but apparently it ruffled your feathers?!?! :shrug: "Over engineering"?!...that's rich! I put on a different finder scope for cripes sakes! :lol:

#204 Sarkikos

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Posted 07 January 2014 - 08:22 AM

I think using a fast 70mm refractor with the slow C90 is a good idea. Then you have the best of both worlds: rich-field wide-field and high-contrast narrow-field. That setup would be more like a dual-telescope than a telescope-plus-finder.

As finder scope on the C90, I've used a 6x30 or an 8x50, both RACI's. The 6x30 has a wider field, the 8x50 goes deeper. But either balance well with the C90 on my 501HDV plus Manfrotto tripod. No problem.

Mike

#205 Binojunky

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Posted 07 January 2014 - 10:37 AM

Has anyone compared the optics of the modern day C90 to the ETX90 (UHTC type)?
I'm very happy with my ETX optically. IT seems that the C90 has more versatility though. Meade doesn't make many of the older adapters, the finder scope is useless..



Ed Ting did a review comparing the optics of the ETX 90, the new C90 and the Questar 90, all were very close to each other, the Questar came out ahead of the C90 which came out ahead of the ETX,DA.
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#206 CollinofAlabama

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Posted 08 January 2014 - 02:50 AM

Mike,

I readily concede the C90 is better for planets than a C70 Travelscope, but ...

When I'm traveling, am I not tempted by the Pleiades? Andromeda? Various seasonal conjunctions, the Milky Way? Not saying I wouldn't want to look at the moon, Jupiter this Winter, Mars this Spring, Saturn this Summer -- I would. And I'd definitely prefer the C90 to the Travelscope 70 for those particular targets, but when I'm traveling, what if I want wider field ones? Also, as another practical matter, viewing -- anything -- at around 50x, tho, yes, less dramatic, especially for planets, is also easier to mount, and can be more satisfactorily done with a light-weight mount that might squawk at 100x. For these reasons, and of course the downright steal of a price. I mean, $70 vs $150. Some might say this is irrelevant, and as the owner of considerably more expensive optical components, I can see that point of view, but when you want "something for nothing", well, when graphed, $70 is a lot closer to zero than $150.

All these reasons conspire for the C70mm Travelscope. Of course, the best solution is to buy either one, wait a few months after the wife digests its possession, then buy the other one, too. :smirk:

#207 CollinofAlabama

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Posted 08 January 2014 - 02:58 AM

Tim,

Of course these are my opinions, and those wanting to add 2" focusers weighing 10 lbs, bazookas, or sparklers to their C90 have some kind of 2nd Amendment right to do so. Just saying "We hold these truths to be self-evident". But if they ain't to you, fire 'me up.

#208 t.r.

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Posted 08 January 2014 - 06:33 AM

The sparklers are my next add-on!!! ;)

#209 Sarkikos

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Posted 08 January 2014 - 07:06 AM

Of course, the best solution is to buy either one, wait a few months after the wife digests its possession, then buy the other one, too. :smirk:


That's the ticket! :waytogo:

Mike

#210 jrbarnett

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Posted 08 January 2014 - 04:49 PM

I'm actually very happy with the stock finder. I use my C90 on a GOTO mount typically, and the included finder is perfectly suitable for centering alignment stars. I wouldn't mess with the finder unless I was going to use the scope on a non-GOTO mount.

- Jim

#211 Sarkikos

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Posted 08 January 2014 - 05:27 PM

Jim,

But doesn't that GOTO mount add quite a bit to the overall weight, even though you can skimp on the finder?

I wonder which would be heavier: C90 + tiny finder + GOTO mount or C90 + 8x50 RACI + photo tripod?

I can carry my C90 + 8x50 RACI + 501HDV + tripod in one hand, down the stairs, out the door, down the porch steps, and then 500' to a site above a pond. Now that's grab-n-go!

Mike

#212 OrdinaryLight

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Posted 08 January 2014 - 06:06 PM

I also like the combination of an 8x50mm (5.6°) RACI finder on a 90mm mak (mine's the Orion) for an ultra-portable; it's still under 5lbs and 11" long. The RACI finder makes star hopping a pleasure and gives nice views of the really big open clusters (Pleiades, Hyades). I find sighting between the finder tube and the main tube gets me close enough to be able pick my initial target up in the 8x50 so that I don't need a red dot.

I think the only thing that might tempt me away would be an AT72ED (5lbs, 12" retracted) for its wider views (26-30x @ ~68° AFOV is a sweet spot for me on a lot of objects) and ability to go over 100x but I know it still won't quite match the mak on planets or the moon (similar brightness, less resolution).

#213 PowellAstro

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Posted 08 January 2014 - 10:15 PM

@ Jim

What GOTO mount do you use with the C90?

#214 tnakazon

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Posted 16 January 2014 - 11:18 AM

I had a problem using this scope with mounts having a side dovetail saddle (e.g. Vixen Mini-Porta II, Orion Versago II) because the finderscope would be in an awkward position (at 7-8 o'clock). Will definitely not use a photo/video tripod for this scope.

Need to use a mount with the dovetail saddle on the bottom of the tripod (e.g. Celestron Astromaster CG2 & CG3 mounts) if you don't want to use mounting rings for this scope.


After owning this scope for almost 2 yrs, finally got a proper mount/tripod for it with the dovetail saddle at the bottom (Celestron Astromaster Alt-AZ mount and tripod). Switched the 8x21 finder with a 8x40mm from my Orion Short Tube 80A (overkill for that scope).

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#215 OrdinaryLight

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Posted 01 February 2014 - 07:58 PM

I was able to see the SN in M82 a couple of nights ago with my 90mm mak. Using an 8x50 RACI finder I star hopped from Dubhe and once in the area I found M81 and M82 with averted vision using a 32mm plossl for 39x. The 1.3° TFOV was plenty wide when viewing these fuzzies. Switching to an 8-24mm zoom the best view of the SN was around 18mm/70x though still required averted vision. Pretty cool to be able to see it in the little mak.

#216 tnakazon

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Posted 05 February 2014 - 09:01 PM

Congrats! Haven't seen it yet - we've been having cloudy evenings with some rain lately here in Southern California. Got some good views of Jupiter (with detail in the cloud belts) and Mars (ice cap visible) a couple of weeks ago with this scope.

#217 jrbarnett

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Posted 05 February 2014 - 11:39 PM

Usually a Nexstar 6/8 SE mount.

Posted Image

A one-hand, self-contained setup (the mount will work on batteries in the base for a medium session).

Regards,

Jim

#218 OrdinaryLight

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Posted 06 February 2014 - 09:55 AM

Got some good views of Jupiter (with detail in the cloud belts) and Mars (ice cap visible) a couple of weeks ago with this scope.


Nice! Was this using the Astromaster mount? Does it track pretty smoothly at higher powers? Any issues with the head slipping when pointed up?

#219 Sarkikos

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Posted 06 February 2014 - 10:58 AM

Usually a Nexstar 6/8 SE mount.

Posted Image

A one-hand, self-contained setup (the mount will work on batteries in the base for a medium session).

Regards,

Jim


I'm contemplating getting a goto. :shocked: If I get one, the Nexstar 6/8 SE mount will probably be it.

Mike

#220 RafaelP

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Posted 06 February 2014 - 11:46 AM

Has anyone tried to take some snap shots of the moon or Jupiter through the C90? Or is the f/11 and 1200mm focal length make it too slow?

#221 PowellAstro

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Posted 06 February 2014 - 12:25 PM

The unit is F/13.8 if you are speaking of the newer C90. It does just fine on the moon and planets. It also does just fine on deep sky with a .5x reducer mounted on the from of a small chip CCD making it F/6.9. This only works with chips of around 12mm or smaller.

#222 RafaelP

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Posted 06 February 2014 - 01:09 PM

I have the newer one. Just couldn't remember the f stop number. Anyone put a full frame mirrorless on theirs? I tried with my new Sony A7r(with proper t adapter) and getting severe vignetting, not sure that is normal or not...

#223 PowellAstro

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Posted 06 February 2014 - 01:40 PM

My EOS 7D shows vignetting too. It's not so bad that a flat field would not correct it. In fact I can remove it in PS3 without a flat field frame.

#224 OrdinaryLight

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Posted 06 February 2014 - 01:41 PM

Has anyone tried to take some snap shots of the moon or Jupiter through the C90? Or is the f/11 and 1200mm focal length make it too slow?


I've only taken a few snapshots but the moon is easy. This is a single frame (1/200 @ ISO 800) with minimal post processing:

Posted Image

Anyone put a full frame mirrorless on theirs? I tried with my new Sony A7r(with proper t adapter) and getting severe vignetting, not sure that is normal or not...


Yes, I see the same thing with a 6D. My understanding is that the 1.25" light path will not fully illuminate the 35mm frame.

#225 RafaelP

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Posted 07 February 2014 - 09:22 AM

Cool, thanks! I took a few quick shots of the moon and Jupiter last night(it was cold!) I was surprised how easy it was to overexpose the moon! I will have to try shorter exposures tonight.


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