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Something for nothing: Celestron C90

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#101 collaredkeeper

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Posted 03 May 2013 - 11:08 AM

Started a post on some updates on the price at Optics Planet for the C90 Setup, the whole bundle now is $140 shipped!

http://www.cloudynig...5837539/page...

Best wishes,
Tony

#102 N7XW

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Posted 09 May 2013 - 06:36 PM

For those of you that have the C90, how do you think it would serve as a spotting scope? Given the tripod should be upgraded. I guess I'm wondering if the optics are good enough to pick out fine detail a few hundred yards away. I have an older C65 "mini-mak" that just does not cut it. Although it is a mak-cass, the optics are nothing to get excited about.

#103 core

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Posted 09 May 2013 - 06:51 PM

I find the current C90 just a tad under 'OK' for a spotting scope; there's a ton of reflection off the inside of the baffle tube, rendering a low-contrast/washed-out image.

#104 N7XW

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Posted 09 May 2013 - 07:11 PM

Thanks Peter.

#105 azure1961p

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Posted 09 May 2013 - 10:57 PM

Yeah but-

A simply flocking material rolled up and inserted into the inside of the baffle is all that's needed. Let go of the paper, it unrolls fitting the sides of the baffle.

This is a simple matter. Also for further contrast enhancement observe in daylight with a dew shade that's a good 8" long. This helps nicely.

Pete
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#106 jrbarnett

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Posted 09 May 2013 - 11:50 PM

Using an Astrozap flexible de shade, ~70% of the reflection issue in daylight is quelled. I enjoy using the scope as a spotter. It's a $140 color free spotter. What's to complain about? :grin:

- Jim

#107 core

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Posted 10 May 2013 - 02:58 AM

Thanks Pete and Jim - guess I shouldn't have relegated my C90 that quickly. Now to go find some good flocking paper ... all I have on hand is the adhesive fuzzy stuff.

#108 moynihan

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Posted 10 May 2013 - 05:51 AM

Using an Astrozap flexible de shade, ~70% of the reflection issue in daylight is quelled. I enjoy using the scope as a spotter. It's a $140 color free spotter. What's to complain about? :grin:

- Jim


That is exactly my experience as well. I originally got it to use as a spotter. star tested one evening and it got assigned to night duty :grin:.
Actually got a second one,for the more rigorous daytime environment.

#109 Binojunky

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Posted 10 May 2013 - 09:57 AM

Thanks Pete and Jim - guess I shouldn't have relegated my C90 that quickly. Now to go find some good flocking paper ... all I have on hand is the adhesive fuzzy stuff.


You can make a perfectly servicable dew shield out of a piece of craft foam available at the dollar store or craft shops,DA.

#110 314Sprout

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Posted 27 May 2013 - 05:43 PM

I have to say that I have really come to appreciate this lowly little C90. Friday night I paired it up with my AT 72 on my DSV-1 to take some wide field pictures of the conjunction of J,V,and M. I was just using the C90 to keep my framing consistent. After they set, I wheeled around for a "quick" look at Saturn, not expecting much with the moon so bright. What surprised me was bagging 5 moons! I expected Titan. I did not expect any others so I jotted down what I saw to check later. 2 moons out at 1000 position at a rings width (Rhea and Dione). 2 twinklings occasionally at the 1100 and 1200 position right along the disk. I couldn't always make them our but I checked at various magnifications and they were consistent in position. Turned out to be Enceledus and Tethys just before passing behind the disk. This little scope is great, and along with the AT-72 and my DSV-1 it is getting me out more evenings than ever before. I have had aperture fever like everyone else, but these have opened my eyes to the fun again.

#111 azure1961p

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Posted 27 May 2013 - 07:32 PM

You bagged Enceladus with a 90mm Maaakkkkkkk???

My respects for both of you. That is one for the books Jim!!!

How is it compared to the 70mm? I heard the Q3.5 us about on par with a TV Pronto/Ranger - do you concur based on your c90?

Pete

#112 Asbytec

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Posted 27 May 2013 - 09:17 PM

Ya, Enceladus was not easy in a 6". Wow!

#113 jrbarnett

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Posted 27 May 2013 - 09:29 PM

The effective throughput of a C90 is equivalent to a ~70mm unobstructed high transmission scope. The advantage of the C90 is that while it delivers the brightness of a ~70mm refractor it resolves as a 90mm instrument. The tradeoff of course is some loss of contrast due to the presence of a CO.

Pitting my C90 head to head with my AT72ED I'd say that they are comparable in optical quality, with the C90 having a slight edge. The AT72ED, however, does a better job of controlling stray light and is better built. The two have such vastly different focal lengths that the experience of the two side by side is quite complementary. The AT72ED provides nice context at lower magnification and the C90, a nice increase in magnification for a closer look.

The DSV-1 is a great value, too. With such a setup (DSV-1, C90 and AT72ED) you have a great, lightweight setup for cruising the Sagittarius Milky Way without the need for a single eyepiece swap. Sweet ride!

:grin:

- Jim
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#114 azure1961p

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Posted 28 May 2013 - 06:48 AM

Thanks Jim. I appreciate the report.

Pete

#115 hardwarezone

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Posted 30 May 2013 - 09:52 AM

Do those cheap 0.5x focal reducer on ebay work with this scope ?

#116 rmollise

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Posted 30 May 2013 - 09:54 AM

They work _somewhat_. Use one with a 25mm eyepiece, and you will get pretty severe vignetting. Most people prefer just using a longer f/l ocular.

#117 Sarkikos

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Posted 30 May 2013 - 10:09 AM

The DSV-1 is a great value, too. With such a setup (DSV-1, C90 and AT72ED) you have a great, lightweight setup for cruising the Sagittarius Milky Way without the need for a single eyepiece swap. Sweet ride!


Sounds nice. Maybe I could rig up something similar for my 90mm Mak and ST80 with 2" Crayford on my SkyView AZ. :thinking:

:grin:
Mike

#118 Binojunky

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Posted 30 May 2013 - 11:04 AM

Well maybe I have dropped on a really good one?, its my second sample, the first was passed on to a friend for favours granted, the second one came from Amazon Ca with free shipping to my door. Daytime views were only limited by heat haze rising and softening the view.
However last week while observing the Moon and Saturn I found myself using a TV 11mm plossl and a TV x2 barlow for a magnification of over x300 with a very acceptable image, not to shabby for a scope that cost less than what I have spent on a binocular or single eyepiece,DA :jump:
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#119 Sarkikos

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Posted 30 May 2013 - 11:23 AM

Sounds like you got a good one. My 90mmm Mak is one I got new from eBay in an auction several years ago. Not bad for $35. :shrug: I think the company stopped auctioning their scopes after that. :grin:

It seems to have the typical overcorrection for these little Maks. But the images aren't bad. When the seeing is good, I often go up to 250-300x for objects that can handle it, such as Saturn or Mars.

It cools down pretty fast. In winter, though, I noticed that warm tube currents will linger. I solved this problem by rigging up a screen in a rubber ring which I place over the visual back when I set it outside to acclimate. Works well and keeps the bugs out in the summer.

The 90mm Mak is mostly my grab-n-go lunar scope. I put my Baader 8-24 Zoom in the focuser stacked in a filter wheel (red, blue and an empty slot). This also increases the magnification a little. But since I bought a C6, the 90mm is starting to see less sky time.

Mike

#120 TG

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Posted 30 May 2013 - 01:15 PM

It seems to have the typical overcorrection for these little Maks.
Mike


Star testing cats with smallish COs often leads to misdiagnosis of spherical correction. I used to have a Tak TSC 225 with a 28% CO. Dead straight Ronchi lines (at f/12, a reliable method of detecting spherical aberration), great mars images:

Posted Image

and yet the star test looked like a 1/2 wave scope's with drastically different shadow breakouts on either side of focus.

Tanveer.
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#121 Sarkikos

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Posted 30 May 2013 - 01:26 PM

Yes, my 90mm Mak definitely shows a different pattern on either side of focus. Looked like overcorrection to me judging from pics in Suiter's book. But, of course, I hope I am wrong.

:grin:
Mike

#122 hardwarezone

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Posted 30 June 2013 - 09:36 AM

I've tried to barlow mine last Friday and the image brightness of Saturn at 200x magnification was acceptable for me.
Details would only appear momentarily as bad atmospheric condition drift in and out.



Would like to ask if the 3 smaller holes at the back, are they part of the collimation system ?
They do seem to be metal screw threads wtih tiny black hex shape underneath.

#123 jag767

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Posted 08 July 2013 - 07:01 AM

Just ordered my C90 with the thread adapter and 2" adapter last week, should have it all tomorrow. really looking forward to seeing what this little scope is capable of!

#124 jag767

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Posted 09 July 2013 - 06:04 AM

Well low and behold it came a day early. Mounted it on a manfrotto with ioptron ball head with no problems, and gave image quality that to be quite frank I did not expect. Great image quality on a night which was far from ideal. The only observation I made which was less than stellar was the focus knob will definitely be in the way of a 2 inch barrel. Thinking I may adapt to sct threads off the built in t threads and use the current back as an extension to resolve the issue.

#125 Usquebae

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Posted 09 July 2013 - 09:13 AM

Hardwarezone - a CN poster gave me collimation instructions [attached] for his Orion Mak, which looks the same as the C90.

Attached Files




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