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Something for nothing: Celestron C90

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#76 GeneT

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Posted 02 March 2012 - 04:30 PM

The only "negative" comment I have right now is that the focuser is on the stiff side, but as I do this morning's conference calls, I'll run the mirror back and forth along the baffle a few times to see if redistribution of lubrication smooths it out any.


Glad to see you get some equipment checked out during those boring conference calls. :grin:
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#77 mwedel

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Posted 03 March 2012 - 02:57 AM

A first light--and first bird--report on the SkyWatcher OTA, with photos, here. The short version: the OTA is fine, and gives a sharp, high-contrast image, but the supplied prism diagonal is surprisingly poor, by which I mean that I had low expectations and it still managed to surprise me with its badness.

I might get a chance to test this SkyWatcher scope against the Celestron C90 later this month. If that comes together, I will definitely report back.

I'm going to have some fun with this little scope. :jump: I only found out about it through this thread, so thanks, folks!

#78 freelancer

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Posted 04 March 2012 - 12:54 AM

Thank you very much for the useful advice, Jim. It is always a pleasant surprise to stumble upon forums like CN (and diyaudio, for another) with experienced folks who are willing to put in the time and effort to educate newcomers.

The LYBAR chair has an elegant minimalism which is very appealing. I viewed sunspots via the projection-on-paper-via-binoculars thing, and will try the solar filter too.

Currently hunting up a good locally available EQ tripod to mount the C90 - photo tripods are sadly no good.

#79 Herr Ointment

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Posted 04 March 2012 - 06:09 AM

Matt.....the review was cool, but the bit on the ostriches was an unexpected bonus. Very interesting.....Thanks!
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#80 mwedel

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Posted 04 March 2012 - 06:41 AM

Thanks for the kind words!

Some updates on the SkyWatcher 90 Backpacker:

- The mount CAN be used with the power off as a manually-aimed alt-az head. I thought otherwise at first, but I was misunderstanding the instructions. You're not supposed to manually slew it once it's been turned on (not surprising), but as long as it's off you're good to go. I put it on a Manfrotto tripod and used it that way this afternoon for birding and this evening to look at the moon, Jupiter, Mars, and Saturn. Movement is a little sticky in manual mode, but the mount is solid, so once I got the scope pointed somewhere, it stayed.

- Seeing still wasn't perfect, but it was MUCH better tonight than it has been, and I can confirm that the scope will do at least 200x (57x/inch). At least my sample will. I had a good time looking at the tiny craters in the sloping rim of Sinus Iridium. I also saw loads of detail on the planets, including about half a dozen bands on Jupiter at 100x. All of these observations were using an Astro-Tech dielectric diagonal rather than the included prism, which has inferior contrast at any magnification but really starts to mush out around 100x. I used the included Plossls for the high-power observations and they were optically fine, although the eye relief gets a little tight.

Hopefully tomorrow I'll have time to put some batteries in the mount and see how it tracks.

#81 n1toga

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Posted 05 March 2012 - 12:18 AM

Hi all,
wanted to buy a tripod/or tripod head combo, capable of carrying the skywatcher table top mount for under a 100 dollars. The cheaper the better...

Thanks
Rahul

#82 esldude

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Posted 05 March 2012 - 01:36 AM

The fellow asking about what eyepieces, I have a suggestion. This isn't a bad scope to use a decent variable eye piece. One in the typical 8mm-24mm range. You won't have the extended wide angle viewing. But if you are planning on showing things to children it works out pretty well. Gives you 50x to 150x without changing eyepieces. Seems a good fit for this scope.

I have used my C90 this way to good effect. I have a Televue 8-24mm variable which I think they discontinued. But it is the same item as a Vixen who made it for Televue and maybe some others. Makes a great simple package. Tripod, scope, the one eyepiece maybe your barlow (might not need it often) and you have all the stuff you need.

#83 Binojunky

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Posted 05 March 2012 - 08:42 AM

I have an older Japan made Celestron zoom eyepiece, must try it in the C90, probably a narrow field of view however for lunar and the planets that may not matter,Dave.

#84 mwedel

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Posted 05 March 2012 - 05:08 PM

The fellow asking about what eyepieces, I have a suggestion. This isn't a bad scope to use a decent variable eye piece. One in the typical 8mm-24mm range. You won't have the extended wide angle viewing. But if you are planning on showing things to children it works out pretty well. Gives you 50x to 150x without changing eyepieces. Seems a good fit for this scope.


I agree. I temporarily have the use of a Celestron 8-24mm zoom, and I tried it out in the SkyWatcher the other night. It's no Baader Hyperion, but it's pretty good, at least in this very forgiving scope, and I'm planning on getting one of my own specifically for sidewalk astronomy and outreaches.

As a Dob guy who hasn't yet sprung for a ParaCorr, it sure is fun to watch stars drift out of the field without changing shape. :lol:

#85 stevemac

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Posted 08 March 2012 - 09:12 PM

Quick question: anyone have significant "play" in the focuser? Meaning you can push/pull the focuser knob into/out of the back of the scope and cause a change in focus? Is there a way to tighten this up?

#86 jrbarnett

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Posted 09 March 2012 - 06:48 PM

Hmm, not for me. Could it be that you are actually sliding the rubber grip sleeve along the underlying metal focuser post? If the post is actually moving in and out when you tug and push it, there's something not right. If you look closely there is an allen head grub screw on the shaft. Perhaps you could push the shaft in and tighten that grub to address the issue.

- Jim

#87 Douglas729

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Posted 10 March 2012 - 09:33 AM

Play in the Focuser?

Uncle Rod and I both had success with a moderate application of grease on the focuser threads...lithium was good for me and actually improved collimation on my C90.

loose threads - details!

#88 stevemac

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Posted 11 March 2012 - 08:07 PM

Thanks Jim, your comment about the grub screws was right on. I loosened both with a 1.5 mm hex key enough that I could remove the knob and collar with the screws altogether. The attached picture shows the result. The brass shaft slides in and out freely. So as far as I can tell the only thing that determines the axial "slop" is how that collar is situated. There's quite a bit of grease and a washer on the backside of the rear cell around where the shaft goes in.

So my fix was to pull the shaft out as much as I could, slide the knob back over and press it into the back of the rear cell while tightening the grub screws. This seems to have fixed the problem, or at least 99% percent of it.

Now for a new question. I've mounted the scope on a Vixen Porta mount. This works great, except that dovetail is on the right side (looking from the eyepiece) instead of the bottom. This puts the focuser at 12 o'clock, above the eyepiece, and the finder down at 7 o'clock, which is awkward, especially when looking near the zenith.

One (possibly bad) idea is to remove and rotate the rear cell 120 degrees clockwise. This would put the focuser and finder in much more convenient locations. My fear is that it would also mess up the collimation, and that I'd botch up what is at the moment a nice telescope. Thoughts?

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#89 Binojunky

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Posted 11 March 2012 - 10:45 PM

I have the same problem with both the C90 and Apex 127, I just bought an inexpensive red dot and stuck the base on with a piece of double sided tape in a position that suited my needs, Dave.PS, moving the back around will cause some grief regarding collimation.

#90 jrbarnett

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Posted 13 March 2012 - 01:44 PM

Steve:

I have the same issue with my Vixen Mini Porta and this scope. It will be a problem with any alt-az mount that offsets the OTA center of mass off of the center axis of the tripod (Vixen Porta, A-T Voyager, etc.).

I have a Lapides Teegul that I use with the scope sometimes, and while I can mount it with the focuser down and finder up, the Teegul has slo-mo knobs on one side of the alt-az head, which turns out to be the wrong side when using this OTA with the Teegul. In other words, I have to reach around to the front to turn slow-mo knobs if I want the OTA in convenient orientation.

One solution for the Vixen Porta might be to add a camera holder shelf and mount the OTA to that:

http://www.optcorp.c...t.aspx?pid=9151

Good luck!

- Jim

#91 stargazer83

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Posted 13 March 2012 - 08:14 PM

Now for a new question. I've mounted the scope on a Vixen Porta mount. This works great, except that dovetail is on the right side (looking from the eyepiece) instead of the bottom. This puts the focuser at 12 o'clock, above the eyepiece, and the finder down at 7 o'clock, which is awkward, especially when looking near the zenith.

One (possibly bad) idea is to remove and rotate the rear cell 120 degrees clockwise. This would put the focuser and finder in much more convenient locations. My fear is that it would also mess up the collimation, and that I'd botch up what is at the moment a nice telescope. Thoughts?


Wouldn't it be easier to get a L Bracket for the Porta Mount? That way the tube sits in there "right side up".
I think The Vixen Porta Mount II comes with a L Bracket so you might be able to purchase a L bracket from various astro dealers.


#92 mwedel

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Posted 13 March 2012 - 10:30 PM

I think The Vixen Porta Mount II comes with a L Bracket so you might be able to purchase the L bracket by itself from rious Astro dealers.


Yep, Orion sells an L-bracket, and although I haven't looked I'll be ScopeStuff has one, too. The MultiMount that comes with the SkyWatcher Mak has a small L-bracket included.

An L-bracket will probably work fine for a 90mm scope. I found that with my Apex 127 I just could not get the balance worked out right; it would be okay at low altitudes but always out of whack at zenith. So I just put the OTA on the mount (a VersaGo II) sideways, and I'm living with the inconvenient focuser placement. My long-range solution will be to get some tube rings, which will also let me hang some more accessories off the scope.

I just came in from having a look at Jupiter with the SkyWatcher 90mm Mak. The seeing is better than usual tonight. With a 6mm Expanse yielding 208x, Jupiter was razor-sharp. The finest details came and went with the seeing, but in the calm moments I could see a ragged edge on the SEB and a little white storm--not the GRS--notching its southern edge. It was one of the most mesmerizing things I have ever seen in a small telescope.

#93 KHHoran

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Posted 12 March 2013 - 01:53 AM

Very interesting read, based on which I'll be purchasing the late-model C90 rather than the Orion Apex 90, as my airplane travel scope to use with my heavy duty photo tripod.

It currently sells for $149.95 on Amazon w/o the tripod and second EP, and $154.95 on Optics Planet. Both have free S&H, with Amazon Prime membership or as a special promo with OP. For $5 I'll pick up the tripod and make some ready cash for other purchases.

Thanks for the excellent analysis on this very affordable scope. I think it will fit nicely in my scope lineup.

-Kim

#94 magnus

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Posted 12 March 2013 - 03:01 AM

Very intressting thread about small maks and thanks Jim for your C90 info!
/Magnus 57N.

#95 hardwarezone

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Posted 29 April 2013 - 02:27 PM

Hi guys,
I have the package with the 12.5mm plossl and tripod.
Would it be okay if I buy a cheap barlow for better planetary viewing ?
200x zoom seem to be pushing it above the practical limit per inch but I have no personal experience to just how dim the image would get and how hard it is to manually align on the alt-az tripod.
Another option would be a cheap 8mm plossl for 150x zoom but the eye relief listed is terrible.

#96 jrbarnett

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Posted 29 April 2013 - 09:48 PM

I think Barlowing the 12.5mm Plossl will give you too much magnification in the little 90mm. The 12.5mm give you 100x and 28x per inch. My own C90 maxes out (i.e., produces the highest magnification it's capable of without image degradation) at around 120x-130x (9mm to 10mm eyepiece).

Regards,

Jim

#97 rmollise

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Posted 30 April 2013 - 07:09 AM

I think Barlowing the 12.5mm Plossl will give you too much magnification in the little 90mm. The 12.5mm give you 100x and 28x per inch. My own C90 maxes out (i.e., produces the highest magnification it's capable of without image degradation) at around 120x-130x (9mm to 10mm eyepiece).

Regards,

Jim


Hmmm... Assuming good seeing conditions, your 90 should be capable of more if your optics are good. Mine (Orange Tube) easily does 200x.

#98 moynihan

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Posted 01 May 2013 - 10:33 PM

In good seeing, i usually get to use a 7mm Ortho (178x)

#99 APTrebor

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Posted 02 May 2013 - 06:10 PM

Just ordered one from Optics Planet (with tripod).

Total was $139 with shipping.

Always wanted to get one of the Orion Apex -- but balked at the price -- so thanks Jim for the heads up.

BTW. Can you collimate the primary like the orions?

~~Andrew~~

#100 jrbarnett

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Posted 02 May 2013 - 07:02 PM

"BTW. Can you collimate the primary like the orions?"

Yesiree!

http://images1.optic...-90mm-spotti...

It sounds like other folks have better luck pushing the magnification with this scope. The transmission losses coupled with the central obstruction makes this scope equivalent to a ~70mm refractor in light throughput. The images get too dim and grainy over about 130x for my tastes, so your mileage may vary on that front. It's a wonderful daytime spotter, too, and still resolves as a 90mm scope. I think of mine as a "folded" long focus 60mm refractor replacement.

Regards,

Jim


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