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Cometron CO-114 4.5" Newt: Vixen optics & GEM

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#1 hottr6

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Posted 12 November 2012 - 10:15 PM

Last year, I had the opportunity to pick up a Celestron "Cometron CO-114". It seems to me that this was a department-store Celestron, a budget-priced version of their venerable C4.5. I bought it because of the Polaris mount, but the OTA looked like hell, a major reason why I paid only pennies for it.
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The Polaris had never been used because of a defect in the manufacturing; the counterweight shaft nut had never been tapped! It was easy to tap the nut for M12-15 threads. The DEC axis was incredibly stiff, due to the interference fit of the bearing. I took off a couple of thous, cleaned the old glue out and relubed, and now the mount is simply glorious to use. I did fit a Vixen saddle to the Polaris, so can now use it with a variety of smaller ‘scopes. I've not fitted the MD-5 drive (also unused) to the RA axis because the mount is so nice to use manually. Another modification made was to use a Super Polaris counter-weight shaft which is a direct replacement for the original threaded rod. This enables me to use the heavier counterweights from a SP.
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I don’t want to get distracted by the mount, as this article is about the Cometron OTA, or as I call it, the "Vometron". The tube had been stored upright for the past 30 years, and obviously had fallen many times against a table or something, because there is a whole series of dents in the OTA at about the same part of the tube. A quick panel-beat of the tube knocked out most of the dents, but it is still ugly. I thought about bondo'ing the dents and painting the tube white (see my avatar to the left), but the grunge-allure of the battle-ship grey tube with dents is too much to resist.

The original optics were trashed. Stored upright, the primary collected dust which corroded the aluminizing. I tested what was left of the Circle-V primary and it is parabolic. I thought of having the 4.5" mirror stripped and aluminized by OWL, but Cary would not respond to my emails. In the interim, I found a set of optics that were rescued from a C4.5, so I snatched them up. In subsequent tests, the replacement mirror is parabolic (Ronchi testing) and diffraction limited (star testing). More on that later.
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The Cometron had optics by Vixen, so I suspect that Celestron used exactly the same mirrors as the C4.5. But there any similarities end. My Vometron was equipped with an extraordinarily poor 0.965" plastic focuser. The 5x24 finder is plastic, including the lens. The mirror cell is plastic. The spyder is the same as the C4.5, but the secondary holder is plastic. The 135mm diameter battle-ship grey tube is thin steel with a crimped seam. The C4.5 uses a tube diameter of around 145mm. Another cost-saving exercise by Cometron. When I bought the replacement mirror, it also came with secondary, spyder, metal 1.25" focuser and primary cell. The primary cell would not fit my grey tube, but the focuser and aluminum secondary holder bolted right up. I had an old but nice Cometron 5x30 focuser from a CO-62 and stalk lying around and that bolted right up. I mounted the rings to a Vixen-style dovetail so I can use it in the modified Polaris saddle.
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First light was surprising. I used first-generation Celestron Silvertops for this review, arguably some of the nicest Plossls ever made. The Vometron easily split Epsilon Lyrae (the "double-double") at 90x. I could easily make out the ring of M57. Only a handful of M13 stars could be individually resolved. I was not able to crack Cassini's, but Saturn's elevation of less than 15 degrees may have been a contributing factor. The Moon was absolutely gorgeous even at 240x (7.5mm Silvertop w/2x TV Barlow) with no image break-down. No false color anywhere. Star testing produced text-book rings in and out of focus.

In my experience this appeared to be a really a nice 'scope with the modifications that I made. Cool-down time was about as long as it took me to fetch the eyepieces after carrying outside the whole rig. Definitely a grab-and-go, this rig was easy to haul around as a complete unit. I'm looking forward to testing this against my also-nice 90mm f/11 achro.
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#2 greju

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Posted 13 November 2012 - 12:57 PM

Your scope somewhat mirrors a purchase of mine from a few years ago and has me re-examining my initial thoughts on that purchase. Bought mine from a fellow CN'er who said it had been sold to him as a Cometron. I doubted it as I had never seen one with a white tube and said this to the seller. Bought it anyways as at least the mirror looked to be in good shape. Looks like I may owe the seller an apology. :rainbow: I know you are out there. :grin: The plastic focuser and the finder and it's mount look the same.

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#3 greju

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Posted 13 November 2012 - 01:02 PM

I also had doubts that Vixen would have used a rolled aluminum tube with a seam in it. Seemed kind of cheesy but evidently they did. IIRC didn't those Tasco red tubes (8V?) with the Vixen logo also have rolled tubes? Like yours, this one has seen it's better days. :grin:

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#4 greju

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Posted 13 November 2012 - 01:04 PM

Another thing I liked about mine was the secondary mount which is mostly metal which might be different than yours. The only plastc here is the actual mirror holder.

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#5 greju

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Posted 13 November 2012 - 01:11 PM

Do you have a picture of the rear of your scope for comparison? Glad to hear of the success you have had with yours. I have a special appreciation for 4 1/2" Newts as it is the first scope that I saw the rings of Saturn with and started my lifelong astronomical journey. Thanks for not only the new knowledge but also the memories. :bow: P.S.- got it and thanks! Are you sure it is the five element? :grin:

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#6 hottr6

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Posted 13 November 2012 - 03:34 PM

Do you have a picture of the rear of your scope for comparison?

Looks the same to me. The original Cometron spider vanes are the same as the metal C4.5 spider vanes, but the secondary holder was plastic.

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#7 Glen A W

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Posted 16 November 2012 - 06:33 PM

I got a c4.5 for Christmas one year back then. The mount was the real gift. The scope itself was an awful dog. I am not sure the secondary was even getting the whole primary, as it seemed dim and was a disappointment to me. I still use the mount most every night with a Skywatcher ED. It's one of the best ever made in that size. I have the original clock drive which still works after a great many hours of use, and it has a polar scope. I have used up to a C8 on it successfully. GW

#8 desertrefugee

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Posted 16 November 2012 - 09:30 PM

I have had two F4.5's. Both were excellent. The only reason I sold the last one was that I acquired an SP-C6.

I'd be surprised if yours was truly a dog. Probably needed a serious collimation.

#9 hottr6

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Posted 20 November 2012 - 08:30 AM

Just wanted to add that I found yet another difference between the Cometron and the C4.5. The front tube ring on the C4.5 is plastic, but it is metal on the Cometron. Score one for the Cometron! :thewave:

The tube cap on the C4.5 has Japanese script on it (presumably the usual disclaimer "Do not look at the sun", etc), whereas the Cometron cap has no writing, and is from a much simpler mould.

#10 BarabinoSr

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Posted 20 November 2012 - 09:17 AM

I have the CO-100 4- inch, I use mine quite a lot .Some of the best views of Jupiter, almost refractor like ,and have used it for solar viewing as well. A great acquisition for you !!! Gary :bow:

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#11 fmt28miata

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Posted 29 July 2014 - 11:21 AM

Looking to revive this post... I just purchased a Cometron CO-114 and have a few questions. I am brand-new to star gazing and am interested in where to obtain a 1.25 focuser from that will work with this scope. Any help is much appreciated!

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#12 Martin

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Posted 29 July 2014 - 12:23 PM

I am sure someone will chime in about a focuser update on this scope but have you tried using a .965 to 1/14 adapter? It just fits into the current focuser and allows you to use 1 1/4 eyepieces. I have one on my Mizar 120mm Newtonian that works quite well. Just a thought. I know on some of these older Newtonians they won't work, won't come to focus, but worth a try.

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#13 DocFinance

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Posted 29 July 2014 - 01:48 PM

There's probably a ring that will replace the original ring on the focuser (the part where the eyepiece screws on). If the full focuser tube is large enough that may be a solution. From what I recall that's a current Vixen part.
Another alternative would be to find a focuser from the Celestron C4.5, which should fit and was originally 1.25 to start with. Astro Parts Outlet might be a quick way to find alternatives.

#14 fmt28miata

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Posted 30 July 2014 - 09:27 AM

These are great suggestions, thanks! I will try an adapter since it is the easiest way and only costs ~$20. Since I picked up the scope for $25 I feel like I can spend a little more to get it up and going.

Also, thanks for the C4.5 suggestion, I will keep an eye out for one so I can take the focuser from it, they look like they still go for a pretty penny though.

#15 DocFinance

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Posted 30 July 2014 - 02:06 PM

What I' m talking about is changing the ring on the focuser. That used to be an option, but only if the draw tube is big enough. Good choice if you can do it.

#16 labmand

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Posted 30 July 2014 - 07:15 PM

http://www.ebay.com/...nian-Focuser...

you not only got a bargain but also a great looking rig, nice.
one of these may work or a nice rcf from jmi (reverse crawford focuser)
You hit the lottery my friend, enjoy your good fortune.

#17 fmt28miata

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Posted 01 August 2014 - 02:37 PM

This is great, thanks Doc and labman... I was able to find a Celestron starhopper 4.5 for cheap, I am wondering if I should take the focuser from that to affix to my CO114 or just use the Starhopper OTA and bolt it to my Polaris mount?!






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