Jump to content


Photo

cgem or cgem dx?

  • Please log in to reply
32 replies to this topic

#1 evilmedic13

evilmedic13

    Vostok 1

  • -----
  • Posts: 104
  • Joined: 22 Jun 2012
  • Loc: Chicago,Il

Posted 12 November 2012 - 09:00 PM

I,m looking to get an explore scientific 127mm apo and a 80mm triplet for ap. I'll be using a dslr, for now, and an orion auto guider to track. I already have an 11" mak-cass w/ wedge. I figure, depending on target and location, I can use one for observing while using the other for ap. I know all 3 have their own niches/ advantages and will use them as such.
My main concern is not overloading the mount. Thank you for any help.

#2 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2550
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 12 November 2012 - 11:26 PM

The problem with the DX is that the scopes you are looking to mount on it might not be heavy enough to balance it. The DX can't be balanced with anything lighter than a C9.25 basically. Obviously, the Mak-Cass will be fine. The other thing is that the DX tripod is simply enormous and unless you really need that, you are just as well off with the standard CGEM and, if for some reason you feel that you need greater stability, you can add an aftermarket spreader and have a much lighter tripod.

#3 austin.grant

austin.grant

    Viking 1

  • *****
  • Posts: 707
  • Joined: 18 Oct 2010
  • Loc: Shreveport, LA

Posted 13 November 2012 - 01:27 AM

The problem with the DX is that the scopes you are looking to mount on it might not be heavy enough to balance it. The DX can't be balanced with anything lighter than a C9.25 basically. Obviously, the Mak-Cass will be fine. The other thing is that the DX tripod is simply enormous and unless you really need that, you are just as well off with the standard CGEM and, if for some reason you feel that you need greater stability, you can add an aftermarket spreader and have a much lighter tripod.


+1. Good advice, and if you do go that route, the TPI Spreader is a fantastic piece of equipment. Once it's "snapped" into place, the tripod is incredibly rigid and stable.

#4 orion69

orion69

    Viking 1

  • -----
  • Posts: 998
  • Joined: 09 May 2010
  • Loc: Croatia

Posted 13 November 2012 - 02:27 AM

The problem with the DX is that the scopes you are looking to mount on it might not be heavy enough to balance it. The DX can't be balanced with anything lighter than a C9.25 basically.


???
Are you saying that CGEM DX can't be balanced with 127mm APO? Are you sure about that? Or have I misunderstood something...

#5 JMac85X

JMac85X

    Vostok 1

  • -----
  • Posts: 187
  • Joined: 13 Sep 2012
  • Loc: California

Posted 13 November 2012 - 03:15 AM

I have a DX mount, I planned on getting a refractor to put on it for widefield imaging. Are you saying only big boulders can be used on the mount to balance it? I was under the impression it was the same thing as the CGEM except for the tripod and higher amperage to the motors to help with heavier loads for imaging.

#6 evilmedic13

evilmedic13

    Vostok 1

  • -----
  • Posts: 104
  • Joined: 22 Jun 2012
  • Loc: Chicago,Il

Posted 13 November 2012 - 04:22 AM

I believe he was referring to my use of the 80mm triplet. I would actually use that for wide field imaging, but that would be piggyback mounted on the sct. I don't know why I called it a Mak-cass, especially since I know it's not. I would also use it as a grab n go on a simple tripod, the 80mm, not the 11" sct. I plan on using the 80 for everything from visual, to imaging and guiding.
My apologies for not being clear, I'm on the back end of a 48 hr shift, with only 4 hrs of sleep. My mind is running like a bugs bunny cartoon right now. The part where the rabbit, or road runner, disappears with 20 different paths for fudd or the coyote to figure out. Needless to say, those 3 scopes have many options/combinations for me to use them in. In my mind anyway.

#7 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2550
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 13 November 2012 - 09:03 AM

The standard CGEM is saddle heavy so that you can mount just about any scope on it and then add counterwieghts on the counterwieght bar to balance the mount. The CGEM DX is just the opposite, it is saddle light. That is because they took the same mount and added a very heavy steel counterwieght bar nut and counterwieght bar (the standard CGEM has an aluminum counterwieght bar nut). As a result, the only way to balance a lighter scope on the DX is to add counterwieght to the scope side of the axis, something that most people are not prepared for even if it was a good idea (think about flexure and DEC balance problems). That is why Celestron only sells the DX in combination with the C9.25 and above. The C9.25 wieghs 20 pounds but the AR127 only weighs 15 pounds so that, by itself, it will probably won't balance on the CGEM DX. Once you add a guider, etc. it may be OK, but it probably won't work for visual use.

Higher amperage to the motors really has little to do with being able to use heavier loads for imaging. All it really does is allow you to use loads that are less well-balanced (which is not a good idea in the first place). A well-balanced mount does not really need more power to move the axis.

#8 evilmedic13

evilmedic13

    Vostok 1

  • -----
  • Posts: 104
  • Joined: 22 Jun 2012
  • Loc: Chicago,Il

Posted 13 November 2012 - 09:39 AM

Ed, sorry if I mislead you, the 127 I was referring to is the ED127, not the AR127.

#9 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2550
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 13 November 2012 - 09:57 AM

Ed, sorry if I mislead you, the 127 I was referring to is the ED127, not the AR127.


With the ED127 being 22 pounds, it should balance on the CGEM DX. This may be an issue for many people who do not have scopes weighing 20+ pounds and are thinking about a CGEM DX. The DX is less versatile than the standard CGEM because of this.

#10 WadeH237

WadeH237

    Apollo

  • -----
  • Posts: 1345
  • Joined: 24 Feb 2007
  • Loc: Snohomish, WA

Posted 13 November 2012 - 10:14 AM

You can balance the CGEM DX with smaller scopes, just not with the Celestron supplied 22lb counterweight.

Losmandy makes 7lb and 11lb counterweights that fit the CGEM DX. At a star party this summer, I loaned out one of my Losmandy weights to someone so that they could balance and 8" SCT on a CGEM DX.

It's a better option than adding weight to the OTA side.

#11 ghataa

ghataa

    Viking 1

  • -----
  • Posts: 625
  • Joined: 20 Jun 2011
  • Loc: Central, NJ

Posted 13 November 2012 - 10:17 AM

That's great info on the counterweights for the DX!

George

#12 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2550
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 13 November 2012 - 10:32 AM

You can balance the CGEM DX with smaller scopes, just not with the Celestron supplied 22lb counterweight.

Losmandy makes 7lb and 11lb counterweights that fit the CGEM DX. At a star party this summer, I loaned out one of my Losmandy weights to someone so that they could balance and 8" SCT on a CGEM DX.

It's a better option than adding weight to the OTA side.


The problem is that Celestron does not include or sell a lighter counterwieght for the DX and the counterwieght bar and nut are so heavy that some scope will never balance on it, so if you buy one thinking that you might use your 80mm or 90mm refractor, you won't be able to (Celestron use to sell some lighter counterwieghts for the CGE but stopped doing so long ago). To use your C8, you will have to find some more expensive counterwieghts from another manufacturer that are not readily available on the used market. This is not something that is obvious from the literature anywhere. There are actually very few counterwieghts available for 1-inch diameter bars and those that are tend to be relatively expensive. I'm sure that the person who showed up at the star party expecting to use the C8 on their DX was probably surprised to find out that they needed to borrow someone else's counterwieght to do so.

#13 drksky

drksky

    Surveyor 1

  • *****
  • Posts: 1760
  • Joined: 31 Aug 2009
  • Loc: Bloomington, IL

Posted 13 November 2012 - 11:25 AM

As stated above, Losmandy has all kinds of weights that fit that counterweight bar, and they're not nearly the cost of something like Cassidy weights. I think the 11 pounder goes for $50 and the 7 for $40 or so.

#14 DaveJ

DaveJ

    Surveyor 1

  • *****
  • Posts: 1760
  • Joined: 07 Jan 2005
  • Loc: NE Ohio

Posted 13 November 2012 - 12:39 PM

There are actually very few counterwieghts available for 1-inch diameter bars and those that are tend to be relatively expensive. I'm sure that the person who showed up at the star party expecting to use the C8 on their DX was probably surprised to find out that they needed to borrow someone else's counterwieght to do so.


First of all, the counterweight shaft of the DX isn't 1", it's 1.25" and there's a whole world of available counterweights - both new and used. I have no problem at all balancing whatever scope I want to mount on mine. I have counterweights to handle the requirements.

#15 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2550
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 13 November 2012 - 02:07 PM

There are actually very few counterwieghts available for 1-inch diameter bars and those that are tend to be relatively expensive. I'm sure that the person who showed up at the star party expecting to use the C8 on their DX was probably surprised to find out that they needed to borrow someone else's counterwieght to do so.


First of all, the counterweight shaft of the DX isn't 1", it's 1.25" and there's a whole world of available counterweights - both new and used. I have no problem at all balancing whatever scope I want to mount on mine. I have counterweights to handle the requirements.


Your reaction suggests that you think I am here to bash the CGEM DX. I happen to be the owner of the CGEM DX Yahoo group and a DX owner myself. Yes, I made a typo in my post and the CW shaft diameter is not 1 inch but is instead 1.233 inches. If you have no problem balancing any scope on the DX, then you must only have heavier scopes and/or some very light counterwieghts available.

I can tell you that my Lunt60PT, 70mm Vixen achro, 80mm triplet APO, 100mm achro, and C8 Edge HD cannot be balanced on the DX with the stock counterwieght. My TMB130 balances with the stock counterwieght moved down 2-3 inches from the top. This is with the heavier ADM dual saddle and knobs on the mount. I have one 11 pound counterwieght that fits on the shaft and even with that I cannot balance the Lunt, 70 and 100mm achros or the 80mm APO. The point is that this is not something that is apparent to someone thinking of buying this mount but these are fairly common sized scopes. The average mount is generally either saddle heavy or evenly balanced. Only mounts meant for large loads are likely to be saddle light.

While 1.25 inch counterwieghts are available, they are much less common and, on average, more expensive pound per pound than the .75 inch counterwieghts that fit many mounts including the CGEM, CG-5, LXD75 and numerous other mounts and can be purchased used for about $10. Availability from Losmandy and Casady of 5 to 15 pound counterwieghts from $50 to $150 a piece does not make them common or cheap.

#16 Pat at home

Pat at home

    Ranger 4

  • -----
  • Posts: 328
  • Joined: 16 Mar 2007
  • Loc: Campbellton, New Brunswick, Canada

Posted 13 November 2012 - 05:56 PM

Most machine shops can make you a counterweight of almost any weight you want and also drill and tap a hole for a set screw. Won't cost anywhere near what telescope suppliers charge.

#17 Jim Romanski

Jim Romanski

    Vanguard

  • *****
  • Posts: 2256
  • Joined: 02 Jan 2005
  • Loc: Guilford, Connecticut

Posted 13 November 2012 - 10:13 PM

Ed makes a valid point. Though not impossible the CGEM DX does not come setup with small scopes in mind.

Sure you can make a counterweight but not everyone will want to go through the hassle. I have a CGEM DX and had to wait around to find a used 7.5 pound counterweight for $40 which is what I thought was reasonable. So there are options just not as available or as cheap as with a 1" counterweight.

Another thing to keep in mind is that stock it uses a losmandy size saddle and not the vixen size. So if your scope has the smaller bar you'll need to buy a larger bar or change the mount saddle. I bought an ADM dual saddle...again more money.

Finally, Ed mentions how massive the mount is. It's a BEAST! I believe it's 110 pounds minus the scope. So you should consider this as well. Not a big deal for me since I roll mine out into the yard but it's too big to carry very far fully assembled.

I use mine with the NP127 and it's like a rock. Eventually I will do some imaging with it and I'm sure it will have no problem. The reason I bought the CGEM DX and not the CGEM is that I intend to use larger scopes on it eventually. I also have a CG5 and I could use that tripod with the CGEM DX head if I want to cut down a bit on weight.

If I was only going to use it for the NP127 the GGEM would do just fine.

#18 neilson

neilson

    Viking 1

  • -----
  • Posts: 538
  • Joined: 22 Aug 2010

Posted 13 November 2012 - 10:47 PM

Hi Everyone,
I have recently bought a CGEM DX and love it. I use a 9.25 Edge and guide scope. If I set the counterweight out of balance while imaging and forget to put it back, then slew, the mount has a hard time. My power supply has an Amp meter and it draws about .55amps when slewing on high speed balanced. When slewing both axes at the same time balanced it draws .80amps. If its way out of balance slewing both axes it might reach 1.00amp. I don't see any advantage of the 2.8amp chip they put in it. When I slew at low speeds it has a hard time. If its out of balance it doesn't move at low speeds some times. I wasn't happy at the lack of power when needed at low speeds. But I really like the heavy rock solid tripod. It makes a big difference when imaging. I like the big counterweight bar but I have to put the 22lb counterweight near the end. I'm around 30lbs. So I drilled out an 11 lb. counterweight from an LX80. It works great. But the counterweight bar is so thick It makes no difference if I put the 22lb. counterweight out near the end. I have never owned a regular CGEM but I am glad I bought the CGEM DX.

neilson

#19 mich_al

mich_al

    Vanguard

  • *****
  • Posts: 2445
  • Joined: 10 May 2009
  • Loc: Rural central lower Michigan Yellow Skies

Posted 13 November 2012 - 11:35 PM

Higher amperage to the motors really has little to do with being able to use heavier loads for imaging. All it really does is allow you to use loads that are less well-balanced (which is not a good idea in the first place). A well-balanced mount does not really need more power to move the axis.


I was begining to think about upgrading to a DX. I have a 30lb OTA on my CGEM and was thinking about adding a pair of binoviewers (3-4lbs) which brings me pretty close to the published max. I'm visual only (occasional Mallincam) and pier mounted. Now it sounds like the DX is really no advantage for me.

Al

#20 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2550
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 13 November 2012 - 11:53 PM

Higher amperage to the motors really has little to do with being able to use heavier loads for imaging. All it really does is allow you to use loads that are less well-balanced (which is not a good idea in the first place). A well-balanced mount does not really need more power to move the axis.


I was begining to think about upgrading to a DX. I have a 30lb OTA on my CGEM and was thinking about adding a pair of binoviewers (3-4lbs) which brings me pretty close to the published max. I'm visual only (occasional Mallincam) and pier mounted. Now it sounds like the DX is really no advantage for me.

Al


Realistically, if you are visual only, then you would probably be just fine with the standard CGEM. If you feel you want more stability in the tripod, just add a better spreader.

#21 JMac85X

JMac85X

    Vostok 1

  • -----
  • Posts: 187
  • Joined: 13 Sep 2012
  • Loc: California

Posted 14 November 2012 - 04:48 AM

So if I want to do wide field imaging with an 80mm on my DX I'm screwed? Or couldn't I just piggyback it on my 11 HD which I believe is 27lbs. Or I make sure the refractor isn't too light? And what about using the fastar, anyone have good success with that? I'm just wondering because I've mine for about two months and I've had balancing issues. When I think it's balanced and slew it the motors will struggle and kind of jump so I bring the counterweight down and that solves my problem

#22 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2550
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 14 November 2012 - 08:44 AM

So if I want to do wide field imaging with an 80mm on my DX I'm screwed? Or couldn't I just piggyback it on my 11 HD which I believe is 27lbs. Or I make sure the refractor isn't too light? And what about using the fastar, anyone have good success with that? I'm just wondering because I've mine for about two months and I've had balancing issues. When I think it's balanced and slew it the motors will struggle and kind of jump so I bring the counterweight down and that solves my problem


Yes. By piggy backing or using a heavier OTA you are adding more weight to the saddle end of the axis which overcomes the issue. Again, the problem is that people don't generally expect this to be an issue in the first place. Personally, this is the only mount that I know of that has this issue (although I expect there are other mounts that are specifically designed for heavy loads only).

If the axes are stiff when the clutches are released, balancing will be difficult if possible at all.

#23 esthel

esthel

    Lift Off

  • -----
  • Posts: 7
  • Joined: 21 Jun 2012

Posted 15 November 2012 - 01:33 PM

I'm thinking about buying a CGEM DX and use a 8" sct with it. Will I be able to balance this with a 11lb weight?

#24 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2550
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 15 November 2012 - 03:06 PM

I'm thinking about buying a CGEM DX and use a 8" sct with it. Will I be able to balance this with a 11lb weight?


It should balance with an 11 pound wieght.

#25 fetoma

fetoma

    Vanguard

  • *****
  • Posts: 2411
  • Joined: 26 Sep 2006
  • Loc: Southern NJ

Posted 16 November 2012 - 01:38 PM

Hi Ed,

You should add an aluminum counterweight shaft for the DX to your offerings, or an adapter to use the CGEM counterweight shaft. ;)






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics