Celestron CGEM DX Opinions Please

[John]

I've been offered a Celestron CGEM DX as a potential mount to handle my Istar 6" F/12 refractor. The scope weighs around 14kg and is around 1.8 metres long. I'm not going to image with it but I'd like a mount that can hold the tube reasonably steady for visual use and at a reasonable height, though the use of a pillar extension if needed. I don't really need the GOTO function but it's part and parcel of the mount so I'll need to find the most straightforward way to use it. I guess it can't be by-passed and the handset just used as a dual axis drive controller ?

I guess using a Losmandy dovetail system would increase stability too ?

Any feedback from those who have used one of these mounts would be very welcome 

[FLO]

The Celestron CGEM DX (and the regular CGEM) are nice mounts but they suffered from a firmware bug which had a tendency to over-correct 'cogging' errors. This was a problem for astro-imagers wanting to autoguide (interestingly the more precise the polar alignment, the more it misbehaved). Celestron have now released a firmware update which has fixed the error but it arrived too late for some owners who have sold their mounts. Today we have no concerns recommending CGEM and CGEM DX mounts, they both perform well and are a pleasure to use. They are also a good buy secondhand (just remember to upgrade the firmware). This is just as well because Skywatcher's AZ EQ6-GT has entered the ring and is a formidable competitor. 

Celestron's CGE saddle does increase stability but differs slightly from the Losmandy-type saddle so if you own a Losmandy-type dovetail it is probably worth checking it will fit first. 

John, if the mount has been looked after and the price is right you really cannot go wrong  

HTH, 

Steve 

[John]

Thanks Steve - that does help 

The scope is fitted with a Vixen compatible dovetail bar as standard so I'll need to get and fit a CGE one.

[Neil27]

I can only agree with the comments from Steve.

I managed to bag a second hand, very lightly used CGEM for a really good price and it is a pleasure to use.

I haven't updated the firmware yet as I am visual only for moment, but I will at some point image and will have a mount that by all accounts from the previous user can go 3 to 4 minutes unguided with a short tube refractor!

I look forward to putting that to the test, who needs a EQ8?....

Neil.

[ollypenrice]

I can only agree with the comments from Steve.

I managed to bag a second hand, very lightly used CGEM for a really good price and it is a pleasure to use.

I haven't updated the firmware yet as I am visual only for moment, but I will at some point image and will have a mount that by all accounts from the previous user can go 3 to 4 minutes unguided with a short tube refractor!

I look forward to putting that to the test, who needs a EQ8?....

Neil.

I do! I have four mounts in the EQ6 area and they won't carry what I need them to carry.

Buying new, I'd go for the AZ EQ6 over the Celestron without a doubt. I've used a CGEM DX and while it is a beefed up NEQ6 I felt it was beefed up where it didn't really need to be and wasn't where it did. Since, like most people, I have a hell of a lot of respect for the NEQ6 this isn't a big complaint, it's just a doubt about the significance of any great difference between the Celestron and the NEQ6.

Olly

[perfrej]

I haven't tried any Celestron mount offerings yet, but I have to agree with Olly. Not because I have heavy scopes, but because I feel that you cannot over-mount a scope. As for 3-4 minutes unguided, well... Where do you draw the line? 30% elongated stars (just visible), less, more? If it does 4 minutes, how do they look, and what happens at five?

I think that either a mount does unguided or it doesn't. The limit in time must be set by some consistent criteria, such as half of the time at which you actually notice that the stars are not perfectly round. If that isn't within the range of normal subs, you do have amount that needs guiding. In fact, I can go as long as stating that if you cannot do half an hour with perfectly round stars why even bother to not guide?

Guiding will put you into hours on end in terms of exposure if you do not have poor polar alignment causing field rotation. You will have perfectly round stars and a happy life.

Thus, the number of minutes a mount can "do" unguided (as per definition above) is not a determining factor in a mount's "quality". I, for one, would rather have a mount that responds well to guiding and does 2 minutes tops of unguided, than one that does 15 minutes unguided and responds poorly to guiding.

Important factors will be consistency, repeatability, and lack of slack. All those can be guided out after finding the proper sub length and the guide factor. A properly handled, and perhaps slightly tuned, NEQ6 is King in this respect, but it doesn't reliably carry much. Again, repeatability is an issue for any mount loaded to the max (as soe have done here on SGL - I don't buy into that).

The NEQ8, which some obviously need, is looking like a true performer as well. It needs guiding so why even bother to find out if it can do 5, 10 or 20 minutes of unguided operation - consistently.

If your Celestron mount is based on the NEQ6 you're in luck. It can be tweaked into a true performer! But please, don't even think about the unguided thing as it is totally besides the point . Once it responds properly to guiding it will a very good companion! I would, however, like to point out the fact that you are looking at a very long focal length as well as physical length and weight, all definitely up at the very top of what an NEQ6 would be able to handle. You may need a beefier mount than you think...

Below the center part of my S2 from last night before the fog descended on me. Living by the Baltic Sea is great in all respects but humidity. You can see the individual pixels from the Tak106/QSI683. Exposure is 20 minutes. Did I guide or did I not? 

Turned into a slight morning rant - y'all have a nice Thursday 

/per

[celkins]

I've been offered a Celestron CGEM DX as a potential mount to handle my Istar 6" F/12 refractor. The scope weighs around 14kg and is around 1.8 metres long. I'm not going to image with it but I'd like a mount that can hold the tube reasonably steady for visual use and at a reasonable height, though the use of a pillar extension if needed. I don't really need the GOTO function but it's part and parcel of the mount so I'll need to find the most straightforward way to use it. I guess it can't be by-passed and the handset just used as a dual axis drive controller ?

I guess using a Losmandy dovetail system would increase stability too ?

Any feedback from those who have used one of these mounts would be very welcome 

I'm very happy with my CGEM-DX that I bought from FLO; handles my 6" R152s without problem.

Carl.