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Celestron CGEM mount


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Hi all,

I so desperately need help with my Celestron CGEM mount, as I am really struggling to align it.

The set up is:-

The mount with a 10" dobsonian tube a top. The counterweights are properly set up and the tube doesn't pull to either side when moved. The latitude scale is set to 53.5, as I live near Leeds.

Here is what I have been doing when outside (apologies if I get order mixed up):-

Set the mount up outside with the counterweights pointing roughly north, there could be a small error here but it would only be by a few degrees either way.

The time is set to my watch which I got the time from the GMT website.

The time is set to Standard Time (last night it was) the only other option was Daylights Saving.

The date was set to 11/12/12 (The correct date as it was after midnight, the date format it MM/DD/YY)

The location was set to Leeds.

Not sure if I missed anything off there, but I basically completed the setup process with the correct information.

What happens when aligning:-

It asked what star I want in the West and I choose one. It slews to it and if off by a few degrees. I find the star manually and centre it, then use the EP adjust to align it.

It asks me for a second star in the West and again after I choose it it slews to it and this time is way off, as much as five to eight degrees. So again I manually find the star and centre it, then align it.

It now asked for a star in the East, so again I choose one and it slews and it out by ten degrees!

Now here is where last night the clouds came in before I could centre it. One previous nights though I have managed to get it aligned and have been ready to roll with my night.

The problem after that:-

Every time I slew to an object it is either just off centre, on the edge of the FOV and sometimes even outside the FOV and I have to manually scan for it. It seems to have more trouble with objects in the East as they are the ones that don't appear in the FOV. The west is a mixture of the other two. It has never managed to find an object and have it perfectly centred.

One the up side once the object is found it does centre and track it.

I know the problem may sound a little weak (Oh no I have to actually find the object myself etc) but I bought the mount to do this for me. Also there will be times I can't see the object due to light pollution and would like to have faith in my mount that the object is centred so I at least know this, rather than scanning for something I can't see from my location.

All advice is welcome, though it may need to be dumbed down as I am struggling a bit with technical terms.

Thank you for making it this far.

Neil

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hi, you say you set the mount up with the counter weights pointing north, are you not using the index marks on the mount? and are you placing polaris in the axis of the mount?

when I do my alignment stars I use a low power EP to start with and use a high power EP for final centering, 9mm or 6mm. I do this for all alignment stars,

your first two stars were in the west and then your third star in the east, do you put in any more or just three,

I use my two alignment stars and three calibration stars, I find this works well,

if you are only going out to look at a few objects and you know where they are, then a two star alighnment may do, but if you are going hunting for faint fuzzys then you do need the full alignment, this is what I find, hope this helps

by placing polaris in the mount axis isnt perfect polar alignment , but it is fine for visual

Edited by space3
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When I say the counterweights are pointing north I mean that is the side of the mount facing north, I wasn't sure how to describe it. Basically then open end of my light bucket is point roughly in the direct of Polaris before I start my alignment proces.

I have been using a 25mm for aligning the stars, if I used anything less I would probably struggle due to how off it has been.

I used to do two star, but found when I slewed to the East the objects were way off, so have been trying three star instead.

How much difference does it make with have the mount facing perfect North? What kind of difference does the wrong do? Do you have your nearest city or your actually co-ordinates?

I haven't done a polar alignment as the mount says I can simple do a two or three star alignment.

I am aiming at viewing a wide range of objects, so I know where they are. Some I haven't seen from this house and don't know if I can, so it's like I said before it would be good to have the confidence of knowing that when the mount slews me to something it will be in the eyepiece and if I can't see it, then it means it is too light polluted.

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youll need to do a polar alignment, unless your going to do a polar alignment using the hand control,

yes use the 25mm EP and centre the star, then pop in a higher power EP and centre it, then pop back in the 25mm EP for your next star and so on,

I put in my cordinates, but your nearest city should be fine,

set up and level tripod, put polaris in the axis of the mount, RA axis, make sure both your index marks are lined up om the mount before you start alignment,

the more stars you use the more accurate your GOTO will be

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After reading the manual I believe I have polar aligned it. Am I right in thinking this is when you get the bubble on the side central and then match the angle on the Polar alignment plate to your latitude, mine is 53.5?

I went out again tonight and got some appauling results, including aligning the mount using Jupiter. Then going away for two minutes and coming back to find it hasn't tracked. Then asking it to find Jupiter and it failing by about one degree. I mean seriously is it me?

Is my scope too big? Is there a secret trick to balancing the scope or the counter weights? I am starting to do daft things like set it Daylights savings and change the date.

I tried to align it twelve times over the course of two hours and never manged it once, please someone tell me this big secret cos as I write this still full of anger I get the feeling I am not part of the big conspiracy, lol. I dont know if my mount might be broken, I mean how hard it is to break these mounts? Do they have a record of breaking?

Thank for your advice btw, it is very appreciated and am open to all advice/ideas.

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Good start is check that 3 locking screws of losmandy "head" between head and dec ax. in mount are tight. I had problem with them earlier and get same type of problems, missed object maybe 0.5-1 deg after alignment. Screws were loose and heavy scope makes head move.

I have one image here, (language is in Finnish)

https://lh4.googleusercontent.com/-pqh_bMx1j3A/T3KT6V-0HiI/AAAAAAAAHqM/AStcJDHtRe4/s640/Picture%2520026.jpg

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When you balance the mount the weights should be on the left and the scope on the right,I suspect your polar align is miles of,I have this mount pier mounted and I choose vega it's usally a bit of not a lot,after I get another star in the west it's bang on ,3 calib stars are always within a 9mm Ep polar scope is needed to void you problem make sure lock screws are right

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In the cold light of day...

I was having a flick through the manual and came across the section talking about "R.A switch" and "GoTo Calibration" I have a skywatchers 10" dobsonian mounted atop mine, so I don't know if trying this will help but am going to give it a go.

Ransu - Thanks for the photo, I had a look and everything there is tight. I also noticed that my tube is attached to the dovetail bar at roughly the same point yours it feels like the weight centre of the tube. Thanks for the advice.

MikeP - I am going to look into this, because it does seem like this could be a possibility as last night it was over ten degree West of Capella (Auriga) and when I aligned it to Capella and then slewed to Regel (which is East of Capella) it merely dropped to low in the South and rested at a point that Regel can never be at from my location. Thanks for the tip, I will let you know.

Todd - When you say the weights should be on the left, do you mean slightly weight it to one side of do you simply mean when you set up the telescope you should level the weights on the left and the tube on the right (horizontally)? I just read in the book the way to ensure you have Polaris in line with the scope, by taking the cap and the screw end off (who reads manuals, doh!) So I am going to try that.

Is it at all possible that there could be a software problem? Or does it sound like its all me?

Cheers once more for the help :)

Neil

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Is it at all possible that there could be a software problem?

Hi Neil,

Whilst you can never rule out a software issue, I would have thought that with the CGEM being quite a popular mount these days, it would be well publicised.

A couple of suggestions:

1 - Have you browsed through the Mounts section in the Forums on the Cloudy Nights website? Cloudy Nights is USA based and the CGEM is very popular over there. There's quite a lot of threads devoted to the CGEM.

2 - Is there an astronomical society near you that you can visit? If there is then I'm sure someone there would be more than happy to help get you sorted.

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I have a CGEM mount, when i first got the mount i had similar issues but my problems were just down to my methods.

Make sure your mount is level, theres a lot of talk says that with a CGEM mount you dont really need to but for the few mins it taks why wouldn't you make it as easy for the mount as possible. Balance the scope per the instructions weights to the left, OTA parrall to the ground and release the RA clutch

Invest in a polar scope for the mount, when i first started setting mine up i didint have one and looking through the axis i could see polaris roughly centred it and thought i was there, then i got my polarscope and realised i was a mile out, they are fairly cheap and will save you a ton of time.

next deffo go with a smaller eyepiece, i use a 9mm illuminated eyepiece its far more accurate.

The best and most recent trick i have learnt is to use the mounts built in polar align feature, once you have done a two star align slew to a star near the meridian & press align the scope will re-slew & ask you to centre the star in the finderscope, press enter, then in the eyepiece and hit align. Its now ready to polar align hit enter when ready and the scope will slew again this time centre the star using the Alt/AZ bolts, you need to undo the sync afterwards but i turn the scope off and re-two star align.

This method allowed me to go from struggling to expose for 5 mins to 20mins+ in one step, my head nearly fell off i was so pleased.

One other piece of equipment you could use to help is a Telrad finder, makes everything so much simpler.

If you'd like i can send you any pics you need that you think might help.

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I just read in the book the way to ensure you have Polaris in line with the scope, by taking the cap and the screw end off (who reads manuals, doh!) So I am going to try that.

Neil

this is what I was getting at! when you have polaris in the axis of the mount, return you mount to the home position, and make sure the index marks on both axis are aligned, look for the index marks in the manual,

so your counterweight shaft will be pointing to the ground, then do your two star align and calibration stars

good luck

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Thanks for the continuing advice.

Mav - I have started again with balancing the scope and have slightly weighted it to the left, so hopefully it will help. I think a polar scope could help. I don't understand how it could be off by as much as ten degrees if Polaris is not completely in the cane of the axis, but we will find out. I thought it could be the time, but after I set it to Daylights savings it was still way out. Any pictures would help actually. The new trick you said, doesn't completely sink in and I may need it explaining as you would a child, haha.

Space - This is my next big idea for the next clear night, fingers crossed and hopefully not me cross.

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You need to set the scope to Standard Time your out of Daylight Savings now.

Deffo want the polar scope, you need to make sure at the very least that Polaris is visible through the axis of the mount. As for polar alignment using the handset........

Do your 2 star alignment as normal, hit enter when in the finderscope & align once centred in the eyepiece, you know the drill..... Rememeber the higher powered the eyepiece the more accurate you'll be.

Once thats done...

1) Pick a star as close to the meridian as you can, i always just check stellarium to see which star is in my view to the south. Pick the star from the 'Named Stars' list on the handset, so......

I) Button 8

ii) then use buttons 6&9 to move up and down through the menu till you get to the 'Named Stars & hit enter

III) 6&9 again to find your star and then hit enter

at this point the scope will slew to the target star lets say Altair.

2) Your now ready to polar align the mount

i) Press Align on the remote & again use 6&9 to move to the polar align menu, press enter

ii) Move to the option that says polar align and again press enter

iii) Read the remote at this point it will start to prompt you on what to do. Press Enter when ready

iv) The scope will slew to Altair and you will be prompted to centre first in the finderscope and then in the eyepiece as you would during your star alignment. Press enter when finished.

3) Now the scope will slew to Altair again, where Altair should be if the scope was polar aligned properly. at this point put the remote down and back away from it.

i) USING ONLY THE ALT/AZM BOLTS recentre the star in the eyepiece, if the star is outside the FOV switch to a say a 20mm, centre using just the bolts then put your high mag eyepiece and keep centering (this is where the illuminated eyepiece helps)

ii) Once you are finished press enter on the remote

4) Lastly you need to un-sync with Altair, there is a way to do this on the remote but for the sake of this example i just turn the scope off then on and re-do the 2 star align, the mount remains polar aligned

This might sound a little long winded but once you have a go its actually quite easy, ive had my mount 2 years and only found out about this thanks to Martin about 3 weeks ago :mad: ive done it once and as i mentioned earlier went from 5 mins exposures to 20min+. As you are doing this the remote is telling you what to do so just take your time to read it as it scrolls.

If they havent changed the manual check out page 37, its all on there

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