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ASCG-5 GT and Meridian

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#1 astroalex

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Posted 03 September 2009 - 07:56 AM

Hi,

I hear tell the ASCG-5 GT has a problem when the tracking hits the Celestial Meridian. Does the mount stop tracking when this happens? Can it "recover" somehow.

Checked my Starry Night program and can see the Meridian is low in the north. Don't think I would cross it anyways.

But, what is going on here with this mount? Think other mounts are prone to this also, except the new CGEM. :confused:

#2 rmollise

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Posted 03 September 2009 - 08:54 AM

Hi,

I hear tell the ASCG-5 GT has a problem when the tracking hits the Celestial Meridian. Does the mount stop tracking when this happens? Can it "recover" somehow.

Checked my Starry Night program and can see the Meridian is low in the north. Don't think I would cross it anyways.

But, what is going on here with this mount? Think other mounts are prone to this also, except the new CGEM. :confused:


The Meridian is the imaginary line in the sky that runs from north to south--through the NCP (Polaris), through your zenith, to the SCP and back around.

All GEM mounts will only track through the meridian for a limited amount of time due to the mechanics of the situation.

#3 mclewis1

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Posted 03 September 2009 - 09:21 AM

There's nothing special about the CG5 ... it's a common trait of all commercial gems. Nothing magical happens to a CG5 when it crosses the meridian. If you keep going manually you risk having pieces bump into each other. How far past depends on the design of the mount, cables, what scope you have, etc. The CG5 and CGEM also have slew and tracking limits that can be set in software (via the hand controller), with these limits properly set the scope will simply stop tracking at some point either at or past the meridian preventing any damage.

The movement used to reposition the mount on an object once you've gone past the meridian is called a meridian flip. If you are tracking an object up to and maybe past the meridian and you then do a goto to the object the mount will do a meridian flip and start tracking the object from the other side of the meridian. If you are using external software to control the mount some versions will even do an automatic flip while your tracking. The CGEM works exactly the same way as the CG-5 and in the latest HC firmware there is also a Meridian function which lets you set some preferences as to how the scope will behave when slewing or tracking around the meridian.

When you first start using a mount it's always best to spend some time getting to know it's idiosyncrasies. Check it's full range of movements with all your gear loaded up and even then keeping an eye on cables and such when your imaging is just a good idea.

#4 LLEEGE

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Posted 03 September 2009 - 09:40 AM


All GEM mounts will only track through the meridian for a limited amount of time due to the mechanics of the situation.

Not exactly correct. Many mounts will track 360° in RA. Depending on OTA orientation, you are only limited by the length or elasticity of the cables. :lol:

#5 Luigi

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Posted 03 September 2009 - 11:23 AM

>>>Many mounts will track 360° in RA. <<<

My G11 did and my CG5 did until I updated the firmware. Now it will only go a max of 110 degrees either side of where the RA axis was when powered up or initialized which equals a max of 20 deg past the meridian.

#6 rmollise

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Posted 03 September 2009 - 04:49 PM



All GEM mounts will only track through the meridian for a limited amount of time due to the mechanics of the situation.

Not exactly correct. Many mounts will track 360° in RA. Depending on OTA orientation, you are only limited by the length or elasticity of the cables. :lol:


You are exactly right. Assuming you don't have a _telescope_ on said mount, anyhow. Details! Always details! :roflmao:

#7 astroalex

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Posted 03 September 2009 - 05:14 PM

Thanks MUCH guys!

Yea, "The Meridian Flip". It's all coming back to me know. Had an Edmund 4in pipe mount and GEM, but didn't really know how to set it up, not having anyone to ask these types of questions too. (CN is the BEST place for this!)

Guess the CG-5 is in my immediate future. Can't stand the jiggles of the AT Voyager with my new AT102ED on it. But, then again guess I'm spoiled somewhat with the solidity that the XT10 has given me. It's funny thou, the XT10I has all the necessary mods, but nothing was done to make it more stabil. What I need is a dob mount that will hold the AT102ED ! :) (Details)

#8 Fred1

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Posted 03 September 2009 - 07:14 PM

Can't stand the jiggles of the AT Voyager with my new AT102ED on it.


My AT Voyager is pretty stable. Two second calm down with my 8"SCT/FS/Binos/24mm Pans/Dewshield on it, which come to just about 19.5 lbs, near the mount's specified limit. Less than 1 second with my 80mm. Be sure all is tightened down, especially the azimuth and altitude clutch screws.

Perhaps my JMI Microslew motors, which I've had since purchasing the mount, are a greater asset than I give credit, as it prevents me from trouching the slo-mo knobs and I have electronic focusing, too.

#9 mclewis1

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Posted 04 September 2009 - 06:50 AM

Can't stand the jiggles of the AT Voyager with my new AT102ED on it.

Al, When I started putting the larger refractor on the Voyager (my 115mm) I too noticed a bit more vibration than I expected (the Voyager was already on a heavier tripod - from a CG-5 - a big improvement).

It took a bit of poking around but I found that the Voyager was starting to loosen up a bit (I had been traveling quite a bit with the mount recently). I decided to take a look at the mechanicals and was able to tighten up two areas. Some of the small set screws on the Alt axis were coming loose and this caused a bit of a rocking motion. The second was just backlash in the slo motion gear. I adjusted/tightened both of these and I'm much happier with the mount when I've got the heavier scope mounted. With the rings and dovetail plate I'm probably putting close to 18lbs on the mount.

#10 LLEEGE

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Posted 04 September 2009 - 02:19 PM


You are exactly right. Assuming you don't have a _telescope_ on said mount, anyhow. Details! Always details! :roflmao:

Depends on where it's pointed and how long the OTA is. :grin:

#11 rmollise

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Posted 04 September 2009 - 04:54 PM



You are exactly right. Assuming you don't have a _telescope_ on said mount, anyhow. Details! Always details! :roflmao:

Depends on where it's pointed and how long the OTA is. :grin:


Normally, I point mine at the sky, but that is just me! :rimshot:

#12 LLEEGE

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Posted 04 September 2009 - 06:45 PM

:shrug: :john:






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