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Pointing problems with EQ-G

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#1 John Downing

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Posted 20 May 2013 - 01:00 AM

Just set up a new OTA on my EQ-G. Had problems getting my pointing errors to less than 50 arcsec. Ran several TPoint models and used that to refine the polar. Got that refined down to about 1 arcmin off in each axis before it got too late. But the pointing remained the same at about 50 arcsec. Is this the best I can get out of this mount? Any advice on how I can get better pointing? Thanks in advance, John (Am using The Sky connected through the hand controller.)

#2 rmollise

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Posted 20 May 2013 - 08:25 AM

Maybe I'm just old fashioned or dumb, but 50-arc seconds sounds pretty good to me. :lol:

I HAVE heard tell of even better with EQMOD, though. ;)

#3 John Downing

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Posted 20 May 2013 - 09:05 AM

Well Rod, I have to admit I have little experience with this mount although I have had it for over two years and don't know what to expect from it. For visual this is fine. But I want to use it for AP & photometry with a 40D and ST-8 repsectively. So with the 40D and larger well defined objects I won't have much of a problem. But with the ST-8 and a 13x20 arsec. fov looking for patterns in faint stars to locate variables it will be more difficult, but not impossible. One thing I am worried about is the mount's having sat idle for a couple of years. Looking for advice about taking it apart, cleaning gears, lubrication etc. With the C925 it is not being weight challenged, good balance, it is quiet when slewing but does groan a bit at the start of a slew.

#4 John Downing

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Posted 20 May 2013 - 09:19 AM

I have been reading a threat (about two years old) about this subject and would like to add that my mount is 'stiff' on both axes which was noted when I balanced it. So my balance probably wasn't as good as I thought. Any recommendations on proper lubrication for the gears?

#5 rmollise

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Posted 20 May 2013 - 10:39 AM

Well Rod, I have to admit I have little experience with this mount although I have had it for over two years and don't know what to expect from it. For visual this is fine. But I want to use it for AP & photometry with a 40D and ST-8 repsectively. So with the 40D and larger well defined objects I won't have much of a problem. But with the ST-8 and a 13x20 arsec. fov looking for patterns in faint stars to locate variables it will be more difficult, but not impossible. One thing I am worried about is the mount's having sat idle for a couple of years. Looking for advice about taking it apart, cleaning gears, lubrication etc. With the C925 it is not being weight challenged, good balance, it is quiet when slewing but does groan a bit at the start of a slew.


I guess I'm not sure why a 1' pointing accuracy would be a problem. Mine routinely puts anything I want on the chip of my Mallincam Xtreme, which is very small indeed, about the size of the ST-8, I reckon. And always in the same general area of the chip. And this is without doing anything more than syncing on three stars with EQMOD. ;)

As long as your mount has been stored in decent conditions, there is no need/reason to take it apart and mess around. Sounds like it is performing very well: "The Only Enemy of Good Enough is More Better." :lol:

#6 Phil Sherman

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Posted 20 May 2013 - 11:06 AM

Older Synta mounts were lubricated with what's been called "black tar" grease that gets very stiff. The only fix is to disassemble your mount, clean out all of the grease and lubricate it with a better grease. I'd strongly recommend visiting the EQ6 forum on YAHOO to get more information about doing this.

There's a couple of ways to fix your pointing problem. You should be using EQASCOM (aka EQMOD) to run your mount from the computer. You can use the hand controller in "PC Direct" mode or buy a USB to RS232 adapter that outputs TTL voltage levels or buy/build a voltage level converter to connect an RS232 output to the mount. EQMOD's pointing model should give you better than a few arcsecs accuracy. If you're permanently pier mounted, you can save and restore the pointing model, avoiding a nightly rebuild of it.

Once you're using ASCOM to control your mount, you can also try using AstroTortilla to point your mount. This tool will take a picture using your camera, plate solve it, then use the results to move the scope to your designated coordinates. You can have it iterate this process until it meets your accuracy specification.

Phil

#7 Phil Sherman

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Posted 20 May 2013 - 11:27 AM

So with the 40D and larger well defined objects I won't have much of a problem. But with the ST-8 and a 13x20 arsec. fov looking for patterns in faint stars to locate variables it will be more difficult, but not impossible.


Are you sure about the FOV with the ST-8? The number seemed small to me so I used an online calculator to check it. I used 9.25"@f/10 for your scope and 1530x1020 9um pixels for the camera. I got the same numbers you have, 20x13, but the results were in arcmin, not arcsec.

Phil

#8 rmollise

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Posted 20 May 2013 - 12:00 PM

Older Synta mounts were lubricated with what's been called "black tar" grease that gets very stiff. The only fix is to disassemble your mount


This was never the case with the go-to models.

#9 EFT

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Posted 21 May 2013 - 10:01 AM

Older Synta mounts were lubricated with what's been called "black tar" grease that gets very stiff. The only fix is to disassemble your mount


This was never the case with the go-to models.


I have actually seen some older EQ-G mounts (not conversions) with the black tar. Hate it!!






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