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Heq5 pro synscan alignment stars choice.

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#1 neptun2

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Posted 17 July 2009 - 05:22 AM

Hi all. I tested my new heq5 upgraded to synscan and was wondering how you choose alignment stars. I read the user manual and decided to use 3-star alignment with reticle eyepiece to achieve best possible accuracy. I made precise polar alignment using the polar scope and after that put the telescope in home position. I expected the first star to be close to the center of 12mm eyepiece view but it was about 5 degress off. I centered it and the second and third star was much closer but not in the fov of the 12mm eyepiece. Is this normal? I used deneb (cygnus), vega (lyra) and dubhe (ursa major) because i have read that bigger star triangle is better for accuracy and this stars corresponded well to the user manual instructions for star selection. After that all objects was near the center of field of view of my nikon d5000 at prime focus and 1150mm focal length. Is my star selection routine correct? Is this behavior and goto accuracy normal? Please share your opinion.

#2 NewAstronomer

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Posted 17 July 2009 - 10:00 AM

I have the atlas eq6 version but I believe the software is the same. I use arcturus dubhe and vega, during 3 star alingment they are all slightly off, I'd visually center, but gotos with DSI at 420mm were all in FOV, very accurate.


One really nice thing for these mounts is EQMOD, using a PC, u can use any star or dso in planetarium software to sync your mount before skewing to a new target. Gotos really accurate all night. I use cartes du ciel right now.

#3 RandallK

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Posted 17 July 2009 - 10:57 AM

Hi Neptun2,

I managed to save this from a previous post somewhere on the CN forum, it seems to work well for me:

"By the way, here's a little trick someone on CN shared a while back for establishing the mount's "home position" accurately - though as I said in the preceding post, it only helps for finding that first alignment star, or if you're not doing a star alignment at all:

1. Rotate the RA axis of the mount until the counterweight bar is parallel to the ground. Use your level to verify, and set the RA setting circle to 6 hours.

2. Rotate the DEC axis of the mount until the telescope is parallel to the ground. Use your level to verify, and set the DEC setting circle to zero.

3. Rotate the RA axis until the counterweight bar is pointing down to the ground and the RA setting circle is at either 0 or 12, depending on which side of the RA setting circle you're using.

4. Rotate the DEC axis until the telescope is pointing north and the DEC setting circle reads your latitude.

This will geive you a pretty accurate "home position", and if your polar alignment is good and your date and time are set correctly in the SynScan, your first alignment star should end up very close to the center of your filed of view."

#4 Skylook123

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Posted 17 July 2009 - 12:55 PM

That home position fix has been a great help to me in getting a good home to start with. That, and a level starting position, seems to make alignment just work out better.

For the Synta, some empirical experience shows that:

1. Reticle eyepiece use during alignment seems to help greatly in GOTO precision;

2. For the Synta, three star alignment is intended to reduce the effects of cone error in the mount setup. If you don't have cone error, a three star alignment will often give worse results than using less stars;

3. One can get pretty good results, if the home position was appropriate, mount level, and with a good polar alignment, with a single star alignment. Home + level + good polar means all you need is one star to fix the sky orientation. Two star adjusts for off-perfect polar. For public outreaches, I can pretty much navigate all around the sky if I'm careful on the setup and not rushed for the polar and home, and only need a 1 star. If I'm off on polar and home, the alignments become awful as well.

I won't go into the twitchy behavior on alignment star choice; almost a black art with this mount. Find a set that works each season, and live with them. But, as I said, if I do the prep right I can get away with a 1-star for most purposes.

#5 astro_baby

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Posted 17 July 2009 - 01:24 PM

I just let the mount/GoTo select its own stars. It always picks bright ones and generally even if the firts slew is off by a long way you can pretty much see where it was aiming for. I use a wide angle EP to start with then make sure the finder is showing the same. Then do the next two stars just using the finder cross hairs.

It works well enough for me I find with the GoTo always finding stuff thats pretty close to the center of a 26mm EP which is close enough for me as a visual observer.

I also always get the mount level and get a polar alignment fix.

#6 neptun2

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Posted 19 July 2009 - 02:09 PM

Thank you very much for this information. I will definitely use the home position fix. I will also make tests with 2 and one star alignments. Clear skies to you.

#7 markan

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Posted 20 July 2009 - 06:34 AM

Good information. I've got the EQ5 Pro and I've been having trouble with the 3-star alignment, although a big part of the problem is my unfamiliarity with the sky and the use of the finder scope. Tonight (I hope) I'll try the home position fix with Arcturus, Dubhe, and Vega. Three stars I know I can find.

And astro baby: I used your Idiot's Guide to learn how to do a polar alignment. It was a big help. :)

#8 RandallK

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Posted 21 July 2009 - 06:21 PM

One day soon, you're going to lose your "home postion". This can be caused by releasing the clutches while the mount is turned on. I've done this a few times!. I always go back to that little procedure and it gets me back in the ball park.

#9 markan

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Posted 23 July 2009 - 06:06 AM

I purchased an Orion EZ finder for my telescope. It made the 3-star alignment a whole lot easier for me using Arcturus, Dubhe, and Vega. I didn't need to level the mount other than use the bubble level when setting up the tripod. I tried the pointing accuracy enhancement last night as well. It worked great for the area of sky I was looking at.(Cygnus)






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