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Do you want to improve GoTo accuracy?

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#26 DaveJ

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Posted 11 April 2013 - 03:10 PM

Glenn, can you put that description of how to get rid of cone error in laymans terminology.


I'm not Glenn, but I've done this with my old G-11. Set your mount up pointing north, exactly as you would for regular viewing. Turn the RA until the counterweight bar is horizontal pointing toward the east. Turn the OTA in DEC until it's pointing at Polaris. Yes, POLARIS - not the NCP!!!!!!! Adjust the AZ manual controls until Polaris is dead center - go ahead and move the OTA in DEC to center Polaris because the DEC position doesn't matter at all here. Got Polaris centered? Good! Now rotate the whole contraption until the counterweight bar is again horizontal, but now pointing toward the west. Move the OTA in DEC and try to get Polaris centered again. If you can't, you have cone error. Determine which end of the OTA needs to move away from the dovetail plate to center Polaris and start shimming until you can repeat this exercise with Polaris staying centered. Remember, movement in DEC doesn't matter - move it until you get Polaris centered as well as possible. I used an old set of metal feeler gauges and kept moving up/down in size until I got the OTA shimmed by inserting them in between the dovetail rail and the OTA rings. Am I making myself clear?

#27 James Cunningham

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Posted 11 April 2013 - 03:15 PM

Thanks. Now I understand. Glenn can be a bit over the top in his choice of wording.
Jim

#28 obin robinson

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Posted 11 April 2013 - 03:21 PM

Get yourself a wide field illuminated cross hair eyepiece.


Agreed 100%. On my satellite spotting rig I have a finder scope which used to be an 8x50 inverted view. I chopped the tube and moved the focuser forward then added a correct image diagonal and crosshair eyepiece.

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I make sure that the time in the handset is EXACT down to the second and the Lat/Long is down to .001 degree. I use a Lowrance GPS to set the clock and the Lat/Long. When setting up alignment I put the star DIRECTLY under the crosshairs of the finder scope. I do a three star alignment as well.

How long does this take? About 3-5 minutes total. I also make sure to "PARK" the scope at the end of the night. I have found that all my gotos are spot on for the entire night.

obin :jump:

#29 fmhill

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Posted 11 April 2013 - 03:22 PM

I've not seen any mention of using a Laptop and software for mount control but as the user of a CGEM DX mount with various telescopes, I use the ASCOM mount control utility with Stellarium and Astrotortilla plate solving software.

Astrotortilla is amazing software, it will aim the mount/OTA for gotos within 1 arcminute or better in a matter of a couple minutes or less... Astrotortilla does not need any mount alignment to work, simply an image from the primary imaging camera or from a guiding camera to work. A plate solve typically takes less than a minute, sometimes longer on a complex image and then will slew the mount to a corrected position of any target you choose in Stellarium...

I no longer use a finder scope or an eyepiece to aim the mount/OTA, Astrotortilla will do it much faster and more accutately than I ever could and I've been doing it for years, long before we had GoTo capable mounts.

Using Astrotortilla, from the time I turn the power switch on the mount to "ON", I can be on target ready to image in five minutes...

Astrotortilla is revolutionary software...

#30 James Cunningham

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Posted 11 April 2013 - 03:32 PM

I have had that program for a while but never could figure out how to use it or even how to input what my coordinates were.
Jim

#31 fmhill

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Posted 11 April 2013 - 03:55 PM

Jim,
Astrotortilla is new software still in development and an advancing technology.. There is a new release just out, Ver. 0.5.1, Assuming you have Windows on a PC or PC Laptop, go to the Sourceforge page for Astrotortilla, look under files and you will see two listings, one for X86 (32 bit) and one for X64 (Windows 64 bit)... This will get you the installer which is updated to automatically load the correct index files which are also recently updated...

If you or anyone else wishes to try Astrotortilla, I would suggest the first thing you do is start a new thread titled "Need Help with Astrotortilla"... I have been a user of Astrotortilla since version 0.2.10 and have helped a number of users get started, however as there is no manual at this point and the "Get Started" documentation is never up to the level of the lastest versions with significant changes, rather than hi-jack this thread, it would be best to have a thread for Astrotortilla itself...

You are also welcome to contact me by PM or e-mail if interested...

#32 mclewis1

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Posted 11 April 2013 - 04:40 PM

Glenn, can you put that description of how to get rid of cone error in laymans terminology. Thanks. Jim

Jim,

First cone error only applies to an EQ oriented mount (your CPC on a wedge for example ... or a gem like your CG-5). You adjust for cone error on Celestron mounts by adding the calibration stars as part of the initial alignment routine.

With a permanently mounted scope you can also spend the time as Dave has described to remove or reduce cone error caused by the miss alignment of your scope(s) and the axis of the mount. This will make things like the initial alignment (gotos) even more accurate.






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