Author Topic: Tell me about GoTo accuracy  (Read 469 times)

acbacema

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Tell me about GoTo accuracy
« on: December 23, 2017, 11:01:30 PM »
I set my CEM25P (nice video), leveled my tripod, polar aligned the mount with the range&app, then one point aligned to Vega.  If slewed fairly close at 560mm focal length.
Crossing across the meridian to ursa major, it looked farther off and that I had to zoom together with my 100-400mm lens (+1.4x extender) to find the celebrity easily.
I synched this celebrity.
Then I went into the local whirlpool galaxy and GoTo perfectly centered it in my own field of view.
(I have a Riegel blog finder I need to get out of my closet.)

Please share your tips on how you optimize your GoTo accuracy and the way you adapt when objects are not in your field of view.

thanks!
David



monsresiwor

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Re: Tell me about GoTo accuracy
« Reply #1 on: December 23, 2017, 11:53:38 PM »
Following a Polar Alignment, I typically do 12 stars for positioning... 3 in each quadrant of the sky... I have not had the circumstance, except maybe the first celebrity, where they were not in the FoV...

junktranasop

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Re: Tell me about GoTo accuracy
« Reply #2 on: December 27, 2017, 07:39:26 PM »
I should have clarified... the HC (hand controller) I have has only a 3 star option... and generally that is fine.... especially for visual astronomy... I don't use the HC anymore. I use Stellarium to control the mount, so you can basically align to as many stars as you like...

For AP work with my CCD, which does not have a pretty 'live view' setting, and a practice pi generally looks like a lot of noise, I like to have my go-to's very accurate, and 12 seems to work very well for me...

bronedproudem

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Re: Tell me about GoTo accuracy
« Reply #3 on: December 28, 2017, 07:04:25 PM »
Quote
I should have clarified... the HC (hand controller) I have has only a 3 star option... and generally that is fine.... especially for visual astronomy... I don't use the HC anymore. I use Stellarium to control the mount, so you can basically align to as many stars as you like...

For AP work with my CCD, which does not have a pretty 'live view' setting, and a practice pi generally looks like a lot of noise, I like to have my go-to's very accurate, and 12 seems to work very well for me...

How do you align your mount with Stellarium? I've been aligning the mount with Nexremote and then using Stellarium for go-to slews.

James Pederson

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Re: Tell me about GoTo accuracy
« Reply #4 on: December 29, 2017, 09:31:20 AM »
Quote
I zero positioned my CEM25P (nice video), leveled my tripod, polar aligned the mount with the scope&app, then one point aligned to Vega. If slewed fairly close at 560mm focal length.
Crossing over the meridian to ursa major, it seemed farther off and I had to zoom out with my 100-400mm lens (+1.4x extender) to find the star easily.
I synched this star.
Then I went to the nearby whirlpool galaxy and GoTo perfectly centered it in my field of view.
(I have a Riegel site finder I need to get out of my closet.)

Please share your tips on how you optimize your GoTo accuracy and how you accommodate when objects are not in your field of view.

thanks!
David


I also use a one-star alignment with an equatorial mount. Accuracy is nearly always right-on with the target very close to center as long as I stay on the same side of the meridian. However, when doing a meridian flip, I usually slew first to a bright star on that side of the meridian and do a new one-star alignment on it before going to the desired target.

Why? Cone error. In most cases there is a misalignment between where your OTA is pointing to and where your mount is pointing to. Doing a one-star alignment compensates for this difference as long as you stay on the same side of the meridian. But do a meridian flip and the difference -- the cone error -- gets doubled obviously decreasing the GOTO accuracy.

Check your mount manual to see if it has either a hardware or software solution to minimize cone error. My mount doesn't offer a solution and that's why I have to re-align after a meridian flip.

By the way, I'm no expert on this. Others may be able to explain this better.
Tom

Noe Subeydhi

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Re: Tell me about GoTo accuracy
« Reply #5 on: December 30, 2017, 07:21:53 AM »
I'm not sure you can do it with your CEM... will that work with EQMOD?

witchcycsuti

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Re: Tell me about GoTo accuracy
« Reply #6 on: December 30, 2017, 02:55:08 PM »
I always sync to any target I'm visiting, even if just a transitory object on the way to my real target. They don't generally come in spot-on centered, but they always come into view of my camera FOV, at which point I can re-center (and re-sync!). My camera FOV is far smaller than the eyepiece FOV.

bardeperdi

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Re: Tell me about GoTo accuracy
« Reply #7 on: December 31, 2017, 08:55:10 AM »
Great tips.
As far as cone error, the CEM25P manual states to do the 3 star alignment. If things are too far off, then I'm shimming.

Interesting about cone error and meridian. Thank you.

Matthew Calhoun

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Re: Tell me about GoTo accuracy
« Reply #8 on: December 31, 2017, 08:55:43 PM »
Quote
I'm not sure you can do it with your CEM... will that work with EQMOD?

Not sure what you're asking will work with EQMOD. EQMOD has an alignment option to only use alignment points on the side of the meridian that the scope is pointing to. If you do this, you'll need some alignment points on both sides and cone error is less of a factor in your GOTOs.

If you're running EQMOD, you're using a computer which ignores any sky alignment you've done using the hand controller. I found that an easy solution to building sky alignment points with EQMOD is to use plate solving with AstroTortilla.

Phil

ciomasbure

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Re: Tell me about GoTo accuracy
« Reply #9 on: January 04, 2018, 05:21:55 AM »
Quote
I don't use the HC anymore. I use Stellarium to control the mount, so you can basically align to as many stars as you like...
Does skysafari do this as well?
I have the starfi coming.

John Edwards

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Re: Tell me about GoTo accuracy
« Reply #10 on: January 09, 2018, 04:22:19 AM »
I do 4 and its still a joke

Elroy Stockton

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Re: Tell me about GoTo accuracy
« Reply #11 on: January 09, 2018, 06:47:54 AM »
Quote
Quote
I don't use the HC anymore. I use Stellarium to control the mount, so you can basically align to as many stars as you like...
Does skysafari do this as well?
I have the starfi coming. 

The answer is yes.
Sent from my iPhone using Tapatalk

ivirlocri

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Re: Tell me about GoTo accuracy
« Reply #12 on: January 10, 2018, 06:44:34 AM »
I use Skysafari with 4 stars, two east, two west and it is as accurate as I am when centring the stars.

If I had an off night I pick a star local to what I am trying to see and centre with it.

The technology works fine for me.

proporasat

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Re: Tell me about GoTo accuracy
« Reply #13 on: January 10, 2018, 08:46:38 AM »
When I use my go to scope I make sure the mount is level and center the alignment stars. Also I use my lowest power eyepiece to give me the widest fov so that most of the time when It slews to the object it's usually in the eyepiece. I consider it more of a "close to"

Doug Woods

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Re: Tell me about GoTo accuracy
« Reply #14 on: January 10, 2018, 09:23:52 AM »
Quote
I always sync to any target I'm visiting, even if just a transitory object on the way to my real target. They don't generally come in spot-on centered, but they always come into view of my camera FOV, at which point I can re-center (and re-sync!). My camera FOV is far smaller than the eyepiece FOV.

That clarifys my head scratching wondering on why, my alignment stars are never centered when using SGP frame and focus.
When using an EP, the very first star would ALWAYS be near center. When I switched to a CMOS camera and SGP, assumed the same would happen but star is SOMETIMES not in the FOV on the SGP screen.