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Equipment Discussions >> Mounts

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nobbygon
super member


Reged: 03/20/09

Loc: Australia
PEC - This can't be right! NEQ6
      #5568172 - 12/12/12 07:41 PM Attachment (60 downloads)

Hi,

I've recently pier mounted my NEQ6 and last night finished my polar alignment so that the star wouldn't move over 10 mins. I've never tried PEC before so decided to give it a go. My results are attached. I captured the data on a DSI II Pro and an Orion short tube 80 (FL 400mm)using PHD. Shot on a star on the meridian near the equator.

I canít believe that my PE is only +9 -12 arcsecs. I was expecting more like +- 30. What could I have done to get incorrect data that would show a PE less than what it really is? Could it be that the scope that I shot the data through has a focal length that is too short?

I wanted to see how my guiding was going and to my surprise I've never seen it as good as this before. OSC index of 0.19 and RMS of 0.12. I've never seen numbers that good before. Maybe itís down to a really accurate polar alignment. Any thought here?

Cheers for any help,
Angus.


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nobbygon
super member


Reged: 03/20/09

Loc: Australia
Re: PEC - This can't be right! NEQ6 new [Re: nobbygon]
      #5568174 - 12/12/12 07:42 PM Attachment (46 downloads)

And the guiding graph

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orlyandico
Postmaster
*****

Reged: 08/10/09

Loc: Singapore
Re: PEC - This can't be right! NEQ6 new [Re: nobbygon]
      #5568328 - 12/12/12 09:35 PM

+10 / -12 is a very good figure. It is possible to get an NEQ6 with that level of precision.

The only reasons I can see for mis-reporting of this figure is (1) not factoring in the declination when importing the PHD log into PECPrep; (2) incorrect pixel size when importing the PHD log; for example the Meade DSI has 9.6 x 7.5 um pixels. If the wrong axis gets chosen when calculating, your PE would be proportionately larger or smaller; and (3) incorrect focal length of the guide scope.

However, given your data (400mm FL and DSI Pro II) that's an image scale of 4.27" per pixel. RMS of 0.12 means you are guiding at (4.27 * 0.12) = 0.51" ! that is an amazing figure, comparable to a Mach1.

The best I can do on my CGEM is 0.18 RMS @ 9.71" / pixel which is 1.75" RMS. This is about 3X your figure. But then again my CGEM has +/- 20" of PE.


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korborh
scholastic sledgehammer
*****

Reged: 01/29/11

Loc: Arizona
Re: PEC - This can't be right! NEQ6 new [Re: orlyandico]
      #5568342 - 12/12/12 09:42 PM

Is that star saturated?

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andysea
Pooh-Bah
*****

Reged: 09/03/10

Loc: Seattle, WA
Re: PEC - This can't be right! NEQ6 new [Re: orlyandico]
      #5568423 - 12/12/12 10:59 PM

Yeah that's about right. I get 0.3"~0.5" RMS with my mounts.
I think it means that the PE is easily guided out right? That NEQ6 is a keeper!

Andy

Edited by andysea (12/13/12 01:27 AM)


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nobbygon
super member


Reged: 03/20/09

Loc: Australia
Re: PEC - This can't be right! NEQ6 new [Re: andysea]
      #5568439 - 12/12/12 11:12 PM

Yeah I'm prety sure the star is saturated. If not it's pretty close. Does that have anyhting to do with how PHD guides?

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korborh
scholastic sledgehammer
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Reged: 01/29/11

Loc: Arizona
Re: PEC - This can't be right! NEQ6 new [Re: nobbygon]
      #5568566 - 12/13/12 01:22 AM

If star is saturated, the centroid calculated by PHD would be incorrect and hence show its not moving. All those saturated pixels and large size of the star can mask the movement of the centroid as information is lost.

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gezak22
scholastic sledgehammer
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Reged: 08/15/04

Loc: On far side of moon. Send help...
Re: PEC - This can't be right! NEQ6 new [Re: nobbygon]
      #5568579 - 12/13/12 01:42 AM

Quote:

Yeah I'm prety sure the star is saturated. If not it's pretty close. Does that have anyhting to do with how PHD guides?




Under 'Tools' there is an option 'Auto select Star' or something like it. It automatically selects the star with the highest SNR in the guide image.


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andysea
Pooh-Bah
*****

Reged: 09/03/10

Loc: Seattle, WA
Re: PEC - This can't be right! NEQ6 new [Re: gezak22]
      #5568763 - 12/13/12 07:32 AM

Quote:

Quote:

Yeah I'm prety sure the star is saturated. If not it's pretty close. Does that have anyhting to do with how PHD guides?




Under 'Tools' there is an option 'Auto select Star' or something like it. It automatically selects the star with the highest SNR in the guide image.



Does that really work? I'm always afraid that PHD will pick a hot pixel by mistake. I have to say I never tried that option tho.

Andy


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EFT
Vendor - Deep Space Products
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Reged: 05/07/07

Loc: Phoenix, AZ
Re: PEC - This can't be right! NEQ6 new [Re: nobbygon]
      #5568957 - 12/13/12 10:30 AM

A mount with +/-30 would actually be a pretty bad example. Your results are on the better side of average which I would consider to be somewhere in the +/-15 to 20 range. Pier mounting and good alignment have not hurt you either.

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gezak22
scholastic sledgehammer
*****

Reged: 08/15/04

Loc: On far side of moon. Send help...
Re: PEC - This can't be right! NEQ6 new [Re: andysea]
      #5569031 - 12/13/12 11:10 AM

Quote:

Quote:

Quote:

Yeah I'm prety sure the star is saturated. If not it's pretty close. Does that have anyhting to do with how PHD guides?




Under 'Tools' there is an option 'Auto select Star' or something like it. It automatically selects the star with the highest SNR in the guide image.



Does that really work? I'm always afraid that PHD will pick a hot pixel by mistake. I have to say I never tried that option tho.

Andy




You bet it works. The reason why it will NEVER select a hot pixel is because PHD knows what hot pixels look like (isolated pixels) while stars have gaussian pixel distributions. PHD is pretty clever.


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andysea
Pooh-Bah
*****

Reged: 09/03/10

Loc: Seattle, WA
Re: PEC - This can't be right! NEQ6 new [Re: gezak22]
      #5569608 - 12/13/12 05:23 PM

Ah! I guess I should have read all the documentation
I will let PHD pick a star the next time I'm imaging!!


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