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AP1200GTO PE curves

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#1 korborh

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Posted 02 March 2013 - 03:08 AM

My AP1200GTO is now almost 2 years old.
I Ran some PE curves tonight when the moon was up. Sampling at 0.48"/px using C11 EdgeHD and Atik 314L+.
Seeing was less than average.

First, the raw captured data before PEC. Shows a smooth and clean sine wave.

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#2 korborh

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Posted 02 March 2013 - 03:09 AM

The raw PE calculated just under 4" p-p.

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#3 korborh

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Posted 02 March 2013 - 03:09 AM

Here is the frequency spectrum of the capture. Note how large is the fundamental relative to the other frequencies indicating a nice sinusoidal and easily correctable PE.

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#4 korborh

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Posted 02 March 2013 - 03:10 AM

Data captured after uploading the measured PEC to the mount. Virtually flat line!

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#5 korborh

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Posted 02 March 2013 - 03:11 AM

The resulting PE - no period found. Good!

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#6 korborh

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Posted 02 March 2013 - 03:12 AM

Frequency spectrum - just noise. PE has been anhilated.

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#7 orlyandico

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Posted 02 March 2013 - 05:02 AM

Did you only use the fundamental for the PEM curve?

On my Mach1 i use the 1, 2, and 3rd harmonics. There is still a residual of about 0.4" after PEM...

#8 korborh

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Posted 02 March 2013 - 12:33 PM

I used linear fit in PemPro which selected 1,2,3 and 4 harmonics as below. You can see the 2,3,4 are insignificant. I used this default selection to program so all four were used.

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#9 orlyandico

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Posted 02 March 2013 - 01:56 PM

hmmm.. i'm always using quadratic or cubic fit. maybe i should use linear fit..

#10 korborh

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Posted 02 March 2013 - 02:22 PM

I usually start with linear fit and check the fit quality using the RMS and scrolling through the whole data in the above dialog box. If the RMS does not change much going to quadratic, I just use linear.
The quadratic fit is usually ok and may work better but higher order fitting can be artificial and not useful for smooth AP mounts.
Your 0.4" corrected (after PEM) seems pretty good to me. Depending on balance and side of pier, I see somewhat different results and corrected PE of 0-0.5".

#11 orlyandico

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Posted 02 March 2013 - 02:25 PM

i'm at 0.4" when east heavy and 0.8" west heavy.

uncorrected is 3.5" east heavy and 6" west heavy.

#12 korborh

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Posted 02 March 2013 - 02:47 PM

That sounds quite good and sub-arcsec. I found it best to have it well balanced but the difference is insignificant when its all under 1". I see no difference with these PE figures with or without correction on my guided images. I usually do PE once in a while to check if nothing sudden is happening to tracking making sure mechanics of the mount are good.

#13 andysea

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Posted 02 March 2013 - 04:09 PM

You guys! I never checked the PE on my mounts but your posts make want to dig into it. So far I just look at my subs and if they look good I don't worry:)
I wonder how my 2005 vintage NJP would compare.

#14 Tom and Beth

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Posted 02 March 2013 - 06:35 PM

Like you, I'm just starting to use PEMpro. Didn't need it when I was 100% visual, but now as I tune the mount I find visual use is even MORE enjoyable. Still have a bit more to do in order to get long exposures with a 3 Meter FL scope,

#15 Mike Clemens

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Posted 02 March 2013 - 09:46 PM

PemPro fixed my AP1200 GTO right up
http://www.pbase.com.../image/94812800

#16 korborh

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Posted 02 March 2013 - 09:55 PM

That looks so much like the the PE curve on mine! Yeah the zero PE is cool.

#17 andysea

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Posted 02 March 2013 - 11:42 PM

hmm I've been wanting to get an AP900 but looking at your results with the 1200 makes me wonder if I should shift gears and keep an eye out for a good used 1200.

#18 korborh

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Posted 02 March 2013 - 11:50 PM

Andysea, I would not recommend you make the choice between the 1200 and 900 based on PE. With the (not very old) AP mounts, the PE is guaranteed to be low and smooth and will <1" pp corrected out of the box.
I would recommend the 1200 if you can pick and move 50lbs without issue. Its a really strong and overbuilt mount, conservatively rated for 140lb payload. They are coming up on Amart used at good prices.

#19 orlyandico

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Posted 02 March 2013 - 11:50 PM

Andy, I don't think there's much different between the Mach1, 900, and 1200. I think it's when you get to the 1600 that you get a smaller native PE (somebody else posted about 1.6" before PEM). But these usual suspects are all in the 3.5" range before PEM.

#20 andysea

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Posted 03 March 2013 - 02:43 AM

True and true! The more I think about it the more the 1200 makes sense given that I already have a 45lb. and a 70lb. mounts.
I do see them come up used for very good prices.






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