Re: PEM Files Upoloaded: Need sanity check


Mike Shade
 

I would agree Ray that more than three worm cycles would be better...however, Roland seemed to suggest quite strongly that three would perhaps suffice...I suspect that this was in regards to somewhat less robust systems e.g., SCTs and such which may have mirror flop among other things that can "pollute" the PEC data. This may be a system specific parameter though. I did fine with the 17" PW/1600GTO and about 300 samples last night (did bin 2x2 for 1.246"/pixel, seemed a bit smoother curve than 1x1 binning). Got a very good curve. Can go 5 minutes unguided with this system. That is way more than adequate and frankly more than I expect.



Mike J. Shade: mshade@q.com

Mike J. Shade Photography:

mshadephotography.com



In War: Resolution

In Defeat: Defiance

In Victory: Magnanimity

In Peace: Goodwill

Sir Winston Churchill

Already, in the gathering dusk, a few of the stars are turning on their lights.

Vega, the brightest one, is now dropping towards the west. Can it be half

a year since I watched her April rising in the east? Low in the southwest

Antares blinks a sad farwell to fall...

Leslie Peltier, Starlight Nights



International Dark Sky Association: <http://www.darksky.org/> www.darksky.org



From: ap-gto@... [mailto:ap-gto@...]
Sent: Sunday, September 24, 2017 9:03 AM
To: ap-gto@...
Subject: RE: [ap-gto] PEM Files Upoloaded: Need sanity check





If you critically read the e-mail regarding capturing PEC data, Roland specifically offers that perhaps 3 worm
cycles is best (and in further discussions this is also mentioned).
In some cases collecting only 3 cycles will work (e.g. good seeing conditions), but I think that 5-6 worm cycles will be better in most cases, for two reasons:

1) There is more samples per each phase of each worm cycle, which will usually result in a better fit if seeing is average or worse.
2) As you increase the total duration of time of capture, the resolution of frequency and amplitude increases (a fundamental property of spectral analysis).

I would agree though that after about 45 minutes the effects from seeing, polar alignment errors, and flexure can start to make RA drift more complex, which may result in a less accurate curve.

-Ray Gralak
Author of APCC (Astro-Physics Command Center): http://www.astro-physics.com/index.htm?products/accessories/software/apcc/apcc
Author of PEMPro: http://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: http://www.gralak.com/apdriver
Author of PulseGuide: http://www.pulseguide.com
Author of Sigma: http://www.gralak.com/sigma

-----Original Message-----
From: ap-gto@... [mailto:ap-gto@...]
Sent: Saturday, September 23, 2017 8:39 PM
To: ap-gto@...
Subject: RE: [ap-gto] PEM Files Upoloaded: Need sanity check



If you critically read the e-mail regarding capturing PEC data, Roland specifically offers that perhaps 3 worm
cycles is best (and in further discussions this is also mentioned). He offers that many more and you may
pollute the data with other factors that are not related to PE including mirror movement, among others. I am
not clear on what "selecting the best 5 out of 11 captured" is supposed to do. Again, reread his e-mail. If you
captured 11 cycles but used the best 5, that may not be an accurate representation of your mount's PE. If
your seeing is that bad, then perhaps make it a point to get out somewhat before dawn when there is a
likelihood of better seeing and gather your data, if possible.

Try this: point the scope at a star just west of the meridian and equator...run the wizard so that it can
configure your system, collect data for three worm cycles, generate a curve, upload to the mount...then
gather data with the PEC on, maybe one or two worm cycles, generate a curve with this data (DO NOT
LOAD THIS SECOND CURVE TO THE MOUNT). You should see a significant reduction in PE. My peak to
peak on my 1600 with Planewave CDK 17 went from 4.75" to a curve of .88". Since my seeing is often
double this-or more, this is fine.

Use your equipment.

Mike J. Shade: mshade@q.com

Mike J. Shade Photography:

mshadephotography.com

In War: Resolution

In Defeat: Defiance

In Victory: Magnanimity

In Peace: Goodwill

Sir Winston Churchill

Already, in the gathering dusk, a few of the stars are turning on their lights.

Vega, the brightest one, is now dropping towards the west. Can it be half

a year since I watched her April rising in the east? Low in the southwest

Antares blinks a sad farwell to fall...

Leslie Peltier, Starlight Nights

International Dark Sky Association: <http://www.darksky.org/> www.darksky.org

From: ap-gto@... [mailto:ap-gto@...]
Sent: Saturday, September 23, 2017 8:05 PM
To: ap-gto@...
Subject: Re: [ap-gto] PEM Files Upoloaded: Need sanity check

I followed all the instructions and have added a screen shot of the results to my folder.

Specifically, to reduce the effects of imaging I selected the 5 best cycles out of the 11 I captured. The graphs
seem pretty tight.

In the model I used the 1-4 components and looked at adding 5 and 16 which had > 0.05 amplitudes, but
they only reduce the RMS 0.001.

I used the cubic model which had the lowest RMS. Normally I would expect that quadratic might be enough,
but give there are at least 4 components, this probably makes sense?

I have not loaded this curve awaiting feedback.

Thanks,

JY

PS I see that the X axis on the graph is not centered around zero. This is with the adjustments checked.

[Non-text portions of this message have been removed]







[Non-text portions of this message have been removed]

Join main@ap-gto.groups.io to automatically receive all group messages.