PHD2 min move calculator

Tamas Kajfis

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Dec 6, 2016, 5:22:53 AM12/6/16

to Open PHD Guiding

Hi All!

I would like to share a minimum movement calculator according due to http://www.myastroscience.com/minmoveinph

FYI Do Not Touch RED cells!!!

min move calculator.xlsx

bw_msgboard

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Dec 6, 2016, 11:09:21 AM12/6/16

to Tamas Kajfis, Open PHD Guiding

Hi Tamas, thanks for posting. We’ve taken a somewhat different approach in PHD2 although there are many ways to look at this question. From our point of view, the min-move should be determined by a measurement “floor”, which is typically either the centroid accuracy or the seeing conditions. Neither has anything to do with the relative image scales of the guider and the imager, and I don’t really see that relationship. If I understand your spreadsheet, you’re saying that the min-move will be driven by the ratio of the main image scale to the guider image scale. So let’s assume you have a QSI camera with its built-in OAG assembly, a pretty common situation. The ratio then is always 1.0, which means your min-move will be the same on a 100mm focal length scope as it is on a 3000mm scope. I don’t think that’s quite what you want. This is why we implemented the high-frequency sampling in the Guiding Assistant as a way to test the seeing and then automatically set a min-move that was some comfortable distance above that. In the case where the seeing effects are minimal (e.g. coarse image scale), we also impose a floor that represents the likely limit of the centroid calculation.

But as I said, this is just one way of doing things. Our goal is to prevent guiding from being the limiting condition on the imaging results. In some cases, we may be working too hard at it if the main imager has a very coarse image scale. And of course, PHD2 doesn’t know what the main image scale is and we haven’t wanted to include that in the configuration parameters.

Anyway, it’s all interesting stuff to think about. It’s certainly true that the min-move values are often the most important things to get right.

Thanks,

Bruce

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Tamas Kajfis

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Dec 7, 2016, 3:14:39 AM12/7/16

to Open PHD Guiding

Hi Bruce!

This is not my formula I just made according to http://www.myastroscience.com/minmoveinphd
btw I still dont know what is the correct options to my equipment
750mm Newtonian, Samsung nx 1000 pixel size 18,15
185mm guider scope, c270 Logitech with pixel size 2,8
I've made a belt upgrade on my EQ3 with astroEQ and also EQmod, zero backlash in the gears.
My last unguided picture was better than guided, its look like PHD over control it, but I dont know why... next time I'll set the min move settings according due to this formula (0,7) if ill have time and clear sky.

Sorry for my bad English.

Best regards, Tamas

bw_msgboard

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Dec 7, 2016, 10:28:19 AM12/7/16

to Tamas Kajfis, Open PHD Guiding

Hi Tamas. If you want to improve the results you’re getting with PHD2, you should probably carefully read this document if you haven’t already done so:

http://openphdguiding.org/phd2-best-practices/

If you decide you want us to help you improve performance, the first thing we’ll ask you to do is to restore the default settings and follow the procedures in the above presentation and the Help section on “Restoring a Working Baseline.”

Good luck,

Bruce

From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of Tamas Kajfis