Re: Tracking and guiding with and without encoders - Part2

Michael Fulbright <mike.fulbright@...>

I haven't given it much thought but if you assume a Gaussian profile for your stars and the guide errors are normally distributed I would think the final FWHM of the star broadened by guide errors would add in quadrature.

sigma_F = sqrt( (sigma_*)^2 + (sigma_g)^2)

where sigma_F is the final sigma of the Gaussian star profile, sigma_* is the unbroadened star profile, and sigma_g is the error guiding.

If you have seeing like me and most stars are around sigma_*=2 arcsec and sigma_g=0.4 arcsec I get sigma_F = 2.04 arc sec.

I'm sure there is work on this in professional journals if someone really wanted to know the answer.

Just a quick search I  found this:

Seems to consider many sources that must be controlled to give the best image resolution including atmospheric and guiding effects.

You could do a test and take a < 5 second exposure of a bright star cluster then take a 300s exposure of a fainter star field and compare FWHM.  Presumably the short exposure is roughly measuring your optics and short term turbulence while the longer would incorporate guiding errors as well.

Michael Fulbright

On 9/17/19 5:14 PM, badgerz49@... [ap-gto] wrote:


You showed images of a mount with "40 arc seconds PE."  Assuming you ran a valid test it only demonstrates that PEC improves guiding if your mount has 40" PE.  I fully expect it would.  That doesn't begin to address whether it improves guiding on an AP mount with less than +/- 3" P-P smooth native PE.

This is bizarre why someone can't run simple tests to hash out how much improvement in guiding encoders offer.  Nothing is stopping AP from testing it, or better yet, enlisting an unbiased source to do the testing.

Regarding guide logs... here's a copy of the email I just sent you - with guide logs from Sep. 4 attached.  I can't imagine they'll be helpful.  I can also provide you PEMPro logs from that same evening if such a thing exists.

--Email below---

There was a lot going on this particular evening ... creating new PEC curves in PEM Pro, running guiding assistant, testing various PHD2 settings, testing PEM on/off, etc.

These logs will be very difficult to draw any conclusions from since I had zero intention of making them clear and intelligible.  What I can tell you is:

PEM was enabled near the end of the night on one of the two mounts.  I believe it was enabled on the file that ends in 201308 but I don't remember for sure.  Total RMS stayed right around Total RMS for the other mount which had guiding disabled.  I did not notice any improvement from when PEC had been disabled either.

I will try and do a proper test tonight.  If there's improvement, that's what I'll report.  I hope there is.


-- End Email --

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