Is there a way to determine average seeing with PHD2 Log viewer?

[Anthony Quintile]

I have been seeing people in forums and elsewhere referring to seeing conditions as expressed as FWHM in arc seconds. Apparently average-good is around 2 arc sec, and one rent-a-scope facility was claiming 1.1 arc second seeing for a series of subs shot in Chile.

Is there something in Log Viewer to which I can refer that will tell me what my FWHM measurement was over a certain recorded guiding log period? Does the FWHM number shown while guiding correlate to this?

[bw_msgboard]

Hi Anthony. There are generally two ways to compute the seeing FWHM,
neither of which can be done very well using the PHD2 data. The best
approach is with a seeing monitor and that's typically what's used at remote
observatories. Lacking that, you can roughly measure it yourself by
shooting a series of 5-10 sec exposures with your main imaging camera and
computing the average stellar FWHM. That assumes, of course, that your
image scale is no larger than about 30% of the expected seeing value. So
accurately measuring a seeing FWHM of 2.0 arc-sec will probably require an
image scale of around 0.6 arc-sec/px - and certainly not more than 1
arc-sec/px. This approach also assumes that the optics are well collimated
and aligned and capable of producing small Airy disks whose size is actually
seeing-limited.

The FWHM values displayed by the Star Profile tool aren't very useful for
getting a quantitative measure of the seeing. The two things are related but
not translatable in a reliable way. The closest thing in PHD2 is the
measurement done by the Guiding Assistant. But that is directed toward
setting a min-move, in pixels, below which the guide star movement is
dominated by seeing effects.

Hope this helps,
Bruce

--
You received this message because you are subscribed to the Google Groups
"Open PHD Guiding" group.
To unsubscribe from this group and stop receiving emails from it, send an
email to open-phd-guidi...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/open-phd-guiding/355d32a4-16e8-454d-9756-2
f0749c8c336o%40googlegroups.com.

[Terry]

If you want to get an idea of what your local seeing conditions are you could try the Metroblue web site.  They provide free weather information for a number of disciplines, including astrophotography.  For astrophotography, they give information like cloud cover, temperature layers, jet stream speed and the seeing conditions.  This link is an example of the information for my location.

https://www.meteoblue.com/en/weather/outdoorsports/seeing/kerikeri_new-zealand_2188874

Maybe this can provide the information you want.

[Anthony Quintile]

Bruce

As always, thank you for this extremely informative answer!

BTW, the Dither app has been flawless since you sorted it.

Thanks again

-Anthony

[Anthony Quintile]

Terry-

I have various apps that forecast seeing and have used this one as well.

I find them to be marginally reliable.

Part of this may be the fact that seeing conditions around where I live vary dramatically depending upon where one is relatively to the highly varied topography. My house is at 6800 ft ASL, I am approximately 5 miles from several 12,000 ft peaks, and 20 miles from a desert basin that’s as low as 4500 ft. There are other contributing factors, but as I have gotten into AP I have come to realize that PHD2 and my mount perform perfectly and the mostly turbulent seeing is my biggest issue.

I actually had a couple of nights of good seeing and my RMS plummeted lower than I had ever seen it, verifying my theory.

Thanks for the advice!

[bw_msgboard]

Glad to hear things are working well for you, Anthony, thanks for the post.

Bruce

-----Original Message-----
From: open-phd...@googlegroups.com
[mailto:open-phd...@googlegroups.com] On Behalf Of Anthony Quintile
Sent: Friday, June 05, 2020 5:49 PM
To: Open PHD Guiding
Subject: RE: [open-phd-guiding] Is there a way to determine average seeing
with PHD2 Log viewer?

--
You received this message because you are subscribed to the Google Groups
"Open PHD Guiding" group.
To unsubscribe from this group and stop receiving emails from it, send an
email to open-phd-guidi...@googlegroups.com.
To view this discussion on the web visit

https://groups.google.com/d/msgid/open-phd-guiding/18310ea9-aa6a-4d0b-ad32-c
5c34b2f3be9o%40googlegroups.com.