Consistent problems suggest
hardware problems, polar alignment, PEC curve issues, flexure, poor guiding
parameters, this sort of thing in that they impact everything consistently.
Unusual or rare problems like you are sharing suggest transient issues the most
likely being seeing. I work with a 17" telescope at .63"/pixel, I
know how seeing can ruin things. If the system returns consistent results and
then all of a sudden doesn't, first thought is seeing. The fact that your
stars were not messed up in one consistent direction is a clue. I did have a
time where my images were horrible all of a sudden and then get good. Finally
went out and found a rather large owl sitting on the edge of the telescope
upper ring. Luckily there was no deposit on the primary mirror.
There are numerous reference on the impact of seeing and how
professionals monitor and search for sites with good seeing.
Mike J. Shade
Mike J. Shade Photography:
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
Antares blinks a sad farwell to fall...
Leslie Peltier, Starlight Nights
International Dark Sky Association: www.darksky.org
firstname.lastname@example.org [mailto:email@example.com] On Behalf Of Cheng-Yang
Tan via groups.io
Sent: Saturday, May 30, 2020 10:53 AM
Subject: [ap-gto] What's the effect of imaging through jet stream?
Hopefully my question is not off topic. But here goes:
I imaged M101 last night (alt at 76 deg and close to the meridian)
with my Mach1GTO and I had to throw away 1/2 my subframes. I examined the bad
subframes and there's no consistent direction for the eggy stars from each
subframe. Some subframe's eggy stars were in RA direction, some were in DEC
direction and some were angled w.r.t. RA and DEC. I looked at the meteoblue
seeing map (attached) and it says that the jet stream was at around 31 m/s last
night. PHD2 guide graph was about 0.5 arcsec rms error for the entire night
which wasn't too bad for the entire session because my image scale is 2.1
Is the above something that I'd expect imaging through the jet stream? Or I
should be looking for something else to blame like flexure?
Thanks (before I start tearing everything apart :) )