Re: What's the effect of imaging through jet stream?


Mike Shade
 

What do the stars look like when you take the system out of focus like for a focus run?  Are they nice concentric circles or do they go from round to oval to any one of a number of shapes?  This can be a rough look at seeing.  The type of seeing can do different things (high seeing like from the jet stream to local seeing from heat rising off of a building).  If you are imaging through a river of moving air, you are likely to see this in your images.  If your system has returned round stars consistently, and all of a sudden it doesn't then something has changed.  If you haven't moved, adjusted, screwed with the imaging train or instrument, changed software settings, anything like that then seeing can be a potential culprit.  If the system has struggled to return round stars and the issues you described are not new, then there is another issue and differential flexure is a likely suspect.  If the jet stream is overhead with that river of fast moving air, seeing will likely be poor.

 

Mike J. Shade

Mike J. Shade Photography:

mshadephotography.com

 

In War: Resolution

In Defeat: Defiance

In Victory: Magnanimity

In Peace: Goodwill

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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...

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From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Cheng-Yang Tan via groups.io
Sent: Saturday, May 30, 2020 12:42 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] What's the effect of imaging through jet stream?

 

Hi Rolando,

   I used a guide scope that is 4.59 arcsec/pixel (focal length 168 mm). Scope is a FSQ106. I plan to image again tonight. Again, the jet stream seems to be quite bad: 45 m/s. So if there's anything else to check, I'm open to suggestions.

 

cytan

 

P.S. I will be upgrading to OAG next week after my SBIG Starchaser SC-2 arrives. This is in preparation for an Adaptive Optics AO-8A in the future.

 

 

On Saturday, May 30, 2020, 02:32:25 PM CDT, uncarollo2 <chris1011@...> via groups.io <chris1011@...> wrote:

 

 

Are you using an off-axis guider or separate guide scope? What is the main scope you are imaging with?

 

Rolando

 

 

 

 

 

-----Original Message-----
From: Cheng-Yang Tan via groups.io <cytan299@...>
To: main@ap-gto.groups.io
Sent: Sat, May 30, 2020 12:53 pm
Subject: [ap-gto] What's the effect of imaging through jet stream?

Hi guys,
   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 arcsec/pixel.

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 :) )

cytan

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