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


Mike Shade
 

I have seen about every geometric shape possible with out of focus stars during a FocusMax run with the 17", worse when the seeing is poor.  According to my seeing monitor, I tend to run around 2" on average, with some periods of significantly better, 1.5" or less and sometimes 3" plus, on the same night.  It can be reasonable right after sunset for about 30 minutes, and can be reasonable before dawn-sometimes.  I have done what is possible around and in the observatory to minimize heat effects (I am in SE AZ), but I can't control the upper atmosphere.  

 

Mike J. Shade

Mike J. Shade Photography:

mshadephotography.com

 

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 southwest

Antares blinks a sad farwell to fall...

Leslie Peltier, Starlight Nights

 

International Dark Sky Association: www.darksky.org

 

From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Glenn
Sent: Sunday, May 31, 2020 6:59 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] What's the effect of imaging through jet stream?

 

cytan,

I generally have poor local seeing, but I am amazed at the variation that is possible. On good nights, guiding with my Mach1 (last generation) is around 0.3-0.4 arc seconds and the resulting HFD of the subframes is in the 2-3 range. On bad nights, particularly when the jet stream is a factor, guiding is 1.5 arc seconds or worse and the HFD is much higher. On the worst night in memory, my HFD was 10+! I thought there was something wrong with my optics—the stars looked like giant snowballs and refocusing did not improve them. But a couple of nights later, guiding and image quality had returned to normal. So in my experience the jet stream can significantly degrade both guiding and image quality. 

Regards,

Glenn

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