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Imaging over house...

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#1 sbharrat

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Posted 27 February 2021 - 05:03 PM

This is related to a recent thread about locating a pier.

https://www.cloudyni...est/?p=10903319

 

Not quite ready to do this yet (summer maybe) but I essentially have my tripod in a fixed spot under a Telegizmo 365. My issue with the current location is that while I have a view to the south, it is broken up by trees so it consists of gap/trees/gap/trees with each gap being about 2h max. I have a much longer unobstructed view to the north BUT that is over my house. I know that you shouldn't image over the house because of the heat currents but I am wondering... how high above the house before this effect is immaterial considering my seeing is never even down to 2? If I pick a minimum alt of 40 degrees, that would be 20-30 ft above my house. 

 

Thanks and cheers!



#2 markb

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Posted 27 February 2021 - 05:34 PM

This may seen silly, but I'd recommend trying it out.

 

I don't do AP but my old home had generally awful seeing so even visual was disappointing.

 

 

Oddly, the only seeing stable enough for rough collimation was...over my roof to Polaris, a bit lower than your 20-30 feet, to my high peaked cape cod roof.

 

I was located in dense NYC suburbs, part of the seeing issue, combined with geographic quirks.. No clue why the Polaris view was better. Perhaps a boundary layer effect on roof currents, some quirk of local development, or, who can say.


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#3 Berny

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Posted 27 February 2021 - 05:46 PM

This may seen silly, but I'd recommend trying it out.

 

I don't do AP but my old home had generally awful seeing so even visual was disappointing.

 

 

Oddly, the only seeing stable enough for rough collimation was...over my roof to Polaris, a bit lower than your 20-30 feet, to my high peaked cape cod roof.

 

I was located in dense NYC suburbs, part of the seeing issue, combined with geographic quirks.. No clue why the Polaris view was better. Perhaps a boundary layer effect on roof currents, some quirk of local development, or, who can say.

Just turn off the heat in the house about 5 hours before you use the scope. lol.gif


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#4 imtl

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Posted 27 February 2021 - 05:51 PM

This may seen silly, but I'd recommend trying it out.

 

I don't think it is silly at all. That's exactly what I did. I tried it and saw at which altitude of an object the house has no effect anymore.


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#5 sbharrat

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Posted 27 February 2021 - 06:44 PM

I don't think it is silly at all. That's exactly what I did. I tried it and saw at which altitude of an object the house has no effect anymore

Yes, of course I thought of trying it out. But what I didn't know was how to evaluate this... If I take images both over the house and in another direction, how do I know the house is having an effect? Would it be something like running it through PI tools to check the FWHM of the stars in each? Any hints as to what kind of differences would be within random and what might be indicating that over house still bad? 



#6 imtl

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Posted 27 February 2021 - 07:09 PM

aim the scope towards the opposide side of the house at the same altitude as you want to check and see what your guiding looks like

Try to take a shortest guide exposures you can for seeing not to have a big effect.

Keep the settings.

 

Now turn your scope towards the house and go to the same altitude. See what you get in matters of guide RMS. Most chances your seeing is going to be much worse. 

 

Start moving the scope up in altitude until you hit some transition zone that things are acceptable.

 

For me it was around 50-55 degrees. Depending on exact location.

 

This is just a stupid suggestion. I'm sure there is a better way to do this.

 

I would honestly not worry about it so much. Take your images and if their not good enough PI subframeselector will pick them up.



#7 sbharrat

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Posted 27 February 2021 - 07:19 PM

aim the scope towards the opposide side of the house at the same altitude as you want to check and see what your guiding looks like

Try to take a shortest guide exposures you can for seeing not to have a big effect.

Keep the settings.

 

Now turn your scope towards the house and go to the same altitude. See what you get in matters of guide RMS. Most chances your seeing is going to be much worse. 

 

Start moving the scope up in altitude until you hit some transition zone that things are acceptable.

 

For me it was around 50-55 degrees. Depending on exact location.

 

This is just a stupid suggestion. I'm sure there is a better way to do this.

 

I would honestly not worry about it so much. Take your images and if their not good enough PI subframeselector will pick them up.

Thanks Eyal. This is definitely a better way. More "results targeted" testing. 




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