Author Topic: To be a better astro-imager ....  (Read 512 times)

Offline John_Gill

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To be a better astro-imager ....
« on: 2019 July 22 01:33:16 »
Hi,

A couple of questions ….

1 - With doing NB or LRGB imaging of an object over multiple night, do you image one filter per night or run a sequence of images with all the filter each night.

2 - When looking at the stars in an image, how far do you zoom in to see if there are elongated or funky stars (especially in the corners).


Any pointer in this regard will be appreciated
John  :-\
APM 107/700 apo on CGX mount
ZWO Optics - Autoguiding
ZWO1600mm and filters
... when there are no clouds ...

Offline John_Gill

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Re: To be a better astro-imager ....
« Reply #1 on: 2019 July 25 02:52:02 »
mmmh, no comments, suggestions, complaints, laughter …. :-\
APM 107/700 apo on CGX mount
ZWO Optics - Autoguiding
ZWO1600mm and filters
... when there are no clouds ...

Offline John Massey

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Re: To be a better astro-imager ....
« Reply #2 on: 2019 July 25 06:58:52 »
If you run each filter on different nights wouldn't you need to take more frequent flats? And doing them in sequence would mean refocus for each filter change in my mind. My 2 cents.

Offline John_Gill

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Re: To be a better astro-imager ....
« Reply #3 on: 2019 July 25 07:19:53 »
Hi,

Each night I take at least 60 flats per filter and about 3 hours of darks.  My filters are supposed to be parfocal, but I don't think so.  So I have to focus manually and that is a pain in the butt.  (Will be buying an electronic focuser (ZWO or Primaluce, but not sure yet). 

Thanks for your input.
John
APM 107/700 apo on CGX mount
ZWO Optics - Autoguiding
ZWO1600mm and filters
... when there are no clouds ...

Offline wvanreeven

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Re: To be a better astro-imager ....
« Reply #4 on: 2019 July 25 07:28:58 »
Please note that I am far from an expert but here are my $0.02:

1. That really depends on a lot of things like whether the weather is expected to stay stable over some time and how patient I am. I guess it is a personal choice and it really also very much depends on what you want to achieve (really deep image, mosaic, a quick series of not-very-deep images etc etc). I am sure more arguments for the one or the other can be found. Perhaps you can try to explain what it is that you are trying to achieve?
2. I usually don't go beyond level 4. Concerning the corners: I made sure that the back focus between the flattener and the sensor is correct so I usually only check for guiding issues.


HTH, Wouter

Offline John_Gill

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Re: To be a better astro-imager ....
« Reply #5 on: 2019 July 25 12:05:04 »
Hi,

I mostly image in NB and nebulae.  I am now trying to gather about 10+ hours per target, hence the questions.  I have been battling with backfocus an recently bought a Barder Varilock extension and I am dialing in the backfocus, so stars roundness should improve :)

Kool, thanks for your input
John
APM 107/700 apo on CGX mount
ZWO Optics - Autoguiding
ZWO1600mm and filters
... when there are no clouds ...

Offline chris.bailey

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Re: To be a better astro-imager ....
« Reply #6 on: 2019 July 26 01:06:05 »
John

I do a lot of long narrowband targets so multiple nights is very much the order of the day. With Narroband I tend to prefer to do one filter a night (or more) though with RGB I will do a run based on collecting the blue subs near the meridian. I am permanently setup and only do flats every few months.

I don't trust my eyes for field flatness and much prefer to rely on things like CCD Inspector

Chris

Offline John_Gill

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Re: To be a better astro-imager ....
« Reply #7 on: 2019 July 26 02:13:41 »
Thanks Chris, I think I need to do something similar.  Why do you do the blue subs near the meridian?
APM 107/700 apo on CGX mount
ZWO Optics - Autoguiding
ZWO1600mm and filters
... when there are no clouds ...

Offline John Massey

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Re: To be a better astro-imager ....
« Reply #8 on: 2019 July 26 06:03:33 »
Color extinction. As you move from the meridian back to the horizon color signal decreases starting with blue, then green and then red. I follow the same procedure as Chris does.