#41  
Old 12-09-2017, 08:41 PM
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Atmos (Colin)
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Those 40 hours in your light polluted back yard would likely be swamped by 4 hours of great dark sky time
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  #42  
Old 16-09-2017, 04:47 PM
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Slawomir (Suavi)
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Hi all,

Encouraged by my initial tests, I decided to decrease the length of Lum subs from 5 minutes to 3 minutes only. On average, Lum subs are sky-limited in about 2 minutes in my location with my rig, but when it occasionally gets darker longer subs might be beneficial, so I decided to stick with 3 minutes.

Last night I was able to collect nearly 3 hours of 3-minute Lum subs and the data seem to be better than with 5-minute subs.

I selected the best (darkest) sub and used it as a reference for making stacks with various number of subs. Removing 10 brightest subs did not make things better and it looks like unless a sub is really bad (read: with bright background), it is better to include all in a stack with significant number of subs.

Perhaps bringing background noise down to st.dev. = 10 ADUs can be done in just 10 hours with 3-minute sky-limited subs, as opposed to 40 hours with 5-minute subs with my rig in my location.

A link to a stack of 55 3-minute Lum subs: http://cdn.astrobin.com/images/thumb..._watermark.jpg


Suavi
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  #43  
Old 17-09-2017, 06:29 PM
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Astrofriend (Lars)
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Hi Suavi,
I did this simple S/N calculator, it's far from perfect but still get ideas how exposure length, readoutnoise, background light and vignetting sum up in the S/N relation at the end.

http://astrofriend.eu/astronomy/tuto...ng.html#part06

With a very low noise camera it doesn't influence so much on the noise if divided on lot of short sub images, but you get better dynamics. But heavy to process all those sub images.

I try to correct it when I found something wrong in the calulations.

At my place my exposure length limit are from 30 to 60 seconds. F/5.3, ISO800, Canond 6D. When our summer house observatory is ready for use I hope I can extend it to 120 to 300 seconds.

/Lars
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  #44  
Old 18-09-2017, 06:37 AM
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Slawomir (Suavi)
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Very thorough investigation Lars

I haven't thought about not using bias but it makes sense what you wrote - since I dither my subs I will see if not using bias for calibration makes things a bit better. I'm sky limited also in about 60s on average nights, and 120s after 11pm on a dark night and when Suncorp switches lights off, and so does a large portion of fellow Brisbane dwellers
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Old 18-09-2017, 03:10 PM
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Astrofriend (Lars)
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Hi Suavi,
Earlier I used Fiswork a lot: http://www.fitswork.de/software/softw_en.php , that software subtract a constant that compare to the dslr camera's bias by automatic. To my Canon DSLR it had been working perfect. You don't have a DSLR so I don't know how well it will perform about bias compensation.

If you find it interesting you can take a look how I do the calibration today:

http://www.astrofriend.eu/astronomy/...roduction.html

I took a look at your photos at Astrobin, very great looking photos. Your telescope looks to have the same design as my TS130 which is bought from Germany. TS are very common in Scandinavia.

I have an older version of this:
http://www.teleskop-express.de/shop/...n-Focuser.html

Very satisfaid with it.

/Lars

Last edited by Astrofriend; 21-09-2017 at 12:18 AM.
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Old 18-09-2017, 05:02 PM
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Slawomir (Suavi)
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Thank you Lars for the links and for your very kind feedback - I am glad you like my attempts at imaging DSOs.

Most of the images on Astrobin were taken with an f/7 102mm TS doublet, but the most recent few were taken with CFF's splendid 105mm at f/6 and one at f/4.5.

TS makes very good telescopes for sure, and the only reason I upgraded mine was that it was a doublet and I wanted a small quality triplet.

These days I exclusively use PixInsight for all data processing, perhaps occasionally I may experiment with FitsLiberator though.
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