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Deep Sky Images / Tulip nebula and Cygnus X-1
« Last post by Einari on 17:39:02, 24 September, 2018  »
One more interesting target from Spain remote observatory.

Just 440 minutes of narrowband photons taken with Esprit 100 and Atik 460EX.

Tried to get also the bow shock of Cygnus X-1 and I think I succeeded.

Deep Sky Images / Re: To bin or not to bin?
« Last post by mcgillca on 12:03:27, 24 September, 2018  »
Dear Dean,

Hi - I think you are slightly undersampling the image. The Nyquist criterion is for a 1-d signal - for 2-d, you actually need an additional square root of 2 in there (so instead of multiplying your 0.42 by 2, its actually 2x root 2), and hence your 0.42"/pixel becomes 1.2" resolution. When you bin 2x2 you are going to 2.4". Being (very very) picky with your image, the small stars look a little blocky and square which is an indication of slight undersampling. Also, not sure how this camera does binning - if it preserves colour, you'd actually combine say pixels 1 and 3, so the pixel size is larger - not sure if behaves as three or four times the size, but anyway larger than just twice the size.

The reason for binning is to remove read noise (typically CCD cameras have one set of read noise if you bin 2x2, instead of 4 separate sets of read noise). However, with most cameras these days, the read noise is typically low - although looking at the specs for your camera, its 16 electrons which is towards the high end. If you are imaging from a dark site, this may set the noise level for the image, but if you are imaging from an urban location, its still likely to be light pollution that's key, rather than the read noise. So if SNR is the key issue, you might want to bin in a dark site, but not at an urban location -but if you want resolution, I'd stick to the 1x1 binning. Most elite images these days use 1x1 binning for colour images, though they will also use filter wheels rather than a one shot colour camera.

Either way, its a pretty image so you should be pleased with the outcome!

Deep Sky Images / Re: Mel15/IC1795
« Last post by Peter Shah on 20:35:02, 22 September, 2018  »
looks great
Deep Sky Images / To bin or not to bin?
« Last post by Dean on 13:44:48, 22 September, 2018  »
The image of NGC7331 was taken on the 5th and 12th September.  The combination of the 2,321mm focal length SCT at f/10 with the Celestron Nightscape 10100 camera has an image scale of 0.42 arc seconds per pixel.  The resolution limit of the system, applying the Nyquist sampling principle, will be 0.84 arcseconds.  Given the seeing in Cornwall is usually between 1.0-2.5 arc seconds limited, I am probably slightly oversampling using the camera un-binned.

To capture this image I experimented with 2x2-binning the camera.  With an image scale of 0.84 arc seconds per pixel and a resolution limit of 1.68 arcseconds, I was actually slightly under sampling the image acquisition (seeing limited resolution was 1.0 and 1.5 arc seconds on the 5th and 12th September respectively).  The 2x2-binned images were captured as a total of 34x600-second light frames.

I used drizzle integration in PixInsight, with a scaling factor of 2x, to compensate for the under sampling. 

I have analysed the results of: a 1x1 un-binned integrated image; a 2x2-binned integrated image; and a 2x2 drizzle-integrated image.  Interestingly, the SNR of the 2x2-binned integrated image was higher than the 1x1 unbanned integrated image, as expected; and the 2x2-binned drizzle integrated image had a further significantly improved SNR over the 2x2-binned integrated (without drizzle) image.  The analysis was carried out using the PI sub-frame selector. 

The significant improvement of SNR of using 2x2-binned drizzle integration rather than 1x1-un-binned integration, appears to also be reflected in an improvement in resolution of structure within the NGC7331 image.  Obviously no process tool can resolve information that does not exist on the CCD in the first place, but the technique does seems to have resolved information that was not so easily extracted in the usual 1x1 un-binned process.

Any thoughts on whether to bin or not to bin welcome.
Announcements & Site Issues / Re: UKAI Closure Announcement
« Last post by afm038 on 15:02:05, 21 September, 2018  »

PM sent.

Announcements & Site Issues / Re: UKAI Closure Announcement
« Last post by Einari on 07:04:11, 21 September, 2018  »
Suddenly I have noticed increase in posts/comments in this forum ... ;)
Deep Sky Images / Re: Mel15/IC1795
« Last post by Einari on 07:03:02, 21 September, 2018  »
Looks very good.
Deep Sky Images / Re: Mel15/IC1795
« Last post by psjshep on 00:59:41, 21 September, 2018  »

Announcements & Site Issues / Re: UKAI Closure Announcement
« Last post by Anne S on 19:21:05, 20 September, 2018  »

Can you try joining the FB group again. I'll keep any eye out for them and approve when I see them


Pm sent.
Deep Sky Images / Re: Mel15/IC1795
« Last post by Annie on 14:35:36, 20 September, 2018  »
Well done indeed. My first scope I bought about 3/4 years ago was a TS Imaging Star 71 and it was excellent in every way.

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