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A few years ago (already? time flies) @gorann and I hoovered the Liverpool Telescope archives and processed most of the DS data that is in there. https://telescope.livjm.ac.uk/Gallery/

Having not much to do yesterday, I returned for scraps. I found three image files on ngc 891, one red image, one green and one blue image. Each has an exposure time of 90 seconds. I combined the three images into one synthetic L image and processed the data as LRGB. So here it is, 4.5 mintues of professional data


(click on the image for a full size view)

Clearly it pays off to have large pixels and a large mirror on a high mountain top. The telescope is an f/10 RC design with a 2 m mirror and a 4K x 4K pixel camera. Pixelsize is 15 um, but all images are binned 2x2, giving an effective pixelsize of 30 um in a 2 000 x 2 000 array.

The master images had a lot of cosmic rays and hot pixels, so in creating the L master I had to use pixel rejection, which I'd not do normally. I removed much of the cosmic rays and bad pixels in the rgb combined image, before stretching. Here's what the original rgb data looked like.


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32 minutes ago, Stub Mandrel said:

Imagine what they could do if they used sensible exposure times 🙂

Imagine what it would cost 🙂

Edited by wimvb

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Imaging time on big telescopes costs money, besides which anything longer than 120 secs will overexpose the sensor.

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54 minutes ago, DaveS said:

Imaging time on big telescopes costs money, besides which anything longer than 120 secs will overexpose the sensor.

I was partrly jesting, partly serious about multiple exposures rather than longer ones.

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1 hour ago, Stub Mandrel said:

I was partrly jesting, partly serious about multiple exposures rather than longer ones.

Some of the image sets in the archives just have single exposures, while other have tens per filter. But the total integration time is seldom more than an hour since exposures are generally never longer than 90 seconds and sometimes as short as 10 seconds.

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