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Old 15-07-2018, 09:01 AM
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rcheshire (Rowland)
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Rho Ophiuchus - rough working

In the spirit of sharing the good and the bad. This is 2 hours 8 mins of a familiar target, which is right overhead and free of steep suburban light gradients. As usual, cloud rolled in at about 2300.

With little time to spend on this hobby and not wanting to spend big, most of my equipment is second hand, modified and old. I try to make the most of it.

32 frames 4 minutes @ ISO200 - cooled 450D -5C. Bias and flats ISO100. Still experimenting with ISO now that I have auto-guiding. I could say that dynamic range seems better with some nice blues and reds showing through, but another hour of data would have been preferable. It's a little subdued.

This preview is straight out of Asterism, with a little tweaking in ImageMagick. Yet to attempt a StarTools version. Will have to work on the preprocessing. I prefer to fix the data during preprocessing, if I can. It produces better results all round. Having said that, image acquisition is the key.

Second image - hot pixels can be seen in a dither pattern. Fixed with a defect map / dark frame in the first image. different rejection parameters - will get around to that later in the week.

I've added an earlier effort, taken 5 or 6 years ago, with a 200mm lens and full frame camera.
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Last edited by rcheshire; 17-07-2018 at 11:19 AM.
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Old 15-07-2018, 09:04 AM
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multiweb (Marc)
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Superb colors and details. Well done.
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Old 15-07-2018, 09:13 AM
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Brillant effort thanks for sharing and showing what can be done.
I love your work.
Alex
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Old 15-07-2018, 02:56 PM
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Anth10 (Anthony M)
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Very impressive result Rohan, smooth image with a nice blend of colours.
I’ve never tried ISO 200 but worth a try given your efforts. Give yourself a pat on the back, look forward to what Startools produces as a comparison too.

Well done!
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Old 15-07-2018, 04:31 PM
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rcheshire (Rowland)
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Thank you all. Low iso seems to work nicely on star fields and bright objects, such as Eta Carina. It could do with a mix of exposure times and / or iso 400 to fill in the speckles. The dynamic range in this region with Antares burning a hole in the frame is a challenge.
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Old 16-07-2018, 08:22 AM
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That's coming through really nicely. What a great target and a lovely comparison to your old wide field spot.

I can't see any noise. Must have been smoothed out with the compression
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Old 16-07-2018, 06:40 PM
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rcheshire (Rowland)
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Thanks Chris. I hope it's not the compression, else, all is lost. A bit of trickery in this case. Bilinear deBayering, which may not be as accurate as other methods, avoids colour artefacts and spottiness in low count image sets. Other than that, heavily noise reduced dark frames and flats, calibrated with a super bias / noise nuked master bias. Finally, touched up with despeckle and sharp. OK for wide field.

Last edited by rcheshire; 17-07-2018 at 11:21 AM.
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Old 16-07-2018, 09:18 PM
Mickoid (Michael)
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Great collection of Rho's there, it is a beautiful part of our winter skies, wonderful result.
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Old 17-07-2018, 07:18 AM
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PKay (Peter)
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Some great images, even better than some I have seen in Deep Space.
Well done Rowland
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Old 18-07-2018, 08:58 AM
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Beautiful. Colours and details compare well with images which have much much more exposure at a mountain dark site. I like the low iso. This is encouraging.
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Old 18-07-2018, 10:11 AM
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rcheshire (Rowland)
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Gentlemen. Thank you again. Comparisons are welcome. The low ISO approach is based on a hunch. It occurred to me to slow things down, under my bluish LED, outer suburban sky, which is immune to sodium filters. Still experimenting. Cooling is a factor.
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