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Old 21-02-2021, 09:50 AM
TrevorW
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Carina Up Close

Carina Up close
Eta Carinae (η Carinae, abbreviated to η Car), formerly known as Eta Argus, is a stellar system containing at least two stars with a combined luminosity greater than five million times that of the Sun, located around 7,500 light-years (2,300 parsecs) distant in the constellation Carina. Previously a 4th-magnitude star, it brightened in 1837 to become brighter than Rigel marking the start of its so-called "Great Eruption". It became the second-brightest star in the sky between 11 and 14 March 1843 before fading well below naked eye visibility after 1856. In a smaller eruption, it reached 6th magnitude in 1892 before fading again. It has brightened consistently since about 1940, becoming brighter than magnitude 4.5 by 2014.



The two main stars of the Eta Carinae system have an eccentric orbit with a period of 5.54 years. The primary is a peculiar star, similar to a luminous blue variable (LBV), that was initially 150–250 Me of which it has lost at least 30 M already, and is expected to explode as a supernova in the astronomically near future.


Capture- 19/2/21 best 80% of 34X90s frames

Scope- GSO 10" CF Truss RC

Mount- Losmandy G11-g2

Camera- QHY 183c 20megapix colour CMOS

Guide/h- Orion SSAG on SVBony 60mm finder

Guide/s- PHD2

Stacked- DSS no darks

Proc- PS CS2
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Old 26-02-2021, 12:44 PM
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Colour is good. The 183 has 2.3 micron pixels which are very small and best suited to a short focal length scope.That scope with those pixels gives you 0.24 arc secs/pixel. Ideal is 1 arc sec/pixel with average seeing of 3 arc seconds. (that simply means you get 3X sampling of the object).

0.24 is going to require mountain top type superb seeing to work well. What you will notice is that images look soft and not sharp.

But if you used 2x2 binning you would get a better result. But even then at 0.47 arc secs/pixel you will require good seeing.

I was imaging at 0.52 arc secs/pixel last weekend and I got good results which surprised me. That was with 3.76 micron pixels.

You should get a nicer result with your QHY268C especially if you bin 2x2.

Pixel size should be matched to the scope's optics for the seeing and the focal length. Its more of a guideline in my experience rather than hard fact.

Greg.
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Old 26-02-2021, 12:54 PM
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Thanks Greg good advice, do you think the 183c would bebetter suited to my ED80 or 110ED with reducer/flattener, then
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Old 26-02-2021, 12:59 PM
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Quote:
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Thanks Greg good advice, do you think the 183c would bebetter suited to my ED80 or 110ED with reducer/flattener, then
Definitely. I used an ASI183 with my AP Honders cope which s 305mm aperture and F3.8 giving a focal length of 1159mm. It worked better than I expected but some nights it was a waste as it showed up the poor seeing too easily.

On nights of good seeing it was quite good and very sharp. I also noticed it was harder to focus than the larger pixelled cameras but also it tended to give rounder stars because there were so many more pixels in each star compared to the larger pixelled cameras.

Your RC focal length is nearly 2X the Honders so double the trouble and double the sensitivity to the seeing.

My CDK17 at almost 3 metres focal length is very sensitive to seeing even with a large pixelled camera. It becomes almost impossible to focus as even keeping the focus steady it would go in and out of focus with successive downloads.

So ideally you choose a focal length to suit your camera and seeing conditions as well as the type of image you want to produce.

A short refractor is not going to get a hot image of most galaxies but is great for wider nebula and star cluster.

Greg.
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Old 26-02-2021, 01:20 PM
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multiweb (Marc)
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Superb close up Trevor. Some terrific details in there and your star field looks good.
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Old 26-02-2021, 02:07 PM
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Nikolas (Nik)
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If you used the 183 at this focal length drizzle the image it will make a difference
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Old 26-02-2021, 02:19 PM
TrevorW
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If you used the 183 at this focal length drizzle the image it will make a difference

OK, how I dribble a lot but drizzle although I don't use it I assume you do in DSS while stacking thanks

Last edited by TrevorW; 26-02-2021 at 03:54 PM.
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Old 26-02-2021, 04:04 PM
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yep drizzle x2 in DSS it does double the processing time however
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