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Old 21-06-2024, 07:01 PM
xiongz (Zonghou Xiong)
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Ngc5189

I thought it might be worthwhile to share a test result imaging NGC5189. Some of latest images in the forum showed so much fine details compared to years ago and completely changed my impression that deep sky images would best be limited to an image pixel scale of about 0.8 arcsec/px, and CMOS cameras with small pixels would require faster apertures. After successfully converting a Skywatcher Quattro 12/F4 to truss structure, saving some 4-5 kg weight using aluminium bars (swimming pool fence bar), I did the same with a Skywatcher astrograph 300F5 that I bought years ago for viewing. I also bought an ASI2600mm and an ASIAIR mini for automated imaging. I tried imaging NGC5189 using GSO RC10, 300F4, and 300F5 in the past few weeks, with my CEM60 mount broken down and fixed myself in-between. 300F4 obviously was brightest but showed less resolutions (it could also be due to unfavourable seeing plus mount tuning issues). RC 10 with a TCD 0.67x reducer at a focal length of about 1340mm showed more details, and 300F5 at a focal length of 1500mm came out the best. Seeing in the past few weeks was average at best. Seeing was in fact a far more deciding factor than image gear performance and/or combinations. In calm Sydney weather with good seeing conditions longer focal lengths can definitely resolve more details on a camera such as ASI2600MM with a pixel size of 3.8 micron. Here is a HOO image of NGC5189 with 46 and 44 subs in 10 min for Ha and Oiii, 3nm Antila filters, cooled to -15 degrees. It isn't as fine as David's incredibly detailed version with a 14 in SCT, but it is nevertheless acceptable to me for a 12 in Newtonian. It could be improved with better seeing and a steadier mount. Of these 46 and 44 subs for Ha and Oiii only 1-2 hours for each filter were with good quiding resolution around 0.5 RMS total.

Clear skies,
John
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Old 24-06-2024, 12:57 PM
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PRejto (Peter)
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Nice effort, John. You have made me want to attempt this taget, but I suspect with 140mm I won't be very successful!
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Old 25-06-2024, 09:37 AM
xiongz (Zonghou Xiong)
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Hi Peter,

Thanks. I think you should be able to get pretty good results. Refactors are sharper in general, but you might need to use newer generation CMOS cameras with smaller pixels. I imaged this target a few year ago with Skywatcher Quattro 10/F4 at 1000mm with an ASI1600mm. My main problem back then was guiding accuracy plus my inexperience with a Newtonian. Since multi-star guiding became available, guiding accuracy of my CEM60 was elevated to levels close to premium mounts. Image scale for focal length of 1000 mm on popular cameras with 3.8 micron such as ASI533/1600/2600 is about 0.8 arcsec/pixel. Calm aussie skies can definitely resolve finer than that, as seen in so many great images in forum. With better sharpness of your scope, you should be able to get great results. I own a Canon 400mm/F2.8 which, with extenders, definitely showed smaller stars than Quattro 10.

Cheers,
John

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Originally Posted by PRejto View Post
Nice effort, John. You have made me want to attempt this taget, but I suspect with 140mm I won't be very successful!
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