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M3 - globular cluster


wimvb

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2,5 hours of RGB data while the moon was at its brightest.

Gear: SW MN190 with ZWO ASI294MM, Optolong RGB filters

Exposure: 20 x 2,5 minutes per channel

Processed in PixInsight.

M3_rot_LRGB.thumb.jpg.7634aae0a7dd43a1e915067b020ea517.jpg

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That is a fabulous M3 Wim.  That is encouraging for me because I am about to pair up my ZWO294MM with my MN190!  Nice to see someone else using this fabulous scope.  Were you using the 294 in bin2 mode?

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1 hour ago, MartinB said:

That is a fabulous M3 Wim.  That is encouraging for me because I am about to pair up my ZWO294MM with my MN190!  Nice to see someone else using this fabulous scope.  Were you using the 294 in bin2 mode?

Thanks Martin. I use the camera in its "unlocked" native bin2 mode. I don't think there is anything to gain with the camera being unbinned. Atm the pixel scale is 0.96"/pixel. At bin1 that would be 0.48"/p. I don't think my atmospheric conditions are good enough to get sharper images at bin1, and my guide error is typically around 0.6 - 0.65" when conditions are good.  At the same time, at bin1, the camera has only 12 bit output, which means a lower dynamic range, and four times larger image files. That alone would bring my processing computer to its knees. For this image alone, that would mean 120 x 92 MB fits files, more than 10 GB of data to process. However, I wouldn't mind if you prove me wrong. That would give me an excuse to go shopping for a new computer. 😄

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2 hours ago, Adreneline said:

Really nice Wim - I love the colours and the way you've achieved so much detail in the core region.

Adrian

Thanks Adrian. I think it's the camera's dynamic range that helps to maintain core detail. The newest generations of CMOS have such low read noise, that you can get away with a large range of exposure times. When I started using the camera, I settled on 90 s exposures for L and 150 s for RGB. But lately, I have used 150 s for all filters, and could even increase RGB to 300 s. Even with my 7 nm Ha filter, I don't have to increase the camera gain, and can still keep my exposures short. I have imaged the monkey head nebula at a standard gain of 120 and exposure time of "only" 300 s with good result. The camera allows for a lot of under- and overexposure.

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5 minutes ago, wimvb said:

The newest generations of CMOS have such low read noise, that you can get away with a large range of exposure times.

I'm interested to read your comments as I have just acquired an ASI294MC-Pro to use primarily with my Canon 200mm alongside the RedCat with ASI1600MM-Pro. I also plan to use the 294 on my 6" RC. I've been conservative so far with only 120s exposures and unity gain but based on your comments manybe there is room for experimentation, especially as I now live in a Bortle 3 region.

Adrian

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Adrian,

I also have the ASI294MC Pro and have had some good results with it. 

I've attached the stacked data from M51 I took last Saturday using a SW Evostar 100ED with 0.85 reducer/flattener and the ASI294MC.

This is 2 hours of 300s subs at 120 gain and offset of 8 in 11MP mode at -10°C. It was stacked in DSS using standard settings, with darks, flats & dark-flats and capture software was APT.

I'm in Bortle 2 and the camera is fitted with a ZWO UV/IR cut filter only.

Have a play with it and see what you think. ;) 

Autosave.tif

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1 hour ago, wimvb said:

Thanks Martin. I use the camera in its "unlocked" native bin2 mode. I don't think there is anything to gain with the camera being unbinned. Atm the pixel scale is 0.96"/pixel. At bin1 that would be 0.48"/p. I don't think my atmospheric conditions are good enough to get sharper images at bin1, and my guide error is typically around 0.6 - 0.65" when conditions are good.  At the same time, at bin1, the camera has only 12 bit output, which means a lower dynamic range, and four times larger image files. That alone would bring my processing computer to its knees. For this image alone, that would mean 120 x 92 MB fits files, more than 10 GB of data to process. However, I wouldn't mind if you prove me wrong. That would give me an excuse to go shopping for a new computer. 😄

Yes, definitely Bin2 with the MN190.  I have used Bin1 with my 200mm lens but my icore7 laptop feels the strain when processing and my folder for my latest image, including pre processing files is just over 200Gb!!!!

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1 hour ago, Adreneline said:

I'm interested to read your comments as I have just acquired an ASI294MC-Pro to use primarily with my Canon 200mm alongside the RedCat with ASI1600MM-Pro. I also plan to use the 294 on my 6" RC. I've been conservative so far with only 120s exposures and unity gain but based on your comments manybe there is room for experimentation, especially as I now live in a Bortle 3 region.

Adrian

If you set the camera to gain=120, you have a steep drop off in read noise, and a boost in dynamic range. This allows you to use shorter exposure times. But (!), always be sure to choose the exposure time so that you stay above the read noise floor. Especially in a dark sky zone, there may be very little sky glow to keep the noise above read level, and you may have to use longer exposure times. Just experiment. I choose my exposure time such that I don't saturate too many stars. This allows me to keep nice star colours (such as in the above image).

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