M47 (Open star cluster) & M42 (Final revision)

[oopfan]

Rick,

Star quality improves as we move on to cameras having a greater Full Well Depth (FWD). Your camera, using gain 115, has a FWD of only 4,000 electrons. My camera has only one gain setting, so FWD is fixed at 13,400 electrons. If you were to choose your lowest gain, then FWD would be 15,000 electrons. Still, as you noticed in my image, the brightest stars are still large. To mitigate that, we need to graduate to seriously expensive cameras having an FWD of 100,000 electrons.

I guess we have different tastes, but I find that images having similar star magnitudes are rather boring, as seen in this image of mine of the star cluster NGC 1664:

NGC-1664_W12-45x60s_R-70x60s_G-35x60s_APP_S15-3-25_SA-35-25_G95_Comparison.jpg (307.49 KiB) Viewed 1086 times

My Perseus Double Cluster received lots of "oohs and ahhs" from the crowd, but my NGC 1664 left them underwhelmed.

I prefer star clusters having a wide dynamic range, preferably embedded in the Milky Way. I adjust my exposure to nicely reveal stars of 17th magnitude after 2 to 3 hours of integration time, even if that means that the bright stars are blown out. I employ a "Newtonian Mask" to add visual interest. Sure, I could capture better images if I spent $5000 for a new camera, but I am very satisfied with what I can do with my $400 camera.

So, I'll leave you with that. I'm sorry it has taken this long. My objective was not to force you to see the universe as I do. My goal was to determine whether your camera's "brightness" was helping or harming image quality. This is why I asked you to lower the contrast. We haven't reached that point yet. We are seeing many more stars now; that is good, but I wanted to see the noise on the surface of outer space. That would tell us if "brightness" is right or wrong.

You've done the best you can do with this data set. For the next cluster, I recommend the lowest gain setting.

Brian

[nexusjeep]

Hi Rick,
For focus you could use the two focus tools in Sharpcap to help dial it in not sure if you are manually or electronically focusing if manual you are going to need the laptop or PC near the scope or get fit jogging backwards and forwards once I achieve a good focus and have started imaging I also tend to watch the FWHM values tab of the live stack to see what the values are doing, there is always some fluctuation due to seeing / transparency changes but it gives a good indication of when things have changed from temperature / equipment elements moving etc. If it changes dramatically then I pause the live stack increase gain and shorten the exposure and then rerun a focus cycle either with the single FWHM selection box or more usually with the multi star FWHM option.

The whole astrophotography journey is a long and sometimes frustrating journey and some nights you really wish yo had taken up something else as a hobby and these still occur on an all too often cycle regardless of how long you have been doing it and how many times you have done the same thing with the same kit but on the nights when it all falls into place then it all becomes worth it. It is also a never ending learning curve and tweaking experience which is another part of the fun

Personally my images are not trying to be scientifically accurate I am just trying to produce an image for myself that I am happy with and want to print as I display them A3 on my wall although I may need a bigger wall or to take some down so you just need to find your own look and feel that suits your requirements as I tend to think of it more as producing a piece of art rather than an accurate historically record and it still amazes me the magnitude and variety of things that you can see in the sky as an amateur astrophotographer and as Brian said in a post elsewhere you can see things with the camera that you could never see with the human eye especially my 53 year old eyes and some cataracts

Cheers
Nick

[RickBG]

Dave,

Thanks for sharing your chronicles of M42. It is inspiring to see the huge progress you made from your very beginnings. The Feb. 2020 post impressed me the most because you did not blow out the core, making the trapezium discernable. Even the "Running Man" looks sharp. Great work!

Rick

[turfpit]

Thanks Rick. The Feb 2020 image was the result of 3 years of effort, study and trial. My big improvements came from a combination over time of:

• More attention paid to focusing by using a Bahtinov mask - a good £20 investment. Better to spend 5 - 10 minutes obtaining good focus rather than spend 2 hours acquired not quite focussed images.

• Acquiring better data by paying more attention to the histogram before capture. Better data will need less processing.

• Moving away from the repeated curves/stretch cycle of Photoshop/GIMP, in my case using Astro Pixel Processor. The repeated stretching will increase noise and destroy star colour. The dedicated astro-processing software usually includes Digital Development Processing which does a better job of bringing out the image but leaving the background as background. This type of software also has facilities for removing light pollution gradients and leaving the data intact.

For focusing, by Zooming to 200% and enabling the Display Histogram Stretch, the 3 parallel lines are clearly visible. At that point I am satisfied with my focus.

focus-with-bahtinov-mask.JPG (60.32 KiB) Viewed 1071 times

You did mention in one of your posts about the darkness of the night sky. That can depend on light pollution, the Bortle value at the site and the background of the image. The image below was captured at a beach on Anglesey (off the coast of North Wales). The site is Bortle 4 and there is no light pollution. M27 has as its background the Milky Way. The image has no black space as it is just full of stars and interstellar dust (detail is lost due to JPG compression). If I capture at home, Bortle 6, then there are less stars in the background. At Bortle 6 I cannot see the Milky Way but at Bortle 4 it is clearly visible to the naked eye. See https://clarkvision.com/articles/color. ... night.sky/

M27-crop2.JPG (287.03 KiB) Viewed 1071 times

M27-crop.PNG (381.43 KiB) Viewed 1071 times

You mentioned about processing being more art than science. I think of it as art supported by science. When taking on a new object I have found it helpful to look on Astrobin and use the search facility to see what type of equipment and capture settings other imagers have used. https://www.astrobin.com/users/turfpit/

This is a long haul hobby which at times can be unforgiving but small insights can lead to large improvements.

Dave