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M52+NGC7635
Posted: Thu Sep 06, 2018 2:53 am
by turfpit
- M52+NGC7635-reduced.jpg (609.53 KiB) Viewed 3375 times
Full scale image here
https://www.astrobin.com/365064/0/
Altair Lightwave 66ED, Celestron AVX mount, Altair 183C
All Star Polar Align (Celestron mount), focus Bahtinov mask, unguided.
SharpCap 3.1
60 x 60s, g=150, black level=100
60 lights
50 darks
50 bias
100 flats
Processed in Siril + GIMP 2.10 (40 minutes total)
Dave
[ALTAIRH183C]
Debayer Preview=On
Output Format=FITS files (*.fits)
Capture Area=5440x3648
Binning=1x1
Pan=0
Tilt=0
Colour Space=RAW12
Fan=On
Temperature=12
Black Level=100
USB Speed=2
Auto Exp Target=121
Frame Rate Limit=Maximum
Analogue Gain=150
Exposure=60000
Timestamp Frames=Off
Apply Flat=None
Subtract Dark=None
#Black Point
Display Black Point=0
#MidTone Point
Display MidTone Point=0.5
#White Point
Display White Point=1
TimeStamp=2018-09-05T21:04:55.4574641Z
SharpCapVersion=3.1.5193.0
Re: M52+NGC7635
Posted: Thu Sep 06, 2018 3:02 am
by oopfan
Great work, Dave!
You picked up the Hydrogen Beta in the Bubble (greenish-blue) and the Hydrogen Alpha in the surrounding nebula (red)
Brian
Re: M52+NGC7635
Posted: Fri Sep 07, 2018 10:35 am
by turfpit
Thanks Brian.
I now have an H-alpha filter and will revisit the Bubble Nebula at next opportunity.
Dave
Re: M52+NGC7635
Posted: Fri Sep 07, 2018 6:16 pm
by mAnKiNd
Hi Dave, very nice fov and detail, was this captured with a filter? I see a blue cast in the balance and I take you're still waiting fo a flattener? I love these two targets together
Re: M52+NGC7635
Posted: Fri Sep 07, 2018 6:23 pm
by turfpit
Minos
Thanks - no filter used. 0.8x reducer/flattener & H-alpha filter arrived yesterday. Just waiting for the weather ……
I might be able to fit M52 + NGC7635 + NGC7510 on a single frame - we will see.
Dave
Re: M52+NGC7635
Posted: Fri Sep 07, 2018 6:47 pm
by turfpit
Minos
Histogram from the Astrobin posting
- blue-cast.PNG (19.43 KiB) Viewed 3307 times
Looks like the colour balance is out - well spotted. Shows there is always room for improvement and don't process at 4am.
Dave
Re: M52+NGC7635
Posted: Fri Sep 07, 2018 9:56 pm
by turfpit
How about this revision Minos? I gave the original stack another run through the image mangler.
Dave
- _revised.jpg (437.15 KiB) Viewed 3302 times
Re: M52+NGC7635
Posted: Sat Sep 08, 2018 8:55 am
by turfpit
Revised image at
https://www.astrobin.com/365064/B/?nc=user
Opinions invited …..
Dave
Re: M52+NGC7635
Posted: Sat Sep 08, 2018 1:38 pm
by mAnKiNd
Hi Dave,
Definitely looks better balanced with no obvious cast. Good job!
One suggestion, not a criticism, is to have a brighter/less clipped black point. I find that because every viewing screen is different, it's better to be on the brighter (
) side than the clipped side of things!
Looking forward to seeing your next work
Re: M52+NGC7635
Posted: Sat Sep 08, 2018 1:42 pm
by oopfan
Dave,
I like that color balance much better.
Getting the color balance right with one-shot cameras is tedious. I prefer to depict reality rather taking artistic license like a lot of astrophotographers do. It is a struggle due to the eye's tendency to see the same color differently the longer you sit in front of the monitor! It would be best to take a scientific approach that would eliminate all guesswork. I have some ideas on that using a
gray card to calibrate the camera. In theory it should work but I haven't worked out the details. I opted for a monochrome camera with a set of RGB filters. Thankfully the filter manufacturer supplied the spectral response of each filter and the camera manufacturer supplied the quantum efficiency of the sensor with respect to wavelength. From that I was able to calculate the proper mix of RGB exposures to get the proper balance.
Absent a scientific approach I would use a star catalog to find and verify the color of stars in your image. I use C2A planetarium software. The SAO catalog classifies stars by
Spectral Type: O, B, A, F, G, K, M, C which covers the range from hot-blue to cool-red stars. Unfortunately the SAO catalog is not that large. Instead I use the UCAC4 catalog which goes down to 18th magnitude or thereabouts. UCAC4 doesn't given you Spectral Type but it does give you
Photometric Magnitudes. The two most widely used wideband filters used in photometry are "B" and "V". If you hold up a "B" filter to white light it is indeed blue. A "V" filter is green. (By the way "V" stands for "visual" but don't confuse it with luminance -- it is green!)
A common computed quantity in photometry is
B-V:
- B-V less than 0 indicate intensely hot blue stars.
B-V below +0.5 indicate somewhat cooler blue stars.
B-V below +1.5 indicates "normal" yellowish stars like our Sun.
B-V greater than +1.5 indicate cool red stars.
The attached image is a composite of an image I took of
NGC 6791 and snapshots from C2A.
Brian