SharpCap Forums

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

Great work, Dave!

You picked up the Hydrogen Beta in the Bubble (greenish-blue) and the Hydrogen Alpha in the surrounding nebula (red)

Brian

Thanks Brian.

I now have an H-alpha filter and will revisit the Bubble Nebula at next opportunity.

Dave

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

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

Minos

Histogram from the Astrobin posting

Looks like the colour balance is out - well spotted. Shows there is always room for improvement and don't process at 4am.

Dave

How about this revision Minos? I gave the original stack another run through the image mangler.

Dave

Revised image at https://www.astrobin.com/365064/B/?nc=user

Opinions invited …..

Dave

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

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