M 42, M43

Astrodude

13139

Deep Sky

Feb 6th, 2023

1987

NGC 1976NGC 1980NGC 1982

Resolution:: 3916x3596 px
File size:: 70054 KB

Show astrometry on hover

Photo description / processing

Because I was shooting with an achromat, strong chromatic aberration appeared around the stars. Can you suggest how to effectively suppress it?

Technical information

Telescope/Lens: Synta BK909
Camera: Nikon D5600
Mount: EQ3-2 Mount (EQDrive belt-modified)
Software: DeepSkyStacker, FitStacker, Adobe Photoshop, Fitswork

Light pollution

Orange, Bortle 6 zone

Date taken: Feb 3rd, 2023

Exposure

147 × 15″ · ISO/Gain: 3200 · Feb 3rd, 2023

Total exposure: 37 m

Comments

praeger

It turned out quite well!
I read somewhere about this method for reducing chromatic aberration in Photoshop:
- Convert the image from RGB color space to Lab (Image > Mode > Lab color);
- In the Layers window, go to the Channels tab and apply the Dust & Scratches filter (Filter > Noise > Dust & Scratches) to the a and b channels (*especially* the b channel), adjusting to taste;
- Convert the image from Lab back to RGB.

Feb 6th, 2023

AstrodudeReply to praeger

I tried it, and it works very well and quickly. The blue tint on the stars is gone. Thank you very much.

Feb 8th, 2023

praegerReply to Astrodude

Please note! You should be more careful with these methods of combating chromatic aberration—they can "wash out" the natural color of blue stars and affect the color of non-stellar objects in the image (nebulae, galaxies, comets, etc.). The most correct approach would be to separate the processing of stars and everything else.

Feb 8th, 2023

Oleg Novoselov

Search online. Removing chromatic aberration in astrophotography
Article by Star Hunter.

Feb 8th, 2023

Oleg Novoselov

Also, you have a Nikon—I don’t remember the model name—but if you shoot in RAW, it doesn’t really matter what ISO you set; the result will be pretty much the same, though the dynamic range does drop. Try shooting at the same shutter speed with different ISO settings, but make sure you shoot in RAW, then play with the files in Photoshop. You’ll see there’s almost no difference. It’s just that at ISO 3200 you can see the image clearly on the screen, while at ISO 100 it looks like nothing is there—but the data is actually captured.

Feb 8th, 2023

AstrodudeReply to Oleg Novoselov

Okay, thanks, I'll give it a try.

Feb 8th, 2023