This is an LRGB composition. However, no actual L exposures were made. The L here is a pseudo L, made with B+V+R+I+OIII+Ha (straight add, no normalization). Similarly, the red is a pseudo red, made with R+I+Ha. The G is made with V+OIII.

Hope you enjoy this NGC 2023, and wish everyone has a happy 2023.

Rev.B is a comparison of images taken through the Johnson B filter and the Cousins I filter. The I filter has an effective wavelength of about 800 nm. This filter looks almost completely black, because its passband is outside human's vision. However, astronomers don't call it infrared. In professional astronomy, light that can be detected by silicon-based detectors (CCD, CMOS) is called "optical" light. Only light with wavelengths too long for CCD to detect is called "infrared." So you won't hear astronomers calling I "infrared" although our eyes cannot see it.

Because of the longer wavelength, I-band light can penetrate thicker layer of dust, while visible blue light can be easily absorbed by dust. This difference can be clearly seen in the B vs. I comparison in Rev.B. The I image has a total integration time of 2.5 hr, while the B image has a total integration time of 4 hr.  The B filter has a lower throughput.  So the two images have comparable amounts of received photons. Even under such a condition, the I image contains many more stars that are not detected at all in the B image. This is because those stars are behind the thick layers of dust and their blue light is absorbed by the dust. In NGC 2023, also because of the absorption effect, you can only see the surface of the nebula in B, while you can see through it in I. In the horse head region, you can see the foreground and background dust reflection in I. On the other hand, in B, you can only see the foreground because the light from the background is blocked by the foreground dust.

Hope you find these interesting.