OK, OK, this is not a rare object, but I have to pay homage to the Horsehead Nebula for a revelation dating back to the 1980s, perhaps even the late 1970s, when I came across a first stunning photo of it: I would have never thought that objects like that could be out there. It was a shock at that time! Young generations for sure do not understand: at that time there was no internet, only books, and you had to look actively for them - space images were rarer stuff than today.

Technically, my initial intention was to add Sii signal to the HO, but I abandoned the idea because Sii was not meaning much to this target, as the signal is very close to the Oiii.
There was a second reason linked to the fact that the ALP-T Sii+Hb filter unfortunately produced huge reflections due to large stars, even placed outside the field, see picture below. This is curious, as the "normal" ALP-T filter in same conditions is behaving perfectly. I informed back Antlia, no answer yet, but be wary if you are an OSC photographer and you are thinking to add a Sii dual to your arsenal. I managed to eliminate the huge reflection by plugging a portion of the Oiii into the Sii image, but, as said, I kept Sii out of the final work anyway. Thanks to @andrea tasselli who tried to help me with the Sii image.

Give me please a suggestion: is it better the fullisize or the cropped version? I cannot decide myself.

B33
The Horsehead Nebula B33 is a small dark nebula part of the much larger Orion molecular cloud complex. It appears within the southern region of the dense dust cloud known as Lynds 1630, along the edge of the much larger, active star-forming H II region called IC 434, Sh2-277.
It is approximately 1375 ly from Earth, and 3.5 ly wide.

NGC2023
NGC2023 is an emission and one of the largest reflection nebulae in the sky, with a size of 10 × 10 arcminutes.
The reflection nebula is illuminated by the Herbig Ae/Be star HD 37903, which has a spectral class of about B2 Ve. The region around the central star is radiating fluorescent molecular hydrogen emission at a near-infrared range. Infrared emission of polycyclic aromatic hydrocarbons has been detected from the nebula's dust.


Picture1: Unprocessed integrated images with dualband filters ALP-T (left) and ALP-T Sii+Hb (right). The huge and multiple reflections are produced by Alnitak, just out of the field.