Color and Ha mosaic (2×1) of M33 in the Triangle. The overlap between the pictures is minimum, but it processes very well with PixInsight Photometric Mosaic.
It is a big dataset as I was doing 1mn per RGB frame and there are 2 tiles (I have now moved to 5mn frames in RGB to reduce the quantity of data), but on the upside the shorter frames allow a very good dynamic range. M33 is very bright, so it was a relatively easy target, done with in a single moonless night.
When I was a kid learning about astronomy, I was told that individual stars, nebulas, or a clusters can only be resolved if they belong to our galaxy, the Milky Way. Any such object, outside our galaxy, is too faint, distant and small to be resolved in an amateur telescope, or so they said. Since then, I have had a particular passion to prove the conventional wisdom false, imaging extragalactic nebulas (the easiest example from the Northern hemisphere is NGC 604, a giant nebula in M33 clearly visible above and below), extragalactic stars (typically supernovas, of which you will find a few on this site) and extra galactic clusters, which will be addressed in an upcoming Andromeda galaxy mosaic.
For processing I went minimalist as usual: I stacked with BPP, combined each tile to a color image, removed the gradients (DBE), did a linear fit of one tile to the other, then combined in a Photometric Mosaic carefully addressing the challenging and (too) thin overlap. After that I addressed the overall color with a photometric color calibration and followed with Multiscale denoise, histogram, and a tiny boost to the red to enhance the extragalactic nebulas (but I was very light as I wanted to remain very close to the true photometric colors). I have not played yet with the Ha layer.
