Sometimes shooting a long exposure results in hot pixels and some times dust on lens becomes apparent if shooting with very small aperture.
Despite having all good qualities the photo looks ugly due to these. I use Canon DPP for post-processing, which works at some extents and removes hot pixels, but if hot pixels are too big then DPP fails.
Attaching an example of dust on lens. There are 4 places (in sky area) where we can notice dust.
I really don't like using Photoshop for post processing but it becomes necessary in these scenarios.
Please let me know if these is any good tool/tutorial for dust or hot pixel removal.