NGC6888, Crescent Nebula in Cygnus.
1 x 30 minutes Ha, 2 x 30 minutes Oiii, processed as RGB: Ha synG Oiii using Carboni actions.
Apogee Alta U8300, APM115/805 APO Refractor, Astrodon 3nm NB filters.
Guided with DSI Pro II and 2x barlow, through Astrodon Monster MOAG, Stark Labs PHD.
Dark calibrated and aligned in Nebulosity, processed in FITS Liberator and PhotoShop.

Additional "lens correction distortion" applied in PhotoShop to round-out corner stars.
However, this technique distorts the overall star field outward radially and misplaces stars relative to a flat star map.
This is the rectangular cropped version to remove the distorted sides.
The field is still distorted, so that any straight lines that are not along a radian will be curved.