M3 10 second exposure, Zhumell urban sky filter. This filter increases the contrast of deep-sky objects like emission nebulae and darkens the background sky by blocking mercury vapor light transmissions and enhancing transmission in the hydrogen beta, doubly ionized oxygen and hydrogen alpha regions of the spectrum. This filter, I have found, is no longer in production. Next filter to purchase is the Optolong L-eNhance filter. Or, the Optolong CLS filter at a lower price does basically the same thing. Image cleaned up with Gimp.