It's M42 season again! It has been a long time since I tried my hand at M42. This one was actually taken from very light polluted San Francisco with a lot of help from my new IDAS LP-2 filter. The LP-2 is a broadband filter which blocks only the wavelengths of light emitted by mercury and sodium vapor lights while allowing the rest of the spectrum to pass through. It doesn't add a lot of exposure time and the difference it makes is rather dramatic!
Unmodified Sony a7R and an Astro-Tech AT65EDQ 65mm f/6.5 refractor on a Losmandy G11. Guided with a 9x50 finderscope and Orion StarShoot autoguider using PHD. 20 x 30 second integrations (for the core) plus 20 x 300 second integrations and five averaged darks all at ISO 1600.
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