Saturday, September 20, 2014

doubles by lucky imaging

Listened to Cotterell's talk from this year's Starfest, video image capturing and processing of double stars. Katrina, attending the session, used my audio recorder.

Not a lot of people doing this. Can do it anywhere. He often observes in his backyard in the city where the visual magnitude is 3.0. Small 'scopes can be used. His next talk will be on scientific measurement.

Talked about seeing conditions. Like planetary imagers, he captures video and then stacks the images. He does minimal processing.

Pointed out that high precision is not required. Does not require an equatorial mount; an alt-az works. Because the exposures are short. Double star imagery does not require darks, flats, bias frames. He uses a Bahtinov mask.

Most of the video he shoots is 90 seconds or shorter.

You need long focal length. But not too long. It's a balance. "Nyquist Theorem." It suggests getting the airy disk to cross two pixels. He shared some numbers and formulae. He uses a Barlow to get f/15 or more for his DSLR camera.

Shared some single shots. Then his new video stacked images. Most done with a Canon 60Da and an 8" SCT.

Pointed out the atmospheric dispersion, the red and blue edging. Some participants suggested correcting this in software. He had not tried this.

He mentioned some processing software. RegiStax for the PC would work although it expects AVI files. AutoStakkert is another PC option. For Mac OS, he uses Lynkeos. He did a demo in the software. Selected a reference frame, cropped the frame, etc. And then changed the gamma.

He said he will share the presentation.


The Nyquist Theorem, regarding resolution and pixel size, is noted at the Starizona web site.

Lynkeos is an open source Mac OS app designed for planetary image processing.

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