Thursday, April 04, 2019

did some math

Really wanted to get it right this time...

Buoyed by the good skies noted at my 6:00 PM walkabout, I researched the upcoming flyover of the International Space Station.

I recalled the pass was going to be around 9 PM. I noted sunset was going to occur at 7:49 PM. I planned to go out early, in darkening skies, so to have lots of time to set up and focus.

Verified the flyover info in the Heavens-Above web site. Peak magnitude: -3.7. Nice and bright! Location in sky: nearly overhead; slightly north. Checked the times.

    Rises 21:03:46 0° 302° (WNW) 2,338 1.9 -13.7°
    Reaches alt. 10° 21:05:52 10° 305° (NW) 1,475 0.4 -14.1°
    Maximum altitude 21:09:10 67° 29° (NNE) 447 -3.7 -14.6°
    Enters shadow 21:10:27 33° 102° (ESE) 711 -3.2 -14.8°

Verified everything in the phone app.

Considered tracking, with the barn door. Very briefly. Then decided to keep it real simple. For this go-round. Get the exposure nailed down.

Charged a pair of camera batteries. Verified the battery grip was installed (for dual batteries). Grabbed the big tripod, double-checking it had the hex plate. Set the camera to M, ISO 100, and bulb. Then changed to ISO 200.

Set an alarm for 9:03 PM (on the phone).

ISS flyover simulated in Stellarium

Ran a simulation in Stellarium. Definitely a northern sky vantage. I'd set up in the southern section of the yard. Checked the visible duration. Stellarium said if I was viewing from the former tent location, near the house, the ISS would clear the roof at 21:08:15 and then enter the Earth's shadow at 21:10:30. So about 2 minutes.

Lots of people do multiple short images and stitch. I did not want to do that...

Worked the math. Found a nice ISS shot against a dark blue sky by Paul Willows. The photographer used f/8 for 15 seconds at ISO 3200. I was planning a single shot at 8 times the duration. I dropped the ISO to a 400 to let me shoot at 2 minutes. Then I opened the aperture to f/5.6 further dropping the ISO to 100. This would be my starting point.

Simulated the field of view in SkyTools to decide on the lens. The kit lens at 18mm was not bad and would likely fit the whole pass. But the 8mm lens would get a lot more sky. Maybe even a planet or two... Installed the fisheye lens, set it to the infinity MARK (which is back about 2.5mm from hard stop). Set to f/5.6.

Decided to use the netbook (with tether) for focus and image capture. Then I wouldn't need the intervalometer. I planned for test shots a few minutes before the flyover to do a final assessment of the exposure.

Switched to red light mode. Suited up (double layered pants, winter coat). Shut off the driveway light. Packed my carry-all. Strapped on the tripod. Headed out the airlock.

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