Friday, December 15, 2017

Nightscapes With a Phone Camera

Sky Scenes

I've been exploring the ability of my Samsung Galaxy 8 Plus phone to image constellations. The maximum exposure time in the "pro" setting is 10 seconds at ISO 800. Only limited faint detail can be captured, but I'm amazed at how well the tripod-mounted camera works at night.

For example, look at the next picture of Orion rising among moonlit clouds on November 27th. Auriga, Taurus, and the Pleiades are also visible.
The next night, November 28th, I captured the same scene when clouds were absent. Constellations are easier to see, but the Moon was one day closer to full. Consequently, the sky is bright.
On December 10th moonlight was absent in the evening. I walked away from neighborhood lights to take pictures in a nearby field. The next image shows a noticeably darker moonless sky as Orion, Taurus, and the Pleiades shine above bare trees.
Trees make a nice foreground in the previous picture, but the branches are very dark. It would be nicer if the branches were slightly illuminated. I next moved to a place where local lights were blocked by surrounding trees and got the following image of Auriga centered between the trees. Perseus, Taurus, and the Pleiades are also visible.
In the previous picture (and others) the image center is noticeably brighter than the upper edges. I wonder if the camera chip is more sensitive in the center, or if there is vignetting. This effect could be removed by flat fielding, but I didn't take a flat field image.

Finally, I walked further away from neighborhood lights to capture the following picture of Orion, Taurus, Auriga, and Gemini rising above pine trees in a nearby soybean field.
I've tried doing constellation photography with my Nikon DSLR, but have encountered several frustrating obstacles. The Nikon will not automatically focus on stars, so I need to manually focus. Unfortunately, the infinity setting for manual focus is not accurate. This means I need to rotate the focus ring back slightly away from infinity and then visually check to see if stars are focused. The visual checking requires several time exposures and subsequent magnifications of the viewing screen in order to see if stars appear as points. While this tedious exercise is going on my hands are getting numb and the camera lens is getting covered with dew. The Nikon DSLR can do long exposures on the "bulb" setting, and this reveals lots of dim stars and faint details. But these long exposures require a tracking mount to keep up with Earth's rotation. On many occasions I've spent the better part of a freezing, hand numbing hour setting up the tracking and focusing the camera only to find the lens covered with dew and useless.

In contrast, the phone camera quickly focuses automatically and does a good job showing the brighter constellation stars. The phone lens doesn't seem to get quickly covered with dew the way my DSLR lens does. Ten second exposures don't require guiding equipment to follow Earth's rotation. The phone/tripod combination is easy to carry from place to place and sets up quickly.

Images like the ones above can easily show satellite and meteor tracks among the constellations even if dim stars are missing. I hope to capture some of these events and display the results in the next few posts.

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People say I'm crazy doing what I'm doing
Well they give me all kinds of warnings to save me from ruin
When I say that I'm o.k. well they look at me kind of strange
Surely you're not happy now you no longer play the game

People say I'm lazy dreaming my life away
Well they give me all kinds of advice designed to enlighten me
When I tell them that I'm doing fine watching shadows on the wall
Don't you miss the big time boy you're no longer on the ball

I'm just sitting here watching the wheels go round and round
I really love to watch them roll
No longer riding on the merry-go-round
I just had to let it go

John Lennon