Aliased Star Trails


Today’s photo is an experiment with some interesting results.

Using the same in-camera app that I used to make the long exposure portion of my fourth photo of the series, I instead pointed the camera at the north star. Using the 50mm lens that I’ve been using for all of the images in the series so far, I stopped down to f/2.8 and let the camera expose for 1.5 hours. Either an artifact of the app’s method of stacking (it stacks consecutive 15 second exposures), or the lower resolution sensor on the a7S (12 MP) combined with a very sharp lens, the resulting photo shows noticeable color aliasing along radial axes every 45 degrees (it makes the colors look like oil on water). I boosted the colors artificially high to make it more apparent.

This problem could be a result of the star showing up as a very fine detail, so fine that its image is as small or smaller than a single color pixel on the sensor. In this case, the camera can’t determine what color the star is properly because its light is only striking a single color so it just assigns that pixel to the one color on which the star happens to be projected. I imagine that it would have been more beneficial for me to actually defocus the image a little bit to blur the stars for a less aliased result. Perhaps if I do another night sky image I’ll try the defocused star trails method for some fun.

Today we worked to get our car ready to drive up to Reno with an oil change, engine degrease, new air filter and a fixed light bulb. Time to get ready to hit the road for an early-ish morning departure.