Sunday, March 1, 2015

Star trails, Version II

In my last post, HERE, I wrote about the making of star trail photos on a rather frosty winter evening. I thought one of the resultant photos, above, was pretty cool. Not bad for a first time effort. Well, I hadn't seen nothin' yet!

I made two hour long exposures, one of which is the photo above. The other one wasn't nearly as good. It was my first effort, and I had allowed too much light to collect via too large of an ISO setting. For the next long-exposure image, I dialed things down and achieved the above result, which was an improvement.

But my research had indicated that making a long series of 30 second exposures would generally yield much better results. The only hitch is that one must digitally stitch the images together, in the order in which they were taken. So, I did indeed take a long series of short exposures, thinking that eventually I'd learn how to sew them all together. Which I did.

See below:

An ENORMOUS improvement on the long single exposure shots! And stitching them together is as easy as pie, thanks to the website! A German by the name of Achim Schaller (who must be a genius) created software that allows multiple exposures of astrophotography shots to be seamlessly melded together, allowing results such as the above image. Thanks to Toni Hartley for showing me how to work the software, too.

There is no question that the second image is far beyond the single shot exposure, for which I kept the camera's shutter open for a whopping 56 minutes. The second shot was achieved by stitching together a total of 84 images. Each exposure was 30 seconds long, and the camera was set to f/4 (wide open on my 17-40mm Canon lens), at a focal length of 17mm and ISO at 500. As mentioned in the previous post, I set the white balance to tungsten, which gives the night sky a steely blue cast. Photogs shooting in RAW could convert to that white balance mode later, in post-processing, but why not get it right of the can. Of course, to shoot uninterrupted 30 second exposures over the better part of an hour, one must use a remote shutter release that will lock in place, thus constantly tripping the shutter until told to quit.

The reason that the second image is superior is in large part due to the much shorter exposures. There was more ambient light where I made this image than is desirable, from nearby houses, farms, and a few distant cities. Thus, the super long exposure shots harvested tons of light, largely blowing out the stars. The short exposures did not keep the shutter open long enough to collect much light other than that of the targeted stars, thus the much showier photo. After shutting down the camera, all that remains is to stitch all of the images together, and as reported earlier that is pretty simple with good software.

I eagerly await the return of the new moon, hopefully with attendant clear skies. Then, a trip to a truly dark corner of earth will be in order.


Jack and Brenda said...

That's a nice photo! Thanks much for the information about the software.
Is the diagonal line a hick-up in the software? Looks too straight to be an airplane.
For dark places, I'd recommend somewhere in the Southwest. Should be able to easily find a great remote place in Canyonlands NP. The darkest spot that I can remember was at the bottom of the Grand Canyon on a moonless night. You could actually hike on the trail with only starlight. It was as though the sky was a solid white with stars.

Jim McCormac said...

Good eye! I have no idea what caused that. Maybe a quirk of the camera. Can't wait to shoot stars out west!