Tuesday, October 19, 2010
Ever since my curiosity led me to try photographing the International Space Station as it flew overhead one evening in June, I've had the desire for closer images with more detail than I got on my first attempt. Using the NASA website, it's easy to tell exactly when the ISS fill fly over any location you enter, and NASA's "skywatch" program calculates the times when it will actually be visible. These are always in times of darkness, or in the early morning or late evening when light from the sun illuminates the space station in the dark sky. Usually the biggest deal breaker to getting photos is the weather. You need a clear sky with few clouds or ideally no clouds to get in the way.
This morning was one of the best opportunities yet for photography. At it's closest point, the ISS was only going to be 221 miles overhead at exactly 6:44:52am. It would come into view from the Northwest about 800 miles away, and be visible to the naked eye a little over 2 minutes prior to passing at its closest distance. After passing almost directly overhead (89 degrees from my location) it would be visible for another 2 minutes or so as it sped away toward the Southeast.
This morning I slept through my alarm and luckily got outside with my camera gear just in time to see it approaching. Usually I find the moon and set my camera focus on it to get a good 'infinity' focus setting, and then switch to manual focus to shoot the ISS, being careful not to touch the focus ring on my 500mm lens. Today I was rushed and there was no moon in sight so I had to use autofocus and hope for the best.
Looking through a long lens and teleconverter at high magnification, it is difficult to even find the bright dot streaking across the dark sky, even though it is clearly visible to the naked eye. And trying to get the camera to auto-focus on it under these conditions is iffy at best.
This morning I managed to get photos of the space station approaching, but unfortunately I lost it after it got closer than 270 miles away. When I found it again through the lens, I shot more photos as it sped away, but none of them were properly focused. The solar arrays are clearly visible in the images of the ISS approaching but still not as close as I had hoped, since I was unable to get a shot of it when it was at its closest distance.
(Click on the image below to see a full size composite showing 7 images of the ISS as it passed over this morning)
Distances listed in the image are calculated using tables from NASA's skywatch program, and interpolating the distances between the 20 second intervals listed. Before doing this, I synchronized the time setting in my camera with an atomic clock to be sure time time stamp on each image was accurate. This allowed me to determine the distance in each photo referencing the NASA charts. You can clearly see that each successive image of the international space station is slightly larger than the previous one, since it is getting closer in each frame. Even though it is difficult to keep the ISS in the viewfinder even at 1000 mm, I have pretty much decided that I need to stack teleconverters to get even more magnification if I ever hope to get a closer shot. This will make it even more difficult to find in the viewfinder, but if I succeed the image will be 40% larger.