[APML] Astrophotography from the ISS....again! pt. 3

And here is part 3

I have seen images of the "barn door" tracker Pettit built while in orbit. It was constructed from the gimbaled IMAX camera mount which was modified with some parts off a Russian Progress resupply rocket. The jackscrew that drives the mount was powered with a Makita cordless electric drill. In the image I saw it looked like there was an eyepiece from a small telescope sticking up out of the assemply. I assumed this to be the "guide scope". It was, but I didn't realize until I was talking to Don about it that the guide scope was actually the optical viewfinder on a Hassleblad camera with a 350 mm lens. Don used the Hassy as a guide scope on the platform for the Nikon digital! The eyepiece and the focus screen reticle made a good crosshair to allow tracking with the drill-powered platform. What is interesting is that he used this to track terrestrial targets, not stars. The station was stable enough for star photography with no tracking, but the movement of the earth below could not be stopped without the tracker.

Don showed me an image of a city taken at night, the city illuminated by its own lights. Not too shabby I said. Then he showed me the same city taken with the barn door tracker. The difference was amazing. In some cases Don was achieving better resolution, at night, using the city's own lights for illumination, than the early Air Force spy satellites achieved back in the early 60's. There was a marked difference in cities by nationality. Chicago and L.A. distinctly showed the effects of sodium vapor street lights while Tokyo was obviously illuminated by mercury vapor lights. Some cities in Saudi Arabia were very bright with multicolored illumination and distinct geometric patterns. They were beautiful.

Pettit also did some rough "densitometry" of the city images and came up with something interesting. A night image of Washington DC is startling because everything inside the square boundaries of D.C. are brighter than the surrounding Virginia or Maryland urban areas. The brightness increase follows the straightline border perfectly. All of D.C. pops out in relief against the darker rest of the area. The Mall shows as a dark black strip in the city, but the Government buildings north of the Mall are so brightly lit that this area of D.C. is actually two f/stops brighter than the rest of D.C. at night. Don did some comparison of cities and D.C. was the brightest night time city in all the U.S.A. with one exception... Las Vegas. Vegas darn near burned out the chip. That is one BRIGHT city. Another cute thing is that in D.C., the Pentagon shows up like gangbusters at night. No, not because it is so bright, but because it is so DARK! After 9-11 the cut the lights around there so much to "hide" the place from Osama's invading hordes that it shows up like a sore thumb as this big black spot.

Part 4 of this string was actually the first one posted.

Robert Reeves +29.484 98.440
reeves10@swbell.net San Antonio, Texas USA