About this time of year we usually get a few nights of clear weather combined with very bright passes of the International Space Station. A couple of weeks ago we had a good one that peaked at magnitude -3.8 (explanation below). That's bright enough to photograph at 1/2000 sec at a reasonable aperture and ISO. I tried this a couple of years ago with the 300mm f/4 and a TC1.4 and was pleased to see obvious structure - more than just a bright dot. This time I repeated the attempt with a 500 mm PF, which gave even more remarkable results. The ISS photos below are from one frame that includes the star Arcturus for reference. Taken wide open at f/5.6, 1/2000th, ISO640. It feels comical pointing a long lens up into the dark sky and snapping away at 1/2000th sec.
In order, the photos are:
(i) Full D850 frame downsampled ~5X to 1600 x 1067. The ISS is the 3x5 pixel speck left of center, Arcturus is a single pixel down and right.
(ii) Downsampled 2X and cropped to 1600 px to include the ISS and Arcturus. You can begin to see some detail.
(iii) Small 100% crop of the ISS.
(iv) Reference 100% crop of the Moon, photographed and processed with all the same settings.
All pushed one stop, lightly sharpened in ACR and converted to jpeg without further sharpening. I also removed some red-green fringing in ACR, which I think was atmospheric, not due to the lens.
At this point in its orbit the station is about 495 km away. It's 73 x 109 m. So this is like trying to photograph the Eiffel Tower from Amsterdam, only the space station is smaller.
Cheers, John
Note - astronomical magnitudes: Apologies to astronomers, but this scale is nuts: It's logarithmic, 5 magnitudes equals a factor of 100 in brightness, and back to front - negative numbers mean bright! (
https://en.wikipedia.org/wiki/Apparent_magnitude). Anyway, -3.8 is brighter than Jupiter, almost as bright as Venus.
