STEP BY STEP

STEP 1

Once your telescope is set up and aligned, aim it at a celestial target: a bright star, a planet or the Moon. Centre it precisely in the field of the camera and then carefully align your finderscope with the optical axis so the views coincide accurately.

STEP 3

You’ll need to adjust the camera parameters by trial and error. For your first attempt, set the exposure to 1/1,000s in ‘daylight’ colour balance mode; with a DSLR set the ISO to 400-1600, with an astronomical video camera set the gain to a medium value.

STEP 5

Spot the ISS with your eyes first, then loosen the mount axis brakes as much as necessary, centre the ISS in the finderscope and track it as smoothly as possible, holding the optical tube, the mount or the counterweight bar. At the end of tracking, stop recording.

STEP 2

Focus the camera on the same target. Fortunately all celestial objects, including the ISS and other satellites, are so far away that all can be considered to be at infinity and need the same focus position. If your focuser features a locking system, use it.

STEP 4

Once you’re ready to shoot, check that the mount is able to follow the whole trajectory of the ISS in the sky. A few instants before the predicted time, aim the telescope in the direction it will appear above the western horizon. Start recording video.

STEP 6

If you succeeded in keeping the ISS within the field for a few seconds or more, use an application such as VirtualDub (http:// virtualdub.org) to extract all video frames in JPEG, TIFF or BMP format. Tweak the sharpest ones in editing software.