If others also can get pictures of the "satellite belt" our chances to detect
unannounced movements increase. Some basic ways to get going if you do
this for the first time...
An aid to aiming your cameras is any software or webpage for antenna alignment.
My favorite is the old SMWlink3 calculator, look for smwlink3.zip. The angles are
then transferred to the camera or tripod head using something like:
http://www.clasohlson.com/medias/sys_master/8872671412254.jpg
(A video tripod head is easier to use and to adjust, pan and tilt are separate.)
100 to 200 mm lenses must be pointing in the right direction or not too far from it.
Looking for the few pixels that are satellites is hard if you have to check a 20 Mpix
image at 100% magnification without a clue where to start. 50 mm lenses cover
a wider angle so I guess you just point it to the south or SSE. Stars and satellites
will still be about the same size in pixels using a 50 mm lens. (I think at least,
some webpages on astrophotography give detailed explanations)
Looking for the "oddball" satellites like Astra 2D and Intelsat 702 makes it easier
to identify the others on the satellite belt. The star trails are a very good way to
measure angles in the pictures. An exposure time of 60 seconds gives star trails that
are exactly 0,25 degrees long no matter what lens or zoom ratio you use.