30 second exposure, F/22, ISO-100. Can only see a few stars.
30 second exposure, F/13, ISO-100. Few more stars, Orion is somewhat visible.
30 second exposure, F/3, ISO-100. Quite a few stars now, light pollution not horrible, foreground trees visible.
My camera has a "multi-exposure" feature, where it will stack images up, but only up to 9 images. This picture is made up of 9 pictures, each 30 seconds at F/4, ISO-100. I manually took each picture and waited about 5 seconds in between each one. So (9 x 30) + (9 x 5) = 5 minute 30 second "simulated" exposure. Starting to get some decent star trails. The almost vertical line is an airplane.
Getting into longer exposures, now. This one is 3 minutes at F/22, ISO-100. Pretty good star trails, but surprisingly dark sky, and only a few visible stars.
Another 3 minute exposure, F/11, ISO-100. Not too bad, sky and foreground are a lot brighter, but more stars are visible. Another airplane.
6 minute exposure, F/14, ISO-100. Even though this one is double the exposure time of the previous picture, by going up to F/14 the overall brightness didn't change much, but the star trails are twice as long. Another airplane, a very common flight path...
Now here is where things get interesting. I set up the camera to take a 30 second picture every 40 seconds, so there is 10 seconds between each picture. Each picture is at F/4, ISO-100. I set the camera to take 45 pictures, so the entire time span is 30 minutes. I then used a program called Image Stacker to stack up all the pictures, and this is the result. I'm not sure what the dot is about the tree left of center is. It may be a stuck pixel, but it only appears in one of the original 45 pictures. Would be easy to clean up, though. It also seems to be the "in" thing to clean up the airplane trails, but I kinda like them. Since the airplanes are visible, the ISS should easily show up using this method. The only problem I foresee is that since each exposure is only 30 seconds, with a 10 second gap in between, the ISS trail will have breaks in it. The solution may be just to shorten the amount of time between each picture. I think the 10 second gap is also why the star trails appear almost dotted, instead of being solid lines.