Why is piggyback photography trivial?
Piggyback photography is easy because the tracking errors are generally much smaller with short focal length lenses than the images of the stars on the film. However when you piggyback with longer focal length lenses we need to guide with a CCD camera, the autoguider in the CCD camera (at the back of the telescope) corrects for tracking errors and gives very good results. The autoguider will be making corrections that are very small compared to your film because the plate scale is different. Piggyback photography is a good choice for taking pictures of targets too large to fit in the telescope: the Andromeda Galaxy, the North American Nebula, the Milky Way star clouds, etc. So, all you have to do is set the camera up and walk away until the exposure is complete.
