ABSTRACT
It is not uncommon for non-astronomers to believe that astrophotography requires a long telescope with considerable magnification and it is quite a shock when they realize just how big some deep-sky objects really are. Even then, astronomers are sometimes dismayed when their shiny new telescope has insufficient field of view to capture the entirety of a large galaxy or nebula. At the extremes, the shortest viable telescope focal lengths are around 350 mm and even with a full-frame sensor, may be too narrow to capture the largest views. In these circumstances most astronomers are aware of mosaics, where side by side image tiles are seamlessly joined to extend the visible field. For the widest views it is not unreasonable to question the need for this complexity, when a normal camera lens might be used from say 12–200 mm focal length. The rationale highlights a secondary benefit of mosaics; that of increasing detail, since a larger aperture instrument captures more light, with higher resolution and at the same time is capturing the image over more imaging pixels at a smaller pixel scale. A third benefit of the underlying mosaic process is its ability to combine images from different instruments, often at different scales and sometimes operating outside the visible electromagnetic spectrum too. There are four main challenges during the execution of a mosaic image prior to image processing:
acquisition planning
tile alignment
tile registration
blending the image
