APS-C = the Canon 1.6x crop DSLRs. I do not seem to use this lens much for astro. If I am aiming for decent, A3-sized prints I have to close it down to f5.6, therefore leading to lengthy integration times. But it is nevertheless a handy lens for quickie astro snaps, e.g. the image above was made on a fixed tripod, no tracking mount. Towards the right you can see the Coal Sack and Crux (the Southern Cross) pointing downwards. I added the extra glow on the principal stars of Crux so as to make it more obvious, not lens flare :-)