Zip13

Hello. Hope it is correct place to ask that question (if not so point me where it should be) Here is my equipment: 1) Nikon d5100 APS-C (crop 1.5) 2) 8mm belomo 3.5A (ex peleng) circular fisheye lens. 3) tripod (no mount, no guiding). I used previously 35mm lens to make pics and later i successfully stacked them in DeepSkyStacker. But now I cannot do it with that superwide lens (most likely bcoz of distortion or ...). I made 27 light frames (iso 6400 , exposure 30, f5.6) and Dark frames with the same settings. When i stack the images the final result not that sharp as it should be (still can see star motion, shorter blurry star trails). Could you help me to setup process for that fisheye lens to stack images of milkiway? What software should I use (IRIS? ISIS? DSS? Nebulosity (expensive but demo still works for me)? Registax?) In IRIS i tried to use grid command, but got warning message "Read error"... but i will look at it soon. Thank you for answers