I saw what a fellow member of my Astro Society had obtained from fairly basic gear and I reckon I should be able to 'afford' something like he has. He is using his elderly DSLR, mounted on an ioptron startracker and is producing pictures of nebulae which I couldn't hope to obtain by eye from my albeit semi rural location near London. Using a stack of images and pasting them together is clearly a good method for noise reduction but would have to do that indoors on my iMac. Two problems here - there are relatively few suitable OS X programs available (for cheap or for free) so I would consider buying an extra machine - a Windows laptop. The very cheapest Windows laptops are really cheap but I have a feeling I could be all night processing a dozen pictures with such a low performer. In terms of i3, i5 and i7 grades, where should I aim? Is Nebulosity a good prospect? I must say, I do not find it at all intuitive and the Licence is around GBP 90, which is not a trivial amount if I don't get on with it any better than with the demo version. Is it worth sticking with or is there something free that's as good on a PC?