I have the 8mm Samyang and use it with my 7D. For the price it's a really great lens if you are ok with manual focus. And why wouldn't you since pretty much everything from 1m away to infinity is in focus if you set it at 1-2m and f/5.6-8. It's great for video also for the same reason.

I don't know about how well it fares in snow and rain but the build quality is definitely great. Feels solid and well constructed.

Also if you keep the camera level in relation to the horizon and crop a little the fisheye effect won't distort the image too much and you can get nice wide images. Here is one example: http://qwrad.wordpress.com/2011/12/1...-construction/ and also you can see a few more in my blog that are of stars and star trails.