Just got the Rokinon FE8M-P 8mm F3.5 Fisheye Lens this month and am pretty excited about it, I shot a few images with it so far and overall very pleased with the results.
I am looking forward to going out with it to do some night time and also interior HDR scenes.
There are a few negatives that I found with this lens –
Chromatic Aberration, which I tame in Lightroom2 and Photoshop CS5, also when processing in Photomatix Pro I check the reduce Chromatic Aberrations box.
Close focus a bit fuzzy, I noticed when I have a subject in the scene too close about 2 or less feet it seems a bit fuzzy (even at f11) compared to the rest of the scene, but I think I have to fiddle with the focus more.
Manual focus, although with this kind of lens you can just set it in between and just shoot although as mentioned prior I think I need to tweak and test the focus setting a bit more.
And the plusses-
Fun lens!!!
The price is not too bad – less than $300 dollars.
Dramatic views. This can really turn an ordinary scene into a really cool scene.
Fun lens!!! ah ok I said that already lol. But my impression overall is that it is indeed a fun lens.
Below are a few sample images that I shot so far. All were post processed in LR2 and also in addition some with Topaz Adjust and Nik Color Efex Pro as well.
In closing although I just barely begun using this lens I am really excited about it. This lens will be a regular addition in my camera bag.
RobertPhotoGraphics 
I can’t wait to see what else you can do with this thing. You almost have me convinced that I can get this instead and use it on a 7D instead of spending the $500-600 for a full frame fisheye. The shots looks great so far.
Great blog post, Rob. I’m currently in the market for a wide angle lens. I’m thinking the Sigma 10-20mm is the best value and option. The other lens was the Pentax 12-24mm which is more expensive. Have you ever used the 10-17mm Pentax fisheye? I loved that lens. Seems like this lens is an affordable option tho.
Thanks for sharing the review and images. Looks like a lot of fun!
Thanks for the comments, @Brian I never used the 10-17mm Pentax although I remember that I was looking at that one and the Sigma 10-20mm at the time and chose the Sigma 10-20 simply because the lens element did not protude and I am able to put filters on it. But overall I like the Sigma but I feel that it is not sharp enough for me even at higher f-stops and my copy seems to have some blurriness on the image sides. And it is a bit heavy although most Sigma’s seem to be.
Having said all this I think if I had to do it again I would opt for the Pentax 10-17mm as Pentax lenses seem to be more sharper and more calibrated to the Pentax K-5 body than other lenses that I have. Just would have to be careful with the front element.
The Pentax 12-24 is just too expensive and F4?
There is another one out there that I would consider but it is a Sigma for low-light concert photography / events – its the Sigma 10mm F2.8, I would use for HDR but since we are on tripods for multiple exposures at high f-stops I really would not get for that.