I would say the 17-40 is a great choice if you are doing landscapes and glidecam with it. Its a really light lens which is nice for smaller glidecams and help counteract the odd weight distrubution of the dlsr. I also would assume with landscapes you would be shooting f8-f11 anyways. Also, for the difference you would be spending you could easily buy a rokinon 24 1.4 or 14 2.8.
The sigma 85mm is awesome and I think its the best compromise for those that shoot both photo and video.
If you compare both canons(1.2 and 1.
, the sigma and the rokinon each has its strengths.
Rokinon is also nice and has the best focusing ring for video but no af for photo. however, That doesn't bother me too much as the af sucked so much on the mark 2 that I just shot everything mf even when i got the mark 3.
The 85 1.2 is amazing but the focusing ring is not. It just feels too loose to use for video imo.
The canon 85 1.8 is a good lens, great for the money but I love the look of the Sigma. Really nice creamy backgrounds, great colors, and pretty sharp at 1.4. I know its not a full stop gain over the 1.8 but sometimes can make the difference between an iso bump. In low light high iso, shadow noise can still be pretty apparent, especial when the camera is moving.
Th sigma 50 is also really great but I also prefer a 35/85 prime combo than 50/85. Im pretty excited for the simga 35, but the rokinon had served me very well for the money.