However, one major disadvantage of a zoom lens is how the iris changes as you zoom. I’ve been stuck before on a shot that started wide at F2, and ended up zoomed in at F4.5, making the image much darker.
I was excited when I got a chance to try out the 18 - 35 mm F1.8 DCH SM lens from Sigma. It delivers a constant F1.8 from 18mm to 35mm, which is fantastic and its affordable; costing just under $800.
I first tried it on a Black Magic Cinema camera with mixed results. I used a Nikon mount Sigma lens on my Meta Bones Speed adapter with results exceeding my expectations. The problem came when I tried to use my Petroff Matt box and follow focus.
My rig uses 18” rods. As it turns out, they were too short. The focus ring on the Sigma is on the front of the lens, which ended up inside of my matte box. This made it impossible to use my follow focus. If I had 24” rods, it might have worked.
If you are using a camera rig without a large matte box, the Sigma works great.
I also got to test it with my buddies’ Panasonic GH3 camera. The GH3 is a small DSLR camera that shoots spectacular pictures and video. The Sigma lens works wonderfully well with it.
Overall, the Sigma 18 to 35 mm lens works wonders. It's a steady 1.8 F-stop from 18 mm - 35 mm and shoots very sharp. The only thing you need to know before you buy one is if it will fit your rig’s Rods, Matt Box, and follow focus.