Finally happy with an all-in-one solution for 16-35mm zoom on my Sony A7Rii! The lens is sharp, suitable for astrophotography, accepts filters, and produces a beautiful sunstar. My biggest concern was how focus would perform "adapted" to a Sony A7 series camera. I did frequent searches online for "will the Canon 16-35 f/2.8L III lens work with a Sony A7Rii camera" and "Sigma MC-11 or Metabones IV adapter for Canon 16-35 f/2.8L III" with few results. Mostly just a sentence or two buried in a forum post. Therefore I took a risk, purchased the combo and ran some tests using them with the Sony A7Rii, A7R cameras and Sony FE 24-70mm f/2.8 GM lens for comparison to see for myself.
Sony FE 24-70mm f/2.8 GM vs Canon EF 16-35mm f/2.8L III USM with Sigma MC-11 attached.
The Sony mirrorless design allows other lens mounts to be used on the camera with the right size adapter serving as a spacer between the Sony camera body and another manufacturer's lens. The adapters range in complexity from "dumb" adapters that make no electronic connection to the Sony and therefore require manual aperture and focus control. To "smart" adapters that strive to make the lens work as if it were a native Sony FE lens. With so many adapters to choose from and new firmware and lenses being released all the time, it is difficult to find accurate information about how a particular combination will work. This review used the latest firmware as of February 5, 2017; Sony A7Rii (Firmware 3.30), Sony A7R (Firmware 3.20), and Sigma MC-11 (Firmware 1.03).
Finally here are the results. The A7Rii focuses quickly in good light using the Phase Detection area. Using the smallest flexible spot it had a few problems in darker corners but selecting an area with more contrast was an easy fix. Surprisingly the Sony FE 24-70 FE f/2.8 GM lens didn't perform any better in some of the lower contrast areas. The A7R Contrast Detection system is much slower but eventually it achieves focus. The few seconds it takes to acquire focus is useable for landscape photography but tedious.
I took the lens out for a sunrise shoot to see how the autofocus was in a true low light situation. Before the sun came up I took this image using the autofocus on the boat launch. The autofocus worked well but I had to help it by placing the flexible spot on high contrast edges in my scene. I was also really impressed with the close focusing distance of just 11" which came in handy for this shot as a nearby tree really limited my ability to move. Flexibility to compose in tight spaces is one of the main reasons I wanted this 16-35mm zoom rather than the many excellent Sony wide angle primes.
16mm, 0.8 sec at f/16, ISO 100, + Sony Smooth Reflections App
The other reason I selected this lens is its f/2.8 maximum aperture. I do a lot of astrophotography and I was tired of carrying a 16-35mm f/4 and a 14mm f/2.8, 18mm f/2.8, and/or 24mm f/1.4 everywhere. Using this lens at night I liked the mechanical manual focus ring much better than the focus-by-wire in many of the new Sony lenses. Also the distance scale is spot on making infinity focus for astrophotography much easier.
16mm, 20 sec at f/2.8, ISO 800, 52 images stacked in StarStax
I often use a polarizing filter around water which this lens accepts easily. There is even room with the lens hood on to get a finger in to turn the filter without smudging the glass. It also produces nice sunstars, personally I prefer the look of them compared to what I've seen of the Tamron 15-30 and Nikon 14-24...which neither can accept a screw on filter.
16mm, 1/4 sec at F/16, ISO 100, C-Polarizer
I hope this helps other Sony users looking for a 16-35mm lens with similar needs as mine. This will be my primary setup until the rumored Sony FE 16-35 f/2.8 GM lens is released. However given the year it took for the Sony FE 70-200 f/2.8 GM to become available...I think I will have this lens for some time.
Below are some 100% crops as requested, bottom center and bottom right corner of the frame, focus point on the fence.
