I'm thinking of buying a Sigma 18-35mm constant f/1.8 with a Sony A mount for my FS700.
The reviews have been generally good...

But today I was wondering, if I were to get the Canon mount... would it work with a Medabones Speed Booster?
Would it become a F.8 lens and 0.71x wider?
Would it vignette, if so at what mm?

Sigma 18-35mm F1.8 Lens Review ? DSLR Video Shooter (http://dslrvideoshooter.com/sigma-18-35mm-f1-8-lens-review/)
Sigma 18-35mm f/1.8 EX DC Field Review - YouTube
Sigma 18-35mm f1.8 Review - a GROUNDBREAKING Lens! - DigiDIRECT TV Ep 036 - YouTube
Sigma 18-35mm f/1.8 Review: The Best Low-Light Zoom Lens By a Mile (http://gizmodo.com/sigma-18-35mm-f-1-8-review-the-best-low-light-zoom-len-950860947)

Bill Kerrigan
Montreal, Quebec, Canada

From what I've read about the lens, it is designed for APS-C cameras. Therefore, if you used the Speed Booster, you'd most certainly get some vignetting.

The Speed Booster is only designed to be used with full frame lenses, and APS-C is not full frame. Actually, APS-C is very close to the Super35 sensor size of the FS700.

I've used APS-C lenses on my FS700 with the non-SB Metabones with very little vignetting issues, so I would gather that you could probably use this lens just fine with a non-Speed Booster adapter.

The Speed Booster is only designed to be used with full frame lenses

I just read a article where the speedbooster was used with the new sigma on a m4/3 camera without vignetting, I thought speedboosters can be had for smaller sensors camera's as well?

Are you sure its even available in A mount? All I find so far is Canon and Nikon mounts.

I just read a article where the speedbooster was used with the new sigma on a m4/3 camera without vignetting, I thought speedboosters can be had for smaller sensors camera's as well?

Yes, there are several types of adapters with speed boosters for sale by Metabones for various lens mounts and camera sensor sizes. But the one the OP talked about was from Canon's EF mount to the FS700. Metabones states themselves that Canon EF-S lenses are not supported on this unit because they are designed for APS-C sensors.

thx for the clarification.

I confirmed with Sigma today that there is no a mount version of this lens, although they did say that they had a lot of requests for an A mount version so one will be announced in December.