As far as I know, the lens is not specifically weather-sealed, so I don't use it outside in the rain, as I don't recognise any explicit rubber seals. Weather protection should also include the designation WR in the lens name.
LG Mandi
It's like Stefan says, it's EF mount. Sigma only has lenses with EF mount, none with EF-S, whether APS-C or full frame (had the 18-35 via MC-11 on the A6300, and no EF-S lenses fit on the MC-11 either without opening the converter and taking out a cover). Must have something to do with licence fees. Btw: it's the same with Tokina, only EF and no EF-S. This is often incorrectly stated here at Digitec.
Hello
It is an EF-S bayonet and as far as I know it goes on all cameras with the EF / EF-S mount. I use it on the Canon EOS 80D and am very satisfied.
Question could be answered more clearly if the camera type was mentioned.
MLG Mandi
Theoretically, the lens can already be mounted on FullFrame cameras. But that makes no sense here, because the lens was developed explicitly for APS-C. Therefore, when used with a FullFrame sensor, you have massive vignetting, which makes the use pointless.
I don't have the 35 mm 1.4, but I am fully satisfied with the 18-35 mm. I would prefer the 18 mm for starlight/low-light photography - I don't think f+0.4 is much use there. I see vignetting with the 18-35 mm more at the lower focal lengths. The 35 mm is not really suitable for macro or portrait photography.
It fits on the 70D. It's a really great lens. It doesn't have an image stabiliser, but for auroras you need a tripod anyway. I have the same lens and will sell it. If you are interested, I would put it here as used. It is still in top condition and very little used.
This is not recommended, as the full-frame camera (6D) will then show strong vignetting.
Optically, the lens was developed explicitly for small format cameras.
Yes, I use the lens like that. Vignetting only occurs when taking photos. From about 24mm it is no longer visible.
Filming is no problem. (No vignetting)
Obviously both the Metabones IV and Sigma's MC11 work quite well with the lens. But I would not expect the same AF performance as with original FE lenses.
Besides, the Sigma lens is designed for APS-C (SIgma Code DC). On the A7II it only works in crop mode with just 9 MP. That somehow makes little sense.
According to Wikipedia, your GH4 has a 'Micro-Four-Thirds' (M43) connection for lenses. And that's exactly what you can set as a filter at digitec. But it seems that the Sigma 18-35 is not available with it (https://www.dpreview.com/forums/post/53950444) or at most with a lens adapter. But I have no idea what restrictions this entails.