Samyang was showing the new XP 10mm f/3.5 at CP+ 2019 in Japan. Samyang claims this is the world’s widest rectilinear prime lens for full frame cameras and that it is “distortion free”. The lens beats out the Laowa 12mm f/2.8 by 2mm.
The lenses optical design comprises of 18 elements in 11 groups, with 7 special optical elements that are said to keep image quality consistent from the center to the edges. There are 3 aspherical elements, 1 high-refractive element and 3 extra-low dispersion elements that have been specifically designed to minimize distortion.
Samyang also claims that the XP 10mm f/3.5 optical quality is good enough for cameras that capture 50+ megapixel photos as well as for 8K video. What you do need to take into account if you want to use it for video is that you can’t attach a traditional variable ND filter to the front of the lens.
We tried the lens out on a Canon 5D Mark III and below you can see some images.
Taken with the Samyang XP 10mm f/3.5 @f/3.5 
Taken with the Samyang XP 10mm f/3.5 @f/3.5 
Taken with the Samyang XP 10mm f/3.5 @f/3.5
The lens does seem to be rectilinear and straight lines do appear to be straight. You do get a lot of perspective distortion out on the edges of the frame and it’s not a lens you would want to be shooting people with. It’s best used for architecture or large landscape vistas. We didn’t find the lens to be that sharp if used wide open, but you can certainly achieve better results by stopping it down.
The Samyang XP 10mm f/3.5 looks to be a good option if you are looking for an ultra wide angle lens if you are using a full frame camera with a Canon EF mount.
The Samyang XP 10mm f/3.5 is currently only going to be available in Canon EF mount when it starts shipping this Spring. A Nikon F mount version will be available down the track. The lens will retail for $1,250 USD which is more than the Laowa 12mm f/2.8 Zero-D Ultra-Wide Angle Lens ($949 USD).
