Dpreview posted a first hands-on of the new Sirui anamorphic lens:

Users of the Panasonic GH5 have a couple of choices over the way they use this lens. It has an Anamorphic Mode that uses the 4:3 sensor area to capture video for de-squeezing in software afterwards. As this mode uses almost the whole sensor, the final image contains 18+MP of data to work with.

When you use this mode with the Sirui 1.33x anamorphic lens the wide aspect gets de-squeezed to a 16:9 format with a higher resolution than you’d get shooting in the normal 16:9 video mode, while the in-camera de-squeeze preview feature allows us to see what we are shooting via the rear screen.

To get the wide, cinematic anamorphic look that most will be expecting you need to shoot in the normal 16:9 mode, with Anamorphic Mode switched off. Even with Anamorphic Mode off you can still use the de-squeeze preview on the rear screen and inform the IS system that you have a 1.33x anamorphic lens attached.

The GH5S can also capture anamorphic footage using its 4:3 region, however, due to the nature of its multi-aspect sensor, the resolution isn’t quite as a high as the GH5 in this mode. Like the GH5, it can also show a de-sqeezed preview of the anamorphic image in-camera.

This is a grab from footage recorded in Anamorphic Mode on the Panasonic Lumix DC-GH5. In this mode the camera records from the whole 4:3 sensor, so the 1.33x anamorphic effect only de-squeezes to 16:9, but it is a higher resolution 16:9 format image than you’d get recording in 16:9 with a normal lens.

Shooting in 16:9 with this lens on a Micro Four Thirds camera will also result in a 2.35:1 CinemaScope aspect ratio, albeit with a longer apparent focal length than on an APS-C/Super 35 sensor.

Preorder at sirui.com/index/optical/anamorphiclens.html