Anamorphic on a7s with external 4k recording

[Kandre]

New to anamorphics. Thinking about buying an external recorder and a FM module or rectilux. Wondering if anyone know the mathematics to calculate what the resolution will be if I go APS-C 4k out to a recorder on the a7s(I know aps-c isnt really 4k but upscaled). So lets say I want to take 4:3 aspect ratio from the super35 crop, does anyone know the theoretical resolution with a 2x anamorphic such as the cinelux?

Want to use the crop mode on a7s to get less rolling shutter as I do alot of handheld and to be able to use wider fov lenses. Is it plausible that I can use a 35mm in a combo like this?

[artiswar]

If you sampled a 2872 x 2160 area of the 4k image, that would be 4:3. I personally would stretch this to 5744 x 2160, softer a bit but optically, due to the anamorphic. The widest I've successfully gone is 37mm and that's with a bit extra digital zoom, with a Hypergonar in the FM.

[dhessel]

Keep in mind that in APS-C mode the 4K is actually more like 2.8k that is internally upscaled to 4k. So your true resolution would be more like 1410 pixels in height. With a 2x and a 2.4 ratio your actual resolution would be 3384 x 1410 even thought the recorded resolution would be 5184 x 2160. One interesting fact about 2x anamorphics on a full frame lens is that the crop factor going from 32:9 (16;9 x 2 in width) to a more normal 2.4 is just about 1.5 which is almost APS-C sized crop. This means most of the time you can use anamorphics designed for s35mm film, like the Lomo's, on a full frame camera without vignetting once cropped down to 2.4.