One more time -- with pixels

[Steve Mullen]

There aren't a lot of S35 13MP sensors that can capture true 4K for JVC to choose from. I would expect they would buy from Sony, but here is one that matches quite well:

AltaSens introduces its first commercially available 4K sensor: the AL41410C. The Super-35 size image sensor delivers 4K cinema frames in either 12-bit or 10-bit depth at up to 72fps. It has a 5.2-μm pixel pitch. Operating the sensor at a 3840 x 2160 resolution at up to 72 fps is ideal for Ultra HD video. Alternatively, the 1920 x 1080 HD format at 240 fps is best for sports broadcast. Its native 4512 x 3008 [for 4096x2048] resolution is available up to 50 fps. At 4512x3008 the chip's resolution is 13.57MP and the LS300 has 13.5MP.

Full effective area is 4512x3008 (13.5MP). At 4512x3008 the diagonal is speced at 28.20mm which is indeed S35.

Super 35 is 24.9mm x 14mm (28.5mm Diagonal)
The diagonal for MFT is 21.63 mm.
Super 16 is 11.9mm x 6.7mm (13.7mm Diagonal)

However, the chip is spec'ed to have a 4K array of 4812x2518 which is 12.1MP. The diagonal of this window is 26.72mm -- which means the effective size is 95% of S35.

So I'll assume VSM @ 100% is 26.72mm.

How many pixels are included in an S35 4K window? About 4096x2048 or 8.39MP (2:1).

How many pixels are included in an S35 UHD window? About 3860x2160 or 8.34MP. (1.78:1)

The VSM setting for MFT is 80%.

How many pixels are included in an MFT window? About 80% of 8.34MP which is 6.67MP.

How many pixels are included in an S16 window? About 13.7/28.5 or 48% of 8.34MP which is 4.0MP.

This suggests that only when a lens designed for S35 or an APS-C sensor is attached, will a 4K or UHD window be captured. ["If you’re shooting strictly Super 35 or smaller formats you have almost the entire range of Rokinon Cine Primes at your disposal including the 8mm, 10mm, 12mm, 14mm, 16mm, 24mm, 35mm, 50mm, and 85mm."] Smaller format lenses will be upscaled to 4K or UHD. MFT requires a 1.25X upscale to UHD. S16 requires a 2.085X upscale to UHD.

There is a review that shows chart sharpness varies by VSM value. Nevertheless, I don't see it on VSM-based zooms.

I'm now very sure that Full Frame lenses will be "cropped" by about 1.5 despite JVC Japan saying no.

Does this explain why the LS300 works differently with some lenses? I don't think so, but this might. "... a 4mm glass plate was positioned near the image plane to accurately model the effect of the filter stack found in micro-4/3 cameras." While the LS300 must have a filter stack -- the ND filter, and likely an OLP, I have no idea if it is 4mm. If it's not, then I expect the LS300 to not behave optically like "other" MFT cameras.