Note: this video was focused by two synchronized motors linearly. So the result is inaccurate.

Sharpness test for Leica Elimarit R 135mm f2.8 and Kowa 8-Z on BMPCC4k.

Conclusion

@2.8 (wide open) is usable (sharpness is acceptable) from 2.5 meters distance.
@4.0 (1 stop close) is usable from 2.0 meters.
@5.6 (2 stop close) is usable from 1.5 meters (nearest).

Actually it depends on the taste of the project. Refer the following test movies for the taste.

Test movie

@2.8

@4.0

@5.6

side by side

Full resolution screengrabs

Technical data

Object distance

1.6, 2.0, 2.5, 3.0m

Lenses

Metabones Speedbooster XL 0.64x
Leica Elmarit R 135mm f2.8 @2.8, @4.0, @5.6
Kowa 8-z 2x anamorphic
(No Variable-Diopter)

Camera

BMPCC4k
fps: 24
Shutter: 45, 90, 180
ISO: 100
BRAW 4K DCI (4096 x 2160) 3:1
Crop factor: 1.22x ( = 1.9 x 0.64 )

Edit

Colored with Davinci Resolve 16 (contrast only)
No crop.

Deliver setting

Youtube 2160p
Resolution: 4096 x 1716 DCI Scope 2.39
Format: QuickTime
Video Codec: H.264
Audio: Main 1 (Stereo)
Audio Codec: Linear PCM