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Is the Cabrio XK 20-120 lens compatible with the Blackmagic URSA Mini Pro 12K?

We've tested the image circle and resolving power of the XK20-120 to understand if it is compatible with the URSA Mini Pro 12K and the results are good

The three factors to consider when checking if a lens is compatible with a camera are:

  • Mount. The XK 20-120 lens and URSA Mini Pro 12K camera both have PL mounts as standard
  • Resolving power
  • Image circle coverage

We’ve conducted tests on the resolution and image circle of the lens and the results show that it will work perfectly on the URSA Mini Pro 12K, with some small caveats to the image circle.

12K Resolution test

In order to test the resolving power of the lens, we placed it on our lens projector that can show up to 400 line pairs per mm

As you can see in the large image (click it to view larger), the lens is able to resolve 400 line pairs per millimetre. This equates to a resolution of 22K. Therefore we conclude that the XK 20-120 provides enough resolution for the Blackmagic URSA Mini Pro 12K.

Image Circle Coverage

The Cabrio XK 20-120 has a minimum image circle of 28.5mm, and a minimum illumination circle of 29.1mm. When we say minimum, this is usually when stopped down to T22, on the widest focal length, and focussing on infinity. However, in order for us to comfortably say it covers a sensor, the sensor should be smaller than 29.1mm diagonally.

FULLY COMPATIBLE MODES: As you can see, the 12K 16:9 and 8K UHD 16:9 modes both require an image circle smaller than the illumination circle of the XK 20-120 so you should be able to use these modes with any combination of focal length, T-stop and focus position.

MOSTLY COMPATIBLE MODES: For the remaining modes, due to the varying size of the image and illumination circles (remember, our specifications are the worst case scenario), there will be some combinations of focal length, T-stop and focus position that may result in slight corner shading. As a general rule, this tends to occur when shooting at the wide end (less that 35mm) at T-stops smaller than T11 and when focus is near to, or at infinity.

In any mode, as the sensor size is greater than our published 28.5mm specification, Fujifilm cannot fully guarantee that the image circle will cover and meet the factory-specified quality tolerances in the far corners of the image.

Real World Test

Bill Bennett ASC conducted a thorough test of the XK 20-120 on the BMD URSA Mini Pro 12K that you can watch below. Heres the summary of his findings

In my opinion, the Fujinon XK 20-120 is totally useable in the 16:9 mode in the BMD 12K camera.  As you will see in the test footage below, shooting up toward the open sky, if the lens is wide open at T3.5 or even stopped down to a T8.0, there is no vignetting to be seen and the lens is zoomed through the entire focal length range, both focused at minimum focus and at infinity focus.  When the lens is stopped down to T22, there is a tiny amount of vignetting visible on the upper and lower right side of the frame, in the range of 40mm to 55mm focal length.  I don’t think it’s a problem, as people shooting with the lens will rarely stop down to T22, especially since this camera has built-in behind the lens Neutral Density filters. 

Bill Bennett ASC

If in doubt, test!

Fujinon Cabrio XK 20-120 at a glance

  • Cost effective “all-in-one” versatile PL Mount lens
  • Cinematic “Look” and matched CCI  |  Parfocal  |  No breathing  |  Optimized for HDR
  • Available with or without dedicated drive unit

Visit the Cabrio range page