Back Street FX6 B4 Feasability Experiment

The first experiment I did a few years ago.

Wanting the flexibility of a traditional B4 constant aperture, parfocal, servo zoom lens I find this setup works well. I have used it numerous times on a variety of broadcast productions using a variety of lenses from 4.5 mm wide angles to 22 x zoom lenses.

Basically it utilises MTF's S35 optically corrected, for three chip lenses being used on single sensor cameras, B4 to E-Mount adapter system. This was designed to work with S35 sensors. I needed it to work in 4K with the FX's FF sensor.

The Sony FX6 has an S35 crop mode. But this is only useable in HD. I needed FF 4K coverage. How did I achieve this?

A number of Sony cameras have CIZ (Clear Image Zoom). In FF 4K this is virtually lossless. Using a standard B4 lens, image circle 11 mm, with its 2 x doubler engaged gives us an image circle of 22 mm. Multiply this with MTF's S35 0.5 x optical block enlargement and you end up with an image circle of 33 mm (22 x 1.5 = 33). Large enough for S35 but not FF.

Now add to this 33 mm image circle an FX6 CIZ of about 1.3 x, and we end up with an image circle of just on 43 mm. Large enough to cover most 43 mm FF sensors. I find the CIZ used can range from 1.2 x to 1.5 x depending on the make, model and range of the B4 lenses used.

NOTE: This setup loses 2.5 stops in sensitivity. A figure that has been no issue with the FX6 even in low light in Custom Mode where the Hi-base ISO of 5000 can be used without any problems. I have not had a negative feedback comment from any network yet on the images we have delivered using this simple cost effective off the shelf setup.

Most B4 lenses can be controlled remotely in regard to focus, iris and zoom with the appropriate rear controls. This makes this B4, MTF and FX6 arrangement quite suitable for broadcast and production work.

Look closely, to see if you can see any undesirable artifacts such as CA for example. Generally the image is pretty free from any undesirable artifacts.

To sum up. In FF terms a 4.5 mm x 11 Wide angle becomes a 17.55 x 11 wide angle zoom. Going from 17.5 mm to 193 mm.

Conversely a B4 7.6 x 22 lens in FF terms becomes a 42.9 x 22 lens. Going from 42.9 mm to a whopping 943.8 mm.