Some S-35 zooms already cover FF (you just didn’t know this!)

This is an extremely brief article to help to explain a lesser-known but extremely valuable tip. 

In summary, film zooms designed to cover S-35 sensors, will also cover Full Frame as well IF used with a 1.5x extender and this is built into several zoom lenses already, such as the Canon Cabrio zooms.

In English, this means that you can use Full Frame cameras with existing PL zooms without needing external image expanders.

Canon Cabrio S-35 zooms all include the built-in 1.5x extender facility, to extend the focal length by 1.5x by means of activating a 1.5x rocker knob and in doing so, cover Full Frame sensors.

Sometimes, we need to hear things several times in order to fully appreciate how useful they are and so it is with the 1.5x lens extension function, which I realised recently not only ‘zooms-in’ by a factor of 1.5 but also necessarily increases the image size, enabling images to cover Full Frame sensors. 

The 3 x Canon Cabrio S-35 zooms below all include the built-in 1.5x extender facility, so that images can be both ‘zoomed-in’ and subsequently, also cover Full Frame simply by using the 1.5x rocker knob.

When used normally (without the 1.5x extender), S-35 zooms will vignette when used with a FF sensor.
When the 1.5x extension is engaged, image focal lengths increases by a factor of 1.5 and will cover FF.

You can of course use a PL lens extender to achieve this as well. VMI stock 2x converters which will both double the focal length and ensure that the resulting images cover Full Frame.

When using lens extenders, sensitivity will reduce

The laws of optics necessarily dictate that if you enlarge an image, then the brightness of the image will also reduced, so the camera operator must be made aware that if the 1.5x extender is used, then the maximum iris of the lens reduces by 1.5x as well.

Some examples using built-in 1.5x converter:
  • Canon CN7 lens: 17mm/T2.95 in S-35, becomes 25.5mm/T4.4 with 1.5x extender and covers FF.
  • Canon CN10 lens: 25-187mm/T2.95 (to T3.95 at 250 mm) in S-35, becomes 37.5-375mm/T4.4 at 37.5 – 281 mm (to T5.9 at 375 mm) with 1.5x extender and covers FF.
  • Canon CN20 lens: 50-560mm/T5 (to T8.9 at 1000 mm) in S-35, becomes 50-560mm/T7.5 (to T13.35 at 1500 mm) with 1.5x extender and covers FF.
Some examples using external 2x PL converter:
  • Angenieux Optimo 15-40/T2.8 in S-35, becomes 30mm-80/T5.6 with 2x extender and covers FF.
  • Angenieux Optimo 45-120/T2.8 in S-35, becomes 90mm-240/T5.6 with 2x extender and covers FF.
  • Angenieux Optimo 24-290/T2.8 in S-35, becomes 580mm-240/T5.6 with 2x extender and covers FF.

Note that external 1.5x converters are also available to achieve lesser magnification and stop loss.

Barry Bassett, March 2021
Images of rocker and lens charts are courtesy of CVP

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