Old hands will remember the days of video lens accessories which projected the image onto a ground glass screen the size of a 35mm film frame, so that a small-sensor video camera could rephotograph it with its inbuilt zoom and capture the characteristics of a larger effective sensor. It was occasionally used on high-end projects, but it was somewhat less than ideal, costing a huge amount of light and quite a bit of sharpness at a time when digital cinema cameras needed all they could get of both.

Now Canon is talking about a modification for its UHD-Digisuper122 and 111 broadcast zoom lenses which creates what the company calls a “novel look”, with “stunning shallow depth of field”. This would be interesting in its own right, but given the current fascination for interesting optical effects, lens aficionados might well take an interest in the techniques underlying what’s been done here – on the basis it might be applicable to other, more everyday concerns.

Needless to say, the company isn’t exactly handing out the manufacturing drawings for the device, but it clearly isn’t a reincarnation of the ground glass adapter. That should provoke sighs of relief from broadcast camera operators around the world whose focus-pulling challenge is already acute enough. Let’s be clear: the lenses we’re talking about in the context of Canon’s biggest broadcast zooms are principal tools of mainstream broadcast camerawork, commonly used on things like live sports OBs, and there are issues of both technology and user experience to consider.

Staggering capability

By the standards of anyone used to stills zooms for much bigger sensors, ⅔-inch box lenses are staggeringly capable. The 122 (the number is the multiplication factor) is an 8.4 to 1000mm zoom lens which achieves an f/5 even at that long (long, long) end. OK, it’s the size of a wheeled carry-on, as such things tend to be, but such is the power of small-chip cameras. That’s why broadcasters still use small-chip cameras, and why the likes of Grass Valley still sweat to wring more and more performance out of ⅔-inch, 3-chip imaging blocks.

Strolling up to the Canon booth at NAB 2025, we discover the 122x zoom in pride of place in the broadcast end of the exhibit. The implementation of Canon’s new idea takes advantage of a deleted feature in the lens’s extender, which was once used to house a 1.5:1 magnifying optic to complement the 2x extender which is still in place. The 1.5x feature was not widely used, and at some point was deleted and replaced with a balancing weight.

The new optical component sits in the same place as the 1.5:1 extender optic would have, so the lens is capable of either 2:1 extended operation (with focal length to, yes, 2000mm), or 1:1 non-extended operation, or 1:1 with the new look. There is no option to use 2:1 extended mode with the new look, although it seems likely that ultra-long extended focal lengths are likely to generate sufficiently shallow natural depth of field that adding other effects would be gilding the lily.

The question, then, is what exactly this new optical component does, because without re-projecting the image onto a surface (such as a ground glass) then rephotographing it, there is no way to alter depth of field. What Canon’s new idea does is not quite accurately described as “shallow depth of field.” Instead, it adds some extra character – in the sense of “character” as coveted by single-camera people – to already-soft parts of the picture.

Softening soft things

It’s certainly a novel look and it does smooth out some of the bokeh characteristics of a lens which was probably engineered with precision and zoom range as priorities over beautiful bokeh. Going by the demo footage shown by Canon at its booth, the effect works best on camera positions looking up at (for instance) baseball players, placing them against a distant crowd. It softens soft things; it won’t add softness to images which don’t already have it.

So, no, this is not a nearly-magical way of decreasing the depth of field of an existing image without the disadvantages of old school ground glass adaptors. It’s clear what demands are being addressed here: the huge interest in big-chip looks for broadcast and simultaneously serving the expertise of live broadcast operators, whose lens-aiming ninjutsu must be permitted to flow freely. Strapping a set of motors onto a cinema lens is an interim solution at best.

That’s also why lenses such as Fujifilm’s HZK 25-1000mm box lens exist; to bring broadcast-style operability to cameras with true Super-35mm sensors, such as the LDX-180, which Grass Valley is introducing at NAB 2025. At a quarter of a million dollars for the HZK lens, though, and lacking the sheer reach of a 1000mm lens on a ⅔-inch camera, it’s clear why other options are being explored. Whether or not they’ll tickle the fancy of broadcasters is another matter – let’s meet back here in twelve months, and if everyone’s big box zoom lenses have novel-look options, we’ll know it’s gone down well.