Using Super 16 lenses on the Blackmagic Cinema Camera: It works for a 1080 HD crop
There are Super 16 lenses that have been sitting around collecting dust for the last 5-10 years, and you can usually scoop some up at bargain prices. That’s because, aside from a minority of Red users, no one’s been using them, due to HD sucking all the wind from its sails like some sort of gigantic cloud vampire. No, I’m not drunk. Yeah so anyways, that all might change now that the Blackmagic Cinema Camera is starting to ship in quantity.
SUPER 16 ZOOM LENSES
The BMCC sensor size is a good chunk bigger than Super 16 (abbreviated “s16” from now on… I’m too lazy to type it out the bazillion more times I’ll need to reference it). But it’s close enough that some s16 zoom lenses will cover the sensor at the higher end of their focal length ranges, probably half to three-fourths of its zoom range, depending on the particular lens. That’s because the image circle of a zoom must be big enough to fill a format’s picture area when at its shortest focal length, ie. zoomed all the way out. And then by principle of a zoom lens, that image circle will get larger as you zoom in. As that image circle gets larger, it can hence fill a larger picture area/sensor. Here is a diagram featuring completely random and arbitrary imagery:
But here’s one thing to keep in mind: some still photography zoom lenses maintain their small image circle due to their particular design, so the same may apply to some s16 zooms as well.
***A LIL’ UPDATE***
Cinematographer John Brawley has posted some frames from his tests of the following s16 lenses…
Angenieux 11.5-138mm T2.3
Canon 6.6-66mm T2.7
Canon 8-64 T2.4
The results don’t look too great for full BMCC sensor coverage. The Angenieux maintains a small image circle, and the Canons show noticeable chromatic aberration outside the s16 picture area, even when they cover the sensor. You can see all the DNGs via his dropbox link in this Blackmagic Forum thread.
A few paragraphs down, I’ve added examples of how these lenses can work for the BMCC via a 1080 center extract.
SUPER 16 PRIME LENSES
I have no idea if they’ll fill the BMCC sensor. Do long focal length primes have larger image circles than their short focal length counterparts? Maybe. Image circle sizes vary from manufacturer to manufacturer, and product line to product line. So the only way to know is to test that specific lens.
HOW TO USE ANY AND ALL SUPER 16 LENSES ON THE BMCC
This might be a big deal for some people. And it’s so simple: just crop into the 1920 x 1080 center pixels of the 2432 x 1366 frame of BMCC footage. Actually, you’ll only have to do that for footage that needs it. Like I mentioned earlier, some lenses will cover the whole sensor. But as a boilerplate, unilateral policy, it’ll work for all s16 lenses, regardless of focal length. Here’s why…
You can click here or on the picture to see a full res version of this BMCC 2432 x 1366 frame diagram. Notice how the Super 16mm picture area is just big enough to cover the extracted 1920 x 1080 HD frame from the full BMCC frame? Boom, there ya go. So it’s all good with using s16 lenses.
Here are some examples of how the 1080 center extract would work with the three aforementioned s16 lenses…
You can click on them to see ’em as full res 10% quality jpegs… which means they’re just for examining the image circle, and not the image quality of the camera. You can get to the original DNGs via this Blackmagic Forum thread. Mucho thanks to John Brawley for letting me use these frames.
I haven’t tested this myself because I’ve yet to get my filthy hands on a BMCC, but numbers don’t lie. There are a few things to keep in mind if you choose to do a 1080 center extract:
- You’ll have to shoot in 2.5K RAW mode. Obviously the downsampled 1920 x 1080 ProRes or DNxHD modes won’t work for this.
- You’ll need to mark the 1920 x 1080 center on your viewfinder. This is actually not that big of a deal. You just get some clear touch screen protective cover, and then make your markings via trial and error… ie. set up a tripod & chart/whatever, import footage & perform the extract, then mark the cover. I do this exact process for certain kinds of VFX shots all the time, it’s easy.
- You’ll have to do the 1080 center extract in post, but it’s hecka easy. Do I even really need to explain this? I will, just in case. In whatever software, make your timeline/composition/whatever 1920 x 1080. Set your BMCC footage to be at 100% scale/size, that way it’s only showing the center. If a particular shot doesn’t need the 1080 extract, then change its scale/size to 79%.
- It’s obviously not going to look as good as the full sensor 2400 x 1350 image that’s been scaled down to 1920 x 1080, because of Bayer filtering mumbo jumbo that you can google. Whether or not the optical resolution is good enough is up to you… but if your basis of comparison is a DSLR/DSLM, then it likely will. From the samples I’ve seen, a 1080 center extraction looks pretty great. And if you do see de-Bayer artifacts, try extracting from a slightly larger area than 1920 x 1080 if your lens’ image circle allows for it.
If you’re thinking it’s just weird and strange to capture image areas that are going to be discarded or unseen by the viewing audience, just keep in mind that it’s standard procedure with most non-anamorphic lensed 35mm shooting formats. Also, cropping in to 1080 on the BMCC is very similar, in principle, to the crop resolution modes of the Red cameras. Plus, really, your work is 99% likely to ultimately be seen in 1080 HD anyway. Is the 1080 center extraction worth all the extra work? Probably only if you just really wanna shoot on a fast cine zoom that’s affordable.
Also, if you’re content with shooting for a 720 HD finish, you can use standard 16mm format lenses… by cropping to 1578 x 888 and then downscaling to 1280 x 720.