Metabones Speedbooster on Super 16

[scott stewart]

I converted an Eclair ACL 1 to run a Metabones speedbooster (.71x will work, the .64x extends back beyond the lens mount too far and will hit the mirror). Test footage came back last week and everything seems to be working. The film loaded was Kodak Vision3 250D. Exposure was metered at listed film speed, which means that the film was actually overexposed by one stop due to the speedbooster adding one stop of brightness. Lenses tested with the Metabones - 10mm Samyang (7.1 equivalent after boost), 28mm Contax Zeiss (20 equivalent after boost), 35mm Contax Zeiss (25 equivalent after boost).

With the speedbooster, the 2.88x crop of super 16 (compared with 35mm full frame stills) becomes 2x which happens to be exactly the same as a m43 sensor size. So wide focal lengths are 18mm/lower, normal are in the mid to high 20mm's, and telephotos are 35mm/above. Some vintage 35mm stills sets line up with this pretty well - Contax Zeiss (18mm, 28mm, 35mm), Leica R (19mm, 24mm or 28mm, 35mm).

I also stacked a speedbooster with a 1.5x Blazar anamorphic adapter to get 2.39:1 with a slight crop of the sides. The anamorphic adapter and speedbooster together work on 24mm and above lenses. The horizontal field of view after speedboost and anamorphic ends up being almost exactly the same as spherical super 35 at the same focal length.

To get the speedbooster to work, I swapped the original c/ts mount on the ACL to a m43 mount. The body also needed a little bit of machining to recenter the lens opening for s16, widen it for a m43 lens rear opening, and remove a bit of the body thickness below the lens mount to allow wider bodied lenses (and the Metabones Speedbooster) to fully seat. I did not add contacts to the lens mount (though I might try to later) so the m43 mount does not work with modern electronic lenses. It does let you use any lens mount adapter available to the m43 ecosystem, the metabones .71x, the viltrox .71x, and fully manual non-electronic m43 lenses so long as the rear of the lens optic doesn't extend too far beyond the mounting flange.

[scott stewart]

Some more details for anyone wondering about speedboosters on any other 16mm cameras. The speedboosters are made for modern mirrorless cameras with their short focal flange lengths - to get an off the shelf speedbooster optic (Metabones or Viltrox) to work you need a similarly short focal flange camera to modify.

Common mirrorless mounts with available speedboosters: EF-M (18mm), E (18mm), M43 (19.25mm), RF (20mm), L (20mm)

Common 16mm camera mounts: C (17.526mm), Aaton (40mm), m42 (45.46mm), PL (52mm)

Anything other than c mount would require the speedbooster optic to mount behind the lens mount and deep inside of the camera body. That would collide with the shutter/mirror system.

Common c mount cameras: Eclair ACL, Eclair NPR, Bolex H16/RX, Beaulieu R16/2016

A speedbooster needs a fairly large flat area around the lens mount to mount without needing to machine the body. The ACL needs a small amount of machining, but doesn't require more room than the body thickness. The NPR shutter/mirror bump sticks out too far on the body and doesn't have enough material left in the body to machine a relief. The Bolex and Beaulieu both have flat fronts.

On the back side of the lens mount/inside the camera, the speedbooster optic sticks in past the back of the original c mount. The .71x sits with the back around 13mm from the film plane, the .64x has to sit with the back of the optic around 10mm from the film plane, the bmpcc .58x sits less than 10mm from the film surface. The .71x barely clears the mirror on the ACL, but runs into the filter holder (and it has to be removed/sealed) - by my measurements it should also clear the prism on the bolex (and might just barely clear the filter holder) - the .64x and .58x will stick back too far and collide with the mirror. If you want .64x or .58x you'd have to use a camera without a reflex system and make sure that everything is collimated and the lens markings are accurate with the speedbooster attached.

[Robert Hart]

Another possibility might be to make a custom support for the speedbooster's optical cell to fit within a film camera body with a separate lens mount in the front. The mirror shutter on some cameras is the deal killer. This was an approach I used when fitting a 0.71x speedbooster to a "Big" URSA camera. Fortunately the throat of the camera was threaded to accept an anti-reflection cone so it was fairly simple to make an internally and externally threaded cylindrical sleeve. 

[scott stewart]

10 hours ago, Robert Hart said:

Another possibility might be to make a custom support for the speedbooster's optical cell to fit within a film camera body with a separate lens mount in the front. The mirror shutter on some cameras is the deal killer. This was an approach I used when fitting a 0.71x speedbooster to a "Big" URSA camera. Fortunately the throat of the camera was threaded to accept an anti-reflection cone so it was fairly simple to make an internally and externally threaded cylindrical sleeve. 

Custom machining a threaded holder/lens mount for a disassembled speedbooster optic is an option that I planned for an NPR prior to getting ahold of an ACL, but the optic is larger in diameter than the c mount opening and would still require a full lens mount swap and come with some functionality limitations.

For other lens mount cameras, the depth that the speedbooster optic has to mount inside the cameras gets in the way of the shutter and mirror. The c mount cameras tend to keep the shutter/mirror systems fairly compact because they don't have much room to begin with - the rear of the speedbooster optic just barely clears the mirror on the acl when at full depth adjustment. Most of the pl mount and even some c mount cameras have an angle to the rotating shutter/mirror assembly that puts moving parts in the path of where the speedbooster optic would have to sit. There might be a few candidate cameras for that, but it would need to be carefully measured for clearance.

[Daniel Ross]

Would something like this ever work on any Arri SR with Zeiss Super Speeds? I had been thinking about doing something like this last year but couldn’t think of a clear way to do it without risking damaging kit or wasting film. Do you think it would be possible?

[Robert Hart]

Scott Stewart. Yes. The cameras with reflex viewfinders and angled spinning mirror shutters cannot be enhanced with a speedbooster suitable for the 16mm/Super16mm film area.

When I converted a SI2K with a Speedbooster for the Blackmagic original cine camera, there was very little workspace between the rear element of the speedbooster optical cell and the inbuilt IR/anti-aliasing filter. 

Another option might be a groundglass relay system like Letus Extreme which can be tricked up to 2K resolution by careful alignment of the prism set to yield an almost 32mm wide frame with 35mm stills camera lenses. You lose contrast but the aesthetic is not entirely unpleasant. 

I tried a spinning groundglass system on a CP16R with a rough test. It is not well organised. The groundglass adapter in this instance only had an image frame 22mm wide hence less resolution from the 5micron groundglass texture. The letters DTC mean direct to camera without groundglass adaptor.
 

What might be interesting would be to try a larger format focal reducer such as the arrangement made to convey medium format imaging to the RED DSMC cameras. From memory, these cameras had a fairly deep and confined throat from the lens mount to the sensor.

The best bet is to live within the means of the available 16mm systems. Shoot slow almost grainless film using the fastest sharpest Super16mm lenses you can get your hands on. It can look sweet like 35mm film shot with a 35mm camera with lens iris at about f4. You have to live with the narrower field of view for the same shallow depth of field yielded by the same focal length.

[scott stewart]

Robert, the .71x speedbooster will work with some reflex 16mm cameras. I just haven't found any that aren't originally c mount that would work. My ACL is currently setup with a speedbooster mounted (in the photo earlier in the thread) and it doesn't collide with the reflex mirror when running. The photos of sample footage at the top are from the camera with the speedbooster mounted. The top photo is from the ACL with the .71x speedbooster and a Contax Zeiss lens, the second photo is with the addition of a 1.5x anamorphic adapter.

The ACL is definitely a special case with the oscillating lollipop mirror - it's more compact than spinning shutter/mirror assemblies. That's why I went with that one for a speedbooster conversion first - it will mount a .71x speedbooster and allow for full range of adjustment while still barely clearing the mirror. By my measurements, a bolex rx should also work if you remove the filter slot.

Anything better than a .71x speedbooster won't work on any 16mm camera with a reflex system. The photo of the rear of the mount earlier in the thread was from a .64x that I test mounted to see how much more space would have to be opened up to get near a super35 look after speedboost. There just isn't enough room behind the .64x or the bmpcc .58x optic to work with any reflex camera.

The .71x still gets the camera to the fov of m43 (2x crop compared to full frame). For comparison, super 35 is usually referenced as having a crop of 1.5x compared to full frame. For FOV/format comparison after boost, I usually look at the effect of the speedbooster on the rendered film area/imager size

Full film areas and speedbooster area equivalents:

Super 16mm film area - 12.52mm × 7.41mm

.71x Speedboosted Super 16mm (film area equivalent) - 17.63mm x 10.44mm

.71x Speedboosted/1.5x Anamorphic Super 16mm (spherical film area equivalent) - 26.45mm x 10.44mm

Super 35mm - 24.89mm × 18.66mm

Academy 35mm - 21.95 mm × 16.00 mm

 

If you then crop for common formats the fov/film equivalents compare as below:

Super 35mm (cropped to 16:9) - 24.89mm x 14mm

Super 35mm (spherical-cropped to 2.39) - 24.89mm x 10.41mm

Academy 35mm (cropped to 16:9) - 21.95mm x 12.35mm 

Academy 35mm (spherical-cropped to 2.39) - 21.95mm x 9.18mm

.71x Boosted Super 16mm (cropped to 16:9) - 17.63mm x 9.92mm

.71x Boosted Super 16mm w/1.5x anamorphic (cropped to 2.39) - 24.95mm x 10.44mm

 

So the fov of the .71x boosted/1.5x anamorphic super 16mm becomes the same as spherical cropped-super35mm if you want to shoot 2.39 format. It makes the boosted/anamorphic super 16mm a closer alternative to 2 perf cropped spherical super 35mm with some benefits (actual anamorphic lens effects, 1 stop added brightness, cheaper), and some downsides (lower perceived resolution, larger relative grain size).

[scott stewart]

18 hours ago, Daniel Ross said:

Would something like this ever work on any Arri SR with Zeiss Super Speeds? I had been thinking about doing something like this last year but couldn’t think of a clear way to do it without risking damaging kit or wasting film. Do you think it would be possible?

It would depend on the size of the mirror/shutter assembly. There is a small amount of room behind the speedbooster optic for a mirror/shutter to fit within.

It also depends on how far back the rear element of the lens sits. Not all lenses are compatible with speedboosters throughout the focus or zoom range. If the rear lens element sits back too far, it will hit the front of the speedbooster optic before you can focus all the way to infinity.