Ursa 4k v1 pl - speedbooster project.

[Robert Hart]

I did not remove the turret because I had no need to get inside behind it. I did not want to introduce any faults.

I expect the URSA main body under the turret will be the same. In the back of the turret there will be separate sockets or plugs which match sockets or plugs in the camera body, maybe Lemo type, like the SI2K which has a docking body for the camera module. On the PL turret, there is probably a blank hole or depression where the lens control plug/socket would be on the EF-Mount turret.

I imagine that at some point BM may have thought of making the turret detachable to be used as a remote camera head on cables like the SI2K P+S recorder unit and the SI2K mini.

[Robert Hart]

For interest of anyone who would like to have a speedbooster in their URSA, I have obtained some numbers from a local machinist.


Costs thus far :-

For both the internal support for the speedbooster optical cell and Nikon F-Mount base only = AU$460-00, plus material.
GST if in Australia = AU$46-00.
Nikon F-Mount supplied separately by camera owner. = Cost unknown. Cost $AU Zero if the Speedbooster is Nikon Mount type.
"Ultra" 0.71 Speedbooster optical cell supplied by camera owner. = AU$610-89.


With used big URSA cams going inexpensively on eBay, a cost of about AU$1010-89, plus AU$102-00 GST probably represents over-capitalisation for the benefit of near-to full stills frame fields-of-view and being wedlocked to Nikon F-Mount lenses.

I have not been able to obtain any information regarding permission related to fitments designed to match registered design and separate supply of the 0.71 "Ultra" optical cell from either Metabones or Caldwell. Each entity seems unwilling or incapable of replying to email queries.

[Robert Hart]

For the sake of those who are curious, I have been a bit slack but finally got around to trying the URSA speedbooster arrangement outdoors in near to real-world conditions at an air show with a Sigma-for-Nikon 50mm-500mm zoom I have used previously on the SI2K camera for ground-to-air vision of aircraft.

Like the SI2K/P+S Technik camera-recorder, the big URSA is a struggle and grunt to cart around and set up on one's own. The URSA mini is obviously a better choice for agile portability. An assistant would make a lot of difference. An eyepiece viewfinder would also make a lot of difference.

The inbuilt mikes work better than I thought they would for ambient sound. To minimise wind buffet, I shoved a sort of fluffy seatcover moustache under the lens mount where the small mike ports are. The audio levels remained fine and the camera's audio recorder also seems to tolerate excessive levels better than I expected.

Except for a small speck on the sensor which indicates I have been careless, there seemed to be no vices with the lens compared to using it without a speedbooster a few months ago. I had to fit an ND.9 filter to keep the exposure level within reason.

When I can muster a greater horsepower computer to reproduce the 4K image, I will assemble and upload a clip.

[Robert Hart]

For curiosity sake here is some vision shot at an airshow last Sunday with the big URSA, the 0.71 Speedbooster in place and a Sigma-for-Nikon 50mm-500mm f4-f6.3 zoom. The vision had gone through two conversions to get it though my rather sad editing computer. Was shot in 3:1 RAW. There was a ND.9 filter on the front to keep the light levels civil. - Yeah I know the framing is all over the place like a dog's dinner. The big URSA balances a little differently to the SI2K on a non-sprung fluid head and I am also out of practice. When chasing aeroplanes it is one of those use-it-or-lose-it skills.

[Robert Hart]

For the curious, I finally got around to measuring the BM URSA's PL-Mount to see if it could be fitted to the camera with the required 4.2mm rearwards re-positioning required to maintain correct focus. I had thought it was not possible but with some machining of the rear of the PL-Mount, the "ears" for rotating the clamp ring, drilling of a new set of screw-holes to match the fastener holes for the intermediate mount ring and deepening of the closed location pin hole, it is doable - JUST.

The intermediate mount ring is replaced by a thinner shim and the screws pass through it.

Because the Speedbooster optical cell uses space within the camera throat only the PL-Mount lenses on Metabones' approved list for the PL-Mount to Sony E-Mount "Ultra" Speedbooster are known to be suitable. Other PL-Mount lenses may fit but some will not because they either penetrate too deep into the mount and touch the Speedbooster optical cell or their image circle is not large enough to cover the full sensor area with the Speedbooster in place.

Apparently the Luca adaptor for Canon EF-Mount is a straightforward substitution without the two-part workarounds I have indulged in. I am not able to work out if there is a set back of the lens mount built into the Luca adaptor or not. So long as it works is all that matters. I do not know if there is yet a PL-Mount version of the Luca adaptor. Maybe someone else can add correct information below for the Luca adaptor.

The image circle of the vintage Angenieux 25-250mm T3.7 zoom lens is no longer large enough to cover the sensor with the Speedbooster in the optical path. Whilst the rear shoulder of the B PL-Mount has to be shortened, enough remains to locate the PL-Mount when used normally. The fit against the turret body remains very snug

[Robert Hart]

Furthur to above, I went down to our local production equipment rental place, Location Equipment in Leederville and had a play with some of their rental lenses on the big URSA with Speedbooster and PL-Mount. Hanging from the ceiling in their test room is a big resolution chart published by Duclos lenses.

Due to the closeness of the front element of the speedbooster optical cell, The ARRI Ultra lens set cannot be used, at least not without some modification. To alter pristine ARRI T1.9 lenses is not good manners and simply not done. I mean, who would put dragster tyres and a supercharger scoop on a Rolls Royce?

There is half a chance that if the shield cones on the rear of the ARRI set can be removed, then there may be in some instances, a working clearance between the rear element of the ARRI lenses and the front element of the speedbooster.

The next cab off the rank was a set of Zeiss CP2 primes. They offer up and fit fine, as Metabones suggest they should by putting them on their approved list.

My objective was to test just how far off infininty focus my relocated fitment of the PL-Mount is. With the CP2 lenses, across their range of focal lengths, infinity focus came in at about 50ft so I do have some shims to make up, which I expected.

With the 85mm lens and the Duclos chart tightly framed, a very slight "donut" effect was observed when trimming focus. This may be attributable to the very slight rearwards position of the lens due to shims being required in the mount.

The 50mm, lens image appeared sharp across its width. There is a small barrel distortion in the image. Again, this may be reduced by correct collimation of the mount.

The 35mm, 28mm and 21mm images also have barrel distortion with a curious astigmatic distortion appearing in the 35mm image. I may need to check again just how straight in the adaptor my mounting of the speedbooster optic is.

I pointed the camera outdoors when I tested for infinity focus. The image from these lenses compared to my old Nikons is of improved apparent clarity and sharpness, just plain sweet to look at.

The image area of field-of-view "as seen" via the camera is close to full frame in width, with probably about 1.5mm missing from the sides.

Location Equipment will be receiving some rehoused Kowa anamorphic lenses soon. So long as they can fit, I will be trying them.