Thread: Ursa mini speedbooster - info sought

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  1. #1 Ursa mini speedbooster - info sought 
    Senior Member
    Join Date
    Sep 2014
    Does anyone know :-

    the distance from the flange face of the URSA Mini EF-Mount to the front face of the IR panel in the camera throat?

    whether the URSA Mini EF-Mount camera has an intermediate adaptor behind the EF-Mount itself or if the EF-Mount attaches directly to the camera body like the original BM4K production camera.

    the distance from the flange face of the URSA Mini PL-Mount to the front face of the IR panel in the camera throat?

    whether the URSA Mini PL-Mount camera has an intermediate adaptor behind the PL-Mount itself or if the PL-Mount attaches directly to the camera body like the original BM4K production camera.

    I chanced to get my greasy hands on an URSA Mini EF for just a few minutes. The mount and attachment screw pattern appears very similar to the original BM4K production camera. I suspect the castwork behind may even be to the same pattern.

    The camera throat and anti-reflection cone also are smaller than the original big URSA. It seems that depth to the IR panel may be less than the big URSA. I did not have time to examine the camera closer, less be able to take the mount off and the cone out to examine the castwork behind.

    It would not have been a good look, gutting out a camera on a cafe table in the Jull Street mall. That little spring behind the release pin would have been itching to fall out and start off an escape and evasion exercise among human feet, chair and cafe table legs.

    The visage of an overweight geriatric on all fours, weaving around through the shanks of disturbed and likely distressed customers and apologising profusely does not bear thinking about.

    It seems, that a Metabones 0.71x speedbooster optical cell may fit within the diameter of the URSA Mini camera throat like with the BM4K production camera. There may be insufficient internal diameter inside the threaded section of the camera throat which retains the anti-reflection cone for an thin walled internally and externally threaded adaptor to support the optical cell.

    The optical cell could probably be mounted using a pressed plastic sleeve but the problem will remain of having insufficient workspace immediately behind the EF-Mount for the mount to be moved 4.2mm rearwards.

    4.2mm of metal might be machined out of the camera body but then all manner of complications like thickness of castwork and weakening of the front structure have to be examined.

    With all the labour involved in stripping the camera body, machining the front, fitting the new parts and the optical cell, then re-assembling, it then becomes more economic just to purchase the URSA Mini Pro and be satisfied with an all-round superior camera.

    I suspect the same will apply to the URSA Mini PL camera.

    BM and Metabones may have known that all along and I have eagerly eaten a regurgitated lunch.

    However, if anyone has the information or could provide images even, this would be appreciated. Possibilities may remain.

    I would dearly like to know how the Luca Adaptor resolves the 4.2mm or near-to setback of the flange faces to restore infinity focus but that is another story.
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  2. #2  
    Senior Member
    Join Date
    Mar 2016
    hi, due to lens deck distance being 4mm shorter on a metabones speed booster, you need to mount the speed booster lens even closer to the sensor. I tried, but couldn't do it because theres a IR filter in the way.

    But a guy called Luca has done it, and is now selling a machined screw in metabones adaptor (or a cheaper generic speed booster type for less) . He has got around the problem of the IR filter being in the way by removing the filter, then putting the filter on the other side of the adaptor. I have one (the non metabones version) and it works really well. Almost the same frame as a full frame stills camera, and surprisingly sharp. I like it so much I am upgrading to the metabones version- maybe its even better quality, but I haven't had any issues with the one I have.
    It also almost doubles the light to the sensor, which is very handy when the Ursa is challenged at anything over 800iso!

    his facebook page is-

    Here is what I posted about mine a while back-

    and here is a review-

    cheers Paul
    Paul Ross Jones

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  3. #3  
    Senior Member
    Join Date
    Sep 2014

    It looks like he built or had built, a custom barrel/optical cell to screw directly into the camera throat.

    Were you able to get infinity focus with the Luca adaptor in place?
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