Thread: Ursa 4k v1 pl - speedbooster project.

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  1. #1 Ursa 4k v1 pl - speedbooster project. 
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    I now have a speedbooster arrangement working with the "big" URSA camera PL-Mount model. The optical cell from the 0.71 "Ultra" Metabones Speedbooster products has been fitted within the throat of the camera and can be used with a modified Nikon F-Mount. Other lens types are not suited to this arrangement due to available workspace within the camera body. The arrangement requires two custom component to be made. These are :-

    Replacement for the anti-reflection cone in the form of an internally threaded barrel to accommodate the 0.71 optical cell.

    Remake of the inner "intermediate" adaptor to become a Nikon F-Mount positioned rearwards of its normal position with flange now 42.0mm from focal plane, compared to the normal position of 46.5mm from focal plane.

    In view of some interest by owners of big URSA 4K, URSA Mini 4K and URSA Mini 4.6K cameras of the PL-Mount type I would like to enquire of people their interest in buying two-piece mod kits for these cameras.

    If sufficient folk were interested to commit, then it might be possible to persuade a third party optical manufacturer, even Metabones, to do a limited production run of kits using the 0.71 "Ultra" optical cell.

    I have absolutely no idea of the price involved and would field this whole project to a manufacturer/vendor as I have not the engineering or business skills to take on something like this.
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  2. #2  
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    Here is a rough and ready twilight test with the big URSA, an added Metabones Speedbooster 0.71 "Ultra" optical cell added into the throat of the camera body and a custom Nikon F-Mount.

    The recording was made at HD resolution on a BM recorder via HD-SDI as I did not have a media card available.


    The lenses used were :-

    Sigma-for-Nikon 14mm f2.8
    Nikon 35mm f1.4
    Nikon 50mm f1.4
    Nikon 85mm f1.4
    Nikon 105mm f1.8
    Sigmatel-for-Nikon 135mm f1.8
    Peleng 8mm f3.5 Fisheye.

    You will observe in the 14mm and the 35mm lenses, some corner softness, noticeable with the 14mm, less so in the 35mm but a known issue with this lens on some speedboosters for some users. This might be remediable with fine adjustments of the position of the speedbooster optical cell.

    Last edited by Robert Hart; 08-01-2017 at 09:59 AM. Reason: My bad. Video load incorrectly done.
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  3. #3  
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    For curiosity only. The accompanying diagrams are not engineering drawings and measurements have not been meticulously checked. The diagram on the right is an estimation of the section of a replacement mount for the speedbooster which would replace the anti-reflection cone in the URSA 4K PL camera turret.
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  4. #4  
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    Quote Originally Posted by Robert Hart View Post
    For curiosity only. The accompanying diagrams are not engineering drawings and measurements have not been meticulously checked. The diagram on the right is an estimation of the section of a replacement mount for the speedbooster which would replace the anti-reflection cone in the URSA 4K PL camera turret.
    Hi Robert, I dont have a actual metabones speedbooster, only a generic one to check. Could you tell me if the "optic" you have a drawing for an incased optic? Ie, is it held together as a group with alloy rings? Or is a loose group of elements?

    I have a modified baffle (or a "anti reflection cone" for a URSA 4.6k that has had the middle machined out- pretty much as far as we dared to go) but the hole is only 37mm, not 37.9. I see this measurement is the ultra" element. Is the older version smaller?

    Is the lens to sensor distance different with the orginal compared to the speed booster mod you have done?

    thanks paul
    Paul Ross Jones


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  5. #5  
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    Quote Originally Posted by paulrossjones View Post
    Hi Robert, I dont have a actual metabones speedbooster, only a generic one to check. Could you tell me if the "optic" you have a drawing for an incased optic? Ie, is it held together as a group with alloy rings? Or is a loose group of elements?

    I have a modified baffle (or a "anti reflection cone" for a URSA 4.6k that has had the middle machined out- pretty much as far as we dared to go) but the hole is only 37mm, not 37.9. I see this measurement is the ultra" element. Is the older version smaller?

    Is the lens to sensor distance different with the orginal compared to the speed booster mod you have done?

    thanks paul
    Sorry Robert, you have answered the lens "set back" measurement in the other thread. 4.2mm.

    cheers paul
    Paul Ross Jones


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  6. #6  
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    The "Ultra" speedbooster optical cell is a complete piece, 5 elements permanently sealed inside, a properly engineered piece. I think the older one is smaller. This one is intended to cover a Sony E-Mount camera sensor which I think is almost the same size as the BM4K sensor. The widest diameter of the optical cell is the threaded section. The 4.2mm setback of the taking lens flange face this slightly less powerful focal reducer introduces, seems to allow fitment with the blue IR filter remaining in its place - just.

    That 37.9mm is the outer diameter of the threaded section. The inner diameter of the Speedbooster housing's threaded section the optical cell screws into is 37.5mm as I measured it with a vernier. That may not be tightly accurate but close.

    If you had to machine the centre of the anti-reflection cone wider to clear your Speedbooster optical cell, then it seems that it is not identical to the cone in the big URSA PL. On my example it is 39.4mm internal diameter at its narrowest point closest to the IR filter.

    If your IR filter is closer to the PL-Mount flange face than 41.5mm, then it may be game over for the URSA 4.6K unless the IR filter is relocated furthur rearwards. That probably means having a smaller sized one custom made. The available space between the optical cell's front element and the rear of the Nikon lenses is very small.

    Inserting the IR filter in that space may also alter the optical character of the optical cell, which may in turn alter its position relative to the sensor and the lens mount flange face setback. It would be a whisker but enough to throw things off.
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    Last edited by Robert Hart; 08-07-2017 at 01:45 AM. Reason: errors
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  7. #7  
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    Here is an image of the completed internal assembly fitted. Yeah I know. I am slack because I have not yet matte-blacked the shiny bits.
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  8. #8  
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    Quote Originally Posted by Robert Hart View Post
    Here is an image of the completed internal assembly fitted. Yeah I know. I am slack because I have not yet matte-blacked the shiny bits.


    cool, thanks robert
    Paul Ross Jones


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  9. #9  
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    Now that the internal piece is complete and the speedbooster optical cell can be easily adjusted, I found that movement of the optical cell forward one and a half turns away from near-contact with the IR filter restored true focus for the Nikon lenses I am using. Because the fitment is inside the camera body, there can be no provision for locking the optical cell with a screw after adjustment without disturbing the adjustment by removing the whole assembly. I will have to make do with a dot of some semi-hardening material at the front-edge of the optical cell and the custom housing.
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  10. #10  
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    Hi Robert,
    Quote Originally Posted by Robert Hart View Post
    Now that the internal piece is complete and the speedbooster optical cell can be easily adjusted, I found that movement of the optical cell forward one and a half turns away from near-contact with the IR filter restored true focus for the Nikon lenses I am using. Because the fitment is inside the camera body, there can be no provision for locking the optical cell with a screw after adjustment without disturbing the adjustment by removing the whole assembly. I will have to make do with a dot of some semi-hardening material at the front-edge of the optical cell and the custom housing.

    Hi Robert,

    I have studied the URSA major and theres heaps of room for the speed booster, a lot more than the ursa mini. So I am considering getting one if I can get a good price on it. I would run EF lenses, so buy a EF turret version. But the web seems to say these are swappable with PL?

    Obviously I will look into it even closer to the time I purchase. But can you answer some general questions about the URSA, as I only know about the ursa mini at this stage?

    - What is the difference between the V1 ursa and V2?
    - Does the V1 go to 80fps in 4k?
    - I read somewhere there is a 240fps option (I am guessing as a cropped 1080p option). Did this ever happen or is this an early promise. What is its fastest fps?
    - How long can you get out of the battery? I was getting under 3 hours with a 95wh with my ursa mini 4.6k.

    thanks heaps, paul
    Paul Ross Jones


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