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URSA 4KV1 PL - SPEEDBOOSTER.


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#1 Robert Hart

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Posted 16 July 2017 - 05:11 AM

The subject of fitting a focal reducer optic to the 4K URSA has surfaced fro time to time. Recently on reduser, there was a post regarding fitting a focal reducer optic within the throat of the DSMC2 style of camera. The results were encouraging.

So prompted and having recently had a big URSA PL turret partially apart in order to design and fit a custom Nikon F-Mount, I also examined the possibility of fitment of the Metabones "Ultra" 0.71 optical cell within the throat of the big URSA camera.

It seems that it is a workable possibility. The flange face of a particular mount is set back about 4.2mm when this optical cell is in the image path.

It is unlikely that PL-Mount cinema lenses can be accommodated. The deep shoulder of the lens mount takes up space. Many of the lenses have rear elements protruding significantly rearwards, which means that many will clash with the front element of the "Ultra" optical cell.

My tests thus far attempting to offer up Cooke Speed Panchros, a Kinoptik Tegea 9.8mm and a Cine Xenon 28mm to the Speedbooster arrangement demonstrates that their rear structures are too far rearwards and clash with the front element of the Ultra optical cell.

The Rokinon Zeen and Zeiss CP2 series of lenses seem likely to work so long as their rear barrel structure is no wider than the opening in the front of the URSA camera body with the intermediate adaptor removed.

Comparitive image pairs with and without the speedbooster element in place can be seen here. The Speedbooster optical cell and 20mm f1.8 Sigma-for-Nikon lens were placed with a primitive jig arrangement for the rough test.

http://www.bmcuser.c...EST-GROUP/page5


Edited by Robert Hart, 16 July 2017 - 05:13 AM.

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#2 Phil Rhodes

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Posted 16 July 2017 - 05:24 AM

Surely this is mainly interesting from the perspective of putting still photography lenses on these cameras? Most of the lenses that are available in full-frame coverage are intended for stills, hence the rebuilt types we see as cinema primes.

 

Sounds good, either way.


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#3 Robert Hart

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Posted 23 June 2018 - 07:50 AM

My apologies for not posting follow-ups. I found myself locked out until I discovered that the password only works at the home page of the forum for logging in, the same as happens on the BM and bmcuser forums. Other sites behave differently, a mystery beyond my meagre comprehension. - Anyway back on to task.

I managed to devise a useful solution for the Nikon F-Mount which I made for the "Big" URSA PL model by machining the "tail" of my Nikon adaptor piece to hold it forward from the rear face of the wide recess in the camera body which normally accommodates a cylindrical adaptor piece. The Nikon adaptor must have two sets of mounting holes to match the distinctly separate patterns of the camera body itself and the adaptor ring which has its own screw holes in it.

I also discovered that the BM URSA PL-Mount can be adapted to work with the speedbooster in place by machining a little off the tail of the mount so that like my Nikon adaptor, it butts against the rear surface in the camera bodywork. A small amount of material must be machined off the rear of the clamp ring and the two finger lugs to clear the front face of the camera body.

I should but have not yet made a spacer piece to surround the shortened tails of my mounts. Unless the mount screws are pulled up carefully and equally to correct tension, it is possible to tilt the mounts which is not good.

The only lenses which are safe to use with the Metabones 0.71 optical call in place are the lenses Metabones has tested and approved. These are as far as I know, the Zeiss CP2 series of compact primes.

Rokinon Cine/Samyang Cine and Xeen PL-Mount lenses should work as they are fullframe SLR based designs which do not penetrate deep inside of the PL-Mount. Most traditional motion picture camera lenses may clash against the front element of the Metabones 0.71x optical cell, damaging the cell and the rear element of the lens. 

Old Cooke Speed Panchro Series 1, 2 and 3 are definitely not suitable. 

Please ignore the colour in this accompanying vision. I am partially colour-blind and cannot colour-grade to save my life. On the "big" URSA, with the 0.71x in place, the 28mm Nikon lens used became usefully wide-angle in the confined workspace of the cottage kitchen. The 58mm Nikon lens field -of-view was usefully wider.

https://www.youtube....h0p7ljhYc&t=94s

 


Edited by Robert Hart, 23 June 2018 - 07:52 AM.

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#4 Robert Hart

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Posted 23 June 2018 - 08:02 AM

Further to the above, an enterprising fellow in Italy has devised a focal reducer to fit within the camera throat of the URSA Mini 4K and URSA Mini 4.6K cameras. It is called the Lucadapter. Unlike my arrangement, it apparently does not require the 4.2mm setback of the lens mount flange faces of the Nikon F-Mount and PL-Mount that my arrangement of the Metabones 0.71x optical cell requires for infinity focus to be preserved.

Because the URSA Mini Pro camera throat is occupied by the ND filter system, it is not suited for fitment of a focal reducer like the Lucadapter or custom adaptor for the Metabones 0.71x optical cell.



Edited by Robert Hart, 23 June 2018 - 08:06 AM.

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#5 Robert Hart

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Posted 23 June 2018 - 08:07 AM

I could not get the link to work as a windowed view in the responsive post second above this post, so here it is again, windowed this time.

Edited by Robert Hart, 23 June 2018 - 08:10 AM.

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#6 Robert Hart

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Posted 23 June 2018 - 08:20 AM

Here are some images of the PL-Mount with Speedbooster installed. You will observe that the rear of the clamp ring now approaches extremely closely to the front of the turret body when the lens is secured.

Attached Images

  • BMURSA4KSPPL2v2.jpg
  • BMURSA4KSPPL3v2.jpg

Edited by Robert Hart, 23 June 2018 - 08:21 AM.

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#7 Robert Hart

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Posted 23 June 2018 - 08:25 AM

Here is an image of the Nikon F-Mount arrangement with the speedbooster installed. The front face of the mount is rearwards within the body of the turret. You will observe extra unused screwholes in the bronze mount adaptor. I have not yet devised a lock pin arrangement which will fit within the available workspace of the PL-Mount camera body

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  • URSA 4KVA SPEEDBOOSTER1 RESIZED.jpg

Edited by Robert Hart, 23 June 2018 - 08:27 AM.

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#8 Phil Rhodes

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Posted 23 June 2018 - 10:28 AM

And where can I get this done?


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#9 Robert Hart

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Posted 08 July 2018 - 12:48 PM

Somebody like Les Bosher in the UK would be able to do it and do it better than I by a huge degree of quality. You would have to buy a Metabones Speedbooster with 0.71x "Ultra" optical cell in it and remove this from the Speedbooster. Nothing destructive has to be done to the optical cell itself so you would be able to re-assemble and resell it if you want. The optical cell is identical across all the "Ultra" 0.71x speedboosters. Used off eBay may be the most affordable way to get one. Metabones or Caldwell Optics will not sell you the optical cells singly. I can provide the construction method and some dimensions. Les Bosher would probably prefer to measure the work to be done himself.

https://www.ebay.com...ltra&_sacat=625

Edited by Robert Hart, 08 July 2018 - 12:51 PM.

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