18mm RED Prime successfully mounted on an ARRI 2B with PL mount conversion.

Correcting the 18mm RED Prime PL Mount

I was talking to a cinematographer friend of mine who reminded me that, quite a number of years ago, I modified his RED Prime 18mm lens so it would work on his PL mounted MovieCam without crashing into the mirror. It seemed fitting to pass on what I did and do the same modification on the 18mm I recently acquired. The problem isn’t that the rear element sticks back into the camera too far, but rather that there is a beauty ring that is threaded into the PL mount itself that is both too long and beveled at the wrong angle. To refresh my memory, I began by carefully comparing the PL mounts on the other RED Prime lenses that work on film cameras to the PL mount on the 18mm to determine the exact amount that needs to be removed from the beauty ring.

All of that data gathered, I removed the PL mount from the 18mm, mounted it on the lathe, indicated the mount true and parallel, and machined it to the correct height and 45 degree bevel. I blackened it with aluminum blackening compound so it matched the rest of the lens set, reinstalled the mount, recollumiated the lens, and tried it on what I thought would be the worst case scenario, an Arri 2B that had been converted to PL mount. (I know this has a 2C door, I converted this 2B camera to have a 2C door on it years ago.) I pulled the aperture plate out of the 2B, slowly rotated the mirror by hand to make sure everything cleared as I calculated, and voilá! An 18mm RED Prime that will work with a film camera!

2 thoughts on “Correcting the 18mm RED Prime PL Mount”

  1. hello!
    i am having that problem with my 18mm RedPrime
    it wont fit into my BMPCC
    how did you take the black ring off? maybe if i manage to take it off it will fit.
    and will you be willing to make a special PL mount for my lens?
    how much will it cost?

    Thanks!!!

    1. Hello! Thanks for your question. I am semi-retired right now and not currently taking on outside work. Let me see if I can talk you through modifying the beauty ring. The beauty ring simply unscrews from the PL mount, but I removed the entire PL mount so I could use the precision surfaces of the PL mount to setup and machine the beauty ring to the correct size and relief angle. A competent machinist should be able to replicate this without issue. I shot a feature with a couple of Blackmagic Studio cameras that had EF mounts on them, and I was able to get EF to PL adapters from Samy’s Camera and B&H Photo. Both adapters required a plate that, on one end screwed into the tripod mounting hole on the bottom of the camera, and the other end screwed onto a port on the PL mount adapter. Later I drilled a 3/8-16″ threaded hole in the support plate that went between the camera and the lens, so that everything was attached to the tripod by the support plate. That seemed to work well.

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