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Hi you all!

I am going to make an adapter to fit different type of lenses (I was thinking B4) to my CP16R because original lenses are not easily available and I'm thus looking for the exact FFD of the original CP16R lens mount. Does anyone happen to know the exact FFD of that mount? by quickly measuring it was somewhere around 40mm or so but one would need .01mm accurate to be able to work on the adapter 🙂  

I can take the other mount dimensions from the lens cap at reasonable accuracy. 

 

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  • 2 weeks later...

I doubt you will achieve the perfect optical result with the B4-Mount lens on a CP16R but it will not be too bad at apertures of about T4-T8. The B4-Mount lenses are set up so that three 3 CCD sensors see the lens image through a prism.

In adaptors for B4-Mount lenses to single CMOS sensor cameras, there is a thick planar optical glass element in the adaptor. This element projects too far rearwards to clear the mirror in the CP16R throat for both the Blackmagic B4 adaptor and P;+S Technink IMS B4 adaptor.

The "in air" flange to focal plane distance for the B4-Mount is 48mm. For the CP16R is it 38.1mm according to another response here.

You will have insufficient workspace for the waist for the CP-Mount clamp ring clearance of at least 6.4mm forwards of CP-Mount flange face plus the at least 5mm plus for the clamp ring of the B4-Mount rearwards of B4-Mount flange. That 11.4mm plus, uses up your available 9.9mm of workspace by about 2.5mm of interference.

You might think you are able to share a total of 2.5mm to be shaved off the rear of the B4-mount clamp ring and the front of the CP-Mount clamp ring except that the CP-Mount clamp ring is a two-layered construction. You will destroy its integrity by shaving anything off it.

That leaves more to be shaved off the rear of the B4-Mount clamp ring and you do not have enough meat on the threaded section to be assured of sufficient strong thread engagement. So the adaptor route is done for, cactus, futile, dead-ended, unless all other moving components are remade - maybe??

Your choices therefore are to make a new CP-Mount tail for the B4-Mount lens or make an entire B4-Mount to replace the CP-Mount on the camera. Making a new CP-Mount tail for the B4-Mount lens will be simpler. 

You might be able to shortcut the process a little by using a salvaged B4-Mount tail off a scrapped lens, longer screws for the tail and a thick spacer between the two. The profile of the two mount systems is very similar with probably about 0.5mm in diameter difference for the wings on the tail outer and inner.

However, the CP-Mount inner shoulder rearward of the flange face is considerably wider which would require a ring adaptor on the B4 tail shoulder. There is also a shroud overhang on the B4 tail which will interfere with the spinning mirror of the CP camera. You would also have to relocate the pin in the B4 tail to engage with the slot in the CP-Mount. 

Good luck with your endeavours. 

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Thanks! 

I am aware of the locking ring issue, I tested it beforehand to find out what type of modifications would be needed to fit the B4 lens to the camera. I have couple of cheap Chinese B4 to EOS adapters which I am intending on using to get the B4 portion of the mount with the B4 locking ring, and then just machining it shorter and making the other necessary parts to fit it in place of the original CP locking ring. 

Alternatively it is possible to machine a new CP mount for the lens itself like you said. But I rather avoid that because I will still want to use the lens on small format video cameras too and it would be nice to use other B4 lenses too with the CP16.

I have used the B4 zoom with the GH4 for many years so I know its characteristics very well and how it behaves on a single sensor camera. The image quality is not an issue with this lens in the conditions I will shoot with it in.  Additionally I am shooting lots of B/W and the possible aberrations would only look nice on it 😄

One issue with the CP16 mount is that the lenses for it are extremely rare so one will usually need to purchase the whole camera package just to get a working lens. So adapting other lenses or changing the camera mount to a more common one is necessary if wanting to use the camera for any real world purposes. B4 lenses, however, are very common and I already have a good one so no need to purchase any extra cameras 🙂

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6 minutes ago, Brian Drysdale said:

I believe it's posable to change the CP 16R camera's lens mount to a PL mount.

yes but wide angles cost a fortune for PL and cheaper lenses are difficult to adapt to PL. my current KMZ lenses made for Kinor16cx-2m don't seem to clear the mirror and fibre screen holder of the CP16R and I don't want to change the mount of those lenses because I need them for other cameras as well.  If there would be Arri Bayonet ---> CP16 adapters available I might consider some cheaper bayonet lenses but the adapters seem to be impossible to get so the best option is to adapt my B4 mounted Fujinon 5.5 - 47mm F1.7 zoom lens to work with the camera. It covers both the wide angles needed AND is fast enough for documentary use AND is cheap because I already have one. Additionally the B4 modification is much easier to do to the CP16R than the PL modification (and like said I don't have suitable wide angle PL lenses for it anyway, the widest working lens being the 28/2 Lomo which is not wide enough.

the biggest problem with the PL mount is that the 54mm mount barrel is too large and protruding to be compatible with the camera without signifiant modifications and machining. And like said, even if the camera would be modified my PL-adaptable wide angles would still be incompatible

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