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Old December 2nd, 2013, 06:09 AM   #1
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B4 mount 2/3 lenses and the BMPCC

There are a lot of B4 mount lenses available in both in SD and HD for 2/3 cameras. There are also adapters that make it possible to mount B4 lenses on Micro Four Third lens mounts. However I cannot find any comprehensive reports on how successful or otherwise B4 lenses are on the BMPCC. Is there something wrong with the idea?

The BMPCC has a sensor size of 12.48 x 7.02 mm and a diagonal of nearly 14 mm whereas the 16:9 sensor of a 2/3 camera has an 11.000 mm diagonal and dimensions of 9.587 x 5.933 mm. These dimensions prompt two questions: -

Firstly can a B4 lens be expected to cover the full area of the BMPCC sensor?

Secondly as the pixels in the BMPCC will be larger and further apart than in an HD 2/3 camera is there much to be gained by using an HD lens instead of an SD lens?

I guess the coverage question would depend on the lens design and its minimum focal length. Any comments or experiences appreciated.
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Old December 2nd, 2013, 10:54 AM   #2
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Re: B4 mount 2/3 lenses and the BMPCC


Here is a clip shot with the SI2K through a B4-Mount TV Nikon ENG lens of the 8mm-125mm with doubler class.

The active area of the SI2K at 2K is 2048 x 1152 5-micron pixels, quoted in other posts as 10.3mm X 5.76mm.

In the top LH corner of the faux-cinemascope cropped image you will observe a trace of a vignette. In a normal 2K 16:9 image the vignette is quite apparent across all corners. As the zoom-in occurs you will observe the vignette moves away then returns momentarily in the zoom range approx. 25mm to 35mm.

I expect the BMPCC camera sensor to see more of a vignette with ENG lenses. I expect the active area of the BMPCC sensor is as declared. It appears to be the larger sensor of the compact camera offset and scanned as a cropped image. The SI2K had a correcting IMS-Mount with a chunk of optical glass which replaces the separation prism of the three-chip cameras. Without this, the image may be softer and one of the opposing colour channels may also be softer.

P+S Technik are examining an IMS-Mount option for the BMPCC. This would enable most lenses known to man to be offered up the camera - and the option of an optical viewfinder with B4-Mount. They will obviously have to decide whether the buyers of a sub$1,000 camera will want to spend from about a half to twice or more of its value chasing lens options for it. The optical viewfinder is similar to the Evolution finder for the ARRI and the Dalsa Digital Cinema camera.

Last edited by Bob Hart; December 2nd, 2013 at 11:07 AM. Reason: error
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Old December 2nd, 2013, 03:08 PM   #3
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Re: B4 mount 2/3 lenses and the BMPCC

There's a pretty good Facebook page dedicated to B4 lenses on M43 cameras that has a lot of great info. As far as I can tell, you need versions that will cover the 1" sensor in order to eliminate the need for a doubler (which makes all of them really long lenses at the wide end) or eliminate the vignette. A little searching will bring up the compatible models from the broadcast heavyweights like Canon and Fujinon. I would love to make one of these work, I have one but it doesn't quite cover the Pocket sensor, I took a chance on a $40 lens and it didn't work out. The lenses for 1" sensors are all pretty spendy on Ebay for something that may or may not work. I haven't seen anything great from adapted broadcast lenses yet, all the test shots I've seen look soft or have other glaring deficiencies to me. I was hopeful I could make one of these work, until I see some good samples, I'm sticking with native m43 lenses.
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Old December 3rd, 2013, 06:52 AM   #4
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Re: B4 mount 2/3 lenses and the BMPCC

Thanks Chris and thanks Bob,

I have to confess I am one of the few who is not a Face-book user so it might be a while before I see your source Chris. The prospects of finding a B4 lens is not looking too good especially if you do not want to use an extender or other extra optics.

I rather got the impression from a few eBay sellers that all you had to do was add a readily available B4 to M4/3 converter to their offering. Some even included the converter.

I have a lot to learn about eBay one described their lens as good which was then defined as: -
G Good - Appears to have been used very heavily with multiple dings, scrapes, scratches and heavy brassing. Glass may have fungus, excessive dust and/or scratches that can affect picture quality.
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