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Sony XDCAM PXW-FS7 / FS5
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Old October 26th, 2016, 08:59 PM   #1
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B4 Adapter for Sony FS7 / FS5 or APSC - DIY Model

Had an idea the other day for an experiment to see if I could mount a 2/3” B4 lens on an FS7 but at a greatly reduced price over the existing solutions presently out there. Currently we have been using the MTF B4 to E-Mount kit. Whilst it’s probably not the best solution it’s cheaper than the IBE B4 unit from Abel Cine and it does a fairly decent job in HD where longer zoom lens capability is required.

https://www.lensadaptor.com/b4-23-sony-e-mount-package

https://www.abelcine.com/store/HDx35...tical-Adapter/

What I came up with after checking out the image circles required to achieve the desired results comes out WAY cheaper than any other solution out there. Now I’m not saying this is the best solution by any means but the optics involved well surpass 16 million pixels resolution capability and are designed to handle 4K. The ultimate end quality will depend in large degree as to just how good the B4 lens is on the front. HD B4 lenses would or should give the best results. There again though we have experienced better results with the very high end SD B4 lenses than the cheaper later HD lenses.

The one thing this setup will do is to increase the length of the B4 lens used. This in itself is not a bad thing if you really need that extra length. The increase in focal length is multiplied by 1.4 times. Obviously there is a light loss involved. This is 1 stop. The B4 lens used must have a 2 x extender to get the best results. Works in exactly the same way as the MTF B4 adapter kit does. Both the MTF and IBE kits have a total light loss of 2.5 stops. 2 stops loss via the 2 x extender and 0.5 of a stop loss on the optics in the MTF case. In the case of the IBE unit you can use a B4 lens without a 2 x extender as the IBE unit has the full 2.5 stops loss through is optics which are designed to be used without a 2 x extender lens.

In the case of this DIY B4 to E-Mount setup the total loss is 3 stops. 2 stops loss via the 2 x extender and 1 stop via the DIY converter. Interestingly if you use a Fujinon or Canon lens that has the 4:3 ~ 16:9 cross over unit something interesting can be achieved. By running the lens in its 4:3 mode you will recover 20% of the lens width lost by the 1.4 x magnification. An example, an 18 x lens multiplied by 1.4 now makes this lens a 25.2 x lens. Subsequently its wide end is also affected by a factor of 1.4. Therefore a 7.6mm wide end would effectively become a 10.64mm wide end.

Let’s do the math. 25.2 x 0.8 equals 20.16. Remember the lens is now reduced in magnification by a factor of 20% in the 4:3 mode. The cross over unit is in fact a focal reducer to reduce the 2/3" 16:9 image circle diameter of 11mm down to 9mm. This image circle is still big enough to work with our DIY B4 adapter. The other effect of a focal reducer is to increase the light transmission gain. Much like a Metabones speed Booster gains you an extra stop in sensitivity. The sensitivity gain in the case of the reduced image circle coming down from 11mm to 9mm in 4:3 mode is just on 0.75 of a stop. When a B4 lens with a cross over mode is used the total light loss of this DIY converter is 2.25 stops. 0.25 of a stop less light loss than the MTF unit that runs with 2.5 stops loss. You may ask why not use the MTF with a B4 4:3 cross over lens. We have tried this and it does not work. With the DIY B4 converter it does. The reason for this is that on the MTF B4 unit the optics are in the front half of the unit and the reduced image circle has no effect. With the DIY B4 adapter the optics are in the rear of the unit and the 4:3 image reduction does work.

In the end this was an experiment that evolved out of my curiosity. It works surprisingly well considering it’s a cobbled together bunch of bits that were not designed for the purpose of making a B4 to E-Mount converter. There is some chroma aberration to be seen under certain conditions but no more than we are seeing on the MTF B4 units. Bearing in mind there is no ALAC / CAC type of electronic CA correction available with any of these B4 to E-Mount adapters it’s not surprising that some is observed now and again. In my experience how much CA is produced is as much a product of the lens used than any other factor.

If anyone wants to see the results they can download a quick and dirty compilation of shots I grabbed out in the back street. At least this way there is no YouTube or Vimeo compression artifacts to cloud the issue.

https://www.sendspace.com/pro/dl/sp3vfu

Sorry about the camera shake and a bit of dust on the lens but it was just to see if this eBay bits and pieces US$372.00 DIY B4 to E-Mount converter would work based on my calculations. A work of art, definitely not!

Would be interesting to hear back from anyone who wishes to try out this B4 to E-Mount adapter experiment.

Chris Young
CYV Productions
Sydney
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Old February 21st, 2017, 11:21 AM   #2
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Re: B4 Adapter for Sony FS7 / FS5 or APSC - DIY Model

Hey, Christopher
I have a completely unrelated question brought up by one of your photographs. In the third photo, where you can see the top cheeseplate (Wooden Camera, or some other manufacturer?) I notice what looks like the old style Betacam shoulder strap attached. Are there 1/4-20 attachments which provide for attaching these old Beta straps? I have several, and love them. Very sturdy and miss the width and security they provided.... I would be so happy to be able to attach one of them to the FS7!
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Old February 21st, 2017, 11:30 AM   #3
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Re: B4 Adapter for Sony FS7 / FS5 or APSC - DIY Model

Never mind.... it didn't take much research to find them. I don't know why I never looked before!
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Old March 1st, 2017, 12:06 AM   #4
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Re: B4 Adapter for Sony FS7 / FS5 or APSC - DIY Model

Why not just buy this and shoot in low light.

Ads - Lens HD - Canon 8-64 T2.4 PL Super 16 Zoom Lens

Three stops is a lot. Even on a FS7.

Ian.
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