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

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!

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!

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.

Re: B4 Adapter for Sony FS7 / FS5 or APSC - DIY Model
 

I am a little confused about the math here...Chris, can you use the term "angle of view" in a sentence to assist? :)

If an old Canon J21x7.8 BIRS has a wide angle view of around 57 degrees, what would this lens's AOV be when 2x and 1.4x are applied to it mounted on the S35 sensor?

As for the 2.5 stops of light loss, this would be 2.5 stops from the lenses native f1.8, so the result after 2x and 1.4x would be around f4.5...similar to the Sony PZ cine lens? I wonder how much better or worse this system would be compared to putting the same lens on say an old PMW350 or HPX2700 once you start adding gain.

Paul

Re: B4 Adapter for Sony FS7 / FS5 or APSC - DIY Model
 

Paul ~

I haven't even looked at my DIY experiment from an angle of view point of view so can't comment on that. The exercise was just done out of curiosity on my part with the bits that were lying around. Always tinkering as to the how and why of things.

Regarding the light loss factors. Disregarding anything else just engaging the 2 x on a B4 is a 2 stop loss. The Olympus 1.4 x adds another stop. Therefore total number of stops lost is 3 stops.

Rule of thumb, multiply the magnification of any adapter by an F/ stop and you will get the light loss involved.
For example the Olympus 1.4 x multiplied by let's say F/5.6 becomes 7.8, near enough to call it F/8.0. A 1 stop light loss there.

Let's take a B4 lens of let's say F/1.6. Multiply that by the 2 x converter. The effective aperture now becomes 3.2. That F/3.2 is an effective 2 x stop loss over 1.6. See the attached chart. Now let's take the Olympus converter's 1 stop loss and add it to the 2 stop of of the B4 with 2 x engaged and we end up with a total of 3 stops lost.

The original MTF B4 to full S35 frame adapter had a 2.5 stop loss. 2 stops on the B4 and 1/2 a stop on the optics in the MTF adapter. My home made experiment leaves a bit to be desired but its math is the same. 2 stops on the B4 but now it's 1 stop on the Olympus 1.4 x. A total 3 stops. Effectively the F/1.6 B4 is now an F/4.5 on an S35 sensor. 1/2 a stop slower that of Sony's own F/4.0 18-110mm zoom but nor limited to 6.1 x as is the case with the Sony 18-110mm. If have at 21 x you get 21 x. It's no low light monster but for long range news, sports in daytime or even under good stadium lighting not a major issue. Our top stadiums are all factored for an F/8.0 shooting aperture.

Alistair Chapman who developed the original B4 to S35 adapter in conjunction with Mike Tappa from MTF Services put a little explanation video together when it was released. He covers FOV and image size etc in that video. Worth a look.


I'm now using MTF's B4 to Super 16 and PL to Super 16 adapters with the FS7 these days. This of course only works in the S16 Center Crop mode on the Sony cameras. This has a 0.8 stop light loss. They work very well for the price. I've shot a fair bit that's gone to air on these units and no complaints from any broadcaster yet... touch wood :)

https://www.lensadaptor.com/b4-23-su...-mount-adaptor

Chris Young
CYV Productions
Sydney

Re: B4 Adapter for Sony FS7 / FS5 or APSC - DIY Model
 

Thanks Chris, and by angle of view I just meant when you point at something at wide angle, do you have the same objects showing on the edges as you would with a native 2/3" camera. I also played with my Canon Sony 1/2" KH21ex5.7BIRS on my A7sII with a 1/2" to E mount adapter...why in the world would anyone produce such a device...it made a fun toy, but required way too much digital zoom to center crop the massive FF sensor!

Paul

Re: B4 Adapter for Sony FS7 / FS5 or APSC - DIY Model
 

As Alistair explains your field, angle of view remains basically the same. You are in effect converting an S35 sensor camera to a 2/3" cam so same or very similar results.

I've only just discovered that Ian Withnall suggested buying S16 glass. This would be great but will only work on cams with the Center Crop function which of course precludes you from shooting 4K. Not that I think I would want to shoot 4k with an S16 or a B4 lens. But there again I can almost guarantee someone will try it. :))

Chris Young
CYV Productions
Sydney

Re: B4 Adapter for Sony FS7 / FS5 or APSC - DIY Model
 

Just did a quick informal low light comparison of my Sony X70 against my A7sII with SD Fujinon A15x8 glass.

The Sony was set to it's maximum 33db gain, and 1/30 sec shutter, with iris set to f4.0. The Fujinon was set to 2x and f1.8, so result was around f4.0. A7sII was set to Super35 with 1.4x crop, 1/30 sec shutter, and the ISO (gain) needed to match the X70 was just 3200. :-\

As a side note, the Sony had to be zoomed in to 13% (wide is "30mm") to match the 8mm focal length field of view of the B4 lens with all the extenders on attached to the A7s.

Paul