New B4 to Sony F3/FS700 Adaptor

[Peter Corbett]

Has anyone seen Alistair's new video about the MTF B4 adaptor? It looks intriguing as I have a (once very expensive) Canon HJ21x7.5 HD zoom here gathering dust. The adaptor costs around two grand in dollars, but the image quality seems more than worth it. Plus they also sell a Hirose to D-tap, so you get full servo control and the remote port on the lens is still free for an SRD pan-handle servo controller.

On my 21X F1.9 zoom, I would get the equivalent of a 19- 400mm para-focal zoom at a max aperture of F4. I was looking at getting an 18-200 or 18-300 Nikon for a run-around lens but this may be a better choice. Alistair says the depth-of-field characteristics (at the maximum aperture of F4), are the same as a dedicated S35 lens.

Video overview of MTF Services B4 2/3″ to super35mm adapter. |

[Noah Yuan-Vogel]

Keep in mind that all characteristics of any HD 2/3" lens with that adapter will have the same characteristics as the same lens without the adapter on a 2/3" camera. I've heard marketing talk about such lenses that implies that those lenses on an S35 will be like an S35 lens and in a sense it is true in the sense that that your Canon HJ21x7.5 f1.9 lens aka 2/3" f1.9 7.5-157mm lens with that adapter on a S35 camera would actually be an f5.0 19.5-408mm which at 19.5mm f5.0 for example will have the same DOF characteristics that it had at 7.5mm f1.9 on your 2/3" camera.

But the marketing sometimes is a little misleading since it sometimes seem to imply your 2/3" lens will suddenly have new capabilities it did not have on 2/3", but that is not the case, it will never have new abilities or shallower DOF or more light gathering with a rear lens adapter.

You will not get less DOF with that adapter, nor will you get more light. Personally f5.0 on S35 is hard to swallow, might be better off with an 18-250 f3.5-6.3 lens for a 1/10th the price...

Hopefully your S35 camera is 2.5 stops more sensitive than your 2/3 camera, which it should be given the scale, but you'll need it.

[Peter Corbett]

Well the F3 is very sensitive, more so than my old Varicam, so the F5.0 vs F3.5 on a DSLR kit lens doesn't concern me too much. I know there won't be more light, there will less, but the constant focus and fast servo zoom is not to be sneezed at.

[Noah Yuan-Vogel]

Odd that the adapter uses a 1.5x extender and requires that the lens has an internal 2x extender. Seems like it would make more sense to have a 2.6x extender built in and then allow people to still use their 2x extenders if they want.

It does seem like its probably a interesting option to have, though it negates any benefits of having a larger sensor. But I guess its probably nice for people who might otherwise feel they need to have a 2/3" camera and an S35 camera. This basically turns your S35 camera into a 2/3" camera so you don't have to own two. Interesting considering a lot of 2/3" cameras are quite expensive.

So I guess none of the automatic functions work since there is no connection with the camera, and you must have to find a way to power the lens externally to get any servo zoom rocker functionality.

I feel like I've seen a lot of HD ENG 2/3" lenses that are either ridiculously expensive or of very poor optical quality. Parfocal is great, as are ENG mechanics for some situations, but given the price of HD lenses and from what I've seen most HD ENG lenses under $10k breathe like crazy and have lots of CA (maybe even more so when not used with the prism cameras they were designed for). Either the Sony SCL-Z18X140 for the F3 or the upcoming Sony SEL18200PZ for NEX FS100/FS700 cameras might be a better option.

[Alister Chapman]

Originally Posted by Noah Yuan-Vogel

It does seem like its probably a interesting option to have, though it negates any benefits of having a larger sensor.

You will still get the benefit of the shallow depth of field. An f1.8 lens becomes f5, at f5 you can still get very shallow DoF, shallower than you would achieve at f1.8 on a 2/3" lens.

Powering a 2/3" lens simply needs the use of a 12v power source and a simple adapter cable. On an F3 this is normally done by using a battery with a D-Tap output. It is harder with an FS100/FS700/Canon as the cameras are 7.2v. You can always use a small 12v battery like one of the swit batts designed for the EX1 or a battery holder that takes 8x AA batteries. Of course you can always still operate the zoom manually.

Another benefit of using an ENG zoom is that if you want to use the camera shoulder mounted it gives you a nice hand grip where you really need it, alongside the lens, not back on your shoulder as with the Sony zooms.

The lens extender is used to provide much of the optical conversion to keep the cost of the adapter as low as possible. We could have done a non extender version but the price would have been significantly higher (5x approx) and it would have only worked on a single model of camera. Including the extra magnification would have made the adapter much longer, the extra length would push the lens out quite a long way from the camera. This was designed as a low cost way to allow users to make use of lenses that might otherwise be collecting dust. It also gives the lowest cost way to get a par-focal servo zoom on a super35mm camcorder. You will almost certainly get less CA using a broadcast lens via this adapter than you would with a prism based 2/3" camera. There are PL mount adapters available from other manufacturers that do not require the use of an extender, but these are significantly more expensive, much longer and require a PL mount.

My adapter is not a replacement for a dedicated s35 zoom like the Fujinon Cabrio ($50k), it will not perform like a prime lens, but it opens up a world of possibilities utilising readily available 2/3" lenses. For example we used them with Fujinon 40x16 lenses to shoot some of the key shots in the Duran Duran film. It was the only way we could get a servo zoom with a focal length of 1.6m.

Do remember that the Sony SCL-Z18X140 and SEL18200PZ are only f3.5 when fully wide and f6.3 at the telephoto end so overall no faster than most ENG lenses would end up and the SEL18200PZ is not truly par-focal, the focus shifts as you zoom.

[Noah Yuan-Vogel]

That's not true, f5.0 on S35 is exactly the same DOF you would get at f1.9 on 2/3". Your depth of field does not get shallower because the no matter how many behind the lens elements you put in, the light still passes through the lens the same way, and the extenders only increase the size of the image circle. It is the same image circle but optically upscaled to a larger sensor. It will have the same attributes as an image from the same lens already had on a smaller sensor without any extenders. This is assuming you use the same amount of the image circle at 2/3" as you do with the extended image circle at S35, which is what these adapters are designed to do.

The effect of the 2.5x is exactly the same crop factor and f-stop factor that gives you the difference in FOV and DOF between 2/3" and S35. You have to multiply the 2/3" lens's focal length and the f-stop by the same number because as the image circle is scaled up linearly, the same photons making up that image circle are spread out, dropping the f-stop value by the same exact factor. A change in DOF would require either a change in front of the lens or some change in the way the lens gathers and projects light, but that has not changed through a rear extender since the rear extender can only change the original image circle, it cannot add photons to the original circle therefore it cannot add DOF.

[Alister Chapman]

I stand corrected. You are quite right. I had to check though and did find a couple of "highly regarded" DoF calculators that also appear to get it wrong.

[Noah Yuan-Vogel]

Maybe the DOF calculators use CoC values that are not proportional to the imager size? DOF should be the same assuming CoC or pixel size is the same relative to the imager size, in this case, for 1080p 2/3" or 1080p S35mm with similar lp/ph resolving power.