B4 to NEX lens adapter with 2x mag on Ebay

[BrianMurphy]

I have a B4 lens that I used on my PMW 300 for back of the hall shots in hotels. Sold the PMW300 still have the lens and was considering trying it on one of my E mount cameras. Saw this on ebay and thought I would ask if anyone has one, has used one or has an educated opinion on it. I am not interested in the Fotodiox or other Asian made ones with no glass to compensate and know that the one made in England works but is very pricey.
Thanks
Brian
https://www.ebay.com/itm/2-3-B4-Mou...857217?hash=item2841df7c41:g:e~MAAOSw3utY5Y9I

 

[cyvideo]

Yes I saw these and was a little confused by them. I wonder how good the optics are in them?

My experience is that with S35 or APSC you need about 2.5 x magnification to cover the sensor. For example the Sony S35 sensor has a diagonal of 27.1mm and a 2/3" sensor has a diagonal of 11.2mm. This creates a crop factor of 2.46 in round figures. In other words these B4 to E-Mount adapters with a 2 x lens would not cover the full APSC/S35 sensor size. I used to have one of MTF's B4 to E-Mount adapters. It had a .5 optical relay built into it and had to be used with a B4 lens with a 2 x converter.

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

In total this gave you a 2.5 x magnification that then covered the S35 sensor. This of course also introduced a 2.5 stop light loss. The only way I can see these eBay 2 x units working on full APSC/S35 sensors would be to use one in conjunction with a B4 with a 2 x doubler unit. This would end up being a 4 stop light loss as you would lose two stops via the 2 x on the B4 plus two stops on the eBay 2 x adapter. 4 stops is a significant amount of light to lose even on a sensitive APSC/S35 sensor. If your B4 was let's say an f/1.8 lens you are going to end up with an effective aperture of around f/5.6.

Alistair Chapman explains the whole concept fairly clearly in this clip.

https://www.youtube.com/watch?v=iqJCFBZDfLQ

I ended up bailing out of the full frame B4 to E-Mount unit because of the subsequent light loss of 2.5 stops. In HD though with a decent B4 the unit worked surprisingly well. In the end I ended up with two of MTF's B4 to S16 adapters, one B4 to PL and one a B4 to E-Mount, the latter specifically for an FS7. These units have a light loss of about 0.7 of a stop so much more suitable overall. Of course these will only work with cameras that have the S16 center crop function available. More than happy with the results considering what's up front was originally designed for and 11mm sensor. No beef from clients or networks so that has been good.

During my musings about using B4s on E-Mount I tried a little experiment and it worked surprisingly well with a B4 with a 2 x converter. It comprised of a B4 to M4/3 mount adapter, an Olympus 1.4 x tele-converter and a m4/3 to E-Mount adapter ring. All mounted with a 15mm rail set up it worked surprisingly well with a decent B4. The Olympus 1.4 x is suitable for 4K so no noticeable issues seen using it. The Olympus 1.4 has a light loss of 1 stop. Add that to the 2 x in the B4 lens and you end up with a total loss of 3 stops. The picture will give you an idea of the bits used. Obviously this adds a magnification factor of 1.4 to the existing lens. On the other hand all the other adapters by their very nature will also have some degree of magnification factor. Hard to cover a 27-28mm sensor with a lens designed for an 11mm sensor without some degree of magnification.



If you do end up with one of those eBay 2 x adapters post back as I for one would be interested to hear you findings.

Chris Young

 

[balazer]

A proper B4 lens converter has a big block of glass that acts like the prism block in a 3-chip camera. This eBay converter doesn't have that, so I wouldn't expect great results at wide aperture settings. Close down the iris enough and it will be o.k.

 

[BrianMurphy]

Update:
The vendor on Ebay has offered to send me one for evaluation and a review. I will keep you posted. He mentioned that the lens in the adapter has 7mm of travel for adjustment so it all sounds interesting and he seems to be knowledgeable as he sell quite a variety of lens adapters.