This was my first article on the NEX system, in May 2010. In this I identified all the types of lens which would be adapted to work with the NEX (and later were), and also proposed a 0.66X reducing converter to adapt Alpha lenses to cover the NEX format with increased aperture:
Here's the relevant bit:
"You name it, the NEX will be able to do it. Telescopes, microscopes, endoscopes, whatever. And Alpha lenses, and MD lenses. There is even enough ROOM with over 25mm the spare to fit a true retrofocus format reduction converter – that is, a 0.66X optical unit which condenses the image from a full frame lens to fit the APS-C sensor. It is already done in the video and ciné world, and these converters have a wonderful bonus. Your 24-70mm f/2.8 SSM lens becomes, with a 0.66X reducing converter behind it, a 16-46mm f/2. That’s right – the same way a teleconverter loses you a stop or two, a format reduction converter gains you a stop.
The same converters also increase resolution, much as teleconverters reduce it. Zeiss can achieve 400 line pairs per millimetre from high grade 35mm format movie lenses when rear-converted to reduce on to 16mm or video.
Will Sony ever make such a converter? Do they even know that Zeiss have designs, and make exactly this type of converter for Arriflex and other systems via Angenieux? Do they realise that rear fitting format-reduction converters can also perform an AF function, allowing a manual focus lens from Nikon, Canon, Contax, Minolta or whoever to be mounted on a converter which has an ultrasonic AF mechanism of its own?
Imagine that – your 50mm f/1.2 Rokkor becomes an autofocus 33mm f/1.0 on the NEX. This is not blue sky thinking, it’s an optical practicality not a mere possibility. However, you don’t want to know the price of Zeiss converters, and for a system like NEX a universal converter might never be possible; it might have to be matched to the prime lens."