So near now and not so far...f0.7 in our longing sweaty hands.

Achieving f0.70 on a Sony Nex-6 APS-C sensor with the Canon EF 50mm f1.0 L is my current fascination in the camera world. Purely aperture speed is what I'm after.

Of course the inspiration stemmed from the after effects of reading articles about the Carl Zeiss 50/f0.70 which I do not recommend for the uninitiated. You see, the Carl Zeiss thingy was actually a medium format monster fitted with a condenser lens (ringing Speed booster) element at the rear to give the lens its worshipped speed.

What am I ranting on about? The revolution of late was last year's debut of the Metabones speed booster. As of today f0.74 is already available with the special Blackmagic cameras with the right speed booster and lens combo but I am referring to the full frame Canon EF 50mm f1.0 L lens shining on a Sony Nex APS-C sensor in this particular blog post.

Sensor sizes and depth of field doesn't even matter anymore. Focal length of the lens is not the bother of the goal as the right length conducive to achieving that goal of f0.70 will naturally fall into place. By my reckoning any lens from 35 - 85mm(full frame equivalent) is about the right ballpark length for the fastest possible lens. In fact, 50mm is possibly the cheapest route to an f0.70 lens. Given the plethora of camera lenses out there, I dare say that they fall into 2 categories:

1) Single lens reflex type(SLR): DSLR, FX or DX(Nikon talk)

2) Rangefinder/Mirrorless type: Leica M-series, Sony A7x, Sony Nex, m43, Fuji-X, etc.

By the way, it is technically easier to make a rangefinder/mirrorless 50mm f1.0 lens than it is to make an SLR 50mm f1.0 lens. Why do I say that? Back focal distance(BFD) is the answer. The BFD is the shortest distance between the surface of the closest lens element and the sensor flat surface. The rangefinder/mirrorless lens enjoys a premium in using up more space whilst the SLR lens is stunted by need of clearance to the reflex mirror flipping up! Lens for lens, rangefinder/mirrorless uses less "refractivity" of the usually exotic glass to get the same job done as compared the SLR lens.

The point here is that rangefinder/mirrorless camera lenses are therefore designed with less optical/technical difficulty (usually smaller, sharper and less distortion...thus the ensuing fame of Leica rangefinder) versus single lens reflex camera type lenses. This is especially true of the wide-angle and normal lenses and in the earlier years of lens design.

Additionally one must note that, to speed up a lens via a condenser lens,

• one has to choose a lens from a larger format sensor than the intended target camera sensor size(condenser works by concentrating light to a smaller area).
• Also the lens chosen must have enough BFD to allow fitment of such a condenser. This usually entails a lens designed for SLR(DLSR) cameras.

If you already own a Leica Noctilux-M 50/0.95 then tough luck! Why? You wouldn't have enough BFD left for a condenser lens. In this regard, the SLR Canon EF 50/1.0 L is the best choice(well there isn't any other faster as of 2014) for speeding up!

I had the initial impression that the 1-stop addition to the Canon EF 50/1.0L would result in an f0.70 lens. However there is a speed limit to the Canon EF to NEX speed booster(and the upgraded Ultra version of 2014 as well) of f0.90 even when an f1.0 native lens is matched with it. Forum asking the designer, Brian Caldwell himself, reveals that f0.70 is actually theoretically achievable.

Refer to: http://www.fotozones.com/live/index.php/topic/47313-speed-up-your-lens/page-7

32mm to 42mm is the magical answer to this blog...

And oh! the new Speed booster Ultra is similarly limited howbeit better...

Refer to: http://www.dpreview.com/forums/post/54306903

There we have it! So near now and not so far.