Metabones introduces Nikon F Speed Booster for NEX and Micro Four Thirds

Thanks ir Bob for the response. So does a 50 mm f/1.8 with a these boosters yield faster shutter speeds for the exact same scene on a APS-C camera vs a full frame camera? I still not quite wrapping my head around it. If the amount of light gathered onto the sensor is a function of focal length, would a wide angle converter in front of the lens yield this so called boosting effect as well? I heard an explanation that the boosting effect comes from gathering the light from the FF lens that has been cropped off by the APS-C sensor but doesn't the FF camera get all the light anyway from the FF lens? Something just doesn't seem to add up.

thinking of unit area is probably the main reason people get it wrong. a unit area of 1cm2 is 1/8.64 = 11.6% on a 35mm full-frame sensor, while it's 1/3.66 = 27.3% on NEX.

what do you want to know by comparing 11.6% of one sensor to 27.3% of another?

if the image quality on, say 11.6% of RX1 is the same as 27.3% of NEX6, we get 0.116 RX1 = 0.273 NEX6, or
NEX6 = 0.425 RX1

Remember when we were young kids running around with magnifying glass and concentrate the sun light into a bright spot of light to burn a piece of paper or light a fire cracker? That's the principle of how speed booster work. gathering light from a FF lens onto a smaller area of a APS-c or M43 sensor.

Thanks, Richard. Quite a chore to manually enter FLs, especially when using zooms. :)

since the factor is 0.71, we get
50 * 0.71 mm f/1.8 * 0.17 = 35mm f/1.3

the cropping factor of NEX is about 1.535 (or 1/0.65)
calculation: sqrt(24 * 36 / 23.5 / 15.6) = 1.535
a 35mm f/1.3 will in turn work as a 55mm f/2 lens.

this is about 0.25 stops less efficient than 100%.

> 50mm f1.8 becomes 100mm f1.8

this is physically impossible.
a 50/1.8 has an aperture size of 50 / 1.8 = 28mm,
a 100/1.8 has an aperture size of 100 / 1.8 = 56mm,
there is no where we can find that 56mm aperture.

a 50/1.8 can only work as a 100/3.5 on 4/3",
the aperture of which is 28mm, that we can find in the lens.

Only the angle of view changes, so a 50mm lens offers the same view (in 35mm equivalent terms) as a 100mm lens would. The aperture remains the same so /in effect/ it functions as a 100mm/f 1.8 lens would on a M4/3 body.

> Only the angle of view changes

for a certain aperture size, half the angle of view means half * half the light coming through that aperture.

it's still f/1.8, but can do exactly the work of an f/3.5 on 35mm full-frame. we cannot directly compare f-numbers across different formats.

>for a certain aperture size, half the angle of view means half * >half the light coming through that aperture

I am afraid not, the only thing that differs when you are mounting a lens in a differently sized sensor is the sensor it self. That means, that while the lens is still 50mm/f 1.8, you are using a smaller portion of the picture the lens can effectively display and the focal lenght is "becoming" 100mm. As the f number is a ratio, in your example, while there is less light reaching the smaller sensor, the ratio is the same as in more light/larger sensor (area); it is the same image each time, after all. That means no DOF changes as well, if the different sensors have the same pixel size and assuming even dof across the image plane

> the sensor it self.

4/3" sensor utilises 1/4 of light gathered by a FF lens.
this is exactly the same as narrower angle of view (or subject area) seen from the other side of the lens (half * half = 1/4).

> the ratio is the same as in more light/larger sensor (area);

well, at the same f-number we get same light within, say 1cm2 regardless of sensor format. but 1cm2 is about 44.5% of 4/3" (A), or 11.6% of full-frame (B). then we get
44.5% A = 11.6% B,
A = 0.26 B. same result again.

I was not clear in my quote, you are right that a full frame sensor is about 4 times bigger than a 4/3", I should have quoted that

>it's still f/1.8, but can do exactly the work of an f/3.5 on >35mm full-frame. we cannot directly compare f-numbers >across different formats.

When you have, say 1 lumen/cm2, this is where the f numnber refers, not in the total area. I guess the problem comes from the use of focal length/aperture to determinate the f number. What happens is that we are using a useful portion of the projected image from the lens to extract the f number; a smaller sensor than the maximum possible (recommended), would not change in any way the luminosity of the image but rather the FOV ; it is true that you are waisting light in that case, but of course there may be gains in lens curvature, corner sharpness etc. by using a lens designed for a sensor larger than the one you are going to put it in

ok, I realized that I am wrong considering the f number as a metric of luminosity. By definition, f number is "focal length/aperture", so in order to use it to have an idea of how bright a lens is, we have to pair it to a specific focal length and divide those two numbers. For example, a lens 50/1.8 is as bright as one of 75/2.7. All the same, a lens of 50/1.8 is less bright than one of 100/1.8. Maybe we have to change the way we interpret the numbers or am I missing something?

Nikon's "[A]perture [I]ndexing" innovation of 1977 was simply a change in the mechanism by which a lens's maximum aperture could be communicated to a camera body. Whether or not an F-mount lens's complies with this standard therefore has absolutely nothing to do my question, nor is it relevant in any way to the Metabones' potential function since - by design - these new adapters do not communicate in any way with the camera.

> what problem does it solve?

currently we lose light mounting a larger frame lens to a smaller frame body. Speed Booster products dress the problem and try to get (at least part of) that light back.

if we can reclaim all of the light perfectly, we also get following side effects (actually they are all hard wired):
same angle of view,
same DoF & bokeh at a certain setting,
same diffraction, and of course
same quality of image at certain quantum efficiency.

or simply put there is no difference in the output image from two different format sensors. you cannot tell which is from which.

we can use smaller lenses when compactness is prefered over image quality, on whatever camera body.

"The whole point of a small sensor system is that it is small."

But NEX isn't a "small sensor system".

It is a mirrorless camera with an APS-C sensor = same size sensor as most Canon & Nikon dSLRs.

Speed Booster just gets rid of the 1.5 crop-factor i.e. 14mm lens will give same view as 14mm on a FF dSLR, instead of 1.5 x 14mm = 21mm.

Only desired for wide-angle and UWA lenses, unless you like losing the crop-factor magnification on your telephoto lenses. :)

Speed Booster tells a simple story that
sensor format is not the decisive factor, lens aperture is.

with Speed Booster we can get same high quality image
from a variety of sensor formats,
as long as the f-number > 0.5.