# Metabones adapter, reduces focal length and increases F-Stop for mirrorless cameras.



## BrianV (Jan 14, 2013)

Metabones - Metabones and Caldwell Photographic Introduce Speed Booster

It looks like Metabones has revisited the use of optics to create an "inverse teleconvertor". This adapter shortens focal length, and gives an increase in F-Stop. I am sure there are some limits, but looks interesting.


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## amolitor (Jan 14, 2013)

Just get a teleconverter and mount it backwards. Same thing!


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## BrianV (Jan 14, 2013)

You made me try that with the Nikon TC-14a. sad to say.... did not work....

One time I used a negative optic to turn a Canon 50/0.95 RF lens into a 35/1.2 with a back-focus to work on a Nikon F.


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## Derrel (Jan 14, 2013)

BrianV said:


> Metabones - Metabones and Caldwell Photographic Introduce Speed Booster
> 
> It looks like Metabones has revisited the use of optics to create an "inverse teleconvertor". This adapter shortens focal length, and gives an increase in F-Stop. I am sure there are some limits, but looks interesting.



WOW--this is simply amazing...huh...makes me want a Sony NEX camera!!!!


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## rexbobcat (Jan 14, 2013)

That's pretty incredible. How does it brighten a lens though...


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## amolitor (Jan 14, 2013)

It brightens the lens by making the focal length shorter. Same size hole, shorter focal length, whattya get?

It ain't no magic, it's just the opposite of a teleconverter.

Nobody every bothered with it in the past, because you needed a world in which long lenses with lots of coverage were somehow a thing you wanted to make in to short lenses _that covered a smaller film area_, at great expense. This world did not exist until Sony's NEX system got all the hipsters excited about converting every damnfool lens to mount on the thing.

People DID want to make long lenses with some coverage into longer lenses that would cover as much or more film area, and they were willing to pay for that. These devices are teleconverters.


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## rexbobcat (Jan 14, 2013)

amolitor said:
			
		

> It brightens the lens by making the focal length shorter. Same size hole, shorter focal length, whattya get?
> 
> It ain't no magic, it's just the opposite of a teleconverter.
> 
> ...



I still dot understand how it manipulates the physics like that. If it's the same size hole I would assume that the same amount of photons are hitting the sensor regardless of focal length.

Same size hole equals...same aperture value?


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## BrianV (Jan 15, 2013)

It takes the image circle that would normally cover a full-frame camera (24x36) and projects it onto a smaller sensor. So, "same number of photons" focused into a smaller image circle.


The Nikon E-series camera of the 1990's did something similar to use a 2/3" CCD in a full-frame camera. It works, will be interesting to see any degradation to the image. 

http://en.wikipedia.org/wiki/Nikon_E_series

I have a Nikon E3. This idea was discussed several years ago on the mu43 forum.


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## amolitor (Jan 15, 2013)

Yup, what Brian said. This is basically why it was a worthless idea until now. Lenses simply didn't have extra coverage, extra light, to be squished onto a smaller area, before the crop sensor showed up.


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## Helen B (Jan 15, 2013)

rexbobcat said:


> amolitor said:
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No, no laws of physics are harmed: the f-number is determined from the focal length and the diameter of the'hole' (actually the entrance pupil).

N = focal length / diameter of entrance pupil*

A normal behind-the-lens teleconverter keeps the entrance pupil and increases the focal length, therefore the f-number rises. These 'inverse teleconverters' shorten the focal length and thus decrease the f-number. Simple really. Getting the optics right isn't always so simple. Angenieux made some a few years ago, and they cost five figures. I'm sure these will be cheaper. More power to Brian Caldwell.

Same number of photons during unit time, but smaller image magnification, therefore brighter image. It's exactly that way with all lenses, and why we use f-numbers for exposure calls instead of aperture diameter (or area).

*This is only an approximation, but it is a useful one and it is accepted by the ISO for general photographic purposes. (The word 'physics' has been used, hence the digression beyond photography.) The accurate physics answer is that the converter magnifies the exit pupil. It is the exit pupil angle that really determines f-number, but the commonly used f-number equation is close enough.


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## amolitor (Jan 15, 2013)

What was Angenieux building these things for? Offhand it seems like an expensive device for converting an expensive harder to build lens (longer) into a cheaper and easier to build lens (shorter), and then there are the coverage issues. I don't think it made any sense for 35mm film lenses, since you'd pretty invariably wind up with a wide/bright lens with falloff at the edges. Well, mostly.

Was the Angenieux product for large format work? There you DO have a variety of film formats and coverages, so it might make sense? You could convert some well beloved 480mm thing suitable for 8x10 to give you the same result on a 4x5 or whatever.


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## Dao (Jan 15, 2013)

rexbobcat said:


> amolitor said:
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When a regular consumer kit zoom lens change the focal length from 18mm to 55mm, the f number changed.  It is simply because the physical opening size did not change with the focal length.  Now, this device simply change the other way like you zoom from 55mm back to 18mm while the physical opening size remain the same.


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## BrianV (Jan 15, 2013)

Angenieux also made lenses for movie cameras, which are smaller format. Video cameras also have very short back-focus.

I have a Polaroid Speed-Magny back for the Nikon F. Use lenses made for 35mm and fill a Polaroid 3x4 picture. It has an El-Nikkor 50mm enlarger lens built into it. This new device is basically a reducer lens.


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## jake337 (Jan 15, 2013)

I wonder if they'll make one for Nikons F mount.  It would be great for hobbyist trying to work a DX camera indoors with tight surroundings.

Was the E series body a regular F mount design as far as converter-to-body?  Or was the converter a non removeable piece of the camera body?


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## KmH (Jan 15, 2013)

rexbobcat said:


> Same size hole equals...same aperture value?



F-stop is a *ratio* of the focal length relative to the lens aperture.

Consider an 18-55 mm f/3.5-5.6 kit lens.

At 18 mm and f/3.5 the diameter of the lens aperture is - 18/3.5 = 5.14 mm wide
At 55 mm and f/5.6 the diameter of the lens aperture is - 55/5.6 = 9.82 mm wide.
With the lens set to f/3.5 at 18 mm, the f-stop is not changed, and the lens is zoomed from 18 mm to 55 mm, the lens aperture actually gets larger.
Note that at 18 mm and an f-stop setting of f/5.6, the aperture diameter is 18/5.6 = 3.21 mm


While f/5.6 is often thought of as a smaller lens aperture than f/3.5 is, the math shows that the lens focal length also has to be considered.


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## Helen B (Jan 15, 2013)

KmH said:


> rexbobcat said:
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> > Same size hole equals...same aperture value?
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This can be confusing, possibly because of the lack of distinction between the physical lens opening and the entrance pupil. The f-number (which is a defined term) is calculated from the diameter of the entrance pupil, not the diameter of the physical opening. The entrance pupil is the image of the physical opening as seen from the front of the lens. Because it is an image, its magnification can change as the front lens elements move during zooming, thus *the size of the entrance pupil can change even though the physical aperture remains the same*. This effect happens with both variable aperture and constant aperture zooms. It may be combined with some change in the physical aperture.

The Angenieux adapters were for video/film zoom lenses - ie things that cost tens of thousands of dollars. Even though I had a few Angenieux zooms I decided they weren't for me, and I don't think they were widely used.

The Metabones website does mention other lens mounts and other camera mounts. The m4/3 version has different optics from the E-mount version. Brian Caldwell has optimized the optics for the different formats.


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## BrianV (Jan 15, 2013)

jake337 said:


> I wonder if they'll make one for Nikons F mount. It would be great for hobbyist trying to work a DX camera indoors with tight surroundings.
> 
> Was the E series body a regular F mount design as far as converter-to-body? Or was the converter a non removeable piece of the camera body?



The "Reduction Optics" were integral to the body, behind the mirror. This was a regular F-Mount camera, basically a Nikon F4 in a new housing.


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## Helen B (Jan 15, 2013)

The Nikon E appears to have used a relay lens system - ie it relayed the normal image to a new image plane well behind the old one. The optics lay at and behind the original image plane, as far as I can tell / understand the principle. This is optically quite different from the Metabones reducer which sits right behind the main lens, in front of the original image plane.


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## BrianV (Jan 15, 2013)

The Nikon E series used both relay and reduction. The full-frame image circle was reduced to a 2/3" CCD. The increase in intensity was expressed as ISO, which was set at "800" for a base for the light meter. The actual sensitivity of the CCD was closer to ISO 50. The relay lens was at the image plane. As stated, "it did something similar" in that in reduced the image circle of the full-frame lens to a detector that was much smaller, and had a big increase in effective ISO as a result.


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## dxqcanada (Jan 23, 2013)

Speed Booster double test! | sonyalpharumors

http://www.metabones.com/images/metabones/Speed%20Booster%20White%20Paper.pdf


http://www.metabones.com/buy-speed-booster


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