Lenses and Optics

Metabones Magic?

Published January 22, 2013

A few days ago I learned about the Metabones Speed Booster. For both of you who haven’t heard yet, this is an adapter containing optical elements and electronic controls that allows you to mount Canon EF lenses to Sony NEX cameras (other versions are planned for other lenses and cameras). The quick summary is the adapter is the opposite of a teleconverter.

A teleconverter spreads out the light leaving the lens so that only the center portion reaches the sensor. The result is the focal length of the lens seems longer (the image is magnified), but at the cost of reducing the amount of light (effective aperture) of the lens. The Speed Booster compresses the light leaving the lens onto a smaller image circle. This makes the focal length seem shorter and actually increases the amount of light reaching the sensor.


The Metabones’ Speed Booster compresses the light leaving the lens into a smaller image circle. Image credit Metabones http://www.metabones.com/images/metabones/Speed%20Booster%20White%20Paper.pdf


The EF to NEX Speed Booster, for example, changes the effective focal length x 0.71, and increases the maximum aperture by 1 stop. A Canon 50mm f/1.2 lens effectively becomes a 35.5mm f/0.9 NEX lens, for example. Videographers all over the internet were singing Hosannah and laying palm leaves along the path of it’s introduction.

I went into my office, shut the door, and sobbed quietly for a while. Why, you ask? I’ll tell you why. About once a day, we get an email saying somthing like, “I just rented a Canon 5D Mk III and shot video of my daughter’s high-school graduation. My footage doesn’t look anything like Vincent LaForet’s. Obviously the camera was defective and I want my money back.”

This adapter was, I thought, going to result in another 50 emails saying, “I just shot video using a generic 50mm f/2.0 lens I bought on eBay with the Speed Booster adapter and Sony NEX VG20 I rented from you. The footage doesn’t look anything like the footage shot with a Zeiss 35mm T1.5 Super Speed shot on a RED Epic. Obviously the equipment is defective and I want my money back.” I know, like I know the sun is going to rise in the east tomorrow, that you don’t put some more glass between a camera and a lens and get a better image.

But marketing hype will be marketing hype and people who want to believe in magic will believe it – and be disappointed when the magic doesn’t happen.

But Then, There Came a Ray of Hope

Then I flipped over to Metabones’ white paper on the Speed Booster and spit coffee. The primary designer of the adapter is Brian Caldwell. If anyone could make optics do magic, he could. He designed, for example, the Coastal Optics UV-VIS-IR Macro lens, an amazing thing that is the gold standard for forensic macro photography. So I read the white paper carefully and it made perfect sense. The White Paper explained how:

  1. The Speed Booster introduces zero (none, nada) spherical aberration, even with an f/0.9 output. That’s amazing. The very complete graphics in the White Paper do show it adds a bit of astigmatism and distortion, though.
  2. Where teleconverters magnify lens aberration, a focal reducer would reduce aberations basically because it would shrink them.
  3. The adapter is physically smaller than a standard, non-optical EF to NEX adapter.
  4. Corner illumination is improved.


After reading the white paper, I became convinced that these things were true. And these are all good things.

There was an additional claim made in the white paper, that MTF (modulation transfer function –  acutance and resolution) was also improved. This one I struggled with. To be blunt, I found this section to be, shall we say, selective, in the comparisons made. I was left with the feeling that it might be using some very specific examples to suggest a general conclusion. The section was a bit more carefully worded than other parts of the white paper, and some information in the graphs, that didn’t quite agree with the claim, was downplayed in the text of the section.

I was willing, however, to be convinced that an FX lens mounted to the Speed Booster would have better corner resolution mounted to a Micro 4/3 than the same lens mounted to a full-frame camera – after all, those Micro 4/3 corners are a lot closer to the center of the image. And that it may, or may not, have better corner resolution mounted to an NEX camera compared to a full-frame camera.

So after my research, my impression was this will be, at least a very useful tool. It may be nearly as good as people hope it will be. In other words, it will, like all other imaging gear ever made, follow Roger’s Law of New Product Introduction (pathway A).

Let’s Do Some Testing Boys and Girls!

OK, first and foremost, this is not going to be a bunch of video samples. That’s not what I do. I’m a testing geek that writes words and makes graphs. But for those who have bravely come this far without a picture to ease the heavy burden of reading, let’s have a look at the Metabones Speed Booster.

Mounted to an NEX-7 (don’t mind the dust, it’s a testing camera)


Note the front glass nicely reflecting the right hand of your humble author.


It’s a nice looking bit of kit – solidly made and well put together. There’s a solid mount for tripods or shoulder mounts underneath. It mounts with a most satisfying thunk and clamps tightly to camera and lens. The optics are close to the surface, though, and some care in handling will be necessary to make sure they don’t scratch.

Let’s Shoot a Few Test Charts

There are a lot of ways to compare lenses with the Speed Booster and not a lot of time, so I tried to choose things that seemed practical. Or cool. Or both.

Starting with cool, I mounted a Canon 14mm f/2.8 II lens, which with the adapter should give us the equivalent of a 10mm f/2.0 NEX lens. That sounds cool to me. Plus I thought we should look at things as extreme as people are likely to get.

We’ll start by comparing simple shots of an ISO1223 chart shot with the lens on a plain adapter and on the Speed Booster. To even things up I moved my position so that the chart filled the image each time, so that we could compare resolution directly. First an overall picture of the chart, followed by center and near corner crops with each adapter.

Canon 14mm f/2.8



Center and near-corner crops from 14mm f/2.8 image


Center and near-corner crops from 9.8mm f/2.0 image


Again, the images were from different distances so that the chart filled the image with both shots. It’s not an optically critical test, but I’d call it a complete success for the Speed Booster. Even spotting the original image 1 stop of light, there’s no significant difference in resolution to my eye.

The change in perspective is impressive. These are shot from the same location with the Canon 14mm f/2.8 mounted to a straightforward adapter first and the Speed Booster second.


14mm f/2.8 on NEX-7


14mm f/2.8 on NEX-7 via Speed Booster

Canon 50mm f/1.2

That was pretty impressive, now lets stress things a little bit more. The Canon 50mm f/1.2 lens brings a few aberrations to the table and with the adapter will be an f/0.9 equivalent. I can’t think of anything that would stress an adapter more than f/0.9. Again, I’ll reposition myself so both shots fill the frame with the chart. We’ll compare the 50mm f/1.2 on top to the Speedboosted 35.5mm f/0.9 below.


Canon 50mm f/1.2 on NEX-7


Canon 50mm f/1.2 on Speed Booster and NEX-7 (35.5mm f/0.9 equivalent)


Again, these are not critical tests, but are carefully lined up, best focus of several shots. And again, the Speed Booster comes out very well.  It may be the illumination boost but the acutance in the center, at least seems a little better with the Speed Booster. I would draw your attention, though, to the difference between vertical and horizontal lines in the corner crop of the Speed Booster image. That’s not an artifact of the shot or alignment. With this lens and camera, at least, the astigmatism seems to be showing up a bit. I also note that the image looks oversharpened, but it’s an unsharpened JPEG and this appearance was consistent on multiple shots.

 Canon 135 f/2.0

I wanted to try the other extreme, and made the assumption that this would be about the longest focal length people would want to use the Speed Booster with. I may be wrong about that, but was running out of time today.


Canon 135 f2 on NEX 7


with Speed Booster (94.5 f/1.4 equivalent) on NEX-7


Again, if there’s any deterioration in image quality with the Speed Booster, even though it’s a stop of aperture wider, I’m having difficulty seeing it. I also don’t notice the astigmatism with this combination.

But let’s test the resolution a bit more critically.

Imatest results

We don’t have multiple copies of the Speed Booster yet, so this is what we did. We took a Canon 50mm f/1.2 lens and tested it on a Canon 5D Mk II camera. Then we tested that same copy on an NEX-7 using a standard adapter. Finally, we tested those same copies (camera and lens) with our Speed Booster.

Usually when talking about Imatest results I’m sampling dozens of copies and give you the average (mean) resolution in the center and a weighted average of all the test points on the lens. But usually we NEVER test lenses on adapters if we can avoid it. Why? Because even the very best adapter still introduces and extra variation in tilt and centering between the lens and the camera.

Let me word this more carefully because it’s important. When the imaging sensor is placed in the camera, it is carefully lined up to be completely parallel to, and centered with, the lens mount of the front of the camera. A tilt of 20 microns may be visible on a very wide angle lens. A tilt of 40 microns almost certainly will be visible. From repair manuals we know that the sensor can be made parallel  to the lens mount within a few microns so that’s taken care of.

But when the big, heavy lens mount rotates into the big, heavy camera mount, chances are it’s not accurate within a few microns. Let’s assume it’s getting close to the 20 micron limit, because we know with high-quality, wide angle lenses we can often see some side-to-side variation. Sometimes obvious with some pixel peeping, sometimes not at all, but frequently enough that I’ve assumed we’re getting close to tolerance.

This is one of those sources of lens-camera variation I talk about so often. Lens 12345 looks great on camera 54321 but not so great on camera 112233. It may tilt a bit more on that second camera mount.

When we add an adapter we’re adding another heavy duty mount and making it more likely there’s a bit of tilt. It’s rarely apparent (with a high quality adapter) at standard or telephoto ranges, but often can be detected with high resolution wide-angle lenses. It may cause no harm at all. It may create too much tilt. I mention all of this because it’s going to explain some of our test results.

Canon 50mm f/1.2 on a Canon 5D Mk II

On a Canon 5D Mk II and our lens shot at f/1.4, the MTF50 was 590 line pairs / image height in the center; 460 lp / ih averaged over the entire lens, and 265 lp / ih in its worst corner with a barrel distortion of 1.2%.

Canon 50mm f/1.2 on a Sony NEX-7

On the NEX-7 with a standard adapter shot at f/1.4, it resolved 625 lp / ih in the center, 485 averaged over the entire lens, and 210 in its worst corner with a barrel distortion of 0.825% (smaller sensor). The difference in the center and overall isn’t surprising – the NEX has a higher pixel density and is using the ‘sweet spot’ from the center of the lens. The fact that the lowest corner is worse is a bit surprising until you see the overall graph of results:


Graph of MTF50 results on NEX camera with standard adapter


Notice the upper left corner is worse and the upper right better, and that the right side of the image resolves better than the left. The lens, which behaved very nicely on a Canon camera, is tilted when shot on this particular NEX-7 with this particular adapter. So, of course, we went and got another adapter. It tilted the other way. And we were out of time. From experience I can say the center resolution number is going to be accurate, the actual weighted average should be a few points higher and the worst corner about 275 or so rather than 210 (275 is the resolution on the less affected corner).

So it is with adapters. And before you scream that the adapter was bad, it wasn’t. The guys put those adapters on other cameras and lenses later and they were either dead even or tilted another way. It is what it is. Also remember we’re churning MTF 50 numbers. You need a big difference to be able to actually see the difference in a photograph, and an even bigger difference for it to affect video.

Canon 50mm f/1.2 on NEX-7 with Speed Booster

On the NEX-7 with Speed Booster adapter and shot at f/0.9, it resolved 720 lp / ih in the center, 410 averaged over the entire lens and 230 in the worst corner. Stopped down to f/1.3 the MTF 50 increased to 800 center, 510 weighted average, and 300 for the worst corner. As advertised, the MTF 50 increased compared to the same lens on no adapter.

However, barrel distortion increased to 1.9%. Remember, however, this is in effect now a 35mm lens, so that number isn’t as big a jump as you would think at first glance. Just to note, there was no sign of tilt with this adapter on this camera.

One thing to note – there was definitely a bit of astigmatism, with horizontal and vertical resolution quite different along the edges of the lens. One other interesting note – we measured primarily MTF 50 as this is the number we work with most frequently. We also checked the MTF 20 numbers and for these combinations the Speed Booster had a similar effect: slightly improved but with greater astigmatism.

A reminder for everyone again – we had one copy of the adapter to play with and limited time. But I’ll have to admit that it seems the folks at Metabones pulled off what they claimed: with the adapter a lens is wider, faster, and even a bit sharper.

A Few Images

There’s not a lot of photogenic material around the Lensrentals Lab, but how often do I get to shoot with a 35mm f/0.9 lens? I’ve included some 100% crop areas in the corners of the scaled down shots.




Now, to get completely subjective, there’s something about the images as far as photography that I don’t like, but it’s hard for me to put a finger on it. But if you look at the crops there’s a bit of a glow around highlight areas, both in-focus (in Sarah’s shirt) and out of focus (the rubber bands).

My first thought was perhaps shooting on an NEX -7 could be the issue, since we know that camera has had some problems with adapted retrofocus lenses. Shooting with a Canon 50mm f/1.2 may also be the culprit – that lens is, well, different. But we repeated the rubber band shot with an NEX-6 and then with both cameras and a Canon 85 f/1.2 and the Speed Booster. To my eye (and remember I’m a techie, so I don’t do subjective all that well), there’s a real tendency for highlights, in and out of focus, to bloom a bit at the widest apertures. It seems to go away by f/2.0 affective aperture.



I’d also add, for those who plan on using it, that the autofocus worked well as far as accuracy. Eventually. You won’t be catching any moving targets unless they are turtles, though. I doubt this is of great import to many people, though.



I think it was pretty obvious that I came armed for battle, ready to slam this product as some marketing overhype. I was wrong less correct than I might have been. The Speed Booster does what they claimed it would do, much to my shock and surprise. It creates a wider-angle, greater aperture lens while retaining resolution and acutance.

It does increase astigmatism a bit, although I doubt this will cause anyone problems unless someone is trying to shoot landscape photography with it. It also seems to create some highlight blooming at very wide apertures. Again, nothing that can’t be worked around and probably not something that will be noticeable with anything but the widest aperture lenses.

It is going to take a while and a lot of people experimenting before we find out what combinations of lenses and cameras are awesome with it, which are fairly good, and which fairly bad. They won’t all be the same. But I suspect most of them are going to be pretty good. And this is going to be a very useful tool. 

Most of the little foibles I’ve seen (including the part about adapter tilt) really only apply to photographers trying to tweek every drop of resolution out of their high-resolution sensor. Video, even 5k video, is more forgiving of a slightly weak corner or a bit of astigmatism.



Roger Cicala


January, 2013

Author: Roger Cicala

I’m Roger and I am the founder of Lensrentals.com. Hailed as one of the optic nerds here, I enjoy shooting collimated light through 30X microscope objectives in my spare time. When I do take real pictures I like using something different: a Medium format, or Pentax K1, or a Sony RX1R.

Posted in Lenses and Optics
  • I have a speed booster dumb question. (Please correct me if i am wrong)

    “Why i cannot have a ef-to-ef speed booster in my canon sl2?”

    Let me break this. all this speed buster talk include 2 aspects

    – mechanical: to adapt X lens to Y camera (as in your example. canon ef lens to sony camera. Or ef to ef-m as we see lot m-50 youtube videos)

    – optical: to get a full frame light cone and compress to smaller than full frame sensor (aps-c, anyone. Pick yours)

    But i cannot find (or understand why not) a speed booster without lens adapter.

    More specific, in a real life scenario, a ef-to-ef speed booster to use in canon dslr with aps-c sensor (sl2).

    In my naive pov, this can reduce my “full frame lens” to “smaller sensor” crop and i can be a happy monkey.

    A blue bird told me we have space limitation to accommodate speedbooster optics …

    … but i love to see your “text and graphics” myth buster explanation

    Peace : )

  • ney frota

    I have a speed booster dumb question. (Please correct me if i am wrong)

    “Why i cannot have a ef-to-ef speed booster in my canon sl2?”

    Let me break this. all this speed buster talk include 2 aspects

    – mechanical: to adapt X lens to Y camera (as in your example. canon ef lens to sony camera. Or ef to ef-m as we see lot m-50 youtube videos)

    – optical: to get a full frame light cone and compress to smaller then full frame sensor (asp-c, anyone. Pick yours)

    But i cannot find (or understand why not) a speed booster without lens adapter.

    More specific, in a real life scenario, a ef-to-ef speed booster to use in canon dslr with asp-c sensor (sl2).

    In my naive pov, this can reduce my “full frame lens” to “asp-c sensor” crop and i can be a happy monkey.

    A blue bird told me we have space limitation to accommodate speedbooster optics …

    but i love to see your “text and graphics” myth buster explanation

    Peace : )

  • Thank you for this review, but it is now five years old.

    Have you had a chance to try the newer Ultra version?

  • Actual high res still photo samples of real world scenes would be more useful than a flat test chart IMO. I wonder whether field curvature of an extreme UWA lens combined with “tilt” as measured here, and combined with narrower DOF at the better apertures might necessitate the use of a smaller aperture; and both would noticeably degrade IQ. This, in addition to a likely increase in barrel distortion and CA at the edges.

  • Nick Seth-Smith

    Hi Roger

    Thanks for the detailed review – most enlightening and helpful. I appreciate your objectivity and detail on the adapter’s performance.

    I do have one question. You (and everyone else) comment that the autofocus is slow and “You won’t be catching any moving targets …”. Can you put some numbers to that please? (Approximate time to focus on a subject from Infinity or min focus distance – comparison to Canon EOS 5D MK II for instance). I realize that performance will vary widely with image composition, lighting conditions, current position of the lens etc.; however some ballpark numbers would help (e.g. 2x slower, 10x slower, 3 weeks on a good day …)

    Many thanks


  • Roger, do you have any clue why this technology first appear to the Nex and not to the Canon Crop cameras that I think are more widespread? I know that EF-s have a smaller circle but I have 3 Crop bodies with 2 EF lenses. Would love to convert them to wider field of view! Regards

  • Flavio Egoavil

    The Metabones’ Speed Booster is what is usually called a “focal reducer”, something that has existed for decades. As correctly mentioned, the Zeiss f0.7 lens used on Barry Lyndon was basically a normal, smaller-aperture planar design with a focal reducer behind.

    Now, what we are we doing is basically optical ‘impedance matching’: Reduce the circle of coverage of the lens to better match the sensor size. In this page, a Canon 50/1.2 is compared used directly on the NEX sensor versus using it through the Speed Booster. I’m afraid this is not a meaningful test. It is already known that to use just a small section of the lens’ coverage circle (i.e. putting a FX lens on a DX camera) would bring suboptimal resolving power (than using a lens tailored for the DX image circle but with the same angle-of-view). This happens for the very same reason than large format (4×5″) cameras give overall greater definition — the smaller the sensor size, the more absolute lines-per-mm demanded from the lens.

    So, a more fair test would be to compare said Canon EF 50/1.2 on a full frame camera whose sensor is of equal resolving power as the NEX’s sensor, and to compare the 50/1.2 lens on the full frame camera versus the 50/1.2 lens on the NEX using the Speed Booster. On both, we’re using the full image circle produced by the lens. But in the second case, this image circle has went through a further process: the Speed Booster. Thus, there will be some image degradation — unless the device is made of unobtainium glass.

    Samuel H is totally right. FX lens on FX sensor will win anytime over a smaller sensor + speed booster, assuming both sensors are of similar technology and resolution.

  • I got the speedbooster so that my 24mm could be a real wide angle, but then my question was: if I have to take a portrait, should I go for the 90mm f/2.8 on the speedbooster, or for the 50mm f/1.4 on a standard adapter?

    So I put the speedbooster against my one dollar resolution chart:

    My conclusion: the SpeedBooster delivers a small sharpness increase. Plus, the DoF and brightness advantages make it a winner. But it’s not as big an improvement as actually going Full Frame.

    My 90mm Elmarit with the SpeedBooster is slightly sharper than both the 50mm or the 90mm on APS-C without SpeedBooster. But it is not as sharp as the 90mm on an actual Full Frame. If all I have is the NEX-5N and I have to take a portrait, 90mm+SB is slightly better (sharper in the center, about the same in the corners) than 50mm with the standard adapter. But 90mm on FullFrame would be a lot better.

    But the DoF and brightness advantages make the SB even better. I can take that portrait with the following settings:
    * APS-C with standard adapter, 50mm lens set at f/2
    * APS-C with SpeedBooster, 90mm lens set at f/2.8
    With the same ISO and shutter speed, I’ll get the same FoV, DoF and exposure in both cases. Now, looking at the tests, it’s easy to see which option has the lead: because I can close the lens a bit, the one with the SpeedBooster is sharper both in the center and in the corners! Not as good as actually going Full Frame, but an improvement for sure, with no downsides whatsoever (because I’ve also checked that bokeh is basically not affected: http://www.similaar.com/foto/lenstests/bokehtests.html)

  • Timmi

    Also, you said that there is no CA… and there is a _significant_ amount that can be seen in that same 50mm+SB shot.

  • Timmi

    The poor results with the 50mm 1.2 are being downplayed a bit too much, imho. the vertical lines in the bottom right are downright blurred.

  • Voodoo Fox

    soounds like this magic ring can also make a m3/4 camera into an equivalent full frame camera if Metabones offers a booster for m3/4 body. grear work indeed. thanks to Metabones.

  • Aaron

    Just saw DPReview’s review of this, but I’m interested in the fact that at exceptionally wide apertures (f/1.0 equivalent) they are actually seeing some loss of light, and point to a DxO article (http://www.dxomark.com/index.php/Publications/DxOMark-Insights/F-stop-blues) which basically says that as you get to the extreme wide apertures, more and more of the light is coming in from the sides at oblique angles, and so many sensors, especially with smaller photosites, are unable to take advantage of that more light and actually capture less light. I could see that, but given the article is from 2010, with more modern sensors with micro-lenses and such, is that as big a factor? I know I’m occasionally obsessed with finding the widest lens I can, even if I rarely would shoot with it completely wide open.

  • @Lisandra

    OM-D is a lot newer tech than a 5D2!

    A D600 would be a better point of comparison in terms of same-age tech

    Which basically misses the point, because, even if it was 2 stops cleaner (it’a actually around 1.5 stops, see link below), it’s still a lot bigger and more expensive. If you can get the same IQ (or nearly the same) on a much smaller and cheaper body-lens combo…


  • Lisandra

    Chris, theres no way, in holy hell, that my 5D mk2 is 2 stops better than my OMD in noise performance. Id say less than a stop even. Three years ago my answer would have been different but now? Yes you can break the laws of physics with good ol fashion engineering. Im not even gonna bother upgrading to the mk3.
    Anywho, no flame wars here, this adapter is right up my alley, im curious about the m4/3s version

  • Lisandra

    So, I cant stop thinking, a .50 reducer that covers the 4/3s sensor is very very possible based on the diagrams, what do you think?. With a 2 stop light gathering boost too
    oops, I drooled a bit on the keyboard…

  • I looked at both center and corner sharpness, they’re all in the link.
    In any case, I know what’s true for my lenses, and obviously don’t know if that can be applied to all other lenses, so, let’s leave it there. Have a nice day!

  • No, those numbers are not relative. The Tamron got a maximum sharpness of around 1 to 1.5 blur units. That’s not a “perfect score”. And the TDP-link you provide clearly shows that it’s far from “ultra-soft”. The lensrentals blog shows that the VC-version is softer than the old non-VC version, which is exactly what the slrgear.com-results will show you.

    In your comparison, you focus at the corners separately to test the sharpness.

  • That’s weird. My bet is that those numbers are relative to the best spot for each lens. Every lens you posted gets a “perfect” spot at one aperture or another. Even the ultra-soft Tamron 17-50 f/2.8 VC gets a perfect center score (and wide open, no less):
    That is not what you’ll find in real life:

    If those numbers are relative, it means that all you know about those lenses you mentioned is that the difference between the center and the corners is bigger in full frame. But the center is probably a lot sharper on full frame.

    Did you check my link?

  • @Samuel H

    No, they were right. Just check this example of the recent Canon 24-70 L II. On the 5D MkIII, there is less sharpness, more distortion, and more vignetting than on the 7D.

    It’s the same for the 70-200 L II:

    And the 14/2.8 II Roger used:

    And it’s not just Canon. Check The Nikon 70-200 F/4, another recent high-quality lens:

    Or a 50mm prime from Nikon:

    I could go on and on, but I think I’ve made my point. Metabones’ claims about the Speed Booster are debatable _at best_.

    The only thing that might improve is CA, which seems to vary from lens to lens. On some it improves because you ‘shrink’ the effect, but on others it gets worse because lenses exhibit CA mostly at the edge of their image circle.

    And distortion shouldn’t be underestimated here. Most RAW-converters handle distortion quite well with their built-in lens profiles, but these profiles don’t work with the Speed Booster attached.

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