Metabones Speed Booster Ultra: Is the Light Gain Worth the Price
Every Micro Four Thirds shooter hits the same wall eventually. You've got a bag of Canon EF glass left over from a DSLR, the sensor is a quarter the area of full frame, and that 24mm wide angle you loved suddenly frames like a 48mm. The Metabones T Speed Booster Ultra exists to undo most of that damage.
It's a 0.71x focal reducer running five elements in four groups. It also costs about what a decent used lens costs, and that's the whole argument against it. So here's what more than a hundred user reviews actually say about the optics, the autofocus, the firmware situation, and the one flare complaint that keeps coming back.
What the Speed Booster Ultra Actually Does
Think of a focal reducer as a teleconverter running backwards. A teleconverter magnifies the middle of the image circle and throws the rest away. This squeezes the whole circle down onto a smaller sensor instead, so light that used to spill past the sensor edges now lands on it.
Two things follow from that. Your field of view widens by the reduction factor, and every f/stop gains roughly a stop of brightness. The aperture number drops because you're concentrating the same light into a smaller area, not because the glass suddenly transmits better.
Metabones builds the Ultra from aluminum alloy with brass mounting rings, which is the right way round. Brass wears slower than aluminum where a lens mount rubs against it, and the alloy keeps the weight sane. There's an anti-reflection coating inside the barrel too, plus a detachable tripod foot with 1/4"-20 threads that drops straight onto an Arca-Swiss clamp.
The Sigma 18-35mm Math
The pairing people actually buy this for is the Sigma 18-35mm f/1.8 on a Micro Four Thirds body. Run the numbers and it's obvious why that combination took over.
Behind the 0.71x reducer, the lens becomes a 12.8-24.9mm at roughly f/1.3. Apply the 2x crop and your framing lands somewhere near a 26-50mm on full frame. Normal zoom range, genuinely fast aperture, no vignetting. One reviewer who went in expecting dark corners said it worked straight out of the box and handed them f/1.3 for low light.
The math runs the other direction too. A shooter using Canon glass on an Olympus body pointed out that a 100-400mm zoom ends up near a 200-800mm equivalent, which is a fraction of what buying that reach natively would cost.
Where the Ultra Part Comes In
Metabones has shipped a few generations of this thing, and Ultra is the one with the revised five-element design. It replaced the original Speed Booster, and it's the version most current comparison tests reach for. There's also an XL variant at 0.64x on some mounts, which pushes reduction harder but only fits certain sensor sizes.
Don't confuse any of these with a plain mount adapter. An adapter is a spacer with electrical contacts and it changes nothing optically. A speed booster puts real glass in the light path, and that glass brings its own character, good and bad. We break that difference down properly in our Viltrox, Metabones, and Kipon comparison.
Build Quality and the Bits You Touch
Reviewers are consistent about the machining. "Very well machined, tight fit, good optical properties" is a typical comment, and several people mention the mount seats with no play at all. The lens release is a push-button lock rather than a friction ring, which is the right call for anything living on a rig.
The included storage case comes up more often than you'd expect for a bit of packaging. It's compact and it's protective, and since this thing rides in a bag between shoots, that counts for something.
Not everybody is happy, though. One Panasonic GH5 owner reported the adapter clicked into place but still had slight movement, enough that a zoom lens shifted framing during video takes. They tried it on two bodies and got the same result both times. Plenty of owners running that exact combination say they've never seen it, so this reads like a tolerance issue rather than a design flaw.
The manual mount versions draw sharper criticism. A Minolta MD user found the inside of the adapter thick enough that rounded aperture levers jammed against it, and described the locking pin as soft enough to bend during ordinary lens swaps. Their verdict was blunt. Fantastic optics, frustrating mount.
Firmware Is Part of the Purchase
Here's the part nobody thinks about until it bites. The Speed Booster carries its own firmware and updates over the port on the side of the barrel. A reviewer shooting interiors found autofocus simply misbehaved in video modes until they ran the update, and it was fine afterwards.
Treat it like any other link in the imaging chain. Check the firmware before a paying job, not during one. Metabones does push fixes for specific lens and body pairings, so an adapter that acts up with one lens might just be out of date.
Image Quality: Sharp Center, One Real Flaw
The sharpness reports are strong, and better than that, they're specific. One owner put the Ultra up against two cheaper focal reducers he already owned, using the magnified focus assist on a GH5. The knockoffs held together at 4x magnification. The Metabones held together at 8x.
Another user adapting a full frame Olympus 50mm f/2 macro onto an OM-D body reckoned it beat the native Micro Four Thirds 60mm f/2.8 macro once dialed in. That's a high bar for an adapter that adds five elements to the path.
"Crystal clear" is the phrase that keeps surfacing for center sharpness. Corner performance draws far less comment here than it does on budget reducers, which tracks with the price gap between them.
The Blue Flare Complaint
Now the one genuine problem. A user shooting Canon glass on a GH5 reported a heavy blue flare in the middle of frame any time a light source hit the front of the lens. Not the usual streak or ghost you get from a bright source near the edge, but a central cast that made shots close to unusable.
That review carries more agreement votes than anything else on the product, which suggests it landed for other people too. Reviewers also point to the internal barrel coating as the fix Metabones intended, which implies the reflection path is a known weak spot in this class of adapter.
Shoot backlit interviews or anything with practicals in frame, and this is the first thing to test inside your return window. Most owners never bring it up, so it isn't universal. The failure mode is bad enough that you want to know early either way.
Autofocus and Aperture Control Depend on Your Body
Electronics are where this adapter turns unpredictable, and nearly all of it comes down to which camera you bolt it to. Panasonic owners have the easiest time of it by a wide margin. Across GH5, GH5S, and G85, reviewers report zero trouble with the EF electronics, body-side aperture control and lens metadata included.
Blackmagic is the rough edge. One Blackmagic Pocket Cinema Camera 4K owner couldn't get iris control working properly with Metabones speed boosters and Sigma Art glass, which left them stuck shooting wide open.
They took it to Blackmagic staff at a road show and got agreement that the two companies needed to sort it out between them. Adapter firmware was current. So was the lens.
Autofocus barely matters to most people running this rig anyway, since the classic pairing is a mostly-manual Art lens on a cinema body. If you do want it, it works, and it works better once you've run that firmware update.
Then there's the compatibility limit that catches people out constantly. The EF version takes full frame EF lenses only, not EF-S. Check the mount marking on your Canon glass, because a white square instead of a red dot means this adapter won't take it, and our roundup of Canon EF lenses for video covers what does.
Which Version You Need, and the Cheaper Options
Metabones sells the Ultra across a long list of mount combinations, and no, they're not interchangeable. Buy the wrong one and it simply won't mount. The version most of these reviews describe is the Canon EF to Micro Four Thirds model, MB_SPEF-M43-BT4, and it's available at B&H rather than on Amazon.
Otherwise, pick by mount. Most side-by-side tests you'll find online run the Canon EF to Sony E version. Beyond that there's a Canon EF to EF-M variant for the old EOS M bodies, a Nikon G to Sony E version, and a PL to Micro Four Thirds cine model with de-clicked aperture handling. Shooting Canon RF, you can compare the RF version on B&H.
Where Viltrox Makes Sense
Plenty of people buy this new and don't need it. That's the honest answer on price, and one reviewer put it bluntly, telling buyers to go check the used market first because a lot of owners eventually work out the adapter doesn't suit their workflow and resell it barely touched.
Cheaper route on Micro Four Thirds is the Viltrox EF-M2 II, which runs the same 0.71x reduction for a lot less money. Shooters who weighed up both kept landing on build quality as the tiebreaker, with the Viltrox described as less sturdy. Optically the gap is narrower than the price gap, though it isn't zero once you start looking at frame edges.
And if you only need the lens to physically mount, with the extra stop being no use to you, skip focal reducers altogether. A plain electronic adapter costs a small fraction of this and adds no glass to degrade.
Who Should Actually Buy It
Optics are what earn the Speed Booster Ultra its reputation. Reviewers who ran it head to head against cheap focal reducers saw a visible sharpness gap, build tolerances hold up under a rig, and the electronics behave themselves on Panasonic bodies. Put a Sigma 18-35mm on a Micro Four Thirds camera and this is still the reference option.
That last stretch of quality is what you're paying for, and whether the stretch earns its keep depends entirely on your work. Shallow depth of field hides a lot of adapter sin. Shoot mostly wide, mostly stopped down, mostly in controlled light, and the cheaper alternatives hold up better than the price difference suggests.
Independent tests back the general picture up. This hands-on with the Ultra covers autofocus behavior on Micro Four Thirds, Photigy's review walks through the crop factor math, and the manufacturer's own page lists which mount and body combinations are supported.
Frequently Asked Questions
Does the Speed Booster Ultra work with EF-S lenses?
No. The Canon EF versions take full frame EF glass only. An EF-S lens sits its rear element too far back and the mount won't accept it, so crop-sensor Canon lenses need a different solution entirely.
How much light does it actually add?
One stop, near enough. An f/1.8 lens behaves like an f/1.3, and an f/2.8 zoom behaves like an f/2. That's a real gain in a dark interior, and it's the single reason most people tolerate the price.
Do I need to calibrate it?
Sometimes, yes. Several reviewers found their lens wouldn't reach infinity focus until they used the adjustment, and one Olympus user had to turn it roughly two thirds of a full rotation to dial in a vintage macro. Read the instructions before you decide the unit is faulty.
Is the Viltrox good enough instead?
For a lot of work, honestly, yes. The Viltrox EF-M2 II delivers the same reduction ratio for much less, and users who ran both say center sharpness is close. The Metabones pulls ahead on mount rigidity and edge performance, which matters more for wide zooms than for a fast prime.
Will it work on an OM-1 or OM-5?
Yes. The Micro Four Thirds version mounts on current Olympus and OM System bodies, and it fits the original Blackmagic Pocket Cinema Camera as well. Compatibility answers on the Micro Four Thirds version confirm both.
Is the flare problem a dealbreaker?
Depends entirely on how you light. Reviewers shooting controlled interiors rarely mention it, and the ones who do describe a central blue cast whenever light hits the front element. Test it against your usual setup early, because a flag or a hood solves it in some situations and not in others.