@apefos : I hope you don't mind me abusing your expertise on the subject, but is there any technical reason why they couldn't make an adaptable front mount? I've got a lot of Konica Hexanons, a few OM's and 3 very long Adaptall telephotos that I'd like to use, but it's unimaginable to get 3 Boosters.

Or can the Hexanons & Adaptalls be converted to OM/FD with proxies?

Thank You Vitaliy. I just got an email from Metabones, they said m4/3 version will be available around June.

@stonebat The Speed Booter EF-M43 will be shorter than a normal EF-M43 adapter. It is covered in the white paper linked on the first page.

@fredfred27 Thanks. I'm too lazy to read the doc :) I guess that's why they can't support Leica R mount.

@kholi

I can't see any point in a passive EF mount, at all. Passive Nikon F (which is already planned), yes.

It would be nice to see if there are any options for PL mount, but I know the design is tricky with PL, regardless of mirrorbox or not.

@itimjim

Most PL lenses wont cover full frame and hence will likely vignette quite heavily on aps-c. the cp2's will be ok i guess. but with m43 a pl mount would be amazing. master primes on the gh2 anyone?

I wonder how long before the Chinese start making copies of speed-booster and selling it on eBay for $30 :)

I really hope they do an mft to Canon FD. This + Tokina 11-16 + BMCC = wide and fast solved.

The Tokina trio: 11-16 2.8, 16-50 2.8, 50-135 2.8 turns roughly into: 8-11 2.0, 11-35 2.0, 35-100 2.0. Can't think of a better set :)

Holy crap, most people here seem pretty confused about this whole thing. Flange focal distance (FFD) refers to the distance between the sensor and the lens' mount. The FFD CANNOT EVER BE CHANGED if the lens is going to focus properly. A lens with a LONGER FFD can be adapted to any mount that is a SHORTER FFD, but not the other way around.

For example, a Canon FD lens has a FFD of 42mm. Canon EF cameras, however, have a FFD of 44mm. This means that the front bayonet of the EF camera is 44mm in front of the sensor. An FD lens, however, MUST be 42mm from the sensor. Therefore, you cannot put an FD lens on an EF camera, because the lens cannot be mounted close enough to the sensor. The EF mount sticks out in the way by 2mm.

Now, for this reason, cameras with a shorter FFD can accept any lens mount type with a longer FFD. It stands to reason, then, that you'd want a camera with as short a FFD as possible. To adapt lenses with a longer FFD, you simply bridge the gap with a correctly-lengthed "adaptor" (which in most cases is a fancy word for a tube with the two different bayonets on either side). This is why mirrorless are so adaptable. They have very short FFDs. (M4/3 is 19.25mm, and Sony's E mount is even shorter at 18mm.)

To adapt straight from the 18mm front of a NEX camera to the 44mm FFD back of an EF mount lens, you need a 26mm adapter to bridge the gap.

However, mirrorless cameras have smaller sensors, and therefore smaller fields of view compared to larger sensor cameras at equal focal lengths.

Metabones looked at that 26mm of empty air between the 18mm NEX camera and the 44mm EOS adapter, and figured they could put some optics in there that would correct for the difference in sensor size between EF cameras and APS-C cameras (NEX).

Now, why would we want a cold mount EF-M4/3 SpeedBooster? Well,

@Paddy mentioned: "From one of the developpers, on another forum: "Passive MFT will be added in March 2013 for Leica R, Alpa, Contax C/Y, Contarex, Rollei and Nikon (including DX and G). An active MFT for Canon EF is planned for the future.""

Canon EF is a shorter FFD than any of the other mentioned mounts, meaning that any lenses in these other mounts could easily be adapted to the EF SpeedBooster. Not so in reverse. A speed booster in these other mounts would not accept any EF lenses. The ideal is a SpeedBoost adapter where the camera side (rear of the adapter) has a LONG of a FFD as possible, and the lens side (front of the adapter) has as SHORT of an FFD as possible. Now obviously, there are limitations to this. MetaBones has put optics in there which take up space. The real question is, how much space do the optics take up? If MetaBones could shorten the front from the 44mm EF mount down to the Konica AR mount at 40.70mm, Minolta, FD (and of course Konica) lenses would be added to the list of adaptable lenses. Also, if MetaBones could change the camera end of the SpeedBooster to, say, the 25.5mm FFD Samsung NX mount, it would be mountable to both M4/3 AND NEX cameras quite easily with an adapter.

TL;DR . . . READ THIS http://en.wikipedia.org/wiki/Flange_focal_distance

Concerning the "light boost" that this sucker gives you, it isn't really making the lens any faster. The lens still transmits the same amount of light as it does on a FF camera. It is just that without any corrective optics between lens and sensor, on a crop sensor camera much of the light from a FF lens doesn't even hit the sensor. As far as I know there is no way this adaptor allows lenses to have a higher T-stop than they do natively on a FF camera. By using the "SpeedBooster" on a crop sensor camera, you are not boosting anything, but rather are gaining back the light that you otherwise would have lost by cropping in (remember: crop sensor) on the lens' image circle.

So, to answer your question, @DrDave "Would you really gain 3-4 stops using a a medium format lens? That seems pretty amazing. What would a Mamiya 110/2.8 turn into? A Mamiya F/0.8?"

Yes and no. F-stops would "increase" (i.e. be brought back up to medium format level), giving you as shallow a depth of field as you get when using this lens on a medium format camera. You would gain back 3-4 T-stops of light that you "lost" by using the lens on a crop sensor camera.

Someone correct me if I am wrong, but I don't think it is possible to actually increase a lens' light intake at the rear end.

@B3Guy Now we need to get someone that makes cheap adapters, Nikon - ALPA (8.7 mm) , Md Minolta - ALPA (5.92 mm) and Canon FD - Alpa (4.2 mm).

I as well don't use lenses with electronics, and I think for those that do it is really safest to use lenses native to their camera body mount.

I've had good luck with basic cold mount adapters from China off of EBay, but I think what @Vitaliy_Kiselev was getting at is that MetaBones could make the SpeedBooster in just one or two core models and ship it with front and rear adapters for various other lens/body mount combinations. SLR Magic has done this with their new 35mm, which I believe has a Leica M mount and ships with either a M4/3 or NEX adapter.

I do not know if EBay seller ciecio7 is still making new adapters, but he makes top quality adapters and might be persuaded to make some kits for the SpeedBooster. I have one of his FD-M4/3 adapters and it is amazing. He already has adapters for OCT-18 lenses, which is pretty niche, so special application adaptors seem to be right up his alley.

I do wonder, though, if the SpeedBooster cuts flare. I generally don't like too much flare, but I'd hate for it to cut flare on the occasion that I actually want some, especially from my anamorphic.