Comparing Focal Adapters: The Metabones Speed Booster vs the RJ Photo Lens Turbo

Here it is, the head-to-head comparison I wish had existed when I needed to make a purchase decision. There’s been a lot of opinions about how one might perform compared to the other, but very few people have tested both side-by-side in a controlled setting.

I can’t tell you how many times I’ve read someone on a discussion group or a comments section state that the Metabones Speed Booster has “better optics” then the Lens Turbo. When asked to qualify that statement, they almost always admit that they haven’t actually compared the two. But the Speed Booster must be better, right? I mean Brian Caldwell designed the optics. It must have some mojo missing from the much cheaper Chinese alternative, right Joe? Maybe. Maybe not. Here’s a crazy thought, why don’t we actually compare images from both?

What is a focal reducer?

Exactly how a focal reducer does it’s magic seems to confuse a lot of people. Put simply, it’s a lens in front of your lens that focuses the full frame image circle onto the smaller M43 sensor.

Simplified comparison of the workings of a simple mechanical adapter vs. a focal reducer

Test Set-up

Camera: Panasonic DCM-GH4K
Lenses: Rokinon Cine 14mm, T3.1; Rokinon Cine 35mm, T1.5
Chart: Datacolor SpyderCheckr, SpyderCube
Lighting: RPS Studio CooLED 100 (key); Daylight (bounce)
Misc.: Expo Imaging Expodisc 2.0 White Balance Filter

Camera white balanced for each lens without either adapter in place so that any color shifts can be compared.

Rather than label reach adapter, I’m going to withhold that info so that you can objectively evaluate the images based purely on what you see. (Let me know which one you think is which in the comments. In a few days I’ll reveal the truth.)

35mm, T4, ISO 200

First up is my go-to lens, the Rokinon 35mm. It’s sharp, decently contrasty and renders color pretty accurately. (It’s starts to sharpen-up around T2.8, but let’s set it at T4 just to be safe.)

Click thumbnails for full 4K stills from in-camera video.

Adapter 1
Adapter 2
  • There’s a slight difference in hue between the two.
  • Adapter 1 offers a slightly wider field of view.
  • Adapter 1 has a bit more contrast.
  • Adapter 2 is a little brighter.
  • Bokeh is identical (as it would have to be. I mention it because people have suggested otherwise.)
  • Sharpness appears nearly identical, but let’s pixel-peep a close-up to be sure:
Adapter 1 detail @ 400%
Adapter 2 detail @ 400%

35mm, T1.5, ISO 200

There’s been considerable chatter that the adapters somehow perform differently depending on aperture settings. This has never made much sense to me, but I’m no optician. Let’s look again with the 35mm wide open:

Click thumbnails for full 4K stills from in-camera video.

Adapter 1
Adapter 2

Maybe someone with better eyes than me can see a difference in performance, but to my eyes each adapter performs the same (relative to itself) regardless of the lens setting.

14mm, T4, ISO 200

Since these adapter provide a wider FOV by projecting more of the lens’ image circle onto the camera sensor, differences in their edge-to-edge performance could be meaningful. let’s see how they stack-up using a very wide lens:

Click thumbnails for full 4K stills from in-camera video.

Adapter 1
Adapter 2

Adapter 1 appears every so slightly sharper, doesn’t it? This is a good time to mention that the focal distance differed between adapters. Adapter 1 required focusing a fraction of a meter farther away than Adapter 2. (For the record, the marked distance on the lens was not correct with either adapter.) The most likely take-away here is that I ever so slightly missed focus with adapter 2.

Adapter 1 detail @ 400%
Adapter 2 detail @ 400%

35mm, Expodisc

With everything going on in the above frames, it’s not easy to notice subtle differences. In order to remove some of the distraction, I shot a grey field by placing an Expodisc in front of the 35mm lens. Even subtle difference in color and brightness should be easy to pick-out.

Click thumbnails for full 4K stills from in-camera video.

Adapter 1
Adapter 2
  • Adapter 1 is warmer and darker.
  • Adapter 2 is cooler and brighter

Now let’s normalize (expand the data to use the entire 8 bits) the image in order to exaggerate the differences.

Adapter 1 normalized
Adapter 2 normalized

Adapter 2 is clearly brighter in the center, but note that it has more pronounced vignetting. How much brighter is Adapter 2 than Adapter 1? If we apply the same amount of normalization that Adapter 1 required to Adapter 2 it looks like this:

Adapter 2 normalized to match Adapter 1 levels

Creating a new image from the difference between the two and analyzing the resulting histogram is a simple way to represent the relative difference. The x axis represents the amount of difference and the y axis represents the number of pixels with that level of difference. A perfect match would result in one spike at the very left.

Delta between Adapter 1 and Adapter 2

The histogram above demonstrates relatively little difference between the images from these two adapters.

14mm, Defocused and white balanced against wall

The Rokinon 14mm is too wide to use the Expodisc, so instead I defocused and shot the nearest wall (after white balancing.) Whereas the Expodisc works to average the total brightness of a scene, this is more of a spot test. As such, results are expected to be different, but still useful.

Click thumbnails for full 4K stills from in-camera video.

Adapter 1
Adapter 2

Very similar results to the 35mm/Expodisc combination. Adapter 1 is warmer and darker, Adapter 2 is cooler and brighter. Once again, lets normalize the data in order to exaggerate this differences:

Adapter 1, normalized
Adapter 2, normalized

The drastic color shift for Adapter 2 is somewhat deceiving because the wall is not really neutral (it’s beige.) Looking at the histogram of the difference is a better indicator of the relative difference:

Delta between Adapter 1 and Adapter 2


I hope I’ve demonstrated that the difference in image quality between the Speed Booster and the Lens Turbo is fairly small, and somewhat open to personal preference. Of course, image quality isn’t the only factor to consider. What about build quality? What about convenience features? This is where the gulf between these two products widens in a more meaningful manner.

Metabones Speed Booster

  • Aperture control for lenses that don’t offer it (Nikon mount.)
  • Electronic focus/aperture control for Canon EF lenses.
  • Removable lens support foot.
  • Machined to very tight tolerance. Mount between adapter and camera, and between adapter and lens both have very little play.
  • Relatively heavy.

RJ Photo Lens Turbo

  • No aperture control (Nikon mount.)
  • No electronic focus/aperture control for Canon EF lenses.
  • No lens support.
  • Machined to less rigid tolerances. Mount between adapter and camera is solid, but mount between adapter and lens has enough play that the lens moves while using a follow-focus.
  • Relatively light.


  • If your only concern is image quality, you can save a significant amount of money purchasing the Lens Turbo.
  • If you shoot in ways that are sensitive to lens stability (rack focusing, for example) or need to support large, heavy lenses then the Speed Booster is worth the extra cost.
  • If you desire electronic control of Canon EF lenses, the Speed Booster is your only choice. Be aware that (like almost all 3rd party options) support from lens to lens is somewhat flaky.
  • If you want to shave every last ounce of weight from your rig, well you should be suing MFT lenses, but if you are going to use an adapter, the Lens Turbo is lighter.

25 Replies to "Comparing Focal Adapters: The Metabones Speed Booster vs the RJ Photo Lens Turbo"

  • Karl
    November 3, 2014 (2:12 pm)

    Thanks for the interesting test. Where can I buy the RJ Lens Turbo? I cannot find any reseller or eBay shop.

  • Pawel
    November 19, 2014 (11:45 pm)

    very cool blog mate. I can clearly see a difference between adapter wide open, but not worth $300 extra 🙂

  • Ryan
    November 30, 2014 (12:39 pm)

    I’m guessing #1 is Metabones. I really hope it is. Can you let me know? Thanks.

    • joe12south
      December 3, 2014 (1:54 pm)

      Yes, #1 is the Speed Booster.

  • Antonio
    December 4, 2014 (4:32 am)

    Hi, It’s the Lens turbo or the lens turbo II ?

    • Sergey
      December 13, 2014 (9:13 pm)

      it’s interesting to me too.. as i understand, there is a 2nd version of RJ on ebay.

      I clearly see the difference on these photos while zooming, especially at wide open we see strong CA on the cube and SpiderLenscal board with SpeedBooster while LensTurbo is absolutely clear. But at f4 SpeedBooster is more pleasant to my eyes. And the photos made by 14mm isn’t unfair for LensTurbo if there is a doubt about focus accuracy.

      Anyway, i think i wouldn’t tell the difference at fullscreen HD without zooming.

      Thanks for your time, tests and explanation, Joseph!
      Your blog goes to my favorite)

  • derugur
    January 2, 2015 (1:27 pm)

    Hi there, i am looking everywhere for Canon EF > M4/3 or a Nikon > M4/3 RJ Lens Turbo 2 Adapter…there is nothing. Maybe there is something wrong with name, there is no “Lens Turbo2” only a upgrade without changing the name?

    Is there a buy-link to the tested RJ product?



  • tuffy2k
    January 3, 2015 (7:23 am)

    FYI – with tripod mount and the Nikons are able to change aperture. Itches my eye to see that as a contra on the RJ :/

  • Howie
    February 14, 2015 (4:40 pm)

    I noticed a couple weird things in both pairs of the 400% crops. Firstly the color cast in both crops is identical. The second thing I noticed was that the 400% crops matched exactly in frame as well despite there being a difference in focal reduction. When I downloaded the clips to peep they download as the same file and use your nomenclature _sb to denote speedbooster as opposed to _lt to denote Lens Turbo. Please clarify.

    • Tom
      April 27, 2015 (1:20 pm)

      Hey Howie – good detective work. I just checked also, and as of 04-27-2015, it’s still the same. The 2 side-by-side comparisons/detail close-ups at 400% are the exact same JPG’s! They are not actually comparing the Speed Booster with the Lens Turbo. It makes it look like the reviewer was tried to hide some deficit that the Lens Turbo may have had. Maybe it was just an honest mistake, though. It’s weird that @joe12south hasn’t replied yet to address this.

      • joe12south
        April 27, 2015 (1:48 pm)

        No conspiracy, just a typo. 🙂 Been busy on paying work and had not been checking the sites comments. Assuming I have the correct original file I’ll correct the link right now.

    • joe12south
      April 27, 2015 (1:59 pm)

      Good catch, Howie. I fixed the links. (To be clear, the thumbnails on the page are correct, it was only the link that was wrong.)

  • Ted
    February 23, 2015 (1:37 am)

    Actually, when I pixel peep, it looks to me like the RJ booster retains more resolution than the Metabones, but the Metabones definitely has better contrast.

  • John
    February 23, 2015 (11:38 pm)

    Hi. I was just wondering if you think the rj lens turbo is sharp enough for 4k on my gh4? Also do you know if rj is the same as roxsen focal reducers?

    • joe12south
      April 27, 2015 (2:06 pm)

      If picking purely on image quality, then I personally don’t find enough of a difference between the two. The fit and finish is much better on the Speedbooster, and it actually makes a difference for me with my heavy-ish cine-lenses. But if money is tight, I have no reservations using the Lens Turbo for 4K.

      Sorry, I don’t know if the Roxsen are the same or not.

  • pedro soto
    April 27, 2015 (2:35 pm)

    hi ,thanks for the comparison / could you please help me? .I just receive your rj speed booster nikon to micro 4/3 , I put it on sigma 18 35mm for nikon mount everything perfect..but now I don’t know how remove the adapter from the lens..there’s something I have to do specific? I try to just remove it but doesn’t work..please help.thanks. looks like stucked.

    • joe12south
      April 27, 2015 (2:58 pm)

      Are you depressing the flange that allows the two to decouple?

  • Bobdoel
    May 14, 2015 (4:29 pm)

    Good review. Would have helped saying metabones or RJ instead of Adapter 1 & 2…

  • that guy
    September 14, 2015 (9:22 am)

    Thank you for this thorough comparison!

  • Luc
    November 1, 2015 (9:33 am)

    Having personally tested them I can agree they are comparable at relatively open apertures. Stopped down it is a totally different story. The optical properties of the RJ are weak when you reduce the light passing through. Deep focus may not be something you care about but if you do and are getting the focal reducer more fore the width than the speed the metabones glass is optically superior at smaller apertures.

  • Scintilla
    March 30, 2016 (4:26 pm)

    I’m seeing noticeably smoother bokeh on #2 in the 35mm shot wide-open (the potted plant and the words on the pig’s shirt). That’s the RJ?

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