One way to modify Contax Zeiss lenses to work with Metabones Speedbooster


One of the things I’ve noticed now that I’m doing the bulk of my shooting on super 35 sensor cameras instead of a full frame DSLR is that my set of Contax Zeiss primes just aren’t getting used that much any more. Why? The lenses, most of which are f/2.8, just don’t look as good when adapted with the crop factor of f/1.5 using the Metabones IV adapter. So, why not just just use them with a Speedbooster?

Answer: because of protruding rear elements (see below) that prevent them from fitting on the Speedbooster.


It’s really quite extraordinary the difference in look that a full frame vs. a super 35 sensor makes with this glass. Using the IV adapter, my 35mm f/2.8 Zeiss becomes about a 52mm lens in terms of field of view. Sometimes the change in field of view is fine – when I want a longer focal length. But another thing happens that’s rarely desirable: what was f/2.8 on full frame now has the depth of field appearance of f/4. And the difference between apparent f/4 and f/2.8 on full frame? Huge.

Over the weekend, it occurred to me that there might be a way around this impasse. Why not get a Dremel tool and grind those nasty rear elements out of the way? A close examination revealed that the elements are useless for video work anyway. I will never be using these lenses, which are permanently cine modified already, for shooting stills on a Contax camera. So I ran across the street to my hardware store and got busy.


First thing was learning about griding wheels – turns out the one you want for this job is the aluminum oxide grinders that are designed for metal work. Pictured above is the B132 grinding stone, which worked great.

To prevent fine metal shavings from falling into the lens, I carefully used painters tape to mask off the rear elements of the lens and block the openings into the lens. Then I made sure my glasses were on, and got busy.


The metal pretty much just melts away with carefully applied pressure.


Bits of metal become flattened and hang over the sides of the real element, which I was able to scrape away with a small screwdriver. I also used a vacuum cleaner to suck out any stray metal dust.


Pulling away the tape reveals the flattened elements.



Now the moment of truth: It fits! I ground down all 5 of my lenses in my set (25mm f/2.8, 35mm f/2.8, 50mm f/1.4, 85mm f/1.4, 135mm f/2.8).



I tried all 5 of the lenses on, and all fit, but I noticed the 35mm in particular was very tight. This and the 135mm were the most difficult to work on, as they were very tight when attached to the adapter. But they seemed to fit OK after repeated grinding sessions. Woo hoo! I’ve got a set of dreamy Zeiss glass with the full frame look on my FS5!


But before you get as excited as I did, let me tell you the rest of the story. When I put one of my Canon L lenses on the Speedbooster, everything seemed fine … except the image stabilization didn’t work. Crap. What did I mess up…

A close look revealed the despite my best efforts at grinding, something had remained on at least one of the lenses that tangled with the last contact in the row. For the Zeiss glass, it doesn’t matter – it’s all manual anyway. But for the Canon lenses, you need every one of those contacts in working order. Sigh.


I’m still not sure what messed that up – but it obviously did. So my solution has to make this Speedbooster my dedicated  “Zeiss only” adapter.


It now lives in the same Pelican case as the Zeiss Contax set. I had to spring for another one to use with my Canon L glass. If were going to do this over again, I’d start by purchasing one of the older Speedboosters (you can find them on Ebay for a few hundred bucks cheaper than the new Ultra Speedbooster that I used), and plan from the beginning to dedicate a Speedbooster to the Zeiss glass, instead of thinking I could continue to use the same one with L glass.


All in all, though, I’m thrilled to have the full frame look back with my Zeiss glass on Super 35 and am looking forward to shooting my next project with this glass. Here’s why:

25mm f/2.8 Zeiss adapted to Sony FS5 with Metabones IV adapter (1.5 crop factor makes approximate field of view of 37mm):

Screen Shot 2016-05-24 at 11.29.14 AM

35mm f/2.8 Zeiss (after grinding) adapted to Sony FS5 with Metabones Speedbooster (.071 crop factor makes approximate field of view 37mm):

Screen Shot 2016-05-24 at 11.29.27 AM

Notice how much more selective the focus is on the orange umbrella in the second frame. If you’re not noticing the difference, click on each image to view at full resolution.

PS. Since this post went live, I’ve learned that Metabones makes a Contax CY -> Sony E mount Ultra Speedbooster. Duh! I would have been much better off just buying that, saving the contacts on my EF Speedbooster, and leaving well enough alone. But then I wouldn’t have had anything to blog about, would I?



46 thoughts on “One way to modify Contax Zeiss lenses to work with Metabones Speedbooster

  1. Henry Gretzinger

    Great post! I just picked up a set of Contax Zeiss primes and they’re treating me well on my a6300 (which I love too). Keep up the good work, I’m digging your blog. Stumbled upon it in a google image search for lightweight matte boxes (I’ve settled on the Genustech Matte Box Lite).

    Cheers, Henry.

    1. Dan McComb Post author

      Hi Henry,
      Yeah that glass is very affordable and looks fantastic. Glad you found the information useful. RE: Genus matte boxes, I have just received their Production Matte Box and am planning to review it soon. They make great stuff for the money, most def.

  2. Jimmy

    I am thinking if MM version differs from AE version. Which version of lens do you own? I am planning to buy MMJ version of contax zeiss glasses and want to know if they need certain mod to work with ef mount to M43 mount speedboosters.

    Cheers, Jimmy.

    1. Jimmy

      Ps. You mentioned the lens damaging the contacts of the speedbooster, so I assume it is the contacts which get in the way of the rear elements (the AE lever?). I know a Chinese C/Y to EF adapter rotates the lens by 90 degrees so that it will not hit the mirror of Canon 5D’s. Basically if you use this adapter the top of lens will face left and the AE lever will not get in the way of the mirror of 5D’s (if you understand what I’m talking about 🙂 ). I am thinking if it will work in this situation.

      1. Dan McComb Post author

        Hi Jimmy, yes, that row of contacts is where the problem comes from. But there really isn’t much room in there apart from that, so I’m not sure that rotating 90 degrees would solve for that entirely. The only way to know is to try it out.

        1. Jimmy

          Thanks for your reply. I’m planning to buy contax glasses later this year and I’ll definitely try it out. If it does fit than it’s a surprise; if is doesn’t fit, I’ll try file the AE lever off…

  3. Thierry

    Hi Dan,
    thank you for your post!
    I’m very surprised of your conclusions about the differences of quality between your 25mm with adapter and your 35mm with Speedbooster! I’ve seen the 2 frames at full resolution, and for me the 25mm with adapter is more sharp than the 35mm with Speedbooster! We can see it on the orange umbrella, on the wood of the barrier, and on the statuette.
    On the other hand, I also possess a series of Zeiss Contax, and I’ve bought the Metabones Speedbooster Contax to Sony E. What a surprise: the lenses are badly fixed to the ring, and move during focusing for example! I sent back the Speedbooster to Metabones, and I wait their reaction for my conclusion about the quality of their rings.

    1. Dan McComb Post author

      Hi Thierry,
      I don’t dispute that the Zeiss with adapter would be sharper than with Speedbooster. But sharpness, for me at least, isn’t the most important metric. For me it’s the whole “look” of the lens, in particular, the depth of field quality. That’s what I really like most about the Speedbooster with my Zeiss. Sorry to hear about your problems with the adapter. Let me know if Metabones makes it right for you.

    2. skip

      I have a recently acquired CY to XF metabones speedbooster that also moves while focusing and its 2020 so Im assuming they have not fixed the problem.

  4. Paul Dussault

    I think I found a good alternative for the little metal thing on the back of the Contax (What makes the aperture stucked at the fastest stop).

    I put my Leitax mount, which fits perfectly on the metabones speedbooster (EF) but the aperture would stay at 1.4 for example. Instead of buffing the metal part, I simply removed it, two littles screws and it was done. I can now have the aperture I want and keep it on my Speedbooster.

    1. Sputnik Pictures

      Brilliant. Thanks for this. I have an entire set of Leitax-modified CY > EF mount lenses, and just bought a Speedbooster and discovered this problem. Glad to know there’s an easy fix!

      1. Sputnik Pictures

        Update: While it’s true that the automatic maximum aperture indexing pin is held in place by only two little screws, it’s actually quite involved to remove it. This may vary from lens to lens, of course.

        For example: on my 21/2.8 CY lens, you can access those two tiny screws by removing the Leitax mount, then the existing rear lens cover + aperture ring. However, due to the shape of the auto indexing tab and the slot it runs in, you still can’t remove the metal tab. It would just rattle around in there, eventually causing problems. The only way to remove it would be to disassemble a large percentage of the lens…more than most people are competent to do. I ended up putting everything back together, then grinding it off as Dan did.

        As I said, this design issue may differ from lens to lens. I’ll ask Paul to update his post, indicating which lens(es) he performed this modification on.

    2. Sputnik Pictures

      Would you please update this post, and let us know which lens(es) you were able to remove the AI tab from? (See my note about problems doing this on the 21/2.8) Please give us the focal length, aperture, and whether it’s the German or Japanese model of that lens (AE or MM). Thanks!

      1. Alex chan

        Do you just have to remove the tab or do you have to remove the tab as well as the protrusion beside it?

  5. Max Brandenburg

    I did the same grinding that you did to mount these lenses onto my metabones EF to m4/3 mount for my gh4. I am using the leitax mount but have encountered a problem. It says problem with the lens mount and won’t let me shoot or take a photo. I have shoot without a lens on and everything. And the metabones speed booster works on my other full manual lens.

    1. Dan McComb Post author

      Hi Max, I sometimes have a similar thing with Sony FS5 when I first mount these lenses. The camera won’t immediately read that it’s a lens, and the screen stays black. The solution that works for me is to press the FS5’s lens release button and slightly rotate the lens as if beginning to change it, then snap it back in. This solution works every time for me. Hopefully it will for you, too.

      1. Max Brandenburg

        Thanks for the reply Dan, sadly after trying that I am still getting the same error message. One person at my local camera store told me that the m4/3 to EF version of the metabones requires an electrical connection, and my Contax lens doesn’t have a chip on the back to communicate with. Do any of your lenses have a chip on the back? I was wondering if that is something that I could potentially buy.

        1. Dan McComb Post author

          None of my old Contax glass has any chips on them. But you can look into Leitax adapters, which do have the required electronic connections on them in case that’s what the camera is looking for.

  6. Teemu Lahtinen

    I have Contax Zeiss 28 2,0 and Metabones C/Y-Nex Ultra adapter. And problems with infinity focus, it seems that problem is not the metal pin but protruding rear lens element on the lens hitting the adapter (front facing lens in Metabones). I have to try adjusting infinity focus on the adapter by loosening the screw and moving elements but not sure if it moves far enough, and if it works with other lenses after that. So it seems C/Y-Nex adapter is not an easy way out after all!

    1. Dan McComb Post author

      Good to know that, Teemu. I am going to take my lenses to a lens repair shop here in Seattle and see if they can do something to fix the infinity focus issue on my 25mm Zeiss lens. Will let you know what I find out.

  7. Erik Naso

    Great post! I have three Contax MMJ on the way. 35mm 2.8, 50 1.4 and 85 1.4. I’ll be using them with a Speed Booster on the GH5. Glad I found this post before I tried to mount them. I also have the Leitax mounts coming. I decided to de-click myself and found what looks like the right damping grease for the job. It’s Nye Lubricants 767A (NG) Heavy Synthetic Damping Grease. I’ve read others use the Light formula but I like a firmer feel and the heavy is designed for this. Thanks again for the heads up. I like your vise setup. Is that all grip gear?

    1. Dan McComb Post author

      Hi Erik,
      I think you’ll really like that lens combination with the GH5. The 85 1.4 in particular is an amazing piece of glass and a real joy to shoot with and has so much personality that I find newer glass almost boring in comparison. re: vise – I used two bits of grip gear, a Mathelini clamp on the counter, and a Mafer clamp to hold the lens. Works great!

      1. Erik Naso

        Can’t wait for them to arrive! Is it necessary to grind both posts all the way down? If you did the mod again would you have done anything different?

        1. Dan McComb Post author

          It may be different with the M34 adapter, but I would assume you will need to get rid of those protruding levers one way or another. If you don’t have the Leitax adapters on yet, you may be able to remove the levers without grinding them by unscrewing them. Might save you some time.

          1. Erik Naso

            I’ll have a look. The lenses will be in this week from Japan and the EF mounts won’t be here from Leitax for 2 weeks. Thanks Dan.

    2. Shri Prasham

      Hi Erik,

      Did you try this method with the GH5. Did it work? I have the 35mm 1.4 and I’m wondering if this method works as the CY- micro 43 metabones adapter I got does not fit snugly. There is a slight give and cause the lens to jerk whenever I pull focus.

      1. Dan McComb Post author

        I had that same issue with play between the lens causing visible disturbance whenever I pull focus. The newer Cine-style Metabones adapters eliminate this problem. They are fantastic for focus pulling.

  8. Birk

    Hi Dan

    What rings are you using in front of the lens? Well, I know it’s 77mm Fotodiox rings, but they cost £35 each, what would you call them? Have been looking for a similar solution for a while!

    1. Dan McComb Post author

      Hi Birk,
      Mine are Fotodiox brand, but the brand doesn’t matter, as they are just cheap bits of metal. They are called “spacer rings” and you want the 77mm-77mm ones. You can find them on Ebay for between $3 and $20. They come in various depths, or you can buy multiples of the shallow ones and stack them to desired depth.

  9. Steinberg

    Thank you very much for this blog post and subsequent comments!

    I’ve just acquired the Zeiss 28mm f2 ‘Hollywood’ Lens (Made in West Germany) to pair with the Metabones XL (EF to MFT) and ran into this exact issue.

    I’m going to take it to a local camera shop and, if they’re stumped, I’m going file down those nodules—and then I’ll see about these infinity focus issues I keep hearing.

    Will report back. Thanks.

    1. Dan McComb Post author

      Hi Steinberg,
      I was able to solve the infinity focus issue on all my lenses by adjusting the set screw on the Metabones adapter. I had to adjust it so far that it begins to contact the inside of the FS5 when I attach the lens, but it got the job done.

      1. Alastair


        What is your test for infinity focusing?

        I recently bought 2x Contax lenses from the Contax Shop in Tokyo. Amazing place.

        The guy asked me to go outside and test the infinity focus to make sure. So I duly did by focusing on the furthest thing I could.

        But a simple google for “checking infinity focus” through up a whole bunch of not so simple answers. Worse still, countless people are pointing out all the problems and issues with simply “focusing on the furthest object” to perform this test.

        Do you have a solid method for testing this?

        1. Dan McComb Post author

          Hi Alastair,
          I also simply focus on the farthest thing in the frame, which from my front porch is the Olympic mountain range. I’m pretty sure that counts as infinity, but if you hear of a more precise method, please let me know!

  10. Alessandro

    Do any of you have the 18mm f/4?
    In addition to the two protruding rear elements that you described, the rear lens itself protrude and it is protected by a sort of metal crown.
    I Don’t know what to do because I’m afraid to scratch the speedbooster lens (I’m using the viltrox)

    1. Dan McComb Post author

      Hi Allessandro,
      The widest lens in my Zeiss collection is 25mm. Sounds like the 18mm could be a problem with those protruding elements. I’d be very careful – it’s easy to damage.

  11. Tasos Kosmatopoulos

    Dan , thank you for this post.
    I wanted to share that i used the fotodiox Contax yashica adapter CY to Ef on my lenses and then mounted them on my 0.64x Metabones Speedbooster on the black magic pocket 4K . I also used it on my metabones EF to Emount adapter without chopping the rear lever. I used it on my 50mm and the 25mm .
    On the Ef to sony mount adapter everything worked.

    On the speedbooster the real lever on both lenses scratched a little bit the plastic of the speedbooster under the pins but not the electric pins at all. So it seems that it works perfectly without sacrifising a speedbooster.
    I will have the infinity focusing checked later on this week on a chart but from a few shots i took all seems fine.

    Maybe it is the leitax adapters that caused your problems? Since i also want to cinemod my lenses and use the leitax adapters as well i am being sceptical.

  12. Alex

    Hey Dan,

    Thanks for this post. Was wondering if you ever found out what protruded and messed up your speedbooster and if it’s avoidable?


  13. Josef

    Hi Dan, thanks for the article. I got rid of the protruding rear elements during the installation of the leitax mount. You just have to unscrew the next four screws to get to the aperture. You can take out the part with the rear element and then work on it without having to think about the glas element of the lens. While the rear aperture is free you can declick it as well.

    Found your blog just recently. Great stuff!


  14. Lotfi Kaz

    Here’s a 2021 Update: You don’t have to do this for modern speedboosters like ULTRA and XL, mine fitted perfectly on the viltrox EF to MFT with cheap ebay CY adapter (Except I had to turn the glass of speedbooster to fix infinity focus) but that’s a seperate issue.

    On the Metabones some lenses might scratch the velvet side only slightly so maybe if you don’t want that you can trim the pins just slightly but not the whole way using a professional or at home with metal cutting plier.

    I think author uses old gen speedboosters since it’s 2016 but I also read this post while my lens is arriving by post and I panicked a lot and this post made me panic even more having to do this to a rare lens.


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