WARNING: you will void your lens warranty by modifying your lens.

Initial customer feedback suggests that it is difficult to find a camera shop who is willing to perform this installation. We believe that your successful deployment should be painless and trouble-free. Therefore, we are now offering installation service. Please review our price list.

N-mount lens + $$$ = EF-mount lens

  1. Prerequisites
    1. Tools and materials required:
      • Lens connector from a Sigma lens (either order part number 9270038 from Sigma or extract from a broken lens) INCLUDED
      • Thin solid copper wire (extract from 80-conductor E-IDE hard drive cable)
      • Temperature-controlled, ESD-safe soldering iron
      • Solder
      • Desoldering pump
      • Solder wick (i.e. desoldering braid)
      • Side cutting piler
      • Micrometer
      • #00 and #0 philips screw driver, JIS Type S (see this)
      • Standard gage block, 2mm or more, or a piece of metal known to be flat and parallel.
    2. Before you proceed, perform testing to ensure the lens functions properly. Turn off or cover up the AF assist light of a Contax N camera body, and try to focus the lens on a wall with no texture or detail to lock on. The lens is supposed to hunt one full cycle, to the closest focusing distance first and then back to infinity. If not, but the lens hunts within a limited distance, send it back to the OEM for service.
    3. Test also the aperture blades by using the depth-of-field preview feature.
  2. Measurements
    1. Except for Planar 85/1.4, remove black shroud from the lens. There are 3 black screws holding the shroud.
      remove black shroud (MS100/2.8)

    2. There are 7 screws holding the mount, 4 large ones from the top and 3 small ones from the side. Gently snap the lens electrical connector off the mount.
      • WARNING: be careful not to pull the delicate flex circuit - if it breaks, the entire computer circuit will have to be replaced by completely disassembling the lens.
      • WARNING: depending on your particular lens, the 4 large screws from the top may be extremely tight. A JIS Type-S screwdriver is essential for their removal, because JIS screwdrivers have thinner blades than ordinary Philips screwdrivers. Also, apply a lot of downward pressure while you turn to minimize the likelihood of stripping.

      remove mount ring (MS100/2.8)

    3. Take out the copper shims between the mount and the lens. Measure the thickness of each copper shim. Measure also the thickness of the mount, excluding the rim. Let the total thickness of the mount and all copper shims be x.
      measure mount thickness (MS100/2.8)

      Tip: when you measure the thickness of the OEM lens mount with a micrometer, the rim of the mount (from the back) may get in the way. Shim the back of the lens mount with a standard gage block, 2mm or more, or a piece of metal known to be flat and parallel. Subtract the thickness of the standard gage block from your measurement.

    4. Measure the total thickness y of the conurusTM replacement mount, both the spacer and the EF mount together. When they are shipped to you, they are already held together in one piece by 4 screws.
      conurus replacement mount

    5. Calculate the difference in thickness, d = x + 4mm - y. Put the combination of copper shims whose sum of thicknesses is the closest to d back to the lens. Remove the rest of the shims and save it in a moisture-free environment in case you wish to reverse the procedure in the future.

      Example
      Thickness of original Contax N-mount = 1.79mm.
      Thickness of copper shims: 0.51mm, 0.31mm, 0.11mm, 0.09mm.
      Total thickness y of conurusTM replacement mount = 6.16mm.
      x = total thickness of original Contax N-mount plus all copper shims = 2.81mm
      Difference in thickness d = 2.81 + 4 - 6.16 = 0.65mm

      The 0.51mm shim and the 0.11mm are the closest to 0.65mm. Therefore, they are put back to the lens. The 0.09mm and the 0.31mm shims are removed and not used.

      WARNING: the above is only an example. Your measurements will certainly turn out to be different. Your lens usually has 2 to 4 shims. Your mount thickness usually falls within the range of 1.40mm to 1.80mm.

  3. Desoldering
    1. Desolder the 10 gold-plated pins from the lens connector using a soldering pump. Use around 650 degrees F or 343 degrees C.
      N-mount lens connector (VS24-85)

      As you desolder, the pins will fall out one by one.

      desolder pins (VS24-85)

      Save the connector pins and the connector plastic ring. They are not used.

      pins, ring and rigid-flex circuit (P85/1.4)
    2. Using solder wick, remove solder from each of the 10 joint until a through hole is seen.
      remove excess solder
    3. If your Sigma lens connector (P/N 9270038) has a flex cable attached to it, desolder the flex cable. We do not need it.
  4. Soldering
    1. Your Sigma lens connector (P/N 9270038) is slightly too long to fit into the mount.

      The Sigma 8-pin lens connector comes in two different styles, and both of them will work. If your connector looks like this, bend each of the 8 pins outwards, until they are almost the same height as the two tiny black dots, one on each end of the connector.

      remove excess solder

      If your connector does not look like this at all, cut 1mm from each pin off using a side cutting plier.

    2. You removed 4 large chrome screws and 3 small chrome screws from the OEM mount. Use 2 of the small chrome screws to secure the lens connector to the conurus mount.
      secure lens connector to mount

    3. Solder the lens connector onto the green conurus circuit board, while the board is still housed inside the conurus mount. The largest pin of the lens connector should be soldered to both pad 2 and pad 3 of the conurus circuit board. The board has two sides: the side with square solder pads goes to the Canon camera and the side with round solder pads goes to the Contax lens.
      solder lens connector

      Note: your Sigma lens connector may look different from what is pictured. So long as it is a 8-pin connector, with one screw hole aligned with the most clockwise pin, and the other screw hole between the first and second most counter-clockwise pin, it will fit.

    4. Remove the 4 large screws holding together the 2 rings of the conurus mount. Remove also the 2 small chrome screws holding the lens connector. You may now remove the circuit board and the lens connector in one piece.
      circuit board/lens connector assembly

      Why? In the previous step you have soldered the lens connector in place while the circuit board is still housed inside the conurus mount. This makes sure everything will fit together when you put them back together. In this step, you remove the circuit board/lens connector assembly from the conurus mount because the mount is heavy and would pull the lens' flex cable by weight and break it while you are soldering the circuit board.

    5. Use thin bare copper wire to join the 10 pads on the bottom of the conurus circuit board and the 10 pads of the lens connector together. Solder the wires to the circuit board first, as shown in picture.
      solder bare copper wires to circuit board

      Except for 50/1.4, make sure the edge of the lens' flex circuit is aligned with the conurus circuit board. Otherwise you will not be able to fit it back to the lens.

      solder circuit board and flex circuit together

      The soldering is done! Your lens now looks like this.

      soldering complete (VS24-85)
  5. Final assembly
    1. Put the replacement spacer onto the lens, again be careful not to break the flex circuit. As can be seen in the picture, there are one top screw hole and one side screw hole of the replacement spacer which should be approximately aligned with the white aperture line of the lens.
      alignment (P85/1.4)

    2. Next, precisely align the 4 mount screw holes of the lens and the replacement spacer. Put the 4 OEM mount screws (larger) back.
      install spacer (VS24-85)

    3. Secure the lens connector onto the replacement EF mount using 2 small chrome screws you removed in a previous step.

    4. The rear shroud of 24-85 and 17-35 must be modified. The rear shroud of 24-85, 100/2.8 and 70-300/4-5.6 can be used without modification. 85/1.4 has no rear shroud.
      • There is a tab protruding from the rear black shroud of Vario-Sonnar 17-35/2.8. When the lens is not fully rotated until it locks on the mount, and you trip the shutter, the mirror will hit that tab and cause damage. Either
        • always mount the lens by rotating it fully until it locks but never leave it rotated halfway and trip the shutter, or
        • file down 2mm from the protruding plastic tab. To ensure the conversion is reversible we will not do this for you.

      • If the lens is 24-85, the rear shroud has 3 screw holes. Cut away one of them as shown in this picture (click to enlarge). Right-hand side is before; left-hand side is after.
        rear shroud modification (VS24-85)

    5. Except for Planar 85/1.4, install the rear black shroud to the back of the EF mount ring using the 3 small black screws supplied. (2 screws for Vario-Sonnar 24-85 rear shroud.)
      install rear shroud to back of EF mount (VS24-85)

    6. Put on the replacement EF mount (with circuit board) and the 4 large chrome screws supplied.
      put EF mount on (P85/1.4)

      put EF mount on (VS24-85)