conurus N-mount to EF-mount conversion: installation

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

You do NOT need to do this installation. We do this for you and we are just showing you pictures of how we do it.

Prerequisites
1. Tools and materials required:
  - 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.
Measurements
1. Except for Planar 85/1.4, remove black shroud from the lens. There are 3 black screws holding the shroud.
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.
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.
  
  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.
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.
6. For Planar 50/1.4 only, save the aperture ring for later and be careful not to lose its tiny ball bearing.
Desoldering
1. For 28-80 and 70-200, desolder the lens connector complete with its flex cable from the green circuit board. Use around 650-700 degrees F or 343-371 degrees C.
2. For all other lenses, desolder the 10 gold-plated pins from the lens connector using a soldering pump. Use around 650 degrees F or 343 degrees C if this is your first time. As you gain experience, and be quick, you may go up to 800 degrees F or 427 degrees C.
  
  As you desolder, the pins will fall out one by one.
  
  Save the connector pins and the connector plastic ring. They are not used.
3. Using solder wick, remove solder from each of the 10 joint until a through hole is seen.
4. If your lens connector has a flex cable attached to it, desolder the flex cable. We do not need it.
Soldering
1. Your lens connector is slightly too long to fit into the mount, 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.
3. Solder the lens connector onto the 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.
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.
  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.
  
  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.
  
  The soldering is done! Your lens now looks like this.
Final assembly
1. For Planar 50/1.4 only, put back the tiny ball bearing and the aperture ring. The aperture ring encoder gear has a small hole. That should be aligned with the white index mark on the lens barrel, when the aperture is set to f/8. The black plastic ring on top of the aperture ring is not used.
2. Put back the correct amount of shims. Put thinner shims underneath and thicker shims on top.
3. Except for 28-80 and 70-200, put the replacement spacer onto the lens, again be careful not to break the flex circuit.
4. Next, except for 28-80 and 70-200, precisely align the 4 mount screw holes of the lens and the replacement spacer. Put the 4 OEM mount screws (larger) back.
5. Secure the lens connector onto the replacement EF mount using 2 small chrome screws you removed in a previous step.
6. The rear shroud of 100/2.8, 24-85, 28-70, 70-200/3.5-4.5 and 70-300/4-5.6 can be used without modification. The 50/1.4, 85/1.4 and 400/4 have 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 and you got a black spacer ring, you put in a M1.4 screw to plug the first small screw hole counting from the 8 o'clock position. Put the brass washers supplied on the second and the fourth small screw hole. The rest of the screw holes are not used. The screw and the brass washers will raise the 24-85 rear shroud just enough that the back of the lens is completely flush.
7. Except for Planar 50/1.4, Planar 85/1.4 and Tele-Apotessar 400/4, install the rear black shroud on top of the conurus black spacer using the 3 small black screws supplied. (2 screws for Vario-Sonnar 24-85 rear shroud with brass washers underneath.)
8. Put on the replacement EF mount (with circuit board) and the 4 large chrome screws supplied (except for 28-80 and 70-200). For 28-80 and 70-200, use 3 of the OEM mount screws and the long chrome screw supplied to fasten the mount.