Using a Conurus converted Contax 85N on a Canon 1Ds Mark II



Bo-ming Tong of Conurus Imaging Corporation pioneered the Contax to Canon conversion process, thus giving Contax N lenses a new lease on life. Using a Contax C/Y lens, or a Hasselblad, or a Rollei, or even Leica-R lens on the Canon dSLRs is nothing new. Buy the appropriate adapter and you have a manual focus lens with stop down metering. Often these adapters are very low quality and have tolerance issues which lead to problem with infinity focus, uneven sharpness across the frame and/or fringing (CA).

Conurus’ approach is NOT just a simple adapter. This is a comprehensive electronic conversion resulting in a fully functional Contax auto-focus lens with auto aperture on a Canon EOS body. The Contax-N lens operates just like any other Canon EF lens.  The Contax mount is replaced with a high precision Canon mount which mounts very smoothly and securely. No adapters, no need for manual focus, no stop down metering. Contax fans can now enjoy Carl Zeiss optics on their Canon cameras - without compromise.

Conurus’ conversion process addresses both hardware and software. The physical mount is changed, custom firmware is loaded into the lens and the electrical contact assembly is replaced. The firmware is upgradable (this is a “factory” upgrade) which is good news if Canon decides to change their protocols with the 1Ds Mark III and subsequent models. Mount tolerances are carefully measured, and if needed shimmed to ensure proper performance at infinity. Each lens is converted to extremely tight tolerances and all these measurements are documented for each lens on Bo-ming’s website (type in your serial number and can see all the measurements recorded during the conversion process).

Part of the conversion process includes “calibrating” the lens’ auto focus. Bo-ming calibrates the lens by testing it on his Canon 1Ds - a time consuming process in itself. The Contax 85N is my third conversion from Bo-ming, and each lens has focused perfectly on my Canon 1Ds Mark II. Accurate auto-focus was one my big concerns, and this has proven to be a non-issue. If focus adjustment is needed, Bo-ming included a micro focus adjustment feature in the firmware whereby the end-user can adjust the lens to their camera. The process is similar to Canon’s new micro focus adjustment in the 1D Mark II and 1Ds Mark III. Instead of the adjustment being store in the body, it is stored in the lens.

Bo-ming’s craftsmanship and attention to detail is excellent - the 85N came back looking as good as it did before its journey. Mounted on the Canon 1Ds Mark II the 85N feels and acts like any other Canon EF lens on the 1Ds Mark II --- it just happens to read “Contax” on the barrel. One big improvement is that now the aperture can be adjusted in 1/2 or 1/3 stop increments. On a Contax camera the aperture is adjusted in a 1 stop increments via the aperture ring. We are getting MORE functionality with the Contax lenses on a Canon body - amazing!


I know this is the “meat” that most people are looking for, but in 2007 my equipment list underwent massive changes and the 85N had to find a new home. At the end of 2007 I purchased a Phase One P25 medium format digital back and the Canon gear was sold to pay for the new gear (update - purchased a Canon 1Ds Mark III in March 2008 and started the 1Ds3 Blog).



Lens Composition

Angular Field of View

Minimum Focus

Diaphragm Action

F-Stop Scale

Filter Size

Filter Connection

Lens Cap

Metal Lens Hood

Metal Cap for Hood

Rubber Hood

Len Pouch


Lens Size

First Year Available

Contax MTF Charts

10 Elements / 9 Groups

25 Degrees @ Infinity

.70 Meters Measured from Front Element

Electromagnetic - Fully Automatic

F1.4 to F22 in 1/3 Stop Increments

82mm, Non-rotating


K-81 82mm Snap-type Plastic Cap


Not Applicable

Not Applicable


800 Grams / 1.76 Pounds

70mm x 84mm / 2.75 in. x 3.331 in.

Fall 2000 - Best Guess

Contax N 85mm Planar MTF