Contax AX

I was unimpressed by the first advertisements and reviews of the Contax AX body, which autofocuses by changing the lens-to-film distance. Contax seemed like a niche player desperately trying to tack a convoluted AF system onto their manual focus lenses. However, I was interested in high quality construction and I did some research on Contax equipment. I became impressed, not only by the quality of the Carl Zeiss T* lenses, but by the cameras themselves. As a result I added a Contax system to my Canon EOS. Here are my thoughts on the AX.

Construction

The AX is a solid camera. It is heavy and big. It weighs 1080 grams without the battery. Particularly, it is deep (72 mm from front to back) in order to accommodate the camera within the camera that must move back and forth to accomplish autofocusing. It is well constructed with high quality materials. The finish is beautiful and smooth. The controls have a very solid feel with just the right amount of resistance for me. It operates positively with good feedback to the photographer. There is no doubt about what the camera is doing. All of the controls (mostly conventional knobs and levers) are really electronic rather than mechanical. There are no loose levers and no free play or wobble in the knobs. The construction is positive and solid throughout. To achieve this Contax starts with aluminum alloy chassis that is quite rigid. The top cover is titanium.

Autofocus

Even without autofocus, the AX would be an excellent camera. The autofocus system is the center of attention because of its unique approach to focusing in 35 mm photography. Adjusting the distance between the lens and the film plane by moving the film plane is old hat to large format users, but the AX is the first application of this method to the 35mm format. The principle is simple, in order to focus on a subject, one can either use the lens to focus or one can move the film plan. In the AX the body does most of the focusing work, not the lenses.

It works like this. In order to focus, the film plane moves back and forth. But for the system to work, the film plane must be accompanied in its travels by the mirror box and the prism/viewfinder assembly. The distance that the film plane moves must be very precise.

There are two big problems Kyocera had to master: (1) how to move the assembly precisely enough; (2) how to move the assembly quickly enough. Relying on its extensive expertise with ceramics, Kyocera developed a ceramic guide rod for this inner assembly to ride on. A ceramic tube slides along the guide rod, providing the necessary precision. Ceramics are almost as hard as diamond, ensuring long life and continuing precision. Thus, the assembly can move precisely enough.

The second big question that strikes almost everyone is how in the heck can you move the weighty assembly fast enough for effective autofocus? The assembly's movement back and forth along the guide rod is powered by a USM (ultrasonic) motor. Being a Canon user, I am familiar with Canon's use of ultrasonic motors in its lenses. They are noted for high torque and very precise placement. The AX AF motor is low-rotation motor that requires only 1.5 rotations of the motor shaft to move the assembly from its front to back positions.

Still, the fact is that an autofocus lens need only move a few lens elements or maybe a couple of lens groups. These weigh far less and have to travel much smaller distances than the heavy film plane / mirror box / pentaprism assembly insider the AX. No matter how well engineered, how can such a system really operate quickly and precisely enough to be effective?

I was a doubter. When I bought my AX, I thought that the autofocus would only be useful in a few selected situations where little fast action was necessary - scenic and still life photos. After having used the AX, I am amazed that it is as fast and accurate as it is. It is not as fast as my Canon EOS 1N, but it is surprisingly close.

The British photography publication "Photon," compared the AX to a Minolta Dynax 9xi and found that the AX performed as well as the Minolta. The review stated that the AX proved just as capable of tracking action, catching suddenly framed images and selecting the correct focus setting.

Special Focus Operations and Limitations

The AX has special advantages and limitations regarding autofocus. Both the advantages and limitations are related to the 10mm of travel through which the film plane moves back and forth.

For macro work, the 10mm movement is like having a 10mm extension tube available at the flick of a lever. This means that normal lenses can operate like close focusing lenses and that wide angle lenses can act like macro lenses. Even with the Carl Zeiss macro lenses, there is an advantage because the 10mm extension can result in even greater than normal magnification.

One limitation is that the 10mm movement of the film plane limits the amount of focusing travel available. The longer the lens, the more travel is required to focus at close distances. So, for example, the 10mm travel is used up before the 180mm lens can focus to its normal closest focusing distance.

The solution is one of those things that sounds much more complicated on paper than in practice. To focus close with longer lenses, it is necessary to rough focus first. This is not a big deal (particularly to someone used to focusing manually), but it is less convenient than other autofocus systems.

The second limitation is a little more complex - the use of lenses with a floating group. Lens designers developed the use of floating groups to maintain sharpness at close focusing distances. As the subject to camera distance decreases, and the lens is rotated to a closer focusing setting, the floating group moves to maintain sharpness. Remember that with the AX, the lens is normally set to infinity, so that the floating group does not have a chance to move to maintain sharpness at closer focusing distances. So.... a lens with a floating group must also be rough focused before allowing the AX's AF to take over.

The viewfinder contains a display that shows the position of the film plane - whether it is in its base position or the degree of extension along its 10mm travel. This is quite useful, so that the photographer knows the amount of extension. This is helpful for close focusing and with lenses having a floating group. The viewfinder also has an in-focus indicator.

Autofocus control is flexible. On the back right side of the camera there is an AF button surrounded by a switch. The switch determines whether the AF is active when the shutter button is partly depressed or when the AF button is pushed. On the top right side of the camera is a lever that determines AF mode - either single shot, continuous tracking, manual focusing or locked at the full 10mm extension for macro work. The camera also uses an AF aid light for dark situations.

Operation

With the exception of the autofocus system, the operation of the AX is modern in function but classic in control layout. There is a shutter speed dial for exposures from 4 seconds to 1/4000. The shutter speed extends from 32 seconds to 1/6000 in Av and P modes. Flash sych speed is 1/200. There is a mode level that selects Av, P, M, Tv modes and is also used to select the ISO and custom functions control.

Either 5mm spot or center weighted TTL metering can be selected. There is a separate exposure check button for those who prefer it to partly depressing the shutter button. There is an AE lock switch. With a custom function, AE lock may also be achieved by partly depressing the shutter button or the exposure check button. Exposure compensation is handled by a dial on the top right side of the camera with +/- 2 EV compensation in 1/3 EV increments.

The viewfinder is bright, relying on a large pentaprism. It shows 95% of the actual field of view at .7x magnification. The viewfinder shows lots of information including focus indication, film plane position, aperture, shutter speed, exposure warning, flash indicator, exposure compensation and exposure counter.

There is no mirror lockup but there is multiple exposure capability. There is also a depth of field preview button. The camera relies on a single 2CR5 lithium battery. A data back is available that can print information on the first two frames or in between frames. There are also eight custom functions that change operations like auto film rewind and leader in/out. There is a self timer, dioptric adjustment with optional lenses, inter-changeable focusing screens. Autobracketing is either +/- .5 EV or +/- 1 EV.

For flash photography there is 5 pin communication with the dedicated Contax flash units. The Contax flash units are excellent - particularly the TLA 360.

Conclusion

I have small hands, so the AX feels like a big package to me. The most particular difference is that the camera is thick from front to back. After using it for a while I no longer notice this, but the initial feel is different than most SLRs. The camera balances and moves very well. The weight and size is not an issue for one used to heavier SLRs. It does not seem much different in these respects than an F4, 1N or RTS III. It is a very comfortable camera to hold and the placement of the controls is quite good. Contax has standardized the general layout of most of the controls on its more recent cameras. This is smart idea and is quite different than most manufacturers whose cameras differ from each other so dramatically in the layout of their controls (Compare a Nikon N70 to an N90 or Canon 1N to Elan IIe).

The general capabilities of the camera are similar to most modern SLRs. The advantage is the design philosophy of its creators. Like all Contax cameras, the AX is solid and straightforward. What it does is similar to its contemporary competition from other companies. How it does it is pure Contax.