With the central and left section of the camera sorted out, it's time to move onto some of the complicated mechanisms that need to be squeezed between the circuits and the front of the lens section on the right hand side. The main mechanism which takes spacial priority over everything else is the autofocus system. It's going to be big, due to the necessity of a motor, and it's going to need good support so the lens unit (the barrel containing the glass elements) moved fluidly without interference from any other component.
FYI - How does autofocus mechanisms work in general? A lens is made up of a series of glass elements. There can be anything from 3 upto 12+ lenses in a typical lens, with more complicated lenses usually including some method of zooming. On a simple prime lens, ie one which doesn't zoom, the group of lens elements focus rays of light to a point of convergence. This point has to land exactly on the image plane, which in a digital camera is the sensor, in order to make a sharp photo. However, there is also a point of convergence infront of the group of lenses, called the focus distance. This point can be anywhere from a few cm infront of the camera, to infinity. When you want to focus on something, you don't want to physically move for the subject to be the correct distance away to land on that focus distance, so instead the lenses move. The group of elements move all together (in simple lens designs), changing the point of focus both behind and infront of the camera. A motor will move the group back and forth until the image sensor see's a sharp image of your subject.
Having designed lenses before and investigated different manual focusing mechanisms I was familiar with traditional focus systems. In an typical electronic autofocus lens, such as one you'd fit to a DSLR, the inner moving barrel containing the glass elements moves up and down by twisting along a screw path. The barrel has pins sticking through a screw shaped slot, and a fixed position motor turns the barrel. As it turns, it is pushed up the screw. You can see in the photos above the screw forms and the gear transmission which drives the barrel around. Simple, elegant, achievable.
While searching online for photos to demonstrate the traditional method of focusing, I stumbled across a new mechanism I hadn't seen before. The mechanism uses a stepping motor to drive a lead screw, which pushes the lenses along rails. This mechanism is present on a new range of lenses from Canon and Tamaron. I'm not sure why this mechanism hasn't been used before now; maybe good stepper motors weren't miniaturised enough.
Either way, this new system is the one I cam going to use in my camera. As the lens group is simply pushed along rails, they don't rotate, which simplifies the design of adjacent components at the front of the camera. I also find this layout more logical, and have some ideas (see scan at the top) of how using rails could help the integrity of the rest of the body.
