December 28, 2013
The EOS-M is Canon's first foray into the interchangeable-lens mirrorless camera market. It is a relatively compact, lightweight, and fairly flexible camera with a sensor that is typically found in an SLR. Similar cameras include the Sony NEX series and the Fujifilm X series. The extremely low cost, among the cheapest APS-C format cameras you can buy, make it great for experimentation. Available at B&H Photo for $349 with 18-55mm lens and Speedlite 90EX Flash.
The lens mount used is Canon's new-for-this-camera EF-M mount. The relatively short flange-to-focal-plane distance of 18mm (vs. 44mm for the EF mount) means that adapters are available for the use of most SLR system lenses.
Let's take a look inside. But first, if you're following along at home, a few notes of warning:
To gain entry, start by removing the side panel exterior screws, including one screw under the left side connector cover.
Next remove the exterior screws around the 1/4-20 tripod mount and the hot shoe, and screws exposed by removing the side panels. This will release the front half of the plastic enclosure. Not much force is required to remove these panels: if you're applying force, there's probably something wrong.
This exposes more screws to be removed.
To remove the rear plastic, you'll need to gently pry a small latch to the left of the hot shoe. Don't immediately pull the plastic cover away: it is attached to the rest of the camera by a delicate flexprint interconnect, which will need to be disconnected.
To disconnect the interconnect, use a small flathead screwdriver to pry up on the orange tab of the connector on the main PCB.
With the rear cover removed, the LCD can now come off. First release the two flexprint connectors so there's no risk of tearing one of them.
In some cases, it can be difficult to wiggle the flex PCB out of the connector: note that there are tabs which you can push on with a screwdriver tip.
Remove the LCD by pushing it up (towards the hot shoe) and pulling the top of the LCD outwards.
The left side panel, the tripod mount, and the LCD bracket can simply be pulled off.
The main logic board is now visible. It can be unscrewed, but before removal, there are a few more flex interconnects and plain wire connectors to disconnect. Tweezers are helpful here, but be very gentle: these are delicate.
The logic board is free. More on the logic board later.
There is a thin sheet metal bracket over the battery compartment which comes off with two screws.
Turning our attention to the other side of the camera, the top frame of the camera can be removed with a few screws.
Next you can unscrew more screws to remove the battery compartment portion.
If you don't want to mess up your focus calibration (the flatness of the focal plane) stop here.
The sensor assembly and shutter is held on to the lens mount frame by three Torx screws against springs. The springs allow for optical adjustment of the sensor to flatten the focal plane. They should not be fully tightened.
The shutter assembly is shown below. We're not going to tear down the shutter assembly here (maybe another time).
The camera uses a cast main "frame" to hold the lens mount. This style of construction makes for a really sturdy platform for such a compact camera. Another flexprint interconnect links the main logic board with the lens: if you wanted to tap the lens-CPU communication without disrupting infinity focus capability, this might be a good place to do it.
The sensor is an 18MP APS-C format CMOS sensor, measuring 22.3mm x 14.9mm. It is made by Canon and also used on the EOS 650D (Rebel T4i), among others.
Covering the sensor is a stack of three components:
A metal retaining frame. This frame is secured by two screws and is shaped with long leaf attachment points, so as to minimize pressure on the filter layers.
The Canon Integrated Cleaning System actuator. This is a filter which vibrates at ultrasonic frequencies to shed any dust that accumulates on its surface.
An infrared blocking filter. This is a dichroic filter, often referred to as a hot mirror, which prevents infrared light above about 750nm from reaching the sensor. When looking at one side, this filter appears pink; when looking from the other side, it appears blue.
The stack can be disassembled with three screws.
The IR blocking filter is sealed to the sensor with black adhesive around the outside. You'll need to cut that adhesive (an X-acto knife works well) if you wish to remove it.
Note that this filter is very delicate. If you're removing it for the sake of converting your camera to IR-only or wide-band, you don't have to worry about breaking it, but if you intend to reassemble the camera, use extreme caution when working near this filter.
Otherwise it will look like this:
The backside of the sensor shows the CMOS controller IC and associated circuitry.
A closer look at the logic board shows the two main chips running the show. The one on the left side is the system control processor, marked with F74964A.
The back side of the board holds the SD card, some power conversion circuitry, and connectors. There is a plastic guard over some traces on the board, because they come in close proximity with other metal parts inside the camera. Be sure that they are back in place if/when re-assembling the camera.
Overall, the camera is actually fairly simple, contains very logically grouped subassemblies, and is easy to work on. Tools required are fairly minimal, and aside from the need to maintain a low-dust environment, this camera is actually very repairable.
If you have any questions, comments, or suggestions, please send them my way!
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