Canon has applied for a patent for a viewfinder design that combines both optical and electronic displays in a DSLR style system. Via a system of mirrored prism the design allows users to benefit from all the advantages of both EVF and TTL optical systems through the same eye piece. Menus can be overlaid on a normal optical view, or a live view function can be used through the viewfinder – which would be of great benefit to video shooters.

In Canon's new hybrid viewfinder design light passes through the lens as usual and is reflected through a ground glass screen into the pentaprism. As it exits the pentaprism is can be supplemented with light from a LCD panel (labelled '9') that is projected through a series of lenses and bounced from a half-mirror (6b) and on to a reflective surface (6). The two sources of light combine and pass to the photographer's eye via the eye piece (8). When the mirror is in the up position the image recorded by the sensor (12) can be sent directly to the LCD panel (9) so the photographer can get a live view of what the sensor is recording. Thus the system combines the best elements of electronic and optical viewfinders.

Through a clever use of optics and a mirrored prism, the new design allows a 'full screen' display across the whole viewfinder. The significance of the system is that DSLRs will be able to gain some of the advantages of mirrorless systems, such as full menus and playback in the viewfinder, and shooting information could be shown across the larger screen instead of just the bottom or sides of the screen. This would also make possible video shooting through the viewfinder, which could become important if technologies like Dual Pixel AF start to replace secondary-sensor PDAF systems. This would eliminate the need to switch between viewfinder and rear screen shooting to change from stills to video mode, creating a more consistent experience.

The system allows menus to be viewed and accessed as they are overlaid on the image produced by the optical finder

The patent description explains that one of the challenges has been to ensure that the image projected from the electronic screen matches that of the optical system, which is why the screen has been placed close to the viewfinder instead of before the prism, where there might have been more room. Being on the viewing side of the prism means less magnification is needed to create an image big enough to coincide with that of the optical view.

The projection system uses a complex set of lenses to reduce the size of the construction so that the manufacturer shouldn’t have to make physically larger cameras to accommodate it. Canon also indicated that it has taken steps to reduce the impact of the half mirror that has been placed in the optical path. It says that the angle of the mirror is optimized to allow as much light to pass as possible.

The heads-up display type viewing system is nothing new, and although it has been discussed in camera circles before we have yet to see a good example of technology combining optical and electronic views. The closest we have come is the hybrid viewfinders used by Fujifilm in the X-Pro and X100 series of cameras, but Canon's method is the first to combine an EVF with a TLL viewfinder, rather than a more rangefinder-style arrangement.

Canon’s patent was applied for in 2014 and the information only just published, so the company may be in a position to introduce the system quite soon. However, as with any patent there's a chance nothing will come of it, no matter how good an idea it is. We will just have to wait and see what, if anything, comes of it.