Canon DSLR Dual Image Viewfinder

Canon DSLR Dual Viewfinder

A pair of recently published Canon patents reveal a new viewfinder system for Canon DSLRs that will allow photographers to “chimp” their shots without ever taking their eye off the viewfinder.  The patent applications filed in the United States Patent and Trademark Office (“USPTO”) under application numbers 12/495,813 and 12/495,814 were each filed on July 1, 2009 and published by the USPTO on January 7, 2010.

The essence of the technology claimed under the patents is an advanced viewfinder system that uses a small backlit LCD or OLED inside of the finder to project previously captured images onto a mirror in the pentaprism, which in turn, is reflected toward the eye of the photographer.  As a result, the photographer sees two images in the viewfinder – the live optical image and the previously-captured image from the LCD.

The purpose of this invention, as stated in the patent, is to help the photographer be more efficient by keeping his or her eye in the viewfinder and not having to pull away from the action in order to check exposure, white balance, focus and so on.

Canon Dual Viewfinder

The layout of the new viewfinder system, as shown in the image from Canon’s patent application above,  would place the electronic preview image on top, the optical image as the main image below it and, finally, the information bar at the bottom of the finder window.  As you can see, the anticipated design calls for a rather small preview image and a much larger optical image that conveys your live image composition.

Canon describes the functionality of the internal LCD in the patent application as follows:

The composite signal generated by the signal processing circuit is output to the liquid crystal display device of the finder apparatus. The liquid crystal display device displays an electronic subject image. The liquid crystal display device is positioned between the pentagonal prism and the eyepiece lens.

The liquid crystal display device includes a liquid crystal display (LCD) element and the backlight. The (LCD) element is a display element that can display a color image. The backlight illuminates a display surface of the LCD from the rear side. The backlight may be constituted by a white light-emitting diode (LED).

The pentagonal prism includes a surface that forms a flat surface continuously extending from a third reflection surface (see FIG. 3). The pentagonal prism and the prism have the same refractive index and are bonded together with an adhesive selected according to the index matching.

The light beam (i.e., light flux) emitted from the liquid crystal display device reflects twice on the inner surfaces of the prism and can reach the eyepiece lens. – USPTO App. No. 12/495,813 at ¶¶ [0062-65]

Who’s It For?

Canon DSLR Dual Viewfinder Close Up

One of  the questions that comes up when reviewing published patent applications is determining what kind of product the proposed technology will end up in.  Obviously, we are talking about a DSLR with an optical viewfinder in the case of these patent applications.  However, which segment is this tech geared toward – pro or consumer?

My take on this tech is that it is geared specifically toward the pro shooter.  For one, size matters.  Pro cameras just have a lot more room to stuff extra bells and whistles into the finder system.  Just look at the Rebel series compared to even the 5-series, let alone the 1-series.  The consumer models do not have the room to stuff another display inside the already-small optical viewfinder.

More importantly, however, is that the need for this tech lies in the pro market segment where getting the shot matters most and means money at the end of the day.  While the most obvious fan of this type of finder system would be the sports shooter, who often does not have the time to chimp on the sidelines during the action, I can see other pros and advanced amateurs benefiting from it as well.

Wouldn’t it be nice to chimp a couple of shots here and there with your eye in the finder?  Posing can be reviewed on the fly without dipping back into the preview function on the rear display to check the past dozen or so shots.

Assuming that this tech is effectively implemented in a pro DSLR, I would expect to see fans and foes of the design.  A big question that comes to mind is whether the secondary display will affect the coverage or magnification of the traditional optical finder.  If it will, then I would expect many more foes.  If, however, Canon can open up the finder window to make room without materially altering the coverage or magnification of the optical display, then it may have a huge feature on its hands.

Taking the Finder System Further

One function not described in the patent applications would be using the electronic viewfinder display as a live view display for video recording.  Anyone who has put forth any serious amount of effort recording video with a DSLR understands that achieving critical focus with only the rear LCD screen is challenging at best.  I find that a third party device like the Z-Finder is essential for maintaining focus while recording video.

Because the signal received by the internal finder LCD is delivered by the processor, it does not take much to deduce that it could also be used for a live display of video.  Application 12/495,813 further notes that LCD-generated image can be viewed regardless of whether the mirror is up or down.

Final Words

As always, remember that we are only talking about possible, future technology here.  Canon and other camera manufacturers file many patent applications each year for which the underlying technology never sees the light of day or at least does not come to fruition for years to come.  As a result, I never recommend making purchasing decisions based on what might come out next week, month or year.  Finally, all of the information within this article is derived from my own opinions on and interpretation of the published and publicly-available patent applications.

If you are interested in how Canon deals with technical issues of temporary memory and image distortion in the pentaprism, you can check out the patent applications for yourself on the USPTO website:

USPTO App. No. 12/495,813

USPTO App. No. 12/495,814

If you have an opinion about this technology, feel free to share it in the comments below.  I would love to hear what you think about putting the secondary display inside the finder system.



  1. Ronny says

    I just looked into the 5D viewfinder and there is quite some empty room inside. The idea is very good of not having to take your eye away from the viewfinder. And from the ‘blueprint’ it even looks feasible. I only wonder how high the resolution of the LCD can be and thus how useful such a projection could be in real life.

  2. Jerry says

    As I see it, review of a photo taken would be useless at that size, however a real time histogram (like in live view mode) would be perfect.