DSLR “Movie Mode” Patent

Mirror - SensorWith the pervasiveness of Live View modes from DSLR makers, it is only a matter of time before similar technology brings a “movie mode” to DSLRs.  While the ability to record video is a common feature among point & shoot cameras, technological challenges make the incorporation of a video recording more difficult in DSLRs.  A recently published patent application by inventor Hiroshi Terada may change all of this.  The patent addresses many of the technological hurdles that have prevented incorporation of a movie mode into DSLRs.

As we all know, DSLRs are designed for optimal performance in capturing still images – and DSLR manufacturers have truly raised the bar over the past couple of years.  Accordingly, DSLRs are specialist tools that have been optimized to have a very narrow focus tolerance and an ever-increasing auto-focus speed.  These features are not quite conducive to smooth video capture.  Additionally, the field-of-view changes, albeit slightly, during auto-focus operation.  Finally, fast and accurate hand-held auto-focus is dependent up accurate phase-difference AF evaluation, which requires a mirror to reflect the image to the AF sensor.

As you can see, getting live image to the image sensor and capturing smooth, in-focus video seems difficult to achieve without sacrificing some still image capture properties of DSLRs.  These obstacles, among others, are what Mr. Terada attempts to overcome in his patent application.

AF Tolerance

Terada’s patent calls for 2 different AF functions – one for still captures and one for movie mode.  In the preferred embodiment of his invention, the focusing tolerance is doubled in movie mode so that there is a deeper range of distances that are “in-focus” according to the AF sensor.

This is because if the focusing accuracy is set high, the photographing lens is driven fractionally as mentioned above to cause a hunting phenomenon or the like, resulting in poor usability.

Terada’s patent also calls for achieving the same results using other focusing methods as well.

The present invention is applicable to contrast AF for performing AF by extracting high frequency components from the subject image signal output from the image pickup device. In this case, a threshold value considered to be in focus in the contrast AF system can vary between still image shooting and moving object shooting, i.e., the threshold value range for moving object shooting can be set wider than that for still image shooting.

AF Speed

In addition to splitting the AF tolerance between still image and movie modes, Terada’s patent calls for two different focusing speeds.  This is necessary to keep the camera competitive with current AF performance for still images that we have all grown to expect from our DSLRs and, at the same time, have smooth AF during the movie mode.  The patent application describes the movie mode AF speed as follows:

After completion of setting the in-focus determination value, the low-speed lens driving mode is set as the lens drive mode . . . . As mentioned above, if the lens is driven in the high-speed lens driving mode during moving image shooting, driving and stopping are repeated fractionally to increase the possibility of causing hunting. Therefore, in the embodiment, the low-speed driving with less acceleration and deceleration cycles is performed during moving image shooting . . . . Since the lens is driven toward the in-focus point smoothly without a hitch, a reasonable picture without a sense of discomfort can be obtained during moving image playback.


AF DiagramAs noted above,  the field-of-view changes slightly during auto-focus on DSLRs.  This would result is a jumpy/erratic video image when the focus point changes during filming.  Terada’s solution is to implement a cropping function during the movie mode.  Terada’s cropping function allows users to zoom (zooming is still performed by the standard manual adjustment ring on the lens), but catches the FOV changes that occur during AF adjustments.

[C]ropping is performed based on the angle-of-view variation . . . during moving image recording unless zooming is performed, so that the angle of view can be maintained constant even if the in-focus position of the subject changes.

. . . .

Further, in the embodiment, image cropping is performed according to the angle-of-view variation of the photographing lens . . . . Therefore, even if the in-focus position of the subject changes during moving image shooting, a constant angle of view can be maintained and hence an image without a sense of discomfort can be obtained. In the embodiment, this cropping is performed only in the moving image shooting operation, but cropping can also be performed during live view display in the still image shooting mode.

Mirror Position

MirrorWe’ve examined the auto-focus obstacles that Terada’s patent addresses; however, the big issue is what to do with the mirror in the DSLR.  The mirror is necessary to reflect the light that passes through the lens to the AF sensor.  In traditional still image capture, once AF is acquired and the shutter button is fully depressed, the mirror rotates out of the path of the light to the image sensor and the shutter opens for the set duration – exposing the sensor to light. In order to operate at 30 frames per second (the video capture speed called for in Terada’s patent), the mirror would have to bounce up and down 3 times faster than the rocket-fast Canon EOS 1D Mark III.  Clearly, that’s not a desirable (or quiet) way to do video on a DSLR.

The patent calls for a mirror that remains in the path of light.  It’s a special mirror though.  It reflects 30% of the light and transmits 70% of the light, allowing the light to make its way to the image sensor without moving anywhere.

The benefits of this semi-translucent mirror are two-fold.  First, the reflected light allows AF to occur via the traditional phase-detection method.  Second, live view (during still shooting) and video (during movie mode) can co-exist with fast AF due the transmittal of light through the mirror.  Live view “still” shooting allows the mirror to retract from the light path upon image capture.  Due to the reduced quality necessary for video capture, the transmitted light is used for movie mode and the light reflected via the mirror is used for continuous AF.

Further, in the embodiment, since the target image quality is different between still image shooting and moving image shooting, the position of the mirror member . . . is changed. In other words, since still image shooting typically requires a high image quality, the mirror member . . . is retracted from the shooting optical path to prevent degradation of image quality caused by the mirror member . . . . On the other hand, since moving image shooting does not require the high quality for still image shooting, the mirror member . . . remains in the shooting optical path to eliminate the time required for inserting and retracting the mirror in order to reduce the time lag to the start of shooting.

Further, in the embodiment, the mirror member . . . is inserted into the shooting optical path upon activation of the camera to reflect part of the subject light beam into the distance measurement/light metering sensor . . . . Therefore, when the release button . . . is pressed halfway to turn . . . on during live view display, light metering and distance measurement can be performed immediately and conveniently in parallel with the live view display.

In the embodiment, the CCD . . . as the image pickup device receives light transmitted through the mirror member . . ., while the distance measurement/light metering sensor . . . receives light reflected by mirror member . . . . However, on the contrary, the digital camera can be configured such that the CCD . . . receives reflected light and the distance measurement/light metering sensor . . . receives transmitted light.


This has seemed inevitable to me for some time now.  Given that all of the major DSLR players feature some form of live view in at least part of their camera lines, I expect that a manufacturer will release a DSLR with a movie mode in the near future, perhaps this year.  Personally, I expect this to be a consumer-grade DSLR, which would fit the market for such a feature.  Additionally, I can see how this feature would be useful among photojournalists in today’s web-intensive media world.

What do you think about have a “movie mode” on your DSLR?  Do you want it now!?  Do you hate the idea?  Would you ever use it?

Source: Pat. App. No. US 2008/0030594.

Movie Mode Process



  1. says

    Interesting patent!

    I’m not waiting for a video function on my dslr, but I wasn’t waiting for live-view as well. It nevertheless proves to be a usefull addition.

    Video on a DSLR might be usefull on certain moments as well.

  2. says

    Honestly, this, along with Live View, are features that I just really don’t see being all that useful. I have the strong sense that camera manufacturers are beginning to cast about for a new feature that will gather headlines – megapixels are becoming functionally irrelevant unless the photographer is doing large-scale commercial work (and those folks use Medium format).

    Honestly, who uses Live View? For what? Maybe for close to ground macro work I could see the usefulness, but holding a DSLR at arms’ length to take a photo? Ouch.

    I have it. Live View is a VR/IS selling tactic! With legions of photographers roaming around holding their DSLRs in front of them like lost tourists, they’ll HAVE to buy image stabilization lenses! Hahahha.


  3. John says

    I think live view and movie mode will only make the DSLR more attractive for “point and shoot” photographers who totally miss the point about having a DSLR. They might buy it and use it with the *sometimes* crappy kit lens for it’s life and do nothing but take snapshots with it and complain when it’s “blurry” cos the subject’s out of focus. Then they’d complain about how bulky it is … and only ever use it in Automatic …

    I think it’s a total ploy to sell more cameras – DSLR’s and make the camera manufacturer’s more money. After all – these “innovations” aren’t at the heart of the DSLR at all – I brought my DSLR because I wanted to have clearer, larger, nicer photos with the creativity of different lenses, and RAW touchup capability and long-exposures. This doesn’t in any way help the image quality – I think that most people buy DSLR’s for their image quality and less so as a statement. But attracting non-technical / photographical types to get a DSLR will only result in much more confusion about lenses … and how to use it. I’ve even been asked how to turn the shutter sound off in a DSLR. HA!

  4. says

    Everyone, it would be an amazing feature for film makers. The reason why DSLRs are better than Point-and-shoots is mostly because the shallow depth of field. The cheapest video camera that can do that is like 19,000 dollars for the body alone.
    live view is almost pointless in my opinion. but being able to capture shallow depth of field video is a dream of mine. I’ve built adapters before for video cameras, but this would be so much better.

  5. craig king says

    Didn’t Konica Minolta have a design for movies in their line of diamage series before they got bought out by Sony

  6. kg says

    This reminds me ery much of the viewfinder system in 8mm and other movie cameras. A prsm split the light, some going to the viewfinder, some to the film. I believe some had mirrors on their bladed shutters, but that introduced flicker, even if it meant all available light was going to the film for every exposure. I’d been wondering whether I’d need a video camera and a DSLR, since I shoot both, but having both in one camera would save weight and hassle.

  7. Joeyabc says

    The Future is now! the d90 from Nikon has a movie mode at 720p, but it will be limited to manual focus and max 5 min vidoes (it has to stop to let the sensor cool down)

  8. VALMAM00 says

    This is just a shortcut to nowhere! Some people can find useful to have a “video mode”, others, no at all. DSLRs’ are mainly designed for still images at the best quality (and creativity freedom) possible. Of course these machines would also include radio or TV, work as a mobile (ha ha!), and as far as you can imagine, and still may be this is not altering the main function -i.e. to make photos correctly, but….

    Anyway, I suspect serious photographers will prefer a goog DSLR -just a DSLR, and a film maker a good video camera, for a long, long time.

    If you’re planning to cross the Atlantic Ocean would much prefer a plane than a helicopter!

  9. says

    Convergent technology works just this way. A new niche is being filled by hybrid Still/Video Cameras at all levels from hand held mobile phones with such capability, all the way to Full size professional SLRs and Video cameras that cross functions between domains. As a longtime pro still shooter that later added video capability to my skill-set, I find the convergence compelling. It not only conforms to my ‘hardware ecology’ – that is, do more with fewer discrete tools. But from a practical standpoint it makes huge sense. Field shooters in both domains profit enormously from being able to perform multiple functions with one device. As my life and yours, become more Net-Centric, we tend to gather content in a voracious and multi-dimensional manner. Switching constantly back and forth between professional and personal, scouting and shooting, still and video is a new niche that is effectively addressed with the hybrid technologies. Someone asked me who would be the driving force from a manufacturer’s standpoint. I’d guess Canon though Sony has parallel expertise as well.
    So the convergent pro-summer image capture device of the future will more likely look like a Still Digicam with a flip-out screen, Full HD capture capability and a plethora of storage options.
    My only hope is that someday they’ll hire a human factors professional to get the GUI/SUI right!

  10. says

    The development of Movie Mode in DSLR is extremely valuable for independent film makers. Up until now we have been forced to use 1.3″ chip CCD or CMOS camcorders which have problems with shallow depth of field. To compensate many digital film makers have purchased expensive 35mm lens adapters in order to use their still camera lenses. The effect has been a vast improvement of using the camera as a storytelling tool. However, with most adapters the light gets cut down by between 1 to 2 stops. With the advent of Movie Mode in DSLRs this changes the whole playing field. A vast range of stills lenses can be used. As the Movie Mode uses the full CMOS chips and down converts the image to 1920 x 1080 pixels an higher quality image can be produced. Though sound may be added to the movie within the camera, I prefer to shoot separate sound and synchronise with a clapperboard. This means the camera operator can concentrate on the visuals while a sound recordist concentrates on the sound quality recorded in a Compact Flash Recorder.
    With a camera such as the Canon EOS 5D MKII coming in at around £2200 this competes well with prosumer HDV camcorders. The desire in the UK will be for a 25fps or 24fps Movie Mode camera and the capability of editing in Apple’s Final Cut Pro, Adobe Premiere or Avid Media Composer.


  1. […] O grande problema é que o sistema de focagem para ser rápido (leia-se baseado em análise de fase) precisa de um espelho, enquanto os sistemas de AF sem espelho (baseados em análise de contraste) são mais lentos. Por isso é que as Point & Shoot demoram tanto tempo a focar. Ora isto pode vir a mudar no futuro próximo. O Live View já existe em alguns modelos e uma patente registada recentemente parece indicar o caminho para se poder ter filmes numa máquina DSLR. […]

  2. […] PhotographyBay publie l’intéressante histoire de Hiroshi Terada, un inventeur japonais qui a mis au point un système permettant d’envisager une fonction d’enregistrement vidéo sur un reflex. Terada est part du constat qu’un reflex était incapable de faire de la vidéo pour diverses raisons. La première est liée au miroir, pour enregistrer de la vidéo un miroir de reflex devrait monter et descendre à une cadence particulièrement irréaliste. Les reflex professionnels les plus rapides atteignent un peu plus de10 images par secondes, pour faire de la vidéo il en faudrait 3 fois plus. […]