Movies recorded with DSLR cameras have been highly rated for their image quality. At the same time, however, it is said that as video cameras, DSLR cameras leave much to be desired in terms of AF performance. In the following, let us try recording movies using the EOS 70D and assess the usefulness of its AF performance. (Edited by: Video Salon, Reported by: Kazuhiko Saika)
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Differences between camcorders and DSLRs
Before the release of the EOS 5D Mark II, camcorders were the main tool for recording movies. During this era, camcorder manufacturers competed against one other in aspects such as autofocusing speed and accuracy, image stabilization, and zoom ratio. However, with DSLR cameras entering the world of movie shooting, new trends have been created, such as beautiful film-like depictions and images with a shallow depth of field. This marked the beginning of a digital cinema age where DSLR cameras with a large CMOS sensor are used.
Although DSLR cameras have attracted the attention of many movie producers, aspects other than image quality still leave much to be desired when compared to video camcorders. One of them is the autofocus (AF) function. While camcorders could carry out the focusing work on their own, the AF performance of DSLR cameras for movie shooting remained a far cry from a level that was practical enough. Therefore, focus was basically adjusted manually in the case of the latter. In other words, handheld movie shooting with a DSLR camera was almost impossible, so it became a common practice to record movies with a DSLR camera secured to a tripod in the same way as is usually done for professional movie cameras.
Of course, securing a DSLR camera to a tripod allows stable images to be captured, but it lacks the mobility and comfort that a video camcorder offers. This was why using a DSLR camera for movie recording did not become a widespread trend among general users.
This sample movie was taken using the EOS 70D. There are three AF modes on the EOS 70D, namely [Face + Tracking], [FlexiZone - Multi], and [FlexiZone - Single]. Here, I chose [Face + Tracking] for this recording. With the camera held in my hands, I altered my distance from the subject, zooming in and out every once in a while. The face detection and tracking performance were excellent. Despite the relatively shallow depth of field (f/4.5-5.6), the camera was able to capture the facial expression of the subject at all times without going out of focus. This allows the photographer to produce high-quality movies by concentrating on the composition and camera operation while leaving the focusing work to the camera.
A Dramatic Evolution in AF Performance
DSLR cameras, defined by features such as the optical viewfinder, have all along been intended for capturing still photos. High-speed and high-precision autofocusing is possible due to the use of a special sensor for phase-difference detection. However, this special AF sensor could not be used during Live View shooting and movie recording because the image sensor always captured images with the mirror locked up in these two cases. Therefore, AF would be performed by detecting contrast in the captured image ("contrast AF") instead.
Although contrast AF enables highly accurate focusing, one of its drawbacks is the difficulty in achieving high-speed AF. Based on this consideration, Canon developed the Dual Pixel CMOS AF, which enables the phase detection AF technology to be applied on the image plane. Because all the pixels on the image plane are able to perform both the functions of phase-difference detection as well as imaging, this allows for fast and highly precise phase detection AF over a wide area without compromising the image quality. This is also a very effective technology for AF during movie shooting.
It is not an overstatement that this new AF method, together with the precise STM lens drive mechanism, took the DSLR movie shooting experience to a new level. With the release of the EOS 70D, we are likely to see a major turning point in the history of movie recording in the near future.
* Unless otherwise stated, the EOS 70D Kit II (EF-S18-135mm f/3.5-5.6 IS STM) was used for this test.
Image sensor: Approx. 22.5mm × 15.0mm (APS-C) CMOS
Pixel count: Approx. 20.2 megapixels
Lens mount: EF
Lens supported: EF (including EF-S)
Recording format: MOV
Movie compression: MPEG4 AVC/ H.264
Compression method: ALL-I/IPB
Recording size and frame rate:
1920 × 1080 (Full HD) - 30p/ 25p/ 24p
1280 × 720 (HD) - 60p/ 50p
640 × 480 (SD) - 30p/ 25p
Recording media: SD/SDHC/SDXC
Monitor: Wide 3.0 inch (approx. 1.04 million dots)
Weight: Approx. 755g (CIPA standard)/ approx. 675g (body only)
Currently a professor with the Faculty of Media and Information Resource at Surugadai University, Mr. Saika was formerly a planning producer at an advertising company and a certified trainer for a high-end editing system. His recent artistic activities centre on videography with DSLR cameras, and he is currently experimenting with 4K videos.
Video Salon started publication in 1980, and is Japan's only niche magazine on videographic equipment. Catering to readers who range from serious amateurs to professionals, it enjoys an established reputation not only for the information it provides on video cameras and editing software, but also on its drive-run reviews on videography with the latest DSLR cameras and its expert tips and tutorials.
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