Sunday, June 30, 2013

Diving Deep Into HDSLRs

By The Editors Published in Digital SLR Cameras
Diving Deep Into HDSLRs

Showing Your Work

HD video files are huge, making getting examples of your work out to potential clients a challenge. Probably the best way to do it is to post the video on Vimeo or YouTube, and send the client a link. A Vimeo PRO Membership provides unlimited HD uploading and lets you control who can watch your videos, and the cost is far less than sending out hard drives. For most natural-appearing video, the shutter speed should be close to 1/2X the frame rate: 1⁄60 sec. for 30 fps, 1⁄50 sec. for 24 fps, 1⁄125 sec. for 60 fps, etc. Faster shutter speeds make the images of moving subjects in each individual frame sharper, but result in a jerky effect when the video is viewed. Conversely, slower shutter speeds result in more blur of each moving subject, but the motion appears smoother when you view the video. You can experiment with different shutter speeds, but the 1/2X frame rate rule of thumb is a good place to start.

Keep in mind that shutter speeds used for video shooting are pretty slow compared to those used for still photography. The fastest common video frame rate is 60 fps, calling for a shutter speed of 1⁄125 sec. per the 1/2X rule of thumb. If you intend to pull still frames from your video, faster shutter speeds are necessary; slow shutter speeds will result in blurred moving subjects, something that's not that noticeable when watching the video, but would be quite evident in a still image. Pros who are savvy to a still + motion workflow slow down the action on set to get sharper frames and use video mode as a 24 fps still camera to get frames that capture the perfect moments in a movement (see "The Beauty Within," DPP, September/October 2012, page 44). Of course, you can always use your DSLR as a still camera to get top-quality still images.

For most natural-appearing video, the shutter speed should be close to 1/2X the frame rate: 1/60 sec. for 30 fps, 1/50 sec. for 24 fps, 1/125 sec. for 60 fps, etc. Faster shutter speeds make the images of moving subjects in each individual frame sharper, but result in a jerky effect when the video is viewed.

Global Shutter

The focal-plane shutter in the DSLR is used only for still photographs. For video, the sensor's own electronic shutter is used (and a good thing, or you'd run through your focal-plane shutter's 150,000-cycle life in about 45 minutes of 60 fps video).

CCD sensors use a global shutter; they effectively expose all the pixels simultaneously. CMOS sensors use a rolling shutter; they effectively expose the pixels row by row starting at the top. With still photos, this doesn't matter much. With video, the rolling shutter can adversely affect moving subjects (and stationary ones when the camera is panned across them) since the subject position will be different as each line of the image is recorded.

Most pro digital camcorders use CCD sensors, and thus don't have the rolling-shutter problems. Most DSLRs use CMOS sensors, and thus do produce rolling-shutter effects. Newer cameras minimize the effects, as does careful shot planning.
Login to post comments
Subscribe & Save!
International residents, click here.