Specifications

Apertures, sensor size and

depth-of-field

Some video shooting tips

If the shutter speed is set between around 1/30 second to 1/125 second, subject movement

will look smooth in finished video files.

The faster the shutter speed, the less smooth the

subject movement will look. However, you could intentionally use a fast shutter speed and

then use ZoomBrowser EX/ImageBrowser to extract still images (several tens of frames per

second) from the video clip.

The large apertures (f/2, f/1.4 and f/1.2) and long focal lengths available with many Canon

EOS system lenses make shallow depth-of-field/selective focus easy to achieve with the

EOS-1D Mark IV. The large APS-H size sensor (approximately super 35 format), midway

between the full size sensor of the EOS 5D Mark II and the APS-C sensor of the EOS 7D,

also contributes to effortless shallow DOF. (The larger the sensor, the longer the focal

length required to produce an equivalent field of view. All else being equal, a longer lens has

a narrower field of view and shallower DOF.)

The majority of professional video cameras in the $20,000 to $80,000+ range have sensors

that are described as 2/3'', according to published product data. These sensors measure

approximately 8.08mm by 6.6mm with a consequent diagonal of 11.0mm. The EOS-1D

Mark IV’s APS-H sensor is 27.9mm by 18.6mm (33.5mm diagonal). By area, then, the

sensor of the EOS-1D Mark IV is approximately 9.8 times larger than the most common

sensor size of professional ENG camcorders. In addition to the implications for depth-

of-field, the EOS-1D Mark IV’s larger sensor size makes high resolution with relatively

large photodiodes possible, resulting in significantly greater low light sensitivity and less

noise than smaller sensors at equivalent ISO settings.

Comparing crop factors is interesting, too. In the world of digital SLRs, crop factor is

defined as the ratio of the diagonal of a full 35mm frame, 43.2mm, to the diagonal of the

frame in question. It often comes up in considerations of how lenses will work on various

camera bodies. Smaller sensors have larger crop factors. The EOS 5D Mark II has a crop

factor of 1. The EOS-1D Mark IV’s is nominally 1.3 and the EOS 7D’s is 1.6. A 50mm

lens has an effective focal length of 50mm on a 5D Mark II, 65mm on an EOS-1D Mark IV

and 80mm on an EOS 7D, in terms of angle of view. On a pro camcorder with a 2/3''

sensor, the crop factor of 3.93 yields an effective focal length of 196.5mm for a 50mm lens.

These numbers help to quantify the new realms of focus differentiation that are achievable

with Canon’s new HD video-capable DSLRs.

With the camera ready to shoot a video, the time lag between pressing the FE lock button

and when the video starts shooting is approximately 0.2 second.

To save videos to a CF card, the card's actual writing and reading speed must be 8MB/second

or faster. If recording to an SDHC memory card, the card must be Speed Class 6 or higher.

IV–3. EOS HD VIDEO CAPTURE