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Exposure Index (ASA) Equivalents for SONY HDW-F900 CineAlta (24p) High-Definition Camcorder

(1) The sensitivity of the HDW-F900 camcorder is roughly equivalent to 320 E.I. (ASA) for Tungsten balanced light (3200⁰K) with your light meter set to 24 frames per second or 1/48th of a second.

Exposure Index (ASA) Equivalents for TUNGSTEN at 24p

(Note: 6db = 1 stop)

NOTE: If you turn the SHUTTER OFF (either with the external switch on the front of the camcorder, or in Paint Menu P12) the shutter speed becomes 1/24th second, which gives an effective shutter angle of 360 degrees. So Shutter OFF literally means NO Shutter! With the Shutter OFF, the sensitivity of the camera is doubled, or increased one stop. So all values in the above table NEED TO BE DOUBLED with the shutter turned off.

(2) The sensitivity of the HDW-F900 camcorder is roughly equivalent to 200 E.I. (ASA) for Daylight balanced light (5600⁰K) with your light meter set to 24 frames per second or 1/48th of a second.

Exposure Index (ASA) Equivalents for DAYLIGHT at 24p

(Note: 6db = 1 stop)

NOTE: If you turn the SHUTTER OFF (either with the external switch on the front of the camcorder, or in Paint Menu P12) the shutter speed becomes 1/24th second, which gives an effective shutter angle of 360 degrees. So Shutter OFF literally means NO Shutter! With the Shutter OFF, the sensitivity of the camera is doubled, or increased one stop. So all values in the above table NEED TO BE DOUBLED with the shutter turned off.

(3) The sensitivity of the HDW-F900 camcorder is roughly equivalent to 500 E.I. (ASA) for Tungsten balanced light (3200⁰K) with your light meter set to 30 frames per second or 1/60th of a second.

Exposure Index (ASA) Equivalents for TUNGSTEN at 60i

(Note: 6db = 1 stop)

NOTE: If you turn the SHUTTER OFF (either with the external switch on the front of the camcorder, or in Paint Menu P12) the shutter speed becomes 1/30th second, which gives an effective shutter angle of 360 degrees. So Shutter OFF literally means NO Shutter! With the Shutter OFF, the sensitivity of the camera is doubled, or increased one stop. So all values in the above table NEED TO BE DOUBLED with the shutter turned off.

(4) The sensitivity of the HDW-F900 camcorder is roughly equivalent to 300 E.I. (ASA) for Daylight balanced light (5600⁰K) with your light meter set to 30 frames per second or 1/60th of a second.

Exposure Index (ASA) Equivalents for DAYLIGHT at 60i

(Note: 6db = 1 stop)

NOTE: If you turn the SHUTTER OFF (either with the external switch on the front of the camcorder, or in Paint Menu P12) the shutter speed becomes 1/30th second, which gives an effective shutter angle of 360 degrees. So Shutter OFF literally means NO Shutter! With the Shutter OFF, the sensitivity of the camera is doubled, or increased one stop. So all values in the above table NEED TO BE DOUBLED with the shutter turned off.

These tables are intended as a guide only. Setting exposures using a light meter isn't always reliable in practice. The only dependable method for accurate exposures is to use a waveform monitor as your "lightmeter". I can not emphasize this recommendation strongly enough.

Why light meters can fail with CCD imagers:

This is my (tentative) theory about why light meters can fail to give correct readings when shooting High Definition (or video in general). Film emulsion are far more blue and ultraviolet sensitive compared to the other colors in the visible spectrum. So manufacturers modify film emulsions to try and get it to see all colors, more or less, equally well (or well enough to get a reasonably rounded image with an acceptable color rendition).

A CCD seems to be the opposite. Adam Wilt writes in his article, "Chip Off The Old Block", that...."CCD's do have a spectral sensitivity, and its more heavily weighted toward infrared than it is toward blue. Each CCD can be optimized for the color it will "see" by using chemical doping to alter its spectral sensitivity" (DV magazine, December, 2000). And this seems to be confirmed when setting black levels on a waveform monitor with the iris fully closed or the lens cap on. The blue signal is considerably more noisy compared to either the red or green signals. So this seems to confirm CCD's are more red and infrared sensitive compared to the other colors in the visible spectrum. And manufacturers try to optimize a CCD to record all colors more or less equally well (or again, well enough to get a reasonably rounded image with an acceptable color rendition). So similar to film emulsions, but the other way around.

Now here is the rub, light meters are configured to see light pretty much as a film emulsion responds to light. So they are biased in the wrong direction for CCD imagers.

In practice, you tend to encounter problems using a light meter to set exposures for a CCD camera with daylight exteriors (especially bright exteriors). Comparatively speaking, there is a lot more blue-wavelength light in the visible spectrum that you are trying to record in this situation. The light meter either has a similar sensitivity to the visible spectrum as film, or it is configured to compensate for this "extra" blue light in terms of the overly blue-sensitive film emulsion. But either way, this is the opposite of the requirements of a CCD imager. So while a light meter measuring a day exterior is giving a good exposure indication for film, it is giving a comparatively poor exposure indication for a CCD.

The light meter, remaining faithful to the needs of the cinematographer, prompts you to reduce relative exposure for daylight exteriors to protect against overexposing the overly blue-sensitive film emulsion. On the other hand, the CCD, with its relatively poor blue sensitivity, requires you to increase relative exposure for daylight exteriors to avoid underexposing the overall image. This is what happens in practice. In other words, your light meter is a tool that will tend to let you down if you are using it in this type of situation (daylight exteriors) to help in determining correct exposures for CCD cameras. It works well for cinematographers, but fairly poorly for videographers. A waveform monitor on the other hand, will always given a better indication regardless of the relative amounts of red, green, and blue light being captured and recorded.

Peter Gray
(near Los Angeles)
P.O. Box 5132
Pine Mountain Club, CA 93222
United States of America
telephone: +1(661) 242-1234

dp@petergray.org