How is a digital camera's sensitivity rated?

[Niels Lindelien]

Hi all,

 

Almost all my experience is with film. In the near future I will be shooting a short on the Panasonic HPX3700. I am conducting a camera test this week and one of the things I would like to nail down is what ASA I believe I should rate the camera at. I often find that manufacturer's listed ratings are a tad high. I have a few other questions as well. If there is anyone who has experience with this camera, I would love to hear your opinions and advice.

 

1. What is the procedure for determining the ASA rating of a digital camera?

 

2. What kind of latitude can I expect out of this camera? I have been told that the proper term here is 'dynamic range', but what I want to know is how many stops over and below do I have before losing detail, not what the minimum and maximum levels of illumination are. Correct me if I'm wrong.

 

3. Is there a procedure for determining latitude?

 

4. How does white balance affect these results? Of course I would look for the sensitivity and latitude using "white" light, but does the WB setting change the sensitivity?

 

I have the ability to view and/or grade the test footage in Autodesk Lustre.

 

Thank you for your time and help.

 

-Niels

[Brian Drysdale]

On certain forums this could start a long thread.

 

Rating the camera isn't hard and fast, it can depend on how acceptable you and the manufacturer find the noise levels and where the highlights start to clip. The easiest way is to use a test chart and a waveform monitor and use your light meter to find the exposure. Although you need to be careful if the camera has a non standard gamma curve or a gamma knee, so the mid grey section of the chart may be safer for setting the actual rating rather than the peak white. The rating of a camera can change depending on the gamma and other settings you're using. You could use the zebras if you don't have a waveform.

 

Here's a pretty standard method for latitude tests.

 

http://www.lightillusion.com/cameralatitude.htm

 

The white balance doesn't change the sensitivity, but it can change the noise levels on some colour channels. This isn't usually a problem with most cameras, but with the RED it's a consideration in tungsten lighting.

 

http://www.cinematography.net/hannover/Hannover%20highlight%20tests.html