I've been digging around on the net to try and find a comparison between ISO on stills camera and Gain on video. Managed to find some answers today, so I thought I'd share.
First of all, a bit of background;
In general : Stills cameras (whether they are dSLR or compact) measure their light sensitivity using the ISO setting, e.g 100, 200, 400, 800 etc. The higher the number, the "faster" the "film", the less light the camera needs to take a correctly exposed photo. In video cameras, light sensitivity is measured in Db (decibels), e.g -3db, 0db, 3db, 6db, 9db. The higher the number, the more the signal from the sensor has been amplified to allow for low light.
The two settings are actually referring to exactly the same piece of electronic magicry, i.e. the amplification placed against the signal received from the sensor, in order to get useful information. In exactly the same way as a badly recorded sound signal will exhibit hiss and crackle when you try and crank up the volume nob to hear what's being said, the stills and video camera will exhibit "noise" when you increase the gain (or ISO in stills speak) to get the most out of the captured image.
How much noise is created from gain, and how quickly, depends on the quality of the sensor.
Background over.....
My Z1 has now been sold, so I'm turning to my EOS 5 Mk II for a lot of video work. My niggling question has been trying to reconcile my canon EOS 5 Mk II ISO settings with the gain settings on my old Sony Z1, i.e. what ISO setting should I set my Canon EOS 5 Mk II on to simulate zero (no noise) gain, and what step increases in ISO would simulate the same increases in gain.
Answers I've found;
An increase in 6 Db gain doubles the light sensitivity i.e. you can shoot in half the amount of light, and get the same exposure. In ISO speak, you would double the ISO rating to double it's light sensitivity, i.e. 200 is twice as sensitive to 100, 400 is twice as sensitive as 200, 800 as 400 etc
The "zero gain" starting point on video cameras is camera specific, i.e. the sony EX1 at 0db will provide a higher exposure then a sony z7 at 0db, which is higher again then a z1 at 0db (modern cameras are better in low light). The sensor sensitivity will also vary dependant on the definition of the video image... but just for the record, the Sony EX1 is at equivalent 400 ISO when recording 1080p at zero gain. ISO will vary between stills camera to stills camera, however it is based roughly around a standard, i.e. 100 ISO on a Nikon 7000 should be the same as 100 ISO on a canon 600d, and a Fuji F31 (just to name some cameras at random). This unfortunately means there is no direct comparison between ISO and gain.
Answers I'm still looking for:
What ISO setting on the Canon EOS 5 Mk II (and other cameras for that matter) would indicate 0db. Why is it important? Well, not only does it align nicely with my video mentality, there is also implication that the odb setting would also be best for overall quality (any increase gain introduces noise, and both increase and decrease around zero gain can introduce a decrease in dynamic range)
I'm throwing the same question up on a couple of other forums, I'll update this with any answers I find....
