Modern cameras have a Base Sensitivity normally given as an ISO value (in Lux Seconds) with some having two Base Sensitivities. To explain how the number is derived for electronic cameras takes a maths degree so we will take it as read. The key points are that the lower the Base ISO value, the more sensitive the camera is to light.
At the Base ISO, the camera will produce the least noise and the highest quality image if exposed correctly with the largest Dynamic Range. If we take our Base ISO as 500 as in the Sony VENICE, we can explain what happens when you increase the ISO. By selecting ISO 1000 (500 x2) we double the electrical signal which is equivalent to doubling the exposure. This allows us to do various things, make a darker image brighter, allows a 180-degree shutter to be used to reduce motion blur (180-degree shutter would half the exposure time and therefore half the light), would allow you to reduce the aperture (close the iris) to get a larger depth of field and so on.
Every time you double the ISO value you double the electrical signal, doubling the exposure. It is possible to go into negative gain, i.e. reduce the ISO value below the Base Level. Two possible reasons for doing this, historically it reduced noise, but it also reduces Dynamic Range. Secondly you can use it to open up the Iris on the lens more for a shallower depth of field at the correct exposure. Cameras with Dual Base ISO values can give you the benefit of a higher value without additional noise. So again, with the Venice, at ISO 2500 you have a Base ISO with more than four times the exposure of 500 but no additional noise. For those used to Video Cameras with gain in dB, 3dB is half a stop, so increasing from Base 500iso to 1000iso is the same as putting in 6dB of gain.
SONY VENICE DUAL ISO
Cameras with Dual ISO
Contact us to learn more about Sony VENICE's Dual ISO and or visit our page to see a full list of features.