Sensor ISO

[Ashim]

Hi,

 

This is one facet of digital camera thats eluding my understanding for quite some while now.

What I'd want to know is the way digital cameras are rated and why?

For eg: f/8@2000lux for 90% white??

Does this mean that digital cameras are calibrated for white just like films are calibrated for 18% gray.

I know I am getting it quite muddled up,but if the above is true then why 90% white??

 

Also how is it possible to use your lightmeter for digital shoots(except for measuring the units of light).

Light meters are basically for film use.

If I expose my window according to the light meter readings at f/8 but I want my window to be 1 stop

brighter, I will expose at f/5.6.

But how do I apply the same logic with digital shoots.

 

Also,the methodology of rating one's digital camera for a particular ASA doesnt convice me.

Film has a gamma of 0.6, its midpoint is 18% gray, has a far greater dynamic range.

Digital has a gamma... linear or variable if I'm right, and the rating of digital cameras on technical manual

(f/8 @2000 lux for 90%white) seems alien to me.

Why then do we use a gray card and correspond it with around 45-55 IRE rating for around mid gray and then rate our sensor accordingly,

instead of using a white card with a corresponding IRE rating and sensor rating...

 

I'd be grateful to the community for ironing these creaes.

 

Help... I need somebody Help!!!