Originally posted by biz-engineer No sure I've followed it all. What's the reference level for measuring ISO? If the output should be 18% gray, what should be the luminescence level of the light source for ISO100 ?
The same as it always has been for iso 100
Originally posted by biz-engineer Why use saturation level instead of 18% gray?
But here is the problem the iso standard holds the cameras metering system to the final output of the camera ( the jpg image) and not the full saturation point of the sensor. Most if not all manufactures use their own level of highlight room protection, if we where to look at any raw file correctly exposed for a card 18% we would see that it is unexposed by what ever they have decided as headroom buffer. The image is then brightened so that jpeg image now looks like 18%.
If you know how much headroom you have in the raw file before any data clips you then can override the cameras metering for a give iso standard and technically you can use an exposure meant for a lower iso rating. Most cameras can give you around 1-1.5stop ( yes twice as much light) more exposure before you start to clip the white in your images.
K-1 EV in manual mode - PentaxForums.com If you look here you can see that I used an exposure that was 1 & 1/3rds higher and basically shot the image using iso standard 1 stop lower.
Now this poses a problem for anyone testing sensors so DXO has made a new term "measured iso"
not to be confused with the iso organisation .
DxO Labs uses a "saturation speed" method in order to measure the (RAW-level) plotted as iso. That metric reflects the maximum sensor-level Exposure ( unspecified by DxO Labs) If they were to use the DSLE instead of the term iso it would lessen allot of the people thinking that their "measured iso" is related to the iso organisation and when they measure a cameras "measured iso" that it does not falls above or bellow the iso standard.
Last edited by Ian Stuart Forsyth; 01-31-2017 at 12:39 AM.