J1 lightmeter calibration - ~3.3eV of highlight headroom.
Lasse Eisele wrote:
Your data don't make any sense to me without a context.
1) "Highlight headroom" means different things to different people. What exactly do you mean by highlight headroom?
Here it's the distance in stops from what the camera spot meter reads and saturation (blown out pixels).
2) How does the camera stand up against other cameras?
This distance is different between cameras and has to be measured. Sometimes it is different even in the same camera when a different jpg process setting is used (I noticed it in the Panasonic GF1. For Nikon cameras I believe Picture Controls does not play role).
3) I had expected less headroom at high ISO but it seems froms your graphs that it's pretty constant from ISO 100 to ISO 6400. Is that normal?
It is normal.
A practical approach if you want to use this information is this:
If you want your J1 spot meter to read close to 18% then set permanent Exposure Compensation + 2/3 EV.