Bulb Ramp Tonal range choice

[vaccine]

Hey guys, is there somewhere that actually explains whats going on for this selection?
Meter for Highlight, Midtones, Shadows.
(10% luma at 35th percentile) etc etc
So for a sunset then moving to timelapse of start aim for shadows?

what is this selection actually telling the camera to do?

[Francis]

It is to determine what part of the curve should be measured when calculating the change of exposure.

Say you take the first picture, and pick the 50th percentile which is at 50% luma. The algorithm is going to adjust the exposure as the scene changes to keep that percentile at 50% luma. Say the scene gets darker and the luma at that percent drops to 25%. The algorithm is going to adjust the exposure by 1 stop to compensate.

Basically you are just picking the value for the algorithm to aim for. It would be much more complicated if it was trying to evaluate the entire histogram and adjust based on multiple points. In general picking something in the middle and getting a decent exposure will work best, like 50th percentile at 50%. Experiment and let others know what worked the best for you.