Thanks for your appreciation Tom. Unfortunately my native childhood language was Dutch, then I had to learn Spanish and Catalan, and English came in the fourth place. Therefore not too many of my neurons are devoted to this language
Hallo Guillermo,
I already thought your family name could have Dutch roots ...
Bart, could you please explain (giving some example if possible) why extra shots can be an advantage against veiling glare?.
Well, I can't make it much clearer than John McCann does in the section from 0:07:25 - 0:13:00 in
this video. The relevant part is at 0:11:00, but you may need to see his introduction to understand where he gets the data from (4 gray scales, and 3 of them with different neutral density filters, together providing a huge subject dynamic range with linear calibration steps).
In short, the recorded signal from our brackets is not exactly linear in the Raw data, despite the fact that the sensor has a linear response. It is caused by (a variable) amount of veiling glare, which adds non-imaging response mostly to the dark end of the tonescale of each bracketed image. The easy way to reduce some of that non-linear stray light is by clipping the shadow end of each contributing bracket except for the first (longest shadow exposure). However, by clipping part of the tonescale, the dynamic range that each bracket can add to the combined dynamic range is reduced, hence the need for more brackets at smaller intervals.
Now that is the easy way to reduce part of the non-linear contributions after they are created. Better results would be available if we can avoid glare as much as possible to begin with, and when we have a good method to calibrate/linearize each raw data bracket before adding it (with a multiplier) to the combined Dynamic range.
Getting a grip on veiling glare starts with avoiding lens flare as much as possible by using good lenses (few lensgroups, black lens edges, good multi-coating, and internal barrel reflection suppression) with large hoods (larger than usual). With those precautions, we will have less veiling glare, but due to the nature of lenses we will still have a substantial part of the image consisting of veiling glare. That's why it's almost impossible to exceed a real dynamic range per bracket that exceeds 8 or 9 stops, as soon as lenses enter the equation (the dirty little secret that John McCann refers to).
Hope that helps.
Cheers,
Bart