I normally don’t like doing this, but i am going to quote a weblog article by someone else. This was a comment on Martin Beek’ s blog article about a Canon Picture Style that i found specially interesting:
I personally have stopped using it (HTP) because it produces vertical banding noise (pattern noise) with almost any ISO number, under some specific conditions. Philip Bloom also reports that he stopped using it. Probably because it produces unpredictable results that are not easy to detect on-set.
HTP further limits your ISO range and gives you an extra amount of noise. Remember than Highlight Tone Priority (HTP) is essentially underexposing all your photos by 1 stop. ISO 200 with HTP is essentially an underexposed ISO 100 RAW data pushed up to look like ISO 200. That’s how it preserve highlights. You’re essentially pushing an underexposed ISO 100 RAW to look like ISO 250 in that image (since you raised exposure in ACR another +1/3 stop).
I personally don’t use HTP as said, but i follow another rule of thumb as an alternative, specially for commercial work that doesn’t allow for experimenting:
1 – use ISO 160, 320, 640, 1250 and 2500 for low contrast / low light shots
2 – use ISO 200, 250, 400, 500, etc. (ISO 100 and 125 are on their own) for well lit / high contrast shots
1, because the broken ISOs have considerably less noise, but also have less latitude (highlights clip at raw 12650)
2, because the whole ISOs have more noise, but retain highlights much better (highlights clip at raw 15300)
Together with Marvels Cine 3.3 this will make your day…
I think that Martin is mostly right, although i have to look up and compare the numbers he quotes. I must add one important remark: this is typically targeted towards shooting video, not RAW photography.