There is some reason for caution when changing from the default using the custom menu settings on a Pentax dSLR, particularly if EV comp has been set. The EVs actually used in the sequence may vary significantly from expected and may include duplicates as an attempt at graceful fail-over for corner cases. I know it sounds lame, but this is where I admit to not remembering all the details except to say that it involved a problem thread a few years back.
As a simple example:
- +1 stop EV comp
- Five step bracket
- Av mode with initial exposure settings f/2.8 @ 1/25s, fixed ISO
- Bracket sequence set as "-0+" meaning -2, -1, 0, +1, +2
What would be the expected values for each of the four exposures?
Time's up! Here are the results, shutter speeds at f/2.8:
- -2 1/50s
- -1 1/25s <---
- 0 1/13s
- +1 1/6s
- +3 1/3s
Note the arrow pointing at the original metered setting for +1 EV comp.
Most people expect a series starting at 1/100s and ending at 1/6s with 1/25s in the middle.
Removing the EV comp results in the expected sequence with 1/25s in the "0" slot. Going back to the default order ("0-+") results in the expected sequence of (0, -1, +1, -2 +2) as in the menu setting description even with EV comp. No this is not covered in the camera manual. On my K-3 (firmware v1.30) the camera provides a small clue as to its plan by shifting the EV bar display one stop to the right so that it appears off-center. It may not do the EV bar shift for all firmware versions or camera models. I don't remember this behavior from before my recent update.
ISO bracketing may also have surprises, for example if the metered bracket extends below the lowest available setting.
Steve