Pentax K-R Operating Manual page 53

Set the exposure compensation steps to
increments of 1/3 EV or 1/2 EV in [1. EV
Steps] of the [C Custom Setting 1] menu
(p.89).
EV Steps
2 1/2 EV Steps
Exposure compensation steps
now set to 1t3 EV
Step interval Exposure Setting Value
1/3 EV +0.3, +0.7, +1.0, +1.3, +1.7, +2.0, +2.3, +2.7, +3.0
1/2 EV +0.5, +1.0, +1.5, +2.0, +2.5, +3.0
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You can take three consecutive images at three different exposure levels
when the shutter release button is pressed. The first image is exposed with
no compensation, the second image is underexposed (negative
compensation) and the third image is overexposed (positive
compensation).
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Standard exposure Underexposure Overexposure
You can set [7. Auto Bracketing Order] in the [C Custom Setting 1] menu
(p.89).
1 O - + Standard --> Underexposed --> Overexposed (default setting)
2 - O + Underexposed --> Standard --> Overexposed
3 + O - Overexposed -> Standard -> Underexposed
4 O + - Standard -->Overexposed -> Underexposed