Pentax K-5 Operating Manual page 25

Changing the Naming System of the Folder
You can select a naming system of the folder for storing images.
Date
PENTX
The two digits of the month and day on which the picture was taken are
assigned as the folder name in the form of [xxx_MMDD]. [xxx] is a
sequential number from 100 to 999. [MMDD] (month and day) appears
according to the display style set in [Date Adjustment] (p.289). (default
setting)
Example) 101_0125: Folder for images taken on January 25th
The folder name is assigned in the form of [xxxPENTX].
Example) 101PENTX
Set in [Folder Name] in the ['N Set-up 2]
menu (p.279).
Creating New Folders
Creates a new folder on an SD Memory Card. A folder is created with the
number following the number of the folder currently being used.
1 Select [Create New Folder] in the [_ Set-up 2] menu and
press the four-way controller ( • ).
The [Create New Folder] screen appears.