On the top left of the camera we have the mode dial (to select exposure mode), the metering mode lever and the exposure bracketing button (hold and turn the front dial to enable / select number of frames, rear dial to select exposure steps).
In the mode descriptions below the we talk about the default function of the front and rear dials, for P, Sv, Tv and Av modes these can be changed via the custom menu, as can the function of the green button in M mode.
Green mode (Auto)
In green mode almost all camera functions are set automatically. The front and rear dials perform not function and the position of the metering mode and AF point levers are overridden to their default 'green' setting. You can not set exposure compensation or use AE lock in this mode. That said all menu related options are still available, such as image size and quality, image parameters.
The unique Pentax 'Hyper-Program' really is as useful as the name suggests. It is clearly a normal program exposure mode but turning the front or rear dial quickly switches the camera into shutter priority (front dial) or aperture priority (rear dial) modes. To return back to full Program mode just press the green button beside the shutter release. This shockingly simple but effective method of going
between the three exposure modes is genius. Note that you can change the program-line from a 'standard' one to hi-speed (favors higher shutter speeds), depth-of-field (favors smaller apertures) or MTF (selects the optimum aperture for the lens used).
The first of two unique-to-Pentax modes, sensitivity priority is a program-line exposure (just like hyper-program) but gives very fast control over sensitivity by providing control over it via the rear dial. This mode is very useful in mixed lighting environments where you may be going from light to dark situations frequently. The selected sensitivity is shown on the status LCD and on the viewfinder status bar.
Shutter priority auto exposure mode, you select the shutter speed and the camera will select the correct aperture based on the metering value and selected ISO sensitivity. Shutter speed is shown on the status LCD and viewfinder status bar, turn the front dial to change. By default the K10D provides 1/2 stop steps, you can optionally select 1/3 stop steps.
Aperture priority auto exposure mode, you select the aperture and the camera will calculate the correct shutter speed based on the metering value and selected ISO sensitivity. Aperture is shown on the status LCD and viewfinder status bar, turn the rear dial to change. By default the K20D provides 1/2 stop steps, you can optionally select 1/3 stop steps.
Shutter and Aperture Priority
The second unique-to-Pentax mode is the 'Shutter and Aperture Priority' mode, you select both the shutter speed (front dial) and aperture (rear dial) and the camera calculates the appropriate ISO sensitivity.
As the name implies, a full manual exposure mode, select the shutter speed with the front dial and the aperture with the rear dial. An 'EV bar' (electronic meter) on the top status LCD and on the viewfinder status bar indicates how near (or far) your selected exposure is from the camera's metered exposure value. You can press the green button at any time to set the shutter speed and aperture as they would be in program mode (using the metered value and selected program-line), making sure you don't miss an unexpected shot if something unexpected happens.
A dedicated Bulb mode, select the aperture using the rear dial and the shutter will remain open for the amount of time you hold the shutter release button or remote. Obviously ideally suited to use with a wired remote.
Designed only to be used with a flash. This mode simply selects the flash x-sync shutter speed, which is 1/180 sec, you can select the aperture using the rear dial.
Allows the retrieval of a previously saved exposure mode setup, in any of the above exposure modes simply select the 'USER' option from the Setup menu to save for retrieval here.
Exposure is metered using sixteen different zones across the frame (diagram from K10D here), each area is measured and situations such as backlighting are automatically compensated for. Note that this mode only works with DA, D FA, FA J, FA, F or A lens (otherwise center-weighted average is automatically selected). You can choose to link multi-segment metering to the AF point or for it to operate independently of it.
Meters the majority of the frame but puts a emphasis on the center area.
Meters only an area at the very center of the frame, as indicated by the spot metering circle on the viewfinder focusing screen.
After changing exposure mode the camera provides a 'guide display' on the LCD monitor which helps to describe the function of that mode. It also provides a quick reference of the current camera settings such as metering, auto focus mode, white balance etc.
Top of camera controls (right)
On the top right of the camera we have the front dial, main power switch which also serves a preview function which surrounds the shutter release button. To the left of this the 'green button' which is used to reset Program mode and has functions in other exposure modes. On the top rear of the camera 'under your thumb' are the rear dial, the AE-Lock, exposure compensation and AF buttons. The function of the front and rear dials can be set on a per-mode basis via the custom menu.
Shooting mode controls
By default turning the power switch to this position enters Live view mode, showing a live feed from the imaging sensor. It can be configured to give traditional, through-the-viewfinder depth-of-field preview or a 'digital preview' which is a single shot taken, but not saved (though it can be saved by pressing the function button).
The green button, a familiar feature on Pentax SLRs, resets the camera exposure in Program mode (if shifted to aperture or shutter priority) and also adjusts the exposure in Manual exposure mode.
Auto exposure lock (AE-Lock)
Pressing this button locks the exposure at the currently metered value for twice the 'meter operating time', which by default would mean twenty seconds or for as long as you half-press the shutter release after locking exposure.
Hold this button and turn the front dial to set exposure compensation. By default the range is -3.0 to +3.0 EV in 1/2 EV steps, if you switch to 1/3 EV steps the range reduces to -2.0 to +2.0 EV.
Pressing this button has, by default, the same effect as a half-press of the shutter release, it triggers the camera's auto focus system to attempt to focus and lock (in AF.S mode, in AF.C it simply begins continuous auto focus). A custom function allows you change the function of this button to 'disable AF' which allows you to (for instance) to auto focus on a point and then hold this button to effect an AF lock (in reality the camera is simply switched to manual focus while the button is held). Also used to focus in Live view mode.
Play mode controls
Turn the rear dial to the left to enter a thumbnail index view.
Turn the rear dial to the right to magnify the displayed image, note that you can customize the initial magnification via the custom menu.
Protect / Unprotect
Press to protect or unprotect the current image, press again to perform this action on all images. This sets the filesystem 'read only' flag which protects the image from accidental deletion using the 'delete' option but does not protect it from formats.