Pentax K-x Exposure

As with most SLRs, three metering methods are available on the Pentax K-x: Multi-segment, Center-Weighted, and Spot. All are accessed through either the Control Panel display on the LCD panel, or through page two of the Record menu. In Multi-segment mode, the camera takes an exposure reading from 16 segments and chooses the best exposure based on brightness and contrast across much of the scene. The Pentax K-x gives you the option to link the AF points to autoexposure in Multi-segment mode, via a Custom menu setting. Center-Weighted metering reads from the center of the frame, but from a fairly large area. Center-Weighted mode is automatically selected if a lens other than a DA, DA L, D FA, FA J, FA, F, or A lens is mounted, or when the lens aperture ring is set at other than "A." Spot metering simply reads the exposure from the very center of the image, so you can pinpoint the specific area of the photograph you want properly exposed. (Spot metering is very handy when you have a subject that's backlit, or that has a very different brightness, either lighter or darker, than the background.)

By default, the AF / AE Lock button triggers autofocus, but you can program it to lock the current exposure settings whenever pressed. (AE Lock is useful when you want to base your exposure on an off-center subject. Point the camera at the subject, lock the exposure, then recompose your shot however you like. Your subject will be correctly exposed, regardless of what might be in the center of the frame when you finally snap the shutter.) Through the Setup menu, you can designate the function of the AF / AE Lock button, and how it works in conjunction with the Shutter button and Autofocus system.

In situations where exposure compensation is necessary, simply press the Exposure Compensation button and turn the e-dial (in all exposure modes except Manual) and the exposure value (EV) will display in the viewfinder and on the LCDs. EV compensation ranges from -3 to +3 EV in increments of 1/3 or 1/2 EV, or you can use the Auto Exposure Bracketing function to automatically bracket an exposure in three increments of either 1/2 or 1/3 EV steps each. AEB is handy for those times when you want to make sure you get just the right exposure for a critical subject, and the order in which the shots are captured can be customized to your preference. Unless using flash exposures, Exposure bracketing works with the camera's Continuous drive mode, allowing all three frames to be captured in a burst by holding down the shutter button.

White Balance
White balance options include Auto (which ranges from about 4,000K to 8,000K), Daylight (5,200K), Shade (8,000K), Cloudy (6,000K), Fluorescent Daylight Color (6,500K), Fluorescent Daylight White (5000K), Fluorescent Cool White (4200K), Fluorescent WarmWhite (3,000K), Tungsten (2,850K), Flash (5,400K), Color Temperature Enhancement (CTE) which is used to retain and strengthen the color tone of the light source, and Manual. Pressing the AWB (left arrow) button brings up the White Balance menu. The Manual option is useful for basing the white balance on a white card. You can also adjust the white balance, controlling the amount of amber, green, blue, and magenta in the color balance using a 2D grid, in any of the selected modes. Pressing the Exposure Compensation button will capture a fresh  image with the current settings, without writing it to the flash card - although if you are pleased with the result you can then press the info button to write the image to the SD card. This ability to "tweak" the white balance, called White Balance Fine Tuning, is very helpful when dealing with difficult light sources. When using Picture or Scene modes, or the K-x's Cross Processing function, white balance cannot be adjusted.

ISO Sensitivity
The Pentax K-x lets you adjust its light sensitivity, in 1, 1/2, or 1/3 EV steps, with options ranging from 200 to 6,400 ISO equivalents. An Expanded Sensitivity Custom menu option increases this range at both ends, allowing sensitivities from ISO 100 to ISO 12,800. Sensitivities higher than ISO 3,200 are not possible when shooting exposures of 30 seconds or longer. An Auto ISO mode in which the camera selects an ISO appropriate to the subject's brightness is also provided. The Auto ISO system seems to adhere to the "1/focal-length for shutter speed" rule, meaning if the focal length is 100mm, the camera will attempt to select a shutter speed of 1/100s and choose a corresponding ISO speed. The default range for Auto ISO is, but you can set both the minimum and maximum ISO. Higher ISO settings are helpful when you want faster shutter speeds under normal lighting, to help freeze fast action.

Noise Reduction
Of course, as with all digital cameras, the higher ISO settings produce photos with more image noise, in much the same way that higher-ISO films show more film grain. To combat this problem, the K-x offers a High-ISO Noise Reduction option through the Record menu, which reduces the amount of image noise at high ISOs. Options consist of Off, Low, Medium, and High, with a default of Medium. Like Pentax's prosumer K-7 DSLR, the Pentax K-x offers the ability to select at what ISO this NR kicks in. Options are ISO 400, 800, 1,600, and 3,200. Regardless of this setting, High ISO NR is always applied to images shot at ISO 6,400 or above. A second type of Noise Reduction called Slow Shutter Speed NR subtracts a second, dark frame to remove noise and hot-pixels depending on the conditions, such as shutter speed, sensitivity, and internal temperature. Settings for that option are On (default), and Off. Regardless of this setting, Slow Shutter Speed NR is always applied on exposures longer than 30 seconds.

Expanded Dynamic Range
The Pentax K-x offers Expanded Dynamic Range options, which attempt to preserve highlights and/or shadows in high-contrast situations. Like the K-7, the K-x offers separate Highlight Correction and Shadow Correction options. Highlight Correction has On/Off settings, while Shadow Correction has three strengths (Low, Medium, and High), along with Off. When Highlight Correction is enabled, the minimum sensitivity is ISO 400 by default, or 200 if Expanded Sensitivity is set on in the first page of the Custom Setting menu.

HDR Capture
The Pentax K-x offers the same High Dynamic Range option which debuted on the K-7. As with that camera, the K-x's HDR mode captures three images in quick succession -- one underexposed, one properly exposed, and one overexposed -- and then combines them in-camera. It uses highlight detail from the underexposed image, and shadow detail from the overexposed image to produce a high dynamic range composite. There are three settings available: Off, Standard, and Strong. When enabled, the HDR mode precludes the use of Raw file format, multi exposure, cross processing, digital filters, bulb exposures, and shake reduction. Also, drive modes except single-frame shooting and remote control are disabled. Since the Pentax K-x cannot microalign images in-camera, a tripod must be used to ensure there is no movement between the three frames. Likewise, HDR capture isn't suitable for moving subjects (at least, unless you're intentionally aiming for bizarre effects). Each HDR capture requires a brief processing time to create the final image, and the three source images can't be saved -- they're discarded when processing is complete.

Multiple Exposure
The Pentax K-x's Multiple Exposure feature allows you to combine 2 to 9 images into a single image as they are being captured. If shooting in Live View mode, the previous image(s) are shown as a semi-transparent overlay on the live view image, as an aid to precise alignment of subsequent images. Pressing the Flash Up / Delete button during shooting discards the previously captured images, and starts the multi exposure anew. ISO sensitivity, shutter speed, aperture, exposure compensation, and AF point can all be adjusted between shots, and the flash can be popped up or closed to use it only on some frames. Pressing the Play, Menu, or Info buttons or powering the camera off saves the multi-exposure image (even if not all shots have been captured), as does adjusting drive mode, flash mode, white balance, custom image or digital filter. Multi-exposure mode is disabled when Cross processing, Digital filters or HDR capture are set, and when the camera is in Movie mode. Interestingly, it *is* possible to save multi-exposure images as a single Raw file, though!

An option called Auto EV Adjustment can average the exposure of each individual shot so that the combined image has the same brightness as a normally exposed individual shot. When disabled, the process is additive, just like shooting multi-exposures on film. To understand the difference, imagine a two-frame exposure where the same point is mid-grey in one image, and near-white in the other image. With auto EV adjust disabled, the same point in the final image will be completely white (clipped in every channel). With the adjustment enabled, the same area will have a brightness halfway between that of the same point in the brighter and darker images. An interesting usage of this feature is that multiple frames can be combined in-camera with averaged exposure to yield a single image with reduced noise / an effective exposure longer than would ordinarily be the case without the use of a neutral density filter.

Custom Image
The Pentax K-x offers the user the ability to apply and modify pre-existing image profiles for use on JPEG images. (Raw files are also tagged with the image parameters, but most Raw processing software other than Pentax's bundled Digital Camera Utility 4 will not obey the tags.) The camera offers seven image style settings: Bright, Natural, Portrait, Landscape, Vibrant, Muted, and Monochrome. The following image parameters can be adjusted for each profile: Saturation (-4 to +4), Hue (-4 to +4), High/Low Key (-4 to +4), Contrast (-4 to +4), Contrast Highlight (-4 to +4), Contrast Shadow (-4 to +4), and Sharpness (-4 to +4). Saturation and Hue can only be adjusted when Monochrome is not selected. When using Monochrome, instead of Saturation and Hue, B&W Filter Effects and Toning options are provided. Filter effects consist of Green, Yellow, Orange, Red, Magenta, Blue, Cyan, and Infrared Color. Monochrome can be further modified with a Toning adjustment which allows you to dial in up to four arbitrary units of either selenium style processing (blues) or sepia style processing (browns). The interface allows you to take a sample image with the preview button, or shows you the last image shot to use as a reference image. Adjustments made in the interface are simulated in the sample image. Of course, you can also select between sRGB and Adobe RGB color spaces in another menu. Cross-processed images don't allow use of the custom image settings.

Digital Filters
The Pentax K-x offers seven canned digital filter effects, plus a Custom setting that allows you to select the amount of each effect to your liking. The seven predefined filter effects are: Toy Camera, Retro, High Contrast, Extract Color, Soft, Star Burst, and Fish-eye. Parameters for each filter can be adjusted. The Custom Filter option allows you to adjust all the parameters: High Contrast (Off, +1 to +5), Soft Focus (Off, +1 to +3), Tone Break (Off, Red, Green, Blue, Yellow), Shading Type (six types), Shading Level (-3 to +3), Invert Color (On, Off), Distortion Type (three types), and Distortion Level (Off, Weak, Medium, Strong). In addition to these capture filters, the K-x offers eight more in Playback mode (Monochrome, Color, Water Color, Pastel, Slim, Miniature, HDR, and Base Parameter Adjust), and up to 20 filters can be combined in Playback mode (with any capture-time filter counting toward the twenty filter total).

Cross Processing
The Pentax K-x offers a new mode that didn't appear on its previous prosumer K-7 digital SLR, which aims to replicate a film technique known as cross-processing. For film photography, the method is to deliberately process one type of film using chemicals intended for a different type, with often surprising effects. The K-x's Cross Processing mode replicates this by adjusting the image after capture with equally unpredictable results, with no way to preview the result before capture, though you do get a rough look at which direction the camera is going to take the shot in Live view mode. It also seems to change what it's going to do, even if they scene doesn't change. Use of the cross-processing mode isn't possible while shooting Raw images, multi-exposures, or high dynamic range captures. With cross-processing enabled, access to the custom image and white balance settings is also disabled. Note that this screenshot was captured with version 1.00 firmware. Version 1.01 adds three presets, as well as being able to assign Cross Processing function to the Green button.

Drive Modes
Like most SLRs, the Pentax K-x offers a number of Drive Modes. Modes include Single Frame, Continuous Lo, Continuous Hi, Self-timer (12 seconds), Self-timer (2 seconds), Remote Control, Remote Control (3 second delay), and Exposure Bracketing. In Single-Frame mode, only one image is captured each time the shutter release button is pressed, even if it is held down. According to Pentax, "Continuous Lo" can record JPEGs (of any resolution / quality level) continuously until the card is full, at an approximate rate of 2 frames-per-second. "Continuous Hi" mode increases the burst rate to 4.7 frames per second, but with a limit of 17 JPEG frames before shooting slows down, when using the highest resolution and lowest compression. Lower-res or higher-compression modes should manage more shots in a burst. When we tested with the highest JPEG quality level, marked with three stars (***), we got 1.85 frames-per-second for over 50 frames for Continuous Lo and 4.32 frames-per-second for 25 frames for Continuous Hi. (Note that our test target is difficult to compress, so buffer lengths using typical subjects are usually better.)

The Pentax K-x also offers two Self-Timer modes for self-portraits or those occasions when you don't want to risk camera shake on a long exposure by pressing the Shutter button to trip the shutter. You can choose between a two- or 12-second countdown. The two-second countdown is useful for times when you're taking a long exposure with the camera on a tripod, and you want to minimize any camera shake from pressing the Shutter button. In this mode, the mirror is raised immediately after pressing the shutter, giving time for vibrations to dampen before the exposure starts two seconds later. The Remote Control modes offered are immediate release, or 3-second delayed release. The Pentax K-x has an IR receiver for wireless remotes, located on the front of the camera. A traditional Auto Exposure Bracketing mode is also provided, where three frames can be taken with programmable bracket value and order.


The images above were taken from our standardized test shots. For a collection of more pictorial photos, see our Pentax K-x Photo Gallery .

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