The Pentax Q provides an alternative called Blur Control to the traditional use of the diaphragm for control of depth of field. We shall take a look at both methods and compare to a K-7 and the Olympus E-PL3.
The aperture is often used to control the depth of field of an image. However, due to the small size of the sensor in the Q, a shallow depth of field cannot be achieved. We photographed our test scene at all available apertures from F1.9 to F8 and found only a limited effect on depth of field. The test, however, revealed something else about the 01 Standard Prime lens: a significant degradation of image quality due to diffraction at F8. The image quality is slightly degraded at F5.6, whereas the lens is impressive from F2.0 to F4. Full open (F1.9) there is a slight softness. Our advice is to avoid F8 and in case of a very bright scene use the built-in 2 stop ND filter and/or the electronic shutter (which goes to 1/8000s where the lens' leaf shutter only reaches 1/2000s).
The effect of aperture is illustrated in the drop down below which provides "100% crops" of the test scene shown above shot at F1.9, F2, F4, F5.6 and F8 at ISO 200. We have included images taken with a 31mm lens on a K-7 for comparison of depth of field and bokeh (out-of-focus rendering).
If you want to isolate the main subject by controlling depth of field, the Pentax Q is not the right choice. A camera with a larger sensor is required so that you can use lenses with a much larger focal length. Pentax has included a blur function on the Q to make up for the inability to achieve a narrow depth of field. We shall look at that next.
Blur control is set on the exposure mode dial. It only works in JPG and will disable RAW shooting should RAW or RAW+ be set. It works best with auto focus lenses where it will keep the area which was focused on sharp, and blur the rest. Or so the theory goes. It works by taking a series of images and overlaying them, so it is preferable to have the camera mounted on a tripod. The alternative is a steady and with shake reduction activated. For our test we sued a tripod and we compared the Pentax Q blur control at the three blur settings available with traditional depth of field for the Olympus set at F2.8, F4 and F5.6. On the Pentax Q we used the 02 Standard Zoom set at 6mm which matches the Olympus 17mm lens in terms of field of view.
As this test shows, we did not have much success with the blur control. The blur was applied quite arbitrarily and did not seem related to the blur setting in any obvious way. The Pentax did manage to keep the area of focus (the withered cactus flower) free from blur, though.
We then moved the auto focus point off center and recomposed the image still keeping the dead cactus flower the point we focused on. This created much more blur but again in a rather unpredictable way.
The result of blur control setting 1 is nicely blurred, but judging from all three images it appears that the camera has a hard time deciding where to place the blur - in front or behind the center of focus. As currently implemented, blur control is no substitute for controlling depth of field with a diaphragm.