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Performance

The K-x always feels responsive and snappy in operation and you'll hardly ever find yourself waiting for the status LED to go off. With 4.7 frames per second its continuous shooting is quicker than the direct competition but as a downside the buffer runs full pretty quickly. The AF system is a bit of a mixed bag. It's now got (like the Nikon D5000) 11 points, offers many options for their selection and is speed wise more or less on par with the competition. However, the fact that you don't see the focus points in the viewfinder sometimes leaves you slightly uncertain about what you've actually focused on. Overall the camera's operational speed is on par with the competition in this segment of the market.

Timings & File Sizes

Timing Notes: All times calculated as an average of three operations. Unless otherwise stated all timings were made on a 4288 x 2848 best quality JPEG (approx. 5,600 KB per image).

The media used for these tests was a 8 GB Sandisk Extreme III (30mb/s edition) SD card

Action
Details
Time, secs
(8 GB Sandisk)
Power Off to On *1   3.3
Power Off to Shot   0.3
Shot to shot time (JPEG) Live View 0.6
Shot to shot time (RAW) Live View 0.7
Switch from live view *2   0.4
Power On to Off *3   0.2

*1 This is the time from turning the switch to the 'On' position to the status display appearing on the LCD monitor (as soon as you would be able to verify camera settings). The K-x briefly shows a very basic status screen before the standard status display comes on. (As you can see from the 'Off to Shot' time this doesn't actually affect how quickly you can begin using the camera (as good as instant) assuming you knew the camera was in the correct mode.
*2 This is the time from pressing the Live View button to the status display appearing on the LCD monitor (as soon as you would be able to verify camera settings).
*3 This is the time from when the switch is set to off till the status LCD going blank.

Continuous Drive mode

To test continuous mode the camera had the following settings: Manual Focus, Manual Exposure (1/500 sec, F5.6), ISO 100. Measurements were taken from audio recordings of the tests. Media used were the same as above.

The tests carried out below measured the following results for JPEG and RAW:

  • Frame rate - Initial frame rate, this was always 4.6 fps (+/- 0.1 fps) at the higher continuous shooting setting and 2.0 fps at the lower continuous shooting setting.
  • Number of frames - Number of frames in a burst
  • Buffer full rate - Frame rate if shutter release held down after burst (buffer full)
  • Write complete - How long after the last shot before the SD lamp goes out

Burst of JPEG Large/Fine images Continuous High

Timing
8 GB Sandisk
Frame rate 4.7 fps
Number of frames 16
Buffer full rate 2.2 fps
Write complete 9.3 sec

Burst of RAW images Continuous High

Timing
8 GB Sandisk
Frame rate 4.7 fps
Number of frames 5
Buffer full rate 1.5 fps
Write complete 5.1 sec

The K-x delivers the specified continuous shooting rate with the High setting shooting at 4.7 frames per second and the low setting at 2.0 respectively. After the buffer has run full (16 frames in High/JPEG or 5 frames in High/RAW) the camera slows down to 2.2 fps in JPEG mode and 1.5 fps in RAW. In RAW+JPEG mode you can shoot four frames before the buffer runs full. The buffer full rate is 0.9 fps.

USB transfer speed

To test the Pentax K-x USB speed we transferred approximately 500 MB of images (mixed RAW and JPEG) from a SanDisk Extreme III (30MB/s edition) SD card. When the K-x is connected to a computer via a USB cable, by default the camera appears on the system as a 'mass storage device' (but you can change this to PTP in the menu). At 10.4 MB/sec the transfer speed in Mass Storage mode has improved and is now not far off from using an external USB 2.0 card reader.

Method
Transfer rate
Pentax K-x USB 2.0 - Mass Storage 10.4 MB/sec
Pentax K-x USB 2.0 - PTP 7.1 MB/sec
Sandisk Extreme III (using built in USB connector) 20.2 MB/sec
SanDisk Extreme III in USB 2.0 reader 11.3 MB/sec

Autofocus speed / accuracy

With its speed of 4.7 frames per second the K-x is leading the pack in the entry level segment in terms of continuous shooting. However, the AF system is, while by no means bad, not quite on the same level. The K-x's SAFOX VIII system comes, like the Nikon D5000, with 11 AF-points but not seeing any focus points in the viewfinder means that you don't always know what you've just focused on. Pentax' official reason for the omission of this (at least for some photographers) important feature is size. The camera's prism would have to be larger with visible AF-points. While this is true most users would probably happily accept a slightly larger prism if it came with visible AF-points.

The AF-point issue aside the system's performance and operation are very decent. You can choose between manual and automatic AF-point selection and 1, 5 or 11 active AF-points. AF-speed is good but not quite as good as some of the competition who come with ultra-sonic AF lenses. While in the Canon and Nikon line-ups this technology has trickled down to the entry-level only higher priced Pentax lenses feature the company's SDM system. The K-x kit lenses use a conventional AF-motor which is a little noisier and can, in some situations, be marginally slower.

Focus accuracy is generally not a problem but very occasionally, in low(ish) light and contrast situations, you'll get a slightly out of focus shot despite of a focus confirmation beep. Having said that, in our 1000+ sample shots this was literally only a handful. The AF occasionally also has a very slight tendency to hunt in low light but all-in all most of the time the SAFOX system does exactly what you expect it to do.

Focusing in live view is a totally different issue though. The contrast detect AF is painfully slow and the focus hunting becomes more and more frustrating the longer you use the camera in live view mode. To be fair none of the competition's contrast detect AF systems are very good but the K-x's is probably in the bottom half of the scale. If you need quicker focusing in live view you can also switch to 'conventional' phase detection AF (although this requires flipping the mirror before you can shoot the shot). Like on almost all DSLRs live view works best in manual focus mode.

Battery life

Pentax is the only manufacturer that uses AA-batteries in some of its DSLRs and it has stuck with this power source on the K-x. When using Lithium batteries you can get an impressive number of frames out of one set. We used the camera on a two weeks holiday, which involved approximately 1000 photos and a number of videos, without having to change batteries. With rechargeables the number of frames per charge goes down to 640 and Alkaline batteries are really only meant as an emergency solution.

Battery type
No Flash
50% Flash use
AA Lithium
1900
1100*
Ni-MH 1900mAh
640
420
Alkaline
210
130

*The 50% Flash use at 23°C figure is the most commonly quoted CIPA figure

Image Stabilizer

Pentax is one of the manufacturers that provide image stabilization in the camera body rather than making it a feature of lenses. There are convincing arguments for both approaches, let's see how the Pentax system fares in our test.

The stabilization test

Twenty hand-held shots were taken of a static scene, half of those with stabilization, half without, the shutter speed was decreased by a stop and repeated (from 1/125 sec to 1/8 sec). The lens used was the Pentax 50 mm F1.4 (producing a 75 mm equiv. FOV), the test chart was 2.0 m away from the camera. to exaggerate the effect of camera shake the camera was only supported with one hand.

The resulting 100 images were then inspected and given a blur score from zero to three where zero represented a very blurred image and three a sharp image with no noticeable blur (see crop examples below). Obviously the amount of blur which is acceptable will depend on your personal taste and the final image size (for instance a '2: Soft' will still look fine as a 4x6 print or in a web gallery). Example crops from these four blur scores can be seen below.

0: Very blurred 1: Blurred
2: Soft 3: Sharp

Hand-held, no stabilization (50 mm lens, 75 mm equiv.)

With no stabilization we could not get any sharp shots at all at 1/8th of a second and couldn't be guaranteed to get sharp shots below 1/60th.

Hand-held, with Shake Reduction (50 mm lens, 75 mm equiv.)

Image stabilization delivers visible results but they are not as impressive as on some of the other systems that we've seen. It generates an advantage of approximately one stop. It appears to be slightly more efficient at very slow shutter speeds where it significantly increases your chances of getting a usable shot and therefore certainly provides a real benefit in many shooting situations.

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