This review is part of long-term testing of the K-5, Pentax’s newest Digital SLR. This installment explores its performance in Continuous Autofocus mode for sports photography.
The Greyhound Racing Session
Saturday morning trials at the local greyhound track provided a number of fast-moving subjects in a controlled environment. These fast-moving dogs provide a real-world challenge to the SAFOX IX+ autofocus system. Human sprinters struggle to get close to running 400m in 40 seconds. The recently lowered greyhound track record for 461m is under 26 seconds, these dogs are fast.
To make life harder for the K-5, the lens used was not one of the front-line SDM beauties but an old Sigma 70-300mm f4-5.6 DL zoom. The Sigma offers the convenience of hand holding. Remember, the K-5 has Image Stabilization built into the camera so it helps even this old lens.
The point of the photos is observing how well the Pentax SAFOX IX+ autofocus System maintains focus on the racing greyhound as it sprints toward the finish line. The K-5 autofocus system superimposes red dots on the viewfinder image indicating the point of focus.
For this session, the K-5 used the default auto selection of the AF point setting, so the system decided what part of the image to focus on. The EXIF data in the image file tells a great deal about the camera settings and equipment used but not which focus point the system chose in Continuous Focus mode. This means that, as well as tracking the dogs through the viewfinder, attention was also paid to which focus points were selected during each photo sequence.
The shooting technique was to start focusing using the AF button on the rear of the K-5 body, or half pressing the shutter button, before the dogs were close enough for the 300mm focal length of the lens from a compositional viewpoint.
It was an overcast morning with a solid cover of gray clouds, great light for portraits as the edges of faces and features become soft and indistinct. This is the opposite of the best lighting conditions for autofocus sensors.
As the dogs passed, the focus point indicated by the red dots in the viewfinder changed as the SAFOX IX+ system rapidly evaluated the changing scene as the camera followed the moving dogs.
Because of the telephoto focal length and the large aperture settings, there is a shallow depth of field in the example digital photos, highlighting where the SAFOX IX+ system focused. This makes it clear in the example photos that the Autofocus system did its job and focused on the dogs, ignoring the adjacent objects on the edge of the track. On the inside edge of the track is the rail for the mechanical lure, so this was a possible distraction for the system.
High Speed Continuous Shooting and Basketball
In the greyhound session, the emphasis was on observing how well the SAFOX IX+ system picked out the moving object from the close background. The photographs were all taken as single shot. This gave the system time to make any changes to the focus between shots.
Because the AF sensors are in the viewfinder pentaprism structure when the mirror moves up to take the shot, it blinds the AF system. A tougher test of the Continuous Autofocus mode is using the high speed continuous shooting mode. This was tried during a recent basketball shoot.
Letting the camera decide the focus point is fraught with danger in ball sports when there are a number of players in the scene. Often there are player or officials between the camera and the player the photographer wants to focus on. This is why Digital SLRs have a range of methods for choosing the focus point for the AF system.
A player driving to the basket away from the the camera with high speed continuous shooting provided the best opportunity in that session to test the system. The examples show that at the top of the key, the ball is in focus, and when it is just above the ring, the focus changed to keep the ball in focus.
Delving into the Pentax AF continuous mode settings, there is a choice between focus priority versus frame rate. The default option is to try to keep the subject in focus, even if it means slowing the frame rate slightly. The brief basketball examples really did not challenge the Pentax k-5’s Autofocus capability in high speed shooting. It does suggest the need to devise further tests for the focusing at high speed continuous shooting.
The Verdict
So far the Pentax K-5’s Autofocus system performed accurately and predictably in sports photography situations. This gives confidence to seek other challenges for the system.
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