Sigma 150-600mm Sport Autofocus Issue

Started Jan 6, 2017 | Discussions thread
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Paul-D700 Junior Member • Posts: 32
Sigma 150-600mm Sport Autofocus Issue

I recently purchased a Sigma 150-600mm Sport lens and am experiencing an autofocus issue. When photographing birds in flight, the lens will often lose focus on the bird, regardless of whether the autofocus is set for single point, 9 points, 21 points, or 51 points. I realize that this is not an uncommon occurrence with any lens, given the often-erratic nature of bird flight.

However, when the 150-600mm loses focus, the lens focus defaults to the minimum focus distance I have set (10m), resulting in a totally blurred image in the viewfinder. Sometimes the very blurred outline of the bird can be discerned, but the lens cannot reacquire focus on the bird -- the viewfinder stays completely blurred. Even when I try to focus on a distant object (e.g., a treeline, etc), the lens will not achieve focus. This occurs regardless of the autofocus setting I use -- pressing the AF-ON (back focus button) has no impact, nor does depressing the shutter halfway. I have to focus on a nearby object (perhaps 30-40 feet away), at which the lens regains focus. By this time, of course, the photo opportunity is long gone. The problem is more pronounced at 600mm, but also occurs at shorter focal lengths.

I am using a Nikon D800 with the following settings: AF-C (continuous autofocus), AF-C priority selection of "Release;" focus tracking with lock-on set to 3, 4, or 5 (the problem persists regardless of this setting), AF-activation of AF-ON only (although changing this setting to "Shutter/AF-ON" does not make a difference in the above problems); and dynamic 9-, 21-, or 51 point focus area with the focus point centered in the viewfinder (the problem persists regardless of the number of focus points).

I have a Nikon 80-400mm lens which I use on the same camera, and it does not exhibit any of the above problems, so I do not think the issue resides with the camera. If that lens loses focus, it does not default to a minimum focusing distance; the bird stays relatively in focus and hence the lens can easily reacquire the bird.

Has anyone with a Sigma 150-600mm Sport (or other long telephoto zoom) experienced a similar problem? Is this normal behavior for a lens at 600mm (i.e., defaulting to a minimum focusing distance)? Does anyone have any suggestions for different settings that might mitigate the problem? The lens has the latest firmware, so that is not the issue.

Paul Lebras

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