Does AF work with small aperture lenses (Sigma 150-500)

Started Jan 25, 2012 | Discussions thread
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Chris J Newman
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Does AF work with small aperture lenses (Sigma 150-500)
Jan 25, 2012

Hi,

I have sometimes considered buying a long telephoto lens, primarily for wildlife. The Sigma 150-500mm F5-6.3 APO DG OS HSM seems to be about the most suitable within a budget that would be sensible for me. Various reviews seem fairly complimentary. I have just noticed that Park Cameras are offering the lens at a good discount until the end of the month, and I wonder whether I should take this opportunity.

But I have one major concern. My camera is a D90. The manual states that the electronic rangefinder can be used if the lens has a maximum aperture of f/5.6 or faster, suggesting this would not work with the Sigma's f/6.3 at the long end of its zoom range. It does not state the same requirement explicitly in the Autofocus section, but information about compatible lenses suggests that autofocus also requires an aperture of f/5.6 or faster. I don’t have the confidence to rely on manual focussing without the aid of a split screen in the viewfinder, particularly when using a small aperture telephoto lens. (With a “normal” prime lens I might be focussing at f/1.8, and then shooting at f/8, so my view would exaggerate any lack of focus, but with a telephoto the viewfinder would be darker, and I would need to work close to f/6.3 to maintain a useful shutter speed.)

Yet none of the reviews on the lens that I have seen have referred to a failure to autofocus at 500mm. I would be grateful if anyone can let me know whether they have experience of autofocussing with this lens on a D90 or D7000. (I ask about its performance on the D7000 because at some time I will probably replace my D90 with a camera with a more modern and higher performance sensor. I might well be tempted by the successor to the D7000.) I don’t want to make the long journey to Park Cameras to try the lens, only to find that I cannot autofocus with it.

I would also be interested in comments about the lens and possible alternatives.

With thanks in advance,
Chris Newman

 Chris J Newman's gear list:Chris J Newman's gear list
Nikon D800
Nikon D7000 Nikon D90 Panasonic Lumix DMC-F5
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