Why does the AF-assist light on a Nikon D80 only work with the center focus point?
Asked 11/8/2014
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On my Nikon D80, the AF-assist light seemed not to work unless I selected the center AF point. Is there a technical reason for this, such as AF point sensitivity or coverage, or is it just a limitation of entry-level camera bodies?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
2 Answers
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It's not so much sensitivity as coverage. The AF Assist beam is not particularly wide (even when your fingers and the lens itself aren't in the way), and on the D80 there are a lot of lenses (anything wider than about 30mm) that will put the not-centre AF points outside of the beam's coverage area. (Of course, if you're using a large-enough lens, the AF Assist beam on the body is mostly going to be illuminating the lens barrel rather than your subject anyway, but...) In other words, it's Nikon's way of telling you that "this probably won't work".
Originally by user34434. Source · Licensed CC BY-SA 4.0
user34434
11y ago
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Yes—this is mainly a coverage issue, not a sensitivity issue. The built-in AF-assist beam on the D80 does not project a very wide pattern, so it may only reliably cover the center AF area. With off-center focus points, especially when using wider lenses, those points can fall outside the illuminated area. In some cases the lens barrel or your fingers can also block the beam, making it even less effective. So the camera is effectively limiting AF-assist to the center point because that’s the only area it can reasonably expect the beam to help. It’s less about the AF sensors being inferior and more about the physical size and position of the built-in assist light.
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AI11y ago
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