Imagery: Auto - Large Table of Contents

EXCERPT page containing first few paragraphs. 2023-10-03 10:29:48

Focus Assist Error (Electronic Rangefinder), Nikon D3x

Autofocus can be quite inaccurate, and anything based on the AF system is subject to the same inaccuracies.

Both Nikon and Canon offer a focus assist feature in their DSLR camera bodies, a sort of electronic rangefinder. Many users welcome it as an effective substitute for autofocus when using a manual focus lens.

But as it turns out, Nikon’s focus assist feature offers accuracy that ranges from so-so to awful, as we show here. It is especially inaccurate with f/1.4 lenses. Using f/2.8 lenses seems to help, most likely from twice the depth of field (2 stops slower) as well as improved contrast for the AF system to interpret.

Canon’s AF assist feature (“green dot”) is not necessarily better than Nikon’s. In both cases, results can very widely with the lens and with the conditions, leading to a situation in which one can never really rely upon the feature for even modest requirements.

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Intrigued? See Focusing Zeiss DSLR Lenses For Peak Performance, PART ONE: The Challenges, or (one topic of many) field curvature.

Variants Live View, Focus Assist available in full article

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