Examples on this page were all taken handheld, with the goal of establishing how well the Nikon D800 focus assist feature (“green dot”) works for manual focus accuracy, e.g., with the Zeiss ZF.2 or other manual focus lenses.
I chose a variety of subjects with different lighting and details in order to get a sense of how well AF-assist works; this is very much a field test, which I consider more revealing and useful than a “scientific” lab test. A lab test of focusing constrains parameters (lighting, subject matter, contrast, etc) so much as to have little relevance to making images in the field.
The precision required for accurate manual focus means that many autofocus lenses are borderline unsuitable for reliable manual focus because of the twitchy and hyper responsive focusing rings (I have one AF lens that shifts focus simply by lifting my hand off the lens!). Good manual focus lenses (e.g. Zeiss) have focusing helicoids, an important consideration for manual focus operation.
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