Professor Newman on...Finding the subject

A look at how mirrorless AF systems may be able to overcome a key shortcoming

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In recent articles I have discussed the operational differences between DSLR and mirrorless AF systems. A short summary is that whilst both operate using the same phase detection principle, the DSLR system is much more selective and can locate subjects without the need for a great deal of computational power. This is mainly due to the fact that a DSLR AF unit operates at a very small effective aperture, so can detect detail whether the subject is far or near. In contrast, a mirrorless AF system usually operates at the lens’ largest aperture, so cannot detect detail far from the plane of focus.