Teach me about macro lenses

Leonard Migliore wrote:

My initial comment about effective aperture assumed a unit-focusing lens like my 55mm Micro-Nikkor, where you focus by moving the entire lens in and out on its helicoid. And this, as you note, is exactly the same with respect to effective aperture as using an extension tube.

But a lot of newer macro lenses are internal focusing and change their true focal lengths as they focus. The effective aperture for such lenses can be anything; it depends on the way the lens was designed. Nikon reports effective aperture for CPU lenses but Canon does not.

But fundamentally, the amount of diffraction blur depends on the effective aperture.

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Leonard Migliore