Macro lens aperture change with close focusing

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Eliot Kramer Regular Member • Posts: 358
Macro lens aperture change with close focusing

Hello.

I understand that when focusing closer to the minimum distance macro lenses have diminishing effective aperture due to internal limitations, etc etc. and for which the camera supposedly automatically compensates with increased exposure/ISO?

Nikon cameras report it and I can see the smaller aperture than what I dialed in initially. (Canon supposedly does not, ? , don't know, don't have access to Canon body, Pentax, Sony??? no idea).

1. So is it actually a reduction in aperture, with the attendant decrease in available light reaching the sensor and an increase in depth of field, or is it a "virtual" reduction in aperture, where the total amount of light is decreased but the depth of field remains as originally dialed in?

This is more of an annoyance, or maybe I am doing something not entirely right, I dial in a certain aperture, focus closer, the aperture goes down, then I want to go back to focusing far but the aperture is stuck and has to be opened up again by turning the controller on the camera. Going back and forth between close and far focusing seems to be very cumbersome with constant manual re-adjustements of the aperture back to what one wanted to correct the close focusing phenomenon.

2. Do different lenses change their apertures at different rates and at different distances?

From my minimal personal experience comparing Sigma 105mm and the new Tamron 90mm  the Tamron seems to close down way faster and at farther distances. I am going to try to quantitate this info, I have seen some scattered tables reporting the relationship between distance and aperture, but information is not widely available for different lenses for comparison purposes.

Thank you.

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