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Would like to see a macro zoom lens

Started 1 month ago | Discussions thread
a_c_skinner Forum Pro • Posts: 13,047
Re: Would like to see a macro zoom lens

There is no light loss, it is an apparent effect an illusion. What happens is that the effective aperture falls, so to keep the same exposure you need to open the diaphragm to get the same effective aperture. This is because the aperture is the ratio of the diameter of the stop and the distance it is from the film/sensor. This latter is usually of course the focal length or so close to it that it makes no difference. All in a perfect lens of infinite thin-ness but the idea is correct.

I'd also add that zooms are unpredictable on additional extension and of course don't zoom, they are merely variable focal length so the focus goes haywire as you zoom.

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Andrew Skinner

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