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<blockquote data-quote="WayneF" data-source="post: 387282" data-attributes="member: 12496">Probably is same physical diameter.&nbsp; The effective or working aperture diameter computed is not the physical diameter, but instead is as seen by the subject, from the front outside, through the magnification of the front elements.&nbsp; The physical diameter is not necessarily even at a focal node.&nbsp;&nbsp; The picture at page top <a href="http://www.scantips.com/lights/fstop.html" target="_blank">Understanding Photographic Aperture f-stop, Shutter Speed, ISO</a> might help.&nbsp; In a zoom, the internal glass lens element positions zoom somewhat (front output angle&nbsp; increases dramatically at wide angle) relative to that physical&nbsp; diameter, which appears as if it sort of zooms back toward sensor,&nbsp; appearing smaller from the front (watch it as you zoom).Just trust it, f/8 is f/8.&nbsp; <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile&nbsp; &nbsp; :)" loading="lazy" data-shortname=":)" /></blockquote>

[QUOTE="WayneF, post: 387282, member: 12496"] Probably is same physical diameter. The effective or working aperture diameter computed is not the physical diameter, but instead is as seen by the subject, from the front outside, through the magnification of the front elements. The physical diameter is not necessarily even at a focal node. The picture at page top [url=http://www.scantips.com/lights/fstop.html]Understanding Photographic Aperture f-stop, Shutter Speed, ISO[/url] might help. In a zoom, the internal glass lens element positions zoom somewhat (front output angle increases dramatically at wide angle) relative to that physical diameter, which appears as if it sort of zooms back toward sensor, appearing smaller from the front (watch it as you zoom). Just trust it, f/8 is f/8. :) [/QUOTE]

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