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<blockquote data-quote="WayneF" data-source="post: 317350" data-attributes="member: 12496">Modern lens coatings make it be not much issue today though, well solved today.&nbsp; In the early days (before WWII lets say), uncoated lenses were a big problem of light loss.&nbsp; In the simplest case, a glass-air surface reflects maybe 4% of the light, and only 96%&nbsp; is transmitted through.&nbsp; This loss occurred at EVERY glass-air surface in the lens.&nbsp;&nbsp; In a complex lens with many glass elements (many instances of such loss), overall transmission was relatively low (requiring more exposure).&nbsp; Today (modern lens coatings), our zooms might have 15 or more glass elements in them (30 surfaces), but this would have been impossible in the old uncoated days.It was less problem for still photography, since our metering methods are so variable anyway, and we look at single pictures. The big problem was movie cameras, where (before zooms), different lenses were rotated into position, and these switches could vary the exposure a little, but visibly.&nbsp; So Hollywood demanded lenses calibrated in actual light transmission, called T-stops instead of f/stops.But coating technology makes it be little problem today. And even if our most complex lenses do suffer a tiny bit, our reflective metering is so variable (much bigger problem), so we would never be able to assign blame.&nbsp; <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile&nbsp; &nbsp; :)" loading="lazy" data-shortname=":)" />Nevertheless, regardless of history, the concept of fstop numbering is that lenses using same fstop will see the same exposure.&nbsp; That is the single purpose of inventing this fstop ratio.</blockquote>

[QUOTE="WayneF, post: 317350, member: 12496"] Modern lens coatings make it be not much issue today though, well solved today. In the early days (before WWII lets say), uncoated lenses were a big problem of light loss. In the simplest case, a glass-air surface reflects maybe 4% of the light, and only 96% is transmitted through. This loss occurred at EVERY glass-air surface in the lens. In a complex lens with many glass elements (many instances of such loss), overall transmission was relatively low (requiring more exposure). Today (modern lens coatings), our zooms might have 15 or more glass elements in them (30 surfaces), but this would have been impossible in the old uncoated days. It was less problem for still photography, since our metering methods are so variable anyway, and we look at single pictures. The big problem was movie cameras, where (before zooms), different lenses were rotated into position, and these switches could vary the exposure a little, but visibly. So Hollywood demanded lenses calibrated in actual light transmission, called T-stops instead of f/stops. But coating technology makes it be little problem today. And even if our most complex lenses do suffer a tiny bit, our reflective metering is so variable (much bigger problem), so we would never be able to assign blame. :) Nevertheless, regardless of history, the concept of fstop numbering is that lenses using same fstop will see the same exposure. That is the single purpose of inventing this fstop ratio. [/QUOTE]

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