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Message: <blockquote data-quote="denco@comcast.n" data-source="post: 3563072" data-attributes="member: 25300"><p>Higher transmission or for that matter better coatings which can lead to higher transmission will never beat aperture when it comes to brightness. A 42mm will under most conditions  be brighter than a 32mm especially under low light conditions. In full daylight you will not notice a huge difference between the two apertures. That is why if you bird mostly during the day a 32mm will work about as good as a 42mm. The 42mm will have easier eye placement due to the bigger 5mm exit pupil versus the 4mm exit pupil on the 32mm but there won't be an enormous difference in brightness. You will notice the difference when you look into the shadows that the 42mm will be a little brighter but that is about it. When it comes to brightness aperture rules. Transmission, coatings and glass quality make a difference but aperture rules.</p></blockquote><p></p>