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Message: <blockquote data-quote="hinnark" data-source="post: 873620" data-attributes="member: 1860">Ed,sometimes short questions are hard to explain with a few words. I´ll try knowing that next questions will arise. But please, I don´t want to discuss about brands in the way of which one is better than the other.The light beam that comes into the binoculars´ objective has a given diameter. After leaving the objective it shines through the prisms. A lot of modern birding bins have undersized prisms which cause a lost of even illumination. The field of view of such bins needs to pump up by the eyepieces. The limits of this is what we see if we have a small sweet spot. Under normal conditions this isn´t visible but I believe there are some effects we can notice. Some of these bins have for example a darker circle shaped area when you look at the bright sky with them. I believe it was S. Ingraham who once wrote about this phenomenon. I also think that the superior low light performance of the Swaro 7x42 has something to do with this.If you take a look at widefield astro EPs, e.g. the Pentax XW series, you´ll see that they are big with big lenses of a wide diameter. The Swarovski 7x42 has this kind of optical design philosopy. It is designed for pure optical performance: a well corrected image with only small amounts of field curvature and astigmatism even at the edge without the need of compromise that comes with weight savings in optical components. I´m tempted to say that enforcement of weight reduction in birding optics caused by potential buyers is the tragedy of our times for those who just want pure optical performance.What does this mean for practical use? I noticed this after several hours of continual use. When I get tired at the end of a long birding day and a lot of kilometers of walking and carrying my equipment my eyes get tired too. This is the moment when an even and wide FOV let me feel how much this supports my eyes. They don´t need to work against the lost of sharpness that comes with a too small sweet spot.Steve</blockquote>

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