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Message: <blockquote data-quote="RJM" data-source="post: 1519562" data-attributes="member: 66340">Kevin, I contend that yes, in practice panning the scope with the zoom is a viable alternative to a widefield at equivalent mags.  And while FoV between the 13x and 27x can be a wash, the 13x image will be much brighter (the often spec'd and relatively useless Relative Brightness = sqrt of exit pupil diameter at work) which might be useful in some low light situations.  BUT, and its a big BUT, what the Adler index (a version of Twilight Factor) so bluntly reveals is that more magnification generally yields better performance and detail. This holds true until you exceed the potential of the objective lens or your eye, which ever gives up first. With the ED50 this would probably occur at ~50x for a lucky few and at ~25x-33x for most. To sum up then, the 27x is probably the most usefull for many situations but it is a one-trick pony and there are scenarios where lower/higher powers of the zoom can be used/needed. The wider FoV and brighter image at 13x may help locate a bird easier while the 40x may reveal delicate details needed for an accurate ID. Digiscopers should only consider the 16x Wide DS. Otherwise you won't have enough light to get shutter speeds needed to prevent image blur. cheers,Rick</blockquote>