The ED50 is a lightweight scope that does not reach a lot of power..20X or 27x are the options for fixed eyepieces or the MC II zoom,with 13x-40x magnification...If you dont wear eyeglasses,the zoom is pretty good optically ,,,The use of ED ,high quality ,glass is the strenght of this scope...the image is very bright,very clean of chromatic aberration and has superb contrast ,also owed to the quality of the Anti reflection coatings,,,pushing the power up to 40X is useful on ocassion ,but the sweet point for the scope,for me is the low power,bright and less shaky of views granted by the 20X or even the 16X...the 27X at times was too dim for me ,and the field of view at close range limits the fast and accurate use unless a pointing device is used(i have a red dot pointer that worked great with the 27X)
the lightweight calls for light support,either hand held,monopod or ultra light tripod (in my view the best solution)but light support is not very stable,thats why I think the 20Xis the best match granting the benefits of excellent field of view(easier to aim) ,brightness and added stability,that pushes resolution in the same way that an IS bin would...so you have a 20X 50mm ED scope..best binocular match...a 7x ED...
a 7 power ED binocular has the same benefits that the scope ..stability in the view ,field of view,exit pupil per mm AND you have a scope the 3x (triples!!!!)the view of your bins, really making the use of a moderate 20X magnification relevant in the field..ED glass would be nice because then you will have that clarity and clean image that would match the ED 50,but since 7x are more forgiving for CA ,any good 7x35/42 would do.The ZEn 7x36 has been praised by all binocular experts as one of the most accomplished ,original and well rounded binos of this last generations..just like the ED50..The other nice 7x that comes to mind is the 7x36 opticron classic..super nice as well,if a bit narrower in the FOV section but lighter and more compact...and with about the same FOV but less aperture,the Bushnell Custom Elite 7x26..also exceptional specially if weight is(and i know It is for You)a concern..I have used these three binoculars(one at a time)with the ED50 side by side in the field andf you can do as serious a birding as any birding serious can be...uh..seriously....