I own Swarovski 8.5x42, Nikon 8x32 SE and Zeiss 8x42 FL and will in a month or two post a comparative review once I have the measure of the Zeiss.
However, I already have some feel for the Zeiss.
In terms of finish, the Swarovski wins IMO due to the use of metal and rubber which appeals to the engineer in me. Swarovski are renowned for the jewellery like feel of their gear. The Zeiss is excellent, but uses plastic for the hinge covering which IMO is less appealing than metal. The rubber armour is excellent and I am sure the Zeiss is well made. The Nikon is also excellent but it's a pity about the cheap and nasty rain guard.
In terms of ergonomics, both the Zeiss and the Swarovski are excellent and the Nikon is pretty good. The Zeiss focus is very fast/coarse and in some respects an advantage, and in others not. Switching quickly between near and far - e.g. when seeing a Kingfisher dart past - is much easier with the Zeiss, but fine focus is not so easy. The Zeiss focus is beautifully smooth with no backlash. My Swarovski has focus is slow with some backlash. The Nikon focus is rather stiff and almost as coarse as the Zeiss. The Zeiss and Swarovski use the same central diopter mechanism. Both are good. The Nikon has a non-lockable rotating eyepiece mechanism which is also very good.
In terms of optics, the Nikon wins closely followed by the Zeiss, not so closely followed by the Swarovski IMO. The Nikon has a beautifully bright, sharp, contrasty image with little field curvature, and it is almost sharp to the edges. The Zeiss and Swarovski both have excellent sharp images out to about 50% from the centre, and then slight softening starts. Both seem about as bad to me from 50% to 80%, but the Zeiss is worst at the edges. It's a minor issue, but it's there. (I was surprised at the amount of off axis softening in the Swarovski. I think most people including myself tend to examine the on-axis and edge performance.) The Swarovski can be improved somewhat by adjusting the focus. The Nikon and Zeiss both have noticeably higher contrast than the Swarovski. Not a lot, but it's there. The Nikon has almost no distortion and the Swarovski a little more. The Zeiss has slight pin cushion distortion noticeable when panning. It's minor but might annoy some people. Swarovski has the highest resolution closely followed by the Nikon and Zeiss in a tie for second place. The difference is academic unless the binocular is held very steady e.g. on a tripod. However, the slight colour fringing always present through the Swarovski reduces the overall clarity compared to the other two. Both the Nikon and Zeiss have very little CA. The Zeiss has none on axis, the Nikon a little, and the Swarovski a fair bit. Off axis the Nikon and Zeiss are about the same i.e. not a lot, and the Swarovski has a fair bit. All three have excellent depth of field. At night the Zeiss and Swarovski show similar performance, and are noticeably brighter than the Nikon (but the difference in what I could see was smaller than expected). The Zeiss sometimes seemed a bit better than the Swarovski due to the higher contrast I expect. However, I have only done a few brightness tests e.g. viewing fields and a dark farmhouse on a moonlit night. I will try some deep sky objects when we get our once a year clear sky. All control flare extremely well. The Swarovski has always struck me as being exceptionally good in this respect but the Zeiss seems to match it, or at least comes close. Overall both the Zeiss and Nikon give a natural 'own eyes' image, whereas the Swarovski is just a little less natural.
I don't pretend that the above are accurate objective comparisons, merely my own experiences. I know of at least one BF user who owns the same three binoculars and I hope he will add comments if he disagrees, or thinks I have missed something.
I would be interested to hear comparisons of the Zeiss FL with a Leica Ultravid or a Nikon HG(L)/LX.
