All good options. I've looked through the Zeiss HD5, and Swaro Z3 and Z5 scopes a fair amount. There are fundamental reasons for performance similarities and differences between theses scopes.
Both the Zeiss HD5 and Swaro Z3 scopes have doublet objective lenses. Therefore the resolution and color fringing at the optical center (zero elevation/windage setting), and resolution at high elevation setting are similar. The Z3 may have an edge over the HD5 in the field of view (erector optics), but I have not done a side-by-side comparison yet, so I can't say for sure. The Z3 does have higher contrast than the HD5 because of lower stray light. As others have said, the Z3 is obviously lighter. On the plus side, the HD5 clearly has the wider zoom range.
The Swaro Z5 is in a different class because it has a triplet objective lens. It has noticeably better resolution at high elevation setting than either the HD5 or Z3. The Z5 also has the Z6 erector tube optics, which are outstanding. For that reason it has a wider sweet spot, or field of view over which the image is crisp. Again, the contrast is higher than the HD5 scopes.
The Z5 optics are so good that the scope can be used at maximum magnification in almost any lighting conditions. The resolution and the contrast holds up very well in bright light and at high elevation settings. In my opinion, the Z5 image quality is comparable to a non-HD spotting scope at the same magnification. Granted, the spotting scope will go to higher magnification and have a wider field of view, but either the 18X or 25X Z5 can still be used to reliably spot details like antler points at ranges far beyond the capability of an 8X or 10X binocular. The ability to effectively use these rifle scopes in place of a spotting scope in some applications makes the Z5 somewhat unique.
For more information on the Swarovski rifle scopes, go to this link:
Swarovski Rifle Scopes
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