Had the opportunity last night to do a little testing of a vortex viper 6.5-20 vs my duralyt 3-12. In the interest of fairness both scopes were kept on 8x.
I have to be honest I fully expected the zeiss to wipe the floor with the vortex given its prestige and also the fact that its a fair chunk more expensive.
My findings were as follow
Zeiss won out over the vortex in terms of glass clarity, Not by a long margin but still notably. The difference was more noticable as the light faded and i was able to pick out fine details better with the zeiss. That been said the vortex crosshair didnt disappear as readily when held against a dark backdrop, although this is attributable to the fact it is thicker in the first place so a double edged sword, worth noting though it is not too thick. In terms of usability both scopes would cope well right out till last light time last night. (overcast with some clear sky)
The vortex has a slightly more fussy eye releif but then given the extra zoom offered its to be expected really. Where the vortex wins out over the zeiss is in the quality of the turrets which are a far more robust feeling and positive clicking system than what is equiped on the duralyt. And also the overall finish of the scope such as having metal as opposed to plastic turret caps, the magnification selection wheel offers more resistance but feels to be better quality and has knurled rubber to assist in grip.
Also worth noting is the warranty offered with the vortex, it truely is buy once cry once as once you have purchased it you could run over it in your landy and they will replace it no quibbles. This was recently proved when my friend wrote off his binoculars which were replaced in less than a week.
Overall I feel it would be a tough decision if I were in the position to be buying new and I was certainly surprised by the vortex. The zeiss has the prestige and edges it in terms of glass quality. But then the Vortex keeps up impresivly well with the glass and surpases the zeiss with its crosshair in low light conditions and its turret adjustment system. The larger magnification is largly a personal preference but its worth noting the viper is only under an inch longer than the 3-12 duralyt and barely heavier.
Please note that all of the above is my opinion from what I have seen in my own testing, I am neither a profesional stalker nor writer but though this review may be of use to some people.
For the minute the zeiss will be staying on my stalking rifle but given time and watching to see how my friend gets on with the vortex I may well sell up and get one myself. Even the comfort of knowing the warranty is a big selling point as I'm not sure about you lot but its alot of money that I dont have to replace should my zeiss be broken by a slip or fall.
All the best