This is not a Nikon optic, but the people here know a thing or two about lense, so I thought I'd ask here. This is the Tamron 12-24 which is supposed to be as good as the twice the price Nikon. I'm not so sure, and in fact this may be one of the reasons for the Nikon. I have cyan edges. Is this chromatic or vignetting? Any way to correct it? Does the Nikon do this? Sigh. I've been chasing my tail lately.