There are plenty of “superzoom” lenses out there, all with kit-quality designs, and primarily distinguished by having focal lengths that extend all the way down into the 20s. But Sigma hasn’t built a new one of these in more than a decade, and that one wasn’t full frame. So it is with some interest that a new Sigma patent heaved itself out Japan’s patent office showing a very “new Sigma” design, complete with more than 20 lens elements. It would be news if Sigma were simply spitting out one of those lens patents that just showed the specific lens design for this new 28-200mm mini monster.
But Sigma’s new patent isn’t really about the contemplated superzoom; it’s about a new method it designed to fix the problem of superzooms. All previous superzooms have increased their focal length ranges at the cost of allowing parts of the zoom range to experience exaggerated color aberrations due to the different color light rays angling off in slightly different directions depending on how much zoom is applied.
Sigma’s patent discusses a complex movement of five lens groups creating different distances of air gaps between them in different circumstances – which, coupled with the groups’ alternate order of positive and negative refractive powers, allows for correction.