It raises the performance bar about 20 years ahead of every other ultra-wideangle SLR lens.
它提高了性能限制是20年之前 ， 所有其他超广角单反镜头。
2
With a crop factor of 1.5x or 1.6x you need special digital lenses to get true wideangle results, but these are readily available and are usually less expensive than their 'full frame' counterparts.