光圈越大越好。
比如这个镜头
http://www.amazon.com/gp/customer-media/product-gallery/B005NX7HY6/ref=cm_cmu_pg_setImg?ie=UTF8&action=setImg¤tImageID=mo32R631S0IDQVP¤tImagePage=2¤tImagePageOffset=7&isremote=0&page=2&pageSize=10&sort=rating&totalImages=31
http://www.amazon.com/gp/customer-media/product-gallery/B005NX7HY6/ref=cm_cmu_pg_setImg?ie=UTF8&action=setImg¤tImageID=mo1P3VR4WK4VUOC¤tImagePage=1¤tImagePageOffset=9&isremote=0&page=1&pageSize=10&sort=rating&totalImages=31
http://www.amazon.com/gp/customer-media/product-gallery/B005NX7HY6/ref=cm_cmu_pg_setImg?ie=UTF8&action=setImg¤tImageID=mo3UK07I19CFJKC¤tImagePage=1¤tImagePageOffset=7&isremote=0&page=1&pageSize=10&sort=rating&totalImages=31
http://www.amazon.com/gp/customer-media/product-gallery/B005NX7HY6/ref=cm_cmu_pg_setImg?ie=UTF8&action=setImg¤tImageID=mo1QQTIK53KTQGK¤tImagePage=0¤tImagePageOffset=0&isremote=0&page=0&pageSize=10&sort=rating&totalImages=31