By tapping two fingers on a photo , a loupe appears . This allows you to instantly see a magnified portion of the image , which is helpful in knowing if a part of an image is in focus .
Attend major ophthalmic , optometric , and loupe exhibitions .
参加专业眼科、验光、放大镜展会。
Each usually comes with a diagram , marking the position of the tiny specks of carbon that can be seen when viewed through a " loupe " , the jeweller 's 10x magnification tool .