目前,国内照片用的放大机,为使感光纸能正确感光,大多采用掌握曝光时间和调整光圈的方法。采用这种方法放大照片,若遇到黑度深浅不一的底片,就需用试纸反复试验曝光几次,才能选出其中一种较正确的曝光时间,作为正式放大照片时的依据,故用这种放大机放大照片,既费时间又费材料,即使是比较熟练的暗室工作人员,放大照片时也免不了这一烦 At present, the domestic photo amplifier, in order to make the photosensitive paper can be sensitive, mostly used to master the exposure time and adjust the aperture method. Use this method to enlarge the photo, if the encounter black and white film, you need to repeatedly test the exposure paper several times in order to choose one of the more correct exposure time, as a formal basis for the enlarged photo, it is used This magnifier to enlarge photos, both time-consuming and costly materials, even darkroom staff more skilled, when you enlarge photos inevitably the trouble