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一般射线探伤工作者,常不考虑工件的情况而只采用一个固定的焦距进行摄片,甚至事前也未曾考虑过为什么采用这个固定的焦距。这样,就可能因为使用了过长的焦距而造成浪费;也可能使用了不足的焦距而降低了照片质量。本文将较深入地探讨这一问题,以期对实际摄片工作有所改进。一般说来,需用的曝光量与所使用的焦距平方成正比,在可能情况下,焦距愈短则愈经济。但是,焦距的缩短是受下面三个主要因素限制的。
The general ray inspection workers, often without regard to the situation of the workpiece and only use a fixed focal length for filming, and even did not even consider beforehand why the fixed focal length. In this way, it is possible to waste because of the use of an excessively long focal length, or to use insufficient focal length to reduce the quality of photographs. This article will be more in-depth discussion of this issue, with a view to the actual photographic work has been improved. In general, the amount of exposure required is proportional to the square of the focal length used and, if possible, the more economical the focal length is. However, the reduction of focal length is limited by the following three main factors.