References
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- Bronkhorst, W. (1927) Kontrast und Scharfe in Rontgenbild, p. 84. Georg Thieme, Leipzig
- Klasens, H. A. (1946) Measurement and calculation of unsharpness combinations in X-ray photography. Philips Research Reports Aug
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- Thorp, J. S. (1949) Electron focussing in a demountable X-ray tube. J. Sci. Instr., 26, p. 201.