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camerawiki: Asanuma catalogue (Jul. 1938): Congo lenses
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camerawiki: Asanuma catalogue (Oct. 1941): Yamasaki Congo lenses
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camerawiki: Column on Congo lenses (Mar. 1951)
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camerawiki: Advertisement by Asanuma for Congo lenses (Mar. 1951)
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camerawiki: Yamasaki Congo 21cm f/4.5 (1)
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camerawiki: Yamasaki Congo 21cm f/4.5 (2)