在AP的資料中 , 0.75倍減焦鏡的算法是The focal length of the 27TVPH Photo-Visual Telecompressor is 700mm or 27.6". Using the formula above, a distance of 175 mm or 6.9" gives the stated 0.75X compression. (700 - 175) / 700 = 0.75 A shorter distance of 140 mm would give a compression factor of 0.80X. (700-140) / 700 = 0.80.
既然GSO的也是標榜0.75 , 但現在搞不清楚它的BF , 何不設法量出這顆減焦鏡的焦距 , 再依公式 , 將0.75固定住 , 那不就知道它的BF應該是多少了嗎 ?
是這樣子嗎 ?
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