itswolf wrote:
看到這段又跑出一個疑問
假設以17-55 f/2.8 為例
在55端, f:/2.8的光圈孔是開到最大
而在17端f:/2.8 其實光圈孔並沒有全開
那麼.......為什麼廠商在17端不全開光圈孔??全開不是可以得到更大的光圈嗎??
希望哪位大大開示一下
樓上的說明就已經提到了，不過這裡再提一次：
光圈值（f-number） = 焦長與光圈開孔直徑的比值 = (focal length) / (aperture diameter)
由於 17mm 焦長比 55mm 短，為了維持同樣的 f-humber，所以 17mm 的光圈開孔會比 55mm 小。
You don't take a photograph, you make it. - Ansel Adams
odyseuss wrote:
看來您還是不了解片幅...(恕刪)
我想您自己也沒看完整篇
該文作者在結論處有提到
3. If you use the same lens on a small-sensor camera and a full-frame camera and crop the 35mm image to give the same view as the digital image, the depth of field is IDENTICAL
況且您該篇回文樓下的wct大所引用的那段回應
Michael - I can't seem to follow your argument and I really don't know quite what you are trying to say. Let me say what I am trying to say.
You take a 50mm lens.
You put it on a 35mm film camera and take a shot.
You put it on a 10D and take a shot. Same distance from your subject.
You now make a print from the 10D image.
You now make a print from the 35mm negative, exactly the same size with exactly the same view - obviously you need to crop the 35mm negative to do this since 35mm film the lens has a wider field of view.
So now you have two prints of exactly the same size and exactly the same field of view (angular coverage).
They both show the SAME depth of field.
也是出自原作者
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