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Creates · ゆきんこの勉強法 | 自修人

江ノ島の南側はこうなっていたのかぁ!|ドローン

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ズームすると暗くなるのは自然

「H-E08018 パナソニック LEICA DG VARIO-ELMARIT 8-18mm/F2.8-4.0 ASPH」。

8mmのときF2.8で、18mmのとき4.0というように、ズームすると暗くなるんだよ。 それには理屈がある。

同じ口径のレンズだから、入力される光量は同じ。

その同じ光量のイメージサークルの一部を拡大表示するのがズームイン。

光量が同じだから、拡大すれば暗く感じるじゃん? 


以下の「●」の集合を、PCなら「Ctrl+マウスホイール」で拡大してみそ?  スマホなら「ピンチアウト」で拡大してみそ? 

単位面積あたりの点の数が少なく(密度が低く)なるよな?  それが「画面が暗くなる」ちゅうことなんや。

ズームインすると単位面積あたりの「光点」の密度が下がるけぇ、暗うなるんやで。

ズームインしても暗くならないレンズ(F2.8通しのズームレンズなど)は、まずレンズを明るくつくっておいて、最も暗い側(広角端)に明るさを合わせて調整しているだけやと思うわ。 ほな、さいなら。

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