[Space Walker]

C Hing,

Please help to describe.

I tried in same place, same time, focusing on the same object by using 3 different lens below.

N 20/2.8
S 30/1.4
N 50/1.4

Used the same aperture F2.8 for all 3 lens, all setting is the same.

Found that shutter speed of S30 and N50 were the same, but N20 shutter speed even faster than that two.

I learnt that the actual aperture diameter is calculated by focal length divided by the aperture f. Further to this, 20mm / 2.8 is only 7.14mm dia, smaller than the other 2 lens at f2.8. The lens hole is smaller but its explosure time even can be faster? Really don't understand.

Whether the speed of lens is based on f value, or the actual aperture diameter, under the same situation??

Thx in advance for your answer.

[d2c]

會員戶口已被刪除，資料已被標示為不顯示

[lambertnh]

曝光量係 Base On 【快門】&【F 值】

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你用緊 A Mode set 左 F/2.8，但 Metering 呢？
用 Spot？用 Center-Weighted？定用 Average？

如果你用 Average 測光，20mm 會 wdie D，測光時咪有偏差囉。

[Space Walker]

Lambertnh,

I used A Mode to set F2.8, by average metering. Thanks.