[dennis1314]

恒定光圈同浮動光圈在影相時有無明顯分別？為甚麼恒定光圈鏡頭會貴這麼多？

[王迦南]

恒定最大光圈值是代表鏡頭在不同的焦點及焦距下，都可達至同一的最大光圈值。

簡單而言，最大光圈值越大，成功拍攝的機會越高，並能適應較惡劣的拍攝環境。

然而，製造恒定最大光圈值的光學技術要求較高，價格相對較昂。

[peterchan04]

睇下 點 浮法...?

恒定光圈.... F2.8

浮動光圈.... F1.4 -- F2.0


噤 就 要 "浮動光圈"....


.

[王迦南]

>>睇下 點 浮法...?

>>恒定光圈.... F2.8

>>浮動光圈.... F1.4 -- F2.0


這個特例和提問並不一樣。但硬要這樣說，則若焦距和其它條件都一樣，這支浮動光圈鏡頭肯定貴過恒定的很多！

[ediot]

Usual case would be more like:

Constant Aperture: f/2.8

Floating Aperture: f/2.0 - 5.6

in which case, the price of the two lens would depend on the size of the focal range.

and which one is better depends on your preference and needs

[cclee001]

The main point is that the more of the aperture, the more of the cost. Lens with 恒定光圈 can keep the largest aperture for all the range, for examples, 17-40 f/4.0.

[cclee001]

Assume the quality for these two Lenses are equal:

1) 17mm - 20mm = f/2.8
17mm = f/2.8
18mm = f/2.8
19mm = f/2.8
20mm = f/2.8

2) 17mm - 20mm f2.8 - f5.6
17mm = f/2.8
18mm = f/3.5
19mm = f/4.0
20mm = f/5.6

“The more of the aperture, the more of the cost.”

[cclee001]

Notice that: The more of the value, the smaller of the aperture, because the value is the inverse value.

e.g. f/2.8 > f/5.6

[dennis1314]

多謝咁多前輩指點！但系如果用MANUAL設定光圈值，咁在不同的焦距是否也能固定在同一的最大光圈呢？我試過用一支恒定光圈鏡和一支浮動光圈鏡，用手動設定在某一固定光圈，但當焦距變動時，光圈也隨之變動？？？？

[MN56]

Fixed aperture is more difficult to be made due to the mechanics rather than the optics because the diameter of 光圈 needs to be changed from time to time in order to keep the fixed aperture values when the focal length is changing . If you always use A, S etc auto mode to take photos, fixed aperture or not is not a big deal, but if you always use M mode to take photos (for examples, take photo in studio with manual lighting). It will be a problem if you used a varible aperture ZOOM lens.

[dennis1314]

Hi MN56, Thanks for your explaination ! Its clear to me now !