[wingoli]

請問 CHing 若 7D加小小白，最大光圈值是不是會由 f2.8 變為F4.48? 如果是，7D 會不會顯示出來?

[王迦南]

小小白的最大光圈值本來就是F4嘛，而套在7D上是不會改變的，加上Extender才會改變。

[wingoli]

Thanks a lot and sorry typo mistake.
即係小白在7D 上200mm F2.8 會變成 320mm f2.8，睇數字好似賺0左, Am I correct? 當然話到底 aps-c 與ff有一段距離啦。

[王迦南]

Yes

[csmarco]

wingoli師兄,
7D用上200mm f/2.8會變成所謂相對焦距320mm f/2.8,睇數字好似係賺咗,
但實際係蝕左一半以上的成像圈.
好像320mm的焦段,但依舊係200mm的景深,始終不變.
重有,200mm變焦鏡的景深,與200mm定焦鏡的景深,是在無限遠遠對焦點,景深才會一樣,
如果在最近對焦點,200mm變焦鏡的景深,與200mm定焦鏡的景深,亦會有很大的差別.
所以,有部份人會誤以為變焦鏡有不足秤的說法.

[h0001244]

Csmarco Ching, can you explain a bit more on below... I never though of that before.
<<<如果在最近對焦點,200mm變焦鏡的景深,與200mm定焦鏡的景深,亦會有很大的差別. >>>

[csmarco]

h0001244師兄,
我好想詳細分析給你知,但現在由於我要趕往銀行處理一點事情,
因銀行快要下班了,回來才答你,請見諒!

[wingoli]

Since I just used FM2 before (not include G9), I do have many technical issues about DSLR. I'm very pleasant to learn from other high hand CHings in here.

Thank you very much!

[h0001244]

Eager for your enlightenment.

[sar999]

所以… 人像攝影最理想的效果是採用全片幅相機。

[王迦南]

真係唔知『200mm變焦鏡的景深,與200mm定焦鏡的景深,亦會有很大的差別』，期待著網友的解說以便學習。



正常情況下，『要用APS-C拍出與FF相同的構圖』，應使用不同焦距的鏡頭才可達致。若硬要使用相同焦距的鏡頭而修改拍攝距離，祇可以得到相同大小的主體，構圖則截然不同，透視率完全改變，影深的比較亦全無意義。

[h0001244]

Further on this topic『要用APS-C拍出與FF相同的構圖』.......
Besides use a lens with focal length 1.6x wider, the aperture has to be 1.3 stop larger as well.

eg. If you shoot in FF with 135mm F2.8, then you need 85mm F1.8 in aps-c

[h0001244]

So, to certain extend of what Wingoli 's expression............you are right

200mm F2.8 in APS-C is having similar depth of view of 320mm F4.5 in FF
But the advantage you have in APS-c is that you can enjoy the F2.8 shutter speed...... this is very useful for tele-photos

eg. under same ISO rating
500mm F4.0 1/500s in aps-c effect should be similar to
800mm F6.3 1/200s in FF
As you can see that aps-c as it is F4.0, it has higher shutter speed just meet the safe shutter speed. While in FF, as F stop is lower, the shutter speed is 2 step lower than 1/800 that require to meet the safe shutter speed.

[csmarco]

變焦鏡是多焦段可供變換使用,但其所定義的焦段鏡頭放大率及景深,
是指在其無限遠對焦時,才能提供相當於定焦鏡的放大率及景深.
舉個例子:EF-S 18-200mm f/3.5-5.6 IS這支高達11倍有多的變焦鏡.
用在1.6x機上,最遠攝端的相對焦距可高達320mm.
而在無限遠的對焦情況下,其還可保留相當於200mm定焦鏡的放大率及景深.
但若它的對焦點離開無限遠而進入最短對焦距離的時候,它可能只有大約135mm定焦鏡的放大率及景深.
故此,有部份人會誤以為變焦鏡有不足秤的說法.

亦即換句話說,我用EF 100-400mm f/4.5-5.6L IS USM,
用上400mm遠攝端時,最大光圈值亦在f/5.6,
在無限遠對焦時,景深會跟EF 400mm f/5.6L USM一致.
但當我把對焦點離開無限遠而進入20米或更短對焦範圍內的時候,放大率跟景深會同時改變.
所以,有些人會覺得,用EF 400mm f/5.6L USM在最短對焦距離3.5米,用上f/5.6,
跟EF 100-400mm f/4.5-5.6L IS USM,用上400mm遠攝端時,同是在對焦距離3.5米時,最大光圈值亦在f/5.6,
但背境淺景深的乳化效果,用EF 400mm f/5.6L USM是會化過EF 100-400mm f/4.5-5.6L IS USM的400mm遠攝端好多.
兩者所相差的淺景深的乳化效果,就是放大率與景深有差異的証明.
就是這個原因.

好多時聽好多師兄講,EF 85mm f/1.8 USM散景靚,在相同的道理,
我把EF 85mm f/1.8 USM設定在f/4的情況下,對焦距離是0.85米,
拎一支EF 24-105mm f/4L IS USM,設定在85mm及f/4的相同情況下,對焦距離亦是0.85米,
再拎一支EF 70-200mm f/4L IS USM,亦設定在85mm及f/4的相同情況下,對焦距離亦是0.85米,
用腳架快門繩拍同一目標,其背境淺景深的乳化效果,必定是EF 85mm f/1.8 USM最好,
EF 70-200mm f/4L IS USM次之,EF 24-105mm f/4L IS USM再次之.
因為倍數越高的變焦鏡,離開無限遠對焦點而進入最短對焦距離時,其放大率不足及景深會轉深的變化會更大.

[h0001244]

I never notice such change in object distance......
Let me try to test the same range for different lenses