[becbec]

總結各用家所言, canon不論什麼型號的dslr, 一部份能精準, 一部份不能, 而配副廠鏡尤差, 是商業策略？還是品質控制問題？不得而知, 但有兩點肯定,【1】對焦有問題的機不是小數目，而且更可能是不能修覆，遇上了會很頭痛，【2】對焦有問題的機的比例遠較其他品牌嚴重。這是我從討論中得到的答案。

原本討論＃＃http://www.dchome.net/viewthread.php?tid=301276&extra=page%3D1

[cwk36]

我 100% 絕對同意 becbec 兄的講法。

Cannon 的 品質控制做得不好，買機就睹你運氣。我不好運，是受害者。
花了三萬有多在 Cannon 身上，換來的全是走焦嘢！

[win3t]

看上面連結...
結論是各說各話....有人食蕉...有人無蕉食

好野....既然係咁 我都無謂發表意見,.......哈哈


奉勸...咁鬼好彩鑊鑊買到食蕉鏡既人，去買冷馬...話唔定會中....

呢牌大騎師成日拉停馬做馬...鑊鑊爆冷.....

[tam_dominic]

我 100% 同意 becbec 兄的結論。

愚見認為 是 can0n 成功的策略 :

寧要大步寛(對焦是用 步進馬達), 以達快速對焦., 因每按shutter 都要對焦.
犧牲 準確度 可取, 因細景深的相只佔少數.

要求不高的人, 可usm 搭夠.

何況 細景深也有機會中焦 :-)
eg. 以吋 計, 11,16,22,29,34...是中焦點.
Tune 前以 24 吋試, 結果走焦, 激憤
Tune 以後 27 吋試, 結果中焦, 好開心

爭拗會不斷持續

Happy shooting !

[tam_dominic]

Sorry 打錯了
"Tune 以後 27 吋試, 結果中焦, 好開心"

應該是 :
Tune 以後 29 吋試, 結果中焦, 好開心

[Rol]

Can any C hing advise any industrial standard to claim correct focus ?

1 MM deviation can be considered as out focus, but at statistic and quality control, the measurement of accuracy is not at one point but a range with standard deviation

For me +/- 1 cm is okay, +/- 2 cm is marginal, did canon or any organization advise their acceptable range ?

If without the standard of focus accuracy, Canon and everybody may not talking the same thing of out focus.

[tam_dominic]

Rol
May be focal length and object distance also are the consideration in the 'Focus Standard' if it exists.

eg.
50 feet object distance with 28mm lens, what is the acceptable range ?
1 foot object distance with 150mm macro lens, what is the acceptable range ?

Happy shooting !

[man1492]

"50 feet object distance with 28mm lens, what is the acceptable range ?
1 foot object distance with 150mm macro lens, what is the acceptable range ?"

Agreed. At least it helps screen out those cameras which found to be having unaccurate focus in all conditions, not just putting uncultivated but educated words together for the sake of kick someone's ass.

[Rol]

Tam Dominic Hing

I don't think need to consider lens focal and focus distance at the focus standard, both factors will affect the depth of field. But no matter what lens the correct focus is only at one point. If focus exactly 20cm but actually go to 21cm, then this is +1 cm deviation.

+1 cm deviation may still within depth of field and get clear photo, but this is still +1 cm deviate from correct focus point.

Actually whether this +1 cm deviation is "acceptable standard" ? this is the question. Canon QC may consider this is acceptable and allow shipping out from factory..

[tam_dominic]

Rol

Now I see your point.

As I observe, the frequency of re-focus on far away object is less than closer ones when I move the camera slowly.

The focus points are determined by the step width of the focusing stepping motor (physical gear and / or firmware) The wider the step width the faster it can focus and less accurate at the same time.

It is therefore I assume :
There are 30 focus points from 6 to 10 feet
==> deviation is 1/15 foot
There are 20 focus points from 11 to 20 feet
==> deviation is 1/4 foot
There are 10 focus points from 21 to 50 feet
===> deviation is 3/2 feet
There are 7 focus points from 51 to 100 feet
==> deviation is 10 feet
There are 5 focus points from 101 to 1100 feet
==> deviation would be 100 feet
There are 3 focus points from 1101 to infinity
==> deviation would be ??

From these assumption, in my humble opinion the standard of focusing accuracy should be a table with the consideration of object distance.

It is just an observation and assumption, no scientific data support.

Happy shooting !

[vaworld]

can0n現有鏡頭差不多全由 Ultrasonic 驅動.
應該唔係 stepping motor 來.

[kingkonghk]

唔好意思, 我又插下咀, 50/1.8係冇Ultrasonic, 由機身摩打推, 理論上, 機身見到唔中焦係唔會開快門, 會不停前後移, 直到機身認為中, 先至影. 如果係話stepping問題, 唔中焦一樣會再前後移, 唔會立亂影. 總之一定要sensor認為對比ok先會影, 除非你set左mf, 又或者長按快門好耐.

會唔會係對焦時o既相關動作出問題? 先check motor後check sensor? 定先sensor後motor? 冇人知, 知o既就係呢樣野一定入body數

[vaworld]

如果真係單純機身問題. 我朋友就唔使拎晒幾枝問題鏡上行一齊 Cal.

[无為]

becbec係大姊姊嚟架？

[kingkonghk]

唔排除cs有d捉心理, 用cs鏡cal完你個body, 你可以話返到去唔得, 要佢再cal過.

要你俾埋支鏡佢, 佢淨係搞body, 支鏡掉埋一邊, 收機時俾返晒你, 你話ok, 簽晒單就冇仇報.