[catcat219]

我曾試過在較黑的地方,以EF-S 55-250 是很難對焦的,只見鏡身前後在轉動,都沒法對焦,那SSWIS是否會快很多,(因有USM),有冇Ching可分享一下

[Obi-Wan]

SSWIS 快快很多!!!
SWIS 快快快快很多!!!

BUT 55-250 is just a cheap cheap lens with quite good optical quality, how can u expect it has similar AF speed as SSWIS?

[catcat219]

當然我知是不能比較,只是在日間,EF-S 55-250不覺怎樣,至少AF速度可接受,但到黑的地方,便....我曾經也試用過一些有USM的lens,在較黑的地方,對焦也是慢一些(比55-250快些),所以我想SSWIS是否也會這樣?

[Obi-Wan]

the AF detection response time is different from the AF speed
the AF speed of course USM is faster
but the AF detection response time depends on the camera and the lens as well as the light intensity. e.g. 7D is faster than 5D2, f4 lens is faster than f5.6 lens.

I have both the 70-200/f4L non IS and 55-250IS
When using on 50D
for 70-200/4L (non IS), the AF speed indoor is quite fast, not much different from outdoor
for 55-250IS, the AF speed indoor is quite slow especially at the 250mm, hunting focus frequently.

Also, there are different versions of USM, some are faster, for details, u can read lens work III

http://www.canon-europe.com/support/documents/digital_slr_educational_tools/en/ef_lens_work_iii_en.asp

[ricklihc]

其實o係較暗地方既時候
有時對唔到焦有ching 提過可能關機身事
小弟用左55-250 年半
好多時好似ching 咁暗位對唔到
而家轉左SSWIS 情況有改善
打個比喻(以450D 計)
10為準55-250 中得2次
SSWIS 中3-4次
USM 對焦係絕對快D

[wesleyyau]

樓主所講o既應該係合焦有困難... 好似obi 兄咁講同對焦速度係兩樣o野...
如果你問小白/小小白會唔會迷... 答案係會o既...
usm 係令對焦快d... 對迷焦冇乜大幫助...
反而機身同埋對焦點真係有影響...
例如你用1系同550D比較... 快門/對焦模組不同... 暗位對焦能力亦不同...
又例如你用十字型對焦點... 同一字對焦點... 十字對焦點水平/垂直分辨率高... 所以冇咁易迷...
如果想測試可以上showroom...
(有錯請指正 ^^)

[catcat219]

我是用50D,50D的對焦系統是否好過550D,50D有九點十字,較550D,只有中間一點是十字,是嗎?有錯請指出.