[zeno_metal]

如題
C兄們有咩意見?

[Obi-Wan]

go see!
http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?FLI=0&API=0&FLIComp=0&APIComp=0&Lens=400&Camera=396&LensComp=401

[zeno_metal]

Thanks! Obi-Wan

不過我還想要點user review~~: )

[zeno_metal]

啊~~忘了說我用的是400D : )

[Obi-Wan]

http://www.photozone.de/8Reviews/index.html

[tototototo]

個test 好似兩支鏡冇咩差別woo~ 咁接近?

[zeno_metal]

really thanks! Obi-Wan

but I seems cannot find a test result about Tokina 16-50..

any C Hing know more about this len?

Thanks! x10000000

[ng389]

http://www.mobile01.com/topicdetail.php?f=248&t=321116

三大副廠APS大光圈標準鏡總論劍

[zeno_metal]

Thanks All C Hing~~~!
原來tokina紫邊咁嚴重@@
而家心裡似乎掙扎在sigma18-50定tamron 17-50...Orz
好多review都旗鼓相當

[Obi-Wan]

http://www.photozone.de/8Reviews/lenses/tokina_1650_28_nikon/index.htm

[zeno_metal]

認真地重新睇過晒咁多位C兄提供ge網頁之後
決定買Sigma~~
Thanks all of C Hing!!!

[Obi-Wan]

I have the sigma 18-50, very sharp as a zoom.

BUT BEWARE of back focus problem in some DSLR, check carefully before u buy, as the QC of sigma is not that good.

* I have 4 sigma lens, 2 has backfocus problem
One 18-200 has slight back focus problem, but not so serious.

Another 18-50 has been exchanged from Sigma.

check
http://photo.net/learn/focustest/

[zeno_metal]

Thanks! Obi-Wan
I'm a beginner and it's my first time to buy a len
can you( or another C Hing) explain what is "back focus"?

[Obi-Wan]

zeno_metal

when u focus on an object, say the eye of a girl facing directly to the camera, & take a photo with the largest aperature, e.g. f2.8.

If the photo turns out the eye of the girl out of focus (not sharp) while the ear is sharp => an example of back focus

If the photo turns out the eye of the girl out of focus (not sharp) while the nose is sharp => an example of front focus

these problem is very common in entry level DSLR from various manufacturer including C, S, N. But higher level models are rare with back focus.

[zeno_metal]

我諗我應該明
即係本來focus主體
卻變成focus了在主體之前的東西就叫front focus
focus了在主體之後的東西就叫back focus

really thanks again and again~Obi-Wan