[kins0n]

小弟遇到三支鏡頭 , 不知如何選擇

Sigma 17-70mm f/2.8-4.5 DC Macro
Tamron SP AF 17-50 F/2.8 XR Di II LD Aspherical [IF] (A16)
Sigma 18-50mm F2.8 EX DC

因為三支鏡價錢十分相近~ 故不知如何取捨!

我想知道三支鏡之中, 邊支成像質素最好?
重有對焦速度如何?

恆定光圈是甚麼?
恆定光圈 同 非恆定光圈 各有甚麼優劣?

[yung2]

呢個網有好多測試可作比較
http://www.photozone.de/8Reviews/index.html

恆定光圈, 以18-50mm F2.8為例,
佢由18mm zoom至55mm最大光圈都係F2.8

非恆定光圈, 以17-70mm F2.8-4.5為例,
佢由17mm zoom至70mm, 最大光圈會由F2.8收至F4.5

[K_C]

The Sigma 18-50 has new version with macro function. But the price is higher than the rest. It cost $3580 because I asked the price last night. I also considering these lens too, since the sigma new version is high cost, I prefer to buy A16.

恆定光圈: Sigma 18-50mm F2.8 EX DC & Tamron SP AF 17-50 F/2.8

非恆定光圈: Sigma 17-70mm f/2.8-4.5 DC Macro

恆定光圈 that mean you change the focus range the 光圈 will not become smaller that can let you take a photo with faster shutter in less light area like indoor. For 非恆定光圈 like 17-70, the 光圈 is 2.8 in 17mm but 4.5 in 70mm. Total 4 classes difference.

[Obi-Wan]

kins0n

compare lens, please goto 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