各位攝影前輩,本人是DSLR Canon 400D新手一名,想請教各位買鏡頭的意見

CANON 初學者有三寶，其中兩寶，你已經有了！

雖然另外一寶不是CANON，但口碑極佳，人人也認為抵食夾大件
就是 SIGMA 70～300 F4-5.6 APO Macro DG
看 示範吧！效果和你要的那2枝 CANON相差不遠！
http://www.ecpz.net/viewthread.php?tid=10727&extra=page%3D1

不過這枝鏡 只需 千五元左右，有餘錢，其實可考慮添置 閃光燈 （430EX）

回答你的問題：
1 CANON 年年有鏡頭出，難免有雷同，近年為1.6 x 的DSLR推出的EFS鏡，更多類似了
。特別貴的鏡，叫“L”鏡（有紅圈），擁有它們，身份像徵！

2 SIGMA 70～300 值得入，影遠得，影近得（MARCO），影人像也有靚的淺景深！

3 買的時候，聲明要行貨，這些大鋪不敢以水充行。水貨都是關係免費保養的問題。

2006-12-13 12:50:17 補充：
EF 70-200mm f/4.0 L USM Zoom慣稱 “小小白”！" 小白"是 恆定光圈 F2.8 那一枝!小白 比 小小白 的 重量 和價錢 都大約多 2/3

if 主要作影人像 then your 50mm f1.8 would be a good start... if so try out the 85mm 1.8 .. it would give out good background blur....

the ideal range of of 人像 is around 80-135mm on Full Frame (35mm film panel)... thus on your 400D (which using a smaller "film panel" thus producing a 1.6x crop of 35mm) your lens selection would be 50mm (on 1.6x crop camera like 400d is around 80mm) and 85mm (on 1.6x crop camera like 400d is around 136mm)

tele lens: for targets further away... I would say that between your choices on question 3 - is older version vs newer version - USM = ultrasonic motor - which is a speical faster motor for you AutoFocus (AF) - briefly lens with USM will AF faster without most of the time. For those lens... I would suggest Sigma's 70-300 Macro - which is the best balance between price and picture quality....
if you do not mind spending a more I STRONGLY SUGGEST Canon EF 70-200 F4L which gives you on of the best picture quality that Canon produces

as for wide... stick to your kit lens... it is not bad of a lens for that price...