Pro: Great image quality, especially for available light portraits shot at f2.8 where you want a pleasingly blurred background. The IS is good but see note below.Con: Weight if you plan on carrying it around all day on a pro camera body.This is a great lens and if I didn't also own the 70-200mm f4.0L IS Canon lens I would have rated it 5 stars. IMHO the f4 is a better all around carry lens if you don't absolutely have to have the f2.8 aperture. The IS in the f4 is Canon's latest and is usable up to 4 stops slower shutter speed than you'd normally need at less than half the weight. The 2.8 version uses the very good, but older, 3 stop IS. On the surface you would think that the f2.8 aperture being one stop faster would place them on even ground where IS is concerned but it does not. the newer IS on the f4 version is INCREDIBLE in operation! To be fair to the 2.8 lens, given the same lighting conditions, it gives you one full shutter speed faster that may make a difference if stopping motion is needed in the shot. My best advice is to not end up with both lenses becuase it is so hard to decide which one to take along!

Great webcam. Excellent looks. The thing that holds ito on the Laptop/Monitor seems to be too large for no reason. I would've made it smaller from a better material, for the price that it is being sold they should've "gone the extra mile".Carl Zeiss optics are supposedly what makes a difference.However the lens is the same size as all the regular webcams.I would've thought that Zeiss optics would use a larger and brighted high index lenses that they are known for, to allow more light to get in and improve image quality as additional benefit.Not so. Well the lens does seem to let more light through then the plastics.but most of the improvements seems to come from post processing of the captured image(this is a speculation at this point, I have not done any professional testing to verify my inference).

I have done a lot of researches before decided on getting this sweet baby. I chose this over the regular f2.8 and f4 IS because I know I want the best. A lot of people complained about the weight and I have to admit it is quite heavy especially carrying it the whole day. After the first day of shooting, I couldn't wait to put my CompactFlash into the digital photo frame to evaluate the quality of the pictures. I immediately forgot about the weight and I appreciated so much on the picture quality. Then I remove the card and load all the pictures on my 24" IMAC. The result are more stunning! Next, I tried printing one of my best shot onto a premium photo paper. You know what I am going to say! The image is tack sharp with great contrast. I tried a lot of other "L" zoom lens including the f4 non IS and none of them give me the same level of quality images. Although I still think prime lens are the best for quality but I don't think you can find a better zoom lens on the market. This is the one!

Fits perfect on my 70-200mm 2.8 L lens and 24-70mm 2.8 L lens.

I have the 16-35mm F4, and indeed the extra 2mm help a bit....but as far as IQ I can't say there is much of a difference.If you have already a canon 16-35mm f4, then there is no need to get this one ( I got it because the 16-35 is now under my wife's fingernails)The 15-35 f2.8 it's different story, if indeed you need 2.8, but same applies to the 2.8 EF variant - 1mm difference.In sum, a great lens, way more compact than my 11-24mm, similar performer as the superb EF16-35mm f4, but as a first UWA or replacement from a 17-40 for instanceRecommended

Isn't the Carl Zeiss optics lens as advertised but it;s a much clearer picture now so... I got that going for me, which is nice.

　EOS 1DXに24-70mm F4 ISを装着（フード逆付）し、仕切りでもう一部屋作ったところに16-35mm F4 IS、さらに上部の小物入れにSPEEDLIGHT 430EXⅡ、予備バッテリーが何とか入りました。　何とか入ったというのは、ボディの頭が出っ張り少し膨らんでしまうこと、ボディをバッグ内で固定するために仕切りクッションで開口部上部を塞ぐことになってしまい、スリングバッグの特性である肩からクルッとまわしてカメラを取り出すということが出来ないというところです。　到着したばかりなのでもっと良いやり方があるのかもしれませんが、とりあえずフルサイズ+縦グリ+標準・広角レンズ装着でも入れることは出来るという報告です。　あと、当方胸囲105cmですが、ベルトを目いっぱい伸ばしてギリギリ背負える感じでしたので、上着を着ると窮屈かもしれません。

I have had this fabulous lens for 2 months now. This is my second lens in Canon's line up of L lenses. I have a 70-200 f4 non-IS also. This is my first wide angle zoom L lens and i have come to know what i have been missing. Till now the widest lens i had was a 50mm f2.5 macro and 50 f1.8. Although on a 1.6x sensor like 20D which i own, this lens is not so wide it performs excellently. The focusing is very fast, sharp crisp images and consistent quality as the aperture range remains the same throughout the entire zoom. This may not be suitable for some the semi-pros or pros since its a little slow being f4, i would recommend this to anyone who does serious photography as a hobby. In indoors too it performs flawlessly. Most of the time i dont use a tripod and its difficult to maintain a fast enough shutter speed especially with aperture more than 8. so if you are like me, then you may want to take a look at the 17-85 IS or the 17-55 IS since the IS compensates atleast 2 stops in low light for hand holding. But if its outdoor then u can easily handhold this and shoot some great photos in good lighting conditions. Also i would like to mention that being a L lens this is a little heavy because of its solid construction. Its also big compared to the other startup lenses. It takes 77mm filters and it can be used even on full frame cameras like 5D. hope you enjoy this lens as much as i am doing.