Some love it, some hate it, I think it's a great lens.......

I've been staring at this lens for quite some time. I've read a LOT of reviews of this lens, some love it, some hate it. I suppose it comes down to whether you can replace the range of this lens with multiple bodies and multiple lenses or whether you can put up with the foibles that this beast offers for the convenience of having a great deal of range and IS all in one package.

Most common complaints involve color halos on frame edges at wide aperatures, lens flaring and a lack of color definition and contrast at all times. I just got mine in the mail yesterday, I went outside and shot about 50 shots and so far I'm perfectly happy with what I'm seeing even at wide open max aperatures and high magnifications in software. I purchased this lens to shoot karate in a gym setting. My old 17-55 kit lens used to be the lens of choice but at times it just didn't have enough high end magnification to shoot anything happening at the other side of the gym. Haven't had a chance to try shooting my usual subject with it yet but after experiences with the IS on my well regarded 28-135 I think the IS will again prove invaluable--I'd shoot with the other lens all the time except that the low end isn't enough when the action is close with the 1.6 magnification factor. The IS can really save a shot when the flash can't keep up and either doesn't go off at all or doesn't properly light the scene (which can be fixed later in software).

What's in the box:
The lens
Warranty card

You don't get hoods with canon commercial lenses, for the price of this monster you should.

Controls:
This lens has the standard focus switch (manual=MF or auto=AF) and an additional switch for turning the IS function on and off.

Build quality:
I've seen complaints that people don't think it's built well, I have to disagree, this is built as well as my 28-135. It doesn't have that cheapo plastic feel that several canon lenses have (like the 50mm 1.8 "plastic fantastic") It has the best quality ring USM motors that offer full time manual focusing (i.e. you don't have to switch into MF mode to touch up the focusing). I find the lens quiet and the zoom moves as smoothly as it does on any other canon non-L-series lens I own. I have no complaints about build.

Focusing:
So far focusing is quick and I haven't had any problems with "hunting" yet even in low light situations. On a 20D the viewfinder is plenty bright enough for manual focusing if you're shooting through glass etc.

Accessories:
As with all lenses the first thing you want is a UV filter to protect the element of your very expensive lens. This one uses 67mm, normally an expensive filter but you can do pretty well on ebay. You also probably want a hood for this one. I've never found it necessary to buy a hood for any of my other lenses shooting indoors but most reviews I've read for this lens say it's a definite want for this lens. The canon hood is pricey at $30.00, you can find generic flower petal hoods on ebay for a lot less--since this is a 17mm lens generic hoods may vignette and interfere with your shot so be sure it's a hood designed for wide angle lenses.

What is IS, how does it affect performance:
IS is an abbreviation for "image stabilization." This lens has a gyro system inside that helps stabilize the lens elements and thus mostly eliminates camera shake. As far as I know canon is the only lens maker offering this kind of thing for consumer lenses. The IS system only stabilizes the lens, it does nothing about a moving subject and it won't do a lot for really violent movement either (like standing on a tossing boat deck during a storm or shooting out of a plane window while hitting turbulence). Normally an experienced photographer can prop themselves against a solid object and perhaps handhold down to around 1/30th of a second or maybe one stop more (1/15th). With the IS system, pictures taken at this normally very slow shutter speed will be sharp because it is gyroscopically accounting for camera movement. I haven't tested it myself but there are reports of handholding a lens with IS at some pretty impressively slow shutter speeds.

Because the system is using battery power I strongly recommend the camera grip with the second battery if you will be shooting a great deal with this lens, with my other lens I would see about 250 pictures instead of the usual 300+ on a single battery, have never run down a battery yet while using the dual setup in the grip.

My experiences:
I prefer extra exposure and so my camera is always set to overexpose a touch with and without flash (usually extra on flash too since I like flash shots a bit on the hot side as well). I did find that I like a touch more overexposure with this lens than with my kit (17-55) lens so you might say this lens is a little dark. So when I use this lens I set extra exposure to half stop instead of a third stop.

This lens like every other canon lens I own, has a stationery front element. This is important for filters such as polarizers whose effect changes according to how they are rotated. A star effect filter would be another example of a filter that needs a stationery front element.

Another complaint I've read deals with color intensity and contrast, I took care of that by going into camera settings and increasing tone, contrast, etc. to max. The first batch of pictures I took with it were on a rainy gray day, using cloudy white balance. I'm happy with every shot I took, colors seem quite adequate and well saturated but the best test will be a bright sunny day.

The biggest test will be this Monday when I can shoot some karate with it using flash. This lens, like all consumer glass is on the slow side but I've generally found that I can get very acceptable flash cycle speed if I shoot in iso 3200 (available only on the 20D) and then process the shots with noise ninja afterwords to dispel some of the noise from the high iso.

I've got at least 30 days to make a final decision on the lens, so far I'm not at all disappointed with it. I think the price is a bit high but since it's the only game in town, Canon can screw the camera owners and we can't do anything but decide whether to buy it or give it a pass because the price is too high. This lens, like any EF-S will only work on a canon digital with a C sized image sensor it will not work on a film body due to differences in the back of the lens. Current compatible bodies are the Rebel, 10D, 20D, it will definetly not work on the new 5D because that one has a full 35mm sized sensor.

update: Got to shoot some action last night. I find that single shot focus mode is not the best choice for this lens while shooting fast action. My old 17-55 seemed to focus best in one shot mode but this lens seems to focus better on fast action in one of the two AI focus modes. I'll need to experiment more with this one. I got a number of great shots last night and all seem sharp and well lighted with the 580EX and a omnibounce diffuser on the flash (using 1600ISO to get the most out of a single flash). On the few occasions the flash didn't fire, the IS saved the shot and they can probably be salvaged in software. I find that the 20D and the Rebel (which is worse than the 20D) have a hard time with white balance in a mixed lighting situation (flash=daylight, surrounding light=sodium or mercury vapor) in the gym so I always use some method of setting a custom white balance to get the best results. The custom white balance shot needs to be taken with the camera at the settings you'll be using (i.e. ISO) as a change in ISO settings will change the white balance again.

update 1-31-06: Well finally got the chance to give this lens a good work out. I was participating in the last karate test but someone else shot using my camera, pictures are great. We also did an outdoor seminar in a park (very bright clear day, morning sun) and those came out great too in the bright sun. I can see why a hood is recommend, did get a few lens flares in a few frames but none of them really ruined the shot or anything. I bought a generic flower petal hood that's supposed to work with this lens I find it vignettes (interferes with the frame) at 17mm, found a person on ebay importing the expensive canon version from hong kong for a bit less than full price so have one of those coming. I just can't understand why so many seem to hate this lens, I just don't see what folks are complaining about. Now I haven't tried to blow anything up to 16X20 or anything and that may be where the flaws get seen but for 8x10 and smaller I've got absolutely no complaints.

update on hood: The canon hood doesn't vignette, probably because it attaches around the lens barrel instead of screwing into the filter threads, I imagine someone is making a generic one that works right but you'd probably have to see it close up and not just in a picture to know for sure it will work correctly (at least the cheapie was only 6 bucks but they look almost the same except for the attachment scheme). It took a month to get the canon hood from China but it was worth the wait I think and I saved about fifteen bucks.