3 out of 10 points and not recommendedNone.Extended on its own, terrible IQ at 300 end.
When I bought my first Canon SLR in 1998, the Elan IIe, I purchased the 28-105 f/3.5-4.5 USM, this 100-300, and a 50/1.8 prime. I took this kit around Europe, and the results I got from the 100-300 were poor, to say the least. I bought it to add range, but found that it only had usuable image quality at the 100mm range. Over about 150mm, I found the lens to have unusable lack of sharpness, poor contrast and terrible CA. Build quality was not great either, and the lens extended/retracted on its own if not held level. I had to put a fat elastic on the zoom control just to make it usable on my trip.reviewed December 7th, 2010 (purchased for $300)
I sold this lens as soon as I got home, good riddance!
6 out of 10 points and not recommendedGreat walkaround zoom for my film camera in 1998Average by today's standard, not great for APS-C DSLR
I bought this lens with my Elan IIe 35mm film camera in 1998. It gave me a lot of fine photographs with that camera, and saw a lot of use as my walkaround lens of choice.reviewed December 7th, 2010 (purchased for $250)
I still have the lens, and I've used it occasionally on my D60 and 60D, but it shows its age and lacks the sharpness of newer lenses made for high-resolution DSLRs. The effective FoV of a 45-168 on an APS-C body makes this not a desirable choice as a walkaround. Performance is also just average.
There are newer, cheaper options that are sharper, more contrasty,and have image stabilization and focal ranges more useful on a crop-sensor DSLR. Because of this, I don't recommend this for DSLR use.
8 out of 10 points and recommendedOutstanding image quality at a good priceSlow AF, only 1:2, life-size converter degrades image
I've had this lens more than a decade, and I still use it more than any other (though I have a EF-S 60 on the way, so that may change tomorrow). When used alone, this is a superb lens for still subjects. It's not a true 1:1 macro, but it is great for photographing smaller items (coins, jewelery, etc) and perfect for copy work. It's tack-sharp across the frame between F/4 and F/8, and has negligible vignetting, CA or distortions.reviewed December 7th, 2010 (purchased for $250)
What's not so great about this lens is its very slow focus motor speed. The little noisy motor can be frustrating when the lens AF decides to hunt in low light.
If you buy this lens, use it for what it is, don't waste money on the "life-size converter". Adding the converter gets you effectively 70mm f/3.5 but reduces sharpness and contributes significant chromatic aberration. Not only that, but you lose the ability to focus at infinity, but that's not the dealbreaker, the purple fringing is. Put the extra money towards a longer focal length macro lens instead of the converter. Canon's 100mm USM macro and Sigma's 105mm both seriously outperform the 50/2.5+converter, FYI.
7 out of 10 points and recommendedCost, IS, Image Quality far better than expected at this price pointPoor build quality, front element rotates, no USM, plastic mount
For what you get, this lens is a steal. The image quality blows away all the other 18-* kit lenses. The IS works great, 4 stops is entirely possible, and the focus is just as fast as early USM lenses, despite not being USM.reviewed December 9th, 2010 (purchased for $130)
The lens is a little soft in the corners at full zoom, but in the center, the performance is surprisingly good, even with compared directly with my 50mm f/2.5 macro. In terms of just image quality, you'll have to pay A LOT more to get a little bit better image.
If you don't need the durability of a professional grade lens, this is an outstanding upgrade from any of the earlier rebel kit lenses, most notably the non-IS precursor to this lens. The only real downside to this lens, as compared to its expensive counterparts like the 17-55, is the rotating front element. Especially at the wide end, it would be nice to be able to use a circular polarizer AND the lens hood for landscape shots, and the rotating front makes that a PITA to achieve.