First of all, here are some shots physically comparing the Sigma 18-125mm DC OS HSM to the Canon EFS18-55mm IS kit lens:
As a DSLR user with limited experience, here are my thoughts on this lens, in no particular order other than positive and negative:
1. Excellent image quality compared to the very good kit lens (EF-S18-55mm IS).
2. Compact size (74mm depth, 89mm length and 67mm filter size) and weight (540g) for such a versatile zoom range.
3. Matches the Canon 28-135mm IS USM in terms of range, albeit from a different starting point. In fact, the 18mm wide-angle coverage may be more useful than than an extra 10mm at the end of the zoom range.
4. Fast auto-focusing due to the Hyper Sonic Motor (lacking in the Sigma 18-200mm OS lens).
5. Optical Stabilizer built in.
6. Petal-shaped lens hood included in the box and not an optional extra as with Canon.
7. Newer and therefore, possibly, better technology than the Canon 28-135mm IS USM and Sigma 18-200mm OS lenses?
8. Reasonably priced compared to the Canon 28-135mm.
9. Good build quality, eg, metal mount.
10. The sample images below demonstrate that I've successfully used this lens in a variety of situations.
1. The faint sound from the lens may unnecessarily deter potential buyers although I certainly do not find it to be distracting.
My conclusion is that the Sigma 18-125mm is an excellent all-in-one, walkaround lens. It will be particularly useful for those users upgrading from a point-and-shoot or superzoom camera for whom the 18-55mm range of kit lenses may be too limiting and/or changing lenses may be a hassle. It is also good value for money as you can buy this lens in the UK for £224 (I originally paid £270 at Amazon).
What about comparing this lens to a superzoom, such as the Canon 18-200mm IS or the Tamron 18-270mm VC? Well, I bought the Canon 18-200mm IS but sold it after two months for a few reasons: The difference between 125mm and 200mm was not as big as I expected, the 18-200mm is bulkier, I had fewer keepers with the 18-200mm IS and the price difference is too great to justify it. For the same cost of a superzoom (about £400), you can buy the Sigma 18-125mm and also get a Canon Speedlite 430EXII. In fact, when I sold the 18-200mm IS, I bought a second Speedlight and a Panasonic DMC-TZ4 (a 10x zoom compact camera with video) as a pocket/travel camera.
Here's a physical comparison of the Canon kit lens, Sigma 18-125mm and the Canon 18-200mm IS:
These are some sample images taken on my Canon EOS 450D, arranged by focal length. They will take a few minutes to download so dial-up internet users beware! For some reason, there's a gap at 100mm+ but some of the 90mm+ shots were taken at 97mm which is close enough for the time being. I'll add more samples when possible. You should also look in the Lens Gallery where I've posted different samples:
There are currently over 1,000 sample images in my Flickr set for this lens. I need to go through them, keeping the best and deleting the rest. I'll also add new photos when possible.