Getting the proper focal length or focal length range is a very important criterion when selecting a lens. And the first attraction to any ultra-wide zoom lens is in fact the ultra-wide focal length range, so let's review what this focal length range looks like. Being a Tamron "Di II" (Digital Camera) lens, the Tamron 10-24 has a smaller-than-full-frame image circle designed to work only on APS-C/1.6x/1.5x FOVCF DSLRs. All of the ultra-wide angle lenses compared in this review are the same in regards to this smaller image circle. Thus, the focal lengths shown for all of the lenses below are similar to 1.6x longer focal lengths on a full frame SLR or DSLR. The Tamron's 10-24mm focal length range frames like a 16-38.4mm lens frames on a full frame DSLR.you likely have an APS-C general purpose lens with a 17 or 18mm wide end - or perhaps a full frame lens with a 24mm wide focal length. You can match (or closely match) one of the sample results above with your widest focal length to determine how the rest of the available focal lengths align with what you already have. When deciding which focal length range is best for you, consider the lens(es) you already have and how the ultra-wide angle zoom focal length range aligns with it. Also consider which focal length range you need in the lens that is mounted while using this lens (with no lens change required).In terms of focal length ranges, the focal length numbers mostly tell the difference. 8mm is wider than 10mm and 24mm is longer than 20mm. The Tamron 10-24 has the longest overall focal length range of this comparison group.Use ultra-wide angle focal lengths to emphasize a foreground subject in relation to a mostly-in-focus background. Landscape and architecture (indoor and outdoor) photographers are two groups with a need for such angles of view. If photographing people is your goal, keep your distance when using this lens - unless perspective distortion is also your goal.Know that built-in flash coverage on most DSLRs will not be wide enough to cover much of the focal length range of this lens. Plan on an alternative method of flash lighting/diffusion if planning to use flash with this lens.Like most of the lenses in this class, the Tamron 10-24mm f/3.5-4.5 Di II Lens has a relatively narrow max aperture, and the max aperture changes over the focal length range. This means that wide open aperture exposure values will change as the lens is zoomed to longer focal lengths.A bright light, such as the sun, in the frame at 10mm is going to result in strong flare effects in your image. The amount of flare effects seen diminishes to nearly none at 24mm.Bokeh (background blur quality) is not easy to discern in a lens this wide - and is not real important for the uses I have for a lens such as this one. In the 10-24mm range, OOF details generally remain tiny, but this 7-aperture-blade lens does not produce especially nice blur quality.Unless you are using manual focus, focus accuracy is very important to final image quality. I have encountered focus accuracy problems with many 3rd party lenses and, as I said at the beginning of this review, I had to return my first two Tamron 10-24mm f/3.5-4.5 Di II Lenses. The third lens focuses accurately most of the time.The Tamron 10-24mm f/3.5-4.5 Di II Lens internally focuses slowly and audibly. The focus ring turns during AF and FTM (Full Time Manual) focusing is not available. The filter rings do not rotate with focusing.The overall shape of this lens is smooth with ribs raised slightly higher on the focus ring than on the zoom ring. The objective end of the lens has a wider diameter than the rest of the lens.The petal-shaped lens hood is included. Tamron's center-and-side-pinch front lens caps are very nice, but the install-in-one-position-only rear caps are not my favorite.