The Canon EF 20-35mm f/3.5-4.5 USM Lens features a short wide angle focal length range with decent build quality at a relatively low cost.
The 20-35 utilizes a metal mount and has decent feel to it. It is a reasonably well built lens.
The Canon EF 20-35mm f/3.5-4.5 USM Lens is rather small and light. It does have a rather large 77mm filter size though. This is good for filter sharing if you also own some of Canon's L Zoom Lenses which typically feature a 77mm filter thread.
Featuring USM (Ultrasonic Motor), the Canon EF 20-35mm f/3.5-4.5 USM Lens focuses fast and quietly. However, I must note that I had some low-light focusing issues with this lens even on a Canon 1-Series Pro body.
The 20-35mm's aperture is medium-wide starting at f/3.5 at 20mm, quickly going to f/4 around 23mm and finally to f/4.5 at 29 or 30mm.
A 5-blade aperture produces 5-pointed OOF (Out Of Focus) highlights when the 20-35 is stopped down.
It is reasonably sharp wide open and improves slightly when stopped down (narrower aperture selected). Corners are a bit soft wide open. Vignetting is strong at wide open apertures - especially at the widest angle focal lengths.
The 20-35 shows some CA (Chromatic Aberration) but it is rather well controlled as is flare.
The 20-35's biggest problem (in my opinion) is barrel distortion on wide end even on a 1.3x FOVCF body. I found it to be very noticeable at 20mm and still noticeable at 24mm.
Who does the Canon EF 20-35mm f/3.5-4.5 USM Lens make sense for? For those who are not interested in the Canon EF 16-35mm f/2.8 L USM Lens or the Canon EF 17-40mm L USM Lens (price or size being the likely reasons) and need a slightly wider angle than the 28-xx or 35-xx normal zoom they already own (or plan to buy). An alternative for consideration would be the Canon EF 20mm f/2.8 USM Lens.
The Canon EF 20-35mm f/3.5-4.5 USM Lens is a decent value in a short focal length range wide angle zoom lens.