The EF 70-300mm f/4-5.6 IS USM telephoto zoom lens has been developed to meet the high-performance standards that today's photographers demand. Improved Image Stabilizer Technology provides up to three stops of shake correction, and the Mode 2 option stabilizes images while panning with a moving subject.
This excellent general purpose zoom is a step up from the previous 75 - 300 mm zoom, with better optical performance at all focal lengths and apertures. I have used it on a Canon EOS 20D for several months and am very pleased with its performance, but see weaknesses below. The lens covers the full 24 x 36 frame so can be used on film cameras or the EOS 5D.
For the focal length range it is light in weight, moderate in size and very reasonably priced. IS works really well making this lens ideal for handheld use even at the longest focal length. There are two IS modes available. A zoom lock prevents barrel creep.
Distortion is low with slight barrel at the wide end and slight pincushion at the long end. Some colour fringing is visible at contrasty edges, easily correctable in Photoshop. Filter size is a handy 52 mm. Field of view on the 20D is equivalent to a focal length range of 112 - 480 mm on full frame.
Strength
Surprisingly good optical performance considering the price. At the short end this lens delivers results indistinguishable from primes and top of the range L zooms. Absolute optical performance declines a little as the lens is zoomed out but I have made clear, sharp, well detailed photos of subjects 3 kilometers away, hand held at 300 mm. Quite impressive. Performance is really good wide open at all focal lengths, improving just a little at f 8 and f 11. A very versatile long zoom, an absolute must for the traveller with a Canon EOS camera.
Weakness
Lens construction and design have some cost saving features, I guess you can't have everything. You either have the cost or the cost saving features.There is no distance scale, which is no big deal. With a long lens like this a distance scale is not much use anyway. The whole front barrel of the lens including the focus ring rotates with auto or manual focussing, be careful where you put the fingers of your left hand. There is no FTM, even though the AF drive is USM. The front lens barrel extends substantially when fully zoomed out.
Buyers note. Some examples of this lens have a strange optical fault, acknowleged by Canon. Images go soft in the corners at the longer focal lengths when the lens is held in the vertical ( portrait ) format orientation. My lens had this problem. Canon fixed it without demur, apparently by replacing one of the lens groups which contained the fault. After the fix the lens is working perfectly. This experience makes a good argument for buying lenses with full manufacturers warranty even though this cost a bit more.
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