[轉貼] Canon EF 24-105mm f/4 USM L IS

Canon EF 24-105mm f/4 USM L IS
Quick Test Report / Review02/11/2006 Special thanks to Guillaume May for providing this lens! IntroductionThe Canon EF 24-105mm f/4 USM L IS was an eagerly awaited lens since the old film days. On full frame (D)SLRs it is surely a near-perfect standard zoom with a 4.4x zoom ratio in combination with a relatively compact size, a relatively low weight and an image stabilizer on top. Some may not like the rather modest max. aperture but then there's always a trade-off somewhere with all zoom lenses. On APS-C DSLRs such as the EOS 350D (used for testing) its field-of-view resembles a classic 39-168mm lens on full-frame cameras so by most standards things aren't quite as interesting here as on a full frame DSLR/SLR. The lens is also sold as a kit lens in combination with the Canon EOS 5D where it certainly makes more sense due to the full frame image sensor of the camera. With a weight of 670g and a size of 84x107mm it is quite a bit more compact and light-weight than the EF 24-70mm f/2.8 USM L. Unlike its cousin the lens has a conventional zoom mechanism so it extends towards the long end of the range. While this feels right somehow the lens hood (part of the package) isn't quite as efficient because it was only optimized to the 24mm setting of the lens. The front element does not rotate during focusing so there're no issues when using a polarizer - without hood at least. The optical construction is made of 18 elements in 13 groups including three aspherical elements (two replica, one glass molded) plus one S-UD (super ultra-low dispersion) element. The min. focus distance is 0.45m resulting is a max. object magnification of ~1:4 at 105mm. The lens features 8 circular aperture blades. Typical for most Canon L zooms the filter size is 77mm. The lens has a ring-type USM drive based on a front-focusing system resulting in an extremely fast AF speed and extremely low AF noise. Full-time manual focusing (FTM) is always possible in one-shot AF mode. The image stabilzer provides an equivalent effect of a 3 f-stops gain in shutter speed for hand-held photography (at cost of slower shutter speeds if exploited to the max). The IS works for static scenes only so there's no 2nd mode for panning. Regarding the nature of the lens this isn't a big drawback because action photography is normally not a primary application. The build quality of this lens is exceptional. No significant wobbling and smooth control ring - almost perfect. The lens is also designed to survive in harsh conditions with a sealing against dust and moisture. It is worth to mention that this lens has been serviced by Canon due to the flare problem present in very early production lenses. DistortionsAt 24mm the lens exhibits very pronounced barrel distortions (1.8%) which is significantly more compared to the EF 24-70mm f/2.8 USM L. From 40mm and up there're slight pincushion distortions but nothing to worry about under most field conditions. 24mm:
40mm:
70mm:
105mm:
The chart above has a real-world size of about 120x80cm. Possibly expect more distortions towards closer focus distances. VignettingOn APS-C DSLRs vignetting is very well controlled with the lens. Wide-open vignetting does not exceed ~0.5EV which is usually not much of an issue in real life situations. One stop down the problem is absolutely negligible. MTF (resolution)The lens produced very good to excellent resolution figures under lab conditions. On an APS-C DSLR the performance is best between 24mm and 70mm where the center resolution is truely excellent throughout the tested aperture range. The borders follow closely behind with very good figures at f/4 and also excellent results beyond. At 105mm there's a slight decrease in quality down to a very good center and good+ boders at f/4. Stopping down helps to boost quality but the local peak quality isn't reached prior of f/11. All-in-all this is a very impressive performance for a 4.4x zoom lens. Below is a simplified summary of the formal findings. The chart shows in line widths per picture height (LW/PH) which can be taken as a quantity for sharpness. If you want to know more about it you may check out the corresponding Imatest Explanations. Chromatic AberrationsChromatic aberrations (color shadows at harsh contrast transitions) can be a problem at 24mm where the average width exceeds 1.5 pixel at the image border at wide open aperture. Stopping down helps to reduce the issue but it remains less than stellar here. To a lesser degree this remains true at 40mm at large aperture settings. Towards the tele range the CA are pretty low and nothing to worry about. VerdictRegarding its equivalent zoom range (39-168mm) on an APS-C DSLR the Canon EF 24-105mm f/4 USM L IS may not be the most sexy lens here but its performance figures are very impressive nonetheless. In fact the resolution results beat those from the EF 24-70mm f/2.8 USM L and match the EF 28-70mm f/2.8 USM L with its much more conservative zoom range (but higher speed). There's a slight decrease in performance at 105mm but even here the quality remains on a very high level. As to be expected from a modern Canon L lens the construction quality is up to pro standards matching its fasters cousins. The lower price tag plus the extra IS should compensate the slightly more moderate max. aperture for most users. Is it a perfect lens then ? Well, there're also downsides like pronounced barrel distortions and higher than expected CAs at the wide-end of the zoom range. However, the package remains extremely attractive if you can live with the rather unattractive zoom range on an APS-C DSLR - similar to other 28-xx or 24-xx zooms this lens is really more meant for 1.3x or FF (D)SLRs.