Đánh giá lens canon ef 17-40mm f4l usm năm 2024
(From Canon lens literature) A new and affordable L-series ultra-wide-angle zoom lens that's ideal for both film and digital SLRs. Superior optics are assured by the use of three Aspherical lens elements, in addition to a Super UD (Ultra-low Dispersion) glass element. Optical coatings are optimized for use with digital cameras. This lens focuses as close as 11 inches (0.28m), and offers both Canon's full-time manual focus and a powerful ring-type USM for fast and silent AF. It has a constant f/4 maximum aperture, and offers the choice of screw-in 77mm filters or a holder in the rear of the lens for up to three gel filters. Finally, it offers weather-resistant construction similar to other high-end L-series lenses. Test Notes The Canon 17-40mm f/4 L is a high quality lens with a full-frame image circle that showed really exceptional performance on the EOS-20D we used to test it with. (The EOS-20D has a nominally APS-C size sensor, so corner sharpness and distortion will be better than if the lens is used on a camera with a full-frame sensor.) Sharpness at maximum aperture is excellent across the board (just a slight decrease in sharpness around 30 mm), and the "sweet spot" for sharpness is unusually broad, with truly excellent results from f/5.6 to f/8 at all focal lengths. Chromatic aberration is moderate at 17mm, very low at 24 and 31mm, and then rises again for large apertures at 40mm. Vignetting is remarkably low, less than 1/4 EV at all apertures and focal lengths, almost non-existent at apertures of f/8 and higher, at all focal lengths 24mm and above. Geometric distortion is a little higher, with about 0.7% barrel distortion at 17mm, although this decreases to only 0.1% pincushion at 40mm. (Again, note that these figures are when used with an APS-C size sensor: Full frame results would doubtless be worse.) All in all, the 17-40mm f/4 L easily justifies its premium price with top-notch optical performance. Full-Frame Test Notes: The full-frame test results for the Canon 17-40mm f/4L demonstrate to some extent just how much full-frame cameras demand from even excellent lenses in the corners. The 17-40 f/4 is an excellent lens, remarkably so on the 20D. ON the 5D, while it's still excellent, some significant softness appears in the corners when shooting wide open. The good news though, is that closing down just one f-stop brings dramatic improvement, and performance at f/8 is truly excellent. At f/11, the corners flatten slightly more, but at the cost of a smidgen of center sharpness as diffraction starts to limit the resolution slightly. As you'd expect, both maximum and average chromatic aberration are a little higher on a full-frame body, due to the larger image circle the lens has to cover. Geometric distortion increases somewhat more relative to its sub-frame performance, particularly at longer focal lengths, reaching about 0.4% pincushion at 29mm, and increasing gradually from there to 40mm. Barrel distortion hits 1% at 17mm. Vignetting is also much more pronounced on the 5D than it was on the 20D, hitting a maximum of about 0.8 EV wide open at 17mm, and about 0.4EV wide open at 40mm. Light falloff does decrease as you stop down though, dropping by roughly half as you move from f/4 to f/8, and decreasing more gradually from there. While there's no question that the 17-40mm f/4L has to work a lot harder around the edges of a full-frame sensor, there's also no question that it remains an excellent optic, one of the true bargains among Canon's lenses. - And if you stop it down, its performance is really exceptional for a wide-angle zoom. A note about the blur plots for this lens - Astute readers will note that the optimal performance appears to be somewhat better (lower BxU numbers) on the 5D than the 20D. We consider this to be an artifact of minor differences in the two cameras' pixel dimensions and in-camera sharpening processing, magnified by the extreme sensitivity of the DxO analysis application and the fine gradations of our graphing scheme. The colors on the graphs make it easy to see variations of considerably less than 1 BxU near the lower end of the graph's range. We've scaled the results to match the performance between cameras as best as possible, but our current gain-only normalization seems to leave the 5D's results looking slightly better at the "good" end of the scale when the "bad" end results are more or less in-line. Given that the differences seen for the optimal conditions are tiny, fractional-BxU unit variations, they really aren't statistically significant. CanonEF 17-40mm f/4L USMCanon EF 17-40mm f/4L USM User Reviews8.6/10average of 56 review(s) Build Quality9.3/10 Image Quality8.7/10
9 out of 10 pointsand recommended by jyli19 (7 reviews) Excellent image quality, quality construction, light weight, affordable Lens hood does not fit tightly Excellent lens of its price. A very affordale alternative to the 16-35mm when willing to sacrifice one stop. This lens can produce exceptional images with great sharpness and color contrast. |