Canon EF 20-35mm F3.5-4.5 USM là ống kính zoom có chất lượng quang học tốt trong một thiết kế gọn nhẹ, chỉ nặng 340g. Lens góc rộng Canon 20-35 USM là ống kính siêu rộng giá rẻ sử dụng cho máy ảnh Fullframe với góc nhìn tương đương tiêu cự 14-24 trên máy ảnh Crop, lens 20-35 USM chuyên sử dụng chụp ảnh phong cảnh, kiến trúc, kỷ yếu, du lịch cho máy ảnh Canon Fullframe như Canon 6D, 6D2, 5D, 5D2, 5D3, 5D4… và sử dụng được cho máy ảnh Crop. Đây là dòng lens góc siêu rộng ngon bổ rẻ trong tầm giá và bền bỉ với đuôi lens kim loại chắc chắn cùng với công nghệ lấy nét siêu âm USM bắt nét nhanh và chuẩn. Canon made earlier FD-series L wide zooms, but the Canon FD system was never a system taken seriously by mainstream pros. This is why Canon gambled that they could dump the entire FD system and start from scratch with a completely new and incompatible system for autofocus cameras, the EOS system and EF lenses. Canon won; Canon's gamble won them the pro market by the early 1990s because Canon's AF system worked great, and Nikon's didn't. This lens, along with the EF 80-200mm f/2.8 L, EF 300mm f/2.8 L and EF 50mm f/1.0 L, was the lens that won the pro market for Canon. Nikon has never gotten the majority of the pro market back because there has never been any strong reason to dump everything and change brands again. Canon won when everyone switched to autofocus, and this was the lens that was designed so well that it helped Canon win it. Mechanics are better than today's lenses, optics are the same and the price is much lower. The only gotcha is that there is no instant manual-focus override: you must move the switch on the lens to get between auto and manual focus. This isn't a big deal for wide lenses, which autofocus much better and faster than we can see to focus them manually. The good news is that unlike all the current Nikon and Canon lenses, knocking the focus ring by accident never moves the focus unintentionally. Feel free to turn the focus ring all you want while in AF, it's ignored. I'm always knocking the focus ring by accident on my Canon and Nikon 16-35mm lenses, and never have this problem with this solid Canon 20-35 L. Compatibility and Formats This L lens is optimized for 35mm film and full-frame digital, and of course works on all 1.3x and 1.6x Canon cameras. This Canon EF EOS 20-35mm f/2.8L works perfectly with every Canon EOS camera ever made, meaning every Canon DSLR and every Canon autofocus 35mm camera made since 1987. This means of course it works great on today's 5D Mark II and Canon 7D, but it works just as well on my original Canon EOS 620 from 1987! As a full-frame lens, this works on all Canon SLRs, regardless of format. As a professional lens, I will be reviewing this lens on full-frame.  Canon 20-35 2.8 L. enlarge. Specifications Compared Name Canon calls this the CANON ZOOM LENS EF 20-35mm f/2.8 L. EF means "electronic focus," meaning that there is an autofocus motor in the lens itself. All Canon lenses since 1987 have been EF. L only means as expensive as L ; it means nothing technically. Optics 15 elements in 12 groups. The front element is an expensive ground aspheric. Floating elements; the optical design optimizes itself as focused. Internal focus and internal zoom; nothing moves externally as focused or zoomed, although the front and rear groups do pump in and out inside the barrel. Focal Length 20-35mm. On 1.3x Canon cameras it will see angles-of-view similar to what a 26~45mm lens would see on a 35mm camera. On 1.6x Canon cameras it will see angles-of-view similar to what a 32~56mm lens would see on a 35mm camera. Clearly this is a silly choice for anything other than a full-frame or 35mm camera. Angle of View (on 35mm and full-frame cameras) 94º ~ 63 º diagonal. 62º ~ 38 º vertical. 84º ~ 54º horizontal. Close Focus 1.6 feet (0.5m) from the image plane, specified. Maximum Reproduction Ratio 1:11.11. Extension Tubes Use the Canon EF-25 or Canon EF25 II to get close-ups to 0.92x at 35mm and 0.66x at 20mm. Diaphragm Front, Canon 20-35 L at 35mm and f/2.8 (EF diaphragm not visible). enlarge. 6 blades. Stops down to f/22. Focus Scale Yes. The ring turns from infinity to the closest focus distance in about 130.º Depth-of-Field Scale No. Infra-Red Focus Indices Focus Scale, Canon 20-35/2.8L. enlarge. Yes, marks for 35mm, 28mm, 24mm and 20mm focal lengths. These marks are probably for the 800 nm wavelength. Filter Thread 72mm. Metal. Does not move, ever. Size Canon specifies 3.1" (79.2mm) diameter by 3.5 " (89mm) long. It doesn't change size as zoomed or focused. Weight 19.360 oz. (548.8g), measured. Canon specified 19.1 oz. (540g) in 1989. Canon specifies 20.1 oz. (570g). Hood Plastic bayonet EW-75, included. Case LH-D13 hard cylindrical case, included. Caps 72mm E72 front, included. (non-ultrasonic cap with black-on-black Canon logo.) Standard EOS cap rear. Introduced October 1989, four full years before Nikon's clumsy 20-35mm f/2.8 AF of late 1993. Quality Made in Japan. Price, USA 2011 December: about $600 used. 1995 December: $1,570 (equivalent to $2,350 with inflation in 2012). 1994 December: $1,469 (equivalent to $2,275 with inflation in 2012). 1992 December: $1,079 (equivalent to $1,775 with inflation in 2012). 1991 December: $1,051 (equivalent to $1,775 with inflation in 2012). Box, Canon 20-35/2.8 L. bigger. Performance Compared Overall The Canon 20-35mm f/2.8 L is mechanically superb and optically as good as Canon's current ultrawide zooms. Every sports pro had one of these in his bag in the early 1990s. This is a 2011 test of a made-in-1994 lens, and it still works great. Autofocus Autofocus is fast but not silent. The Arc Form Drive (AFD) motor whines a little as it zips around. Auto/Manual Switching You must move the AF-MF switch to change modes. AF Speed AF is fast!, as Canons always are. AF Accuracy and Consistency Even at f/2.8, all my shots are dead-on at every focal length on my Canon 5D Mark II. Yes! Manual Focus Manual focus is easy; just move the switch and turn the ring. Bokeh Bokeh, the quality of out-of-focus areas as opposed to the degree of defocus, is beautiful. Backgrounds melt away if you're at f/2.8 and are close enough to throw the background out of focus. Focus Breathing Focus breathing (the image changing size as focused) is mostly of interest to cinematographers who don't want the image changing size ("breathing") as the lens is focused among different subjects. The image from the Canon 20-35mm f/2.8 L gets very slightly smaller as focused more closely. I doubt you'd ever notice it. Color Rendition The color balance of this 20-35mm f/2.8 L matches my other Canon EF lenses. Distortion The Canon 20-35mm f/2.8 has plenty of barrel distortion at the 20mm end and not much pincushion distortion at the 35mm end. Distortion becomes more barrel at closer distances. Use these values in Photoshop's Lens Distortion tool to remove most of it: © 2011 KenRockwell.com. All rights reserved. Like all Canon ultrawide lenses even today, this distortion is complex and never completely corrects with a simple tool like Photoshop. There is always some residual waviness left after these corrections at all focal lengths. Guess what? It has . Surprise! Ergonomics Canon 20-35/2.8L. enlarge. This is a solid little hunk of lens. It feels great; it's all made of alloy, not nasty plastic like the newest Canon 16-35mm f/2.8L II and Canon 17-40mm f/4L. The only downside is needing to move the AF-MF switch to swap modes, but the good side of that is that one never needs to worry about bumping the focus ring by accident in autofocus and messing up a shot by accident as happens with newer USM lenses. Falloff (darkened corners) Some falloff is visible at f/2.8 at 20mm, and otherwise it's invisible. My Canon 5D Mark II (as of firmware 2.0.4) doesn't have the data to correct this automatically in its Peripheral Illumination Correction menu option. If you go find the data and load it into your camera (I'm too lazy), it should correct for this automatically. I've greatly exaggerated this by shooting a flat gray target and presenting it against a gray background. Canon 20-35mm f/2.8 L falloff on full-frame No peripheral illumination correction f/2.8 f/4 f/5.6 20mm © 2011 KenRockwell.com. All rights reserved. Filters, Use with Filters are easy; there's no problem with vignetting even with thick or rotating filters. The sturdy metal threads don't move. Fat 7.65mm thick (excluding rear threads) Tiffen filters work great. My 8.6mm-thick (excluding rear threads) rotating grad filter likewise works without vignetting, but it's close. There is no need for expensive "thin" polarizers. Flare and Ghosts Canon 20-35 L flare, worst case. much bigger. (5D Mk II, 20mm at f/8.) The 20-35 has a little bit more ghosts than the newer Canon ultrawide zooms, but not by much. To get it to look this bad, I had to zoom out to 20mm, put the direct disk of the sun in the corner, put something dark in the rest of the frame, and lock the exposure on the darker object to increase the exposure to show this. Other than this nonsense, it's flare and ghost free. Lateral Color Fringes The curse of Canon, there are plenty of lateral color fringes. Unlike Nikon digital SLRs, Canon DSLRs still can't correct for this automatically, so you'll often see green-red fringes at the sides if you're looking for them. If it really bothers you, shoot Nikon instead of Canon, because the newest Canon 16-35mm f/2.8L II and Canon 17-40mm f/4L have some, too, although a little less. Mechanics Rear, Canon 20-35 f/2.8 L. enlarge. The Canon 20-35mm f/2.8 L is all metal: barrels and all. It's much tougher than the plasticy Canon 16-35mm f/2.8L II and Canon 17-40mm f/4L, HA! Filter Threads Metal. Hood Mount Metal. Identity Ring Metal. Fore Barrel Metal. Focus Ring Metal, rubber-covered. Mid-barrel Metal. Internals Seem like metal. Zoom Ring Metal, rubber-covered. Zoom Cams Feel like metal. Rear barrel Metal. Moisture seal at mount No. Mount Chromed metal. Markings Paint. Serial Number Engraved into bottom of lens barrel and filled with white paint. Date Code Yes, printed on the rear light shield. See Canon Date Codes to find your lens' birthday. This sample is stamped UI 0203, meaning February 1994. Noises When Shaken Mild rattling. Made in Japan. Sharpness Lens sharpness doesn't matter much, but it sure distracts amateurs who confuse lens sharpness with picture sharpness. Yellow. much bigger. (5D Mk II, 35mm at f/8.) Julian. Canon 5D Mk II with Canon EF 20-35mm f/2.8 L, 20mm at f/8. Full-Rez. As shot on the 5D Mark II, it's as sharp as the Canon 16-35mm f/2.8L II and Canon 17-40mm f/4L. I compared them all directly against one another at the test range. Important is that these are the most difficult of all photographic lenses to design and build. Ultrawide lenses are difficult because of the crazy variations in angles involved and the tighter manufacturing tolerances required for the shorter focal lengths. Zooms make everything ten times more difficult, both in design and in manufacturing tolerances. Therefore if you try these comparisons for yourself, know that every shot will be different, and every position of the frame in every shot will be different. One side will be sharper than the other, and different focal lengths will vary greatly as well. In actual comparison, at some settings the Canon 16-35mm f/2.8L II or Canon 17-40mm f/4L were clearly better than this 20-35mm, and in just as many cases, this 20-35 L was clearly superior and one of the others looked like mush! The 20-35 is sharpest at the longer settings. It will get softer on the sides at 20mm, but so do the other Canon ultrawide zooms. Like many ultrawides, the field seems curved at times. It seems to curve the subject plane of best focus closer to you at the sides at the 20mm end. This means tests on flat subjects or at infinity won't look that great, but in real-world indoor, nature and landscape photography, the results will be even better. In actual practice, none of Canon's ultrawide zooms is all that great. Nikon's 16-35mm VR and 14-24mm lenses are in a completely different class, which is why some people use adapters to use Nikon wide lenses on their Canon cameras! Spherochromatism I see no spherochromatism, and didn't expect to see any. Spherochromatism, misnamed "color bokeh" by laymen, is when out-of-focus highlights take on color fringes. The Canon 20-35/2.8L 's out-of-focus highlights have no color fringes. Spherochromatism is a completely different aberration from . Sunstars With its traditional 6-bladed diaphragm, this Canon 20-35mm f/2.8 L makes muted 6-pointed sunstars on brilliant points of light. Compared Compared Canon 20-35 USM, 20-35mm f/2.8 L, 17-40mm f/4 L and 16-35/2.8II. enlarge. Canon 20-35 USM, 20-35 L, 17-35mm, 17-40mm and 16-35mm L II. enlarge. See Canon Ultrawide Zooms Compared. Usage Compared AF - MF Switch Leave this in AF. Set it to MF to deactivate autofocus, or to focus by hand. The focus ring isn't connected to anything in the AF position. Focus Point I haven't had any problem with this lens, but with my other Canon ultrawide zooms I usually get the most accurate focus with the center AF area. Recommendations Compared I can't overemphasize how great it feels to have a lens with an all-metal barrel. Unlike Canon's newer lenses, this 20-35 L feels tough and precise. The Canon 20-35mm f/2.8L is the lens that helped Canon win the professional market away from Nikon. It has the same optical quality as the other Canon ultrawide zooms, so if you want to save money and get a smaller, tougher lens with less distortion, go for it! If you get one of these 20-35mm lenses, consider the matching Canon EF 80-200mm f/2.8 L, which is built and works just as well, and shares the same marvelous all-metal construction and 72mm filter thread. 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