Canon T3i Optics
Canon EOS Rebel T3i Optics
The Rebel T3i kit is available with two lens choices. One is an updated variant of a lens first introduced with the Rebel XS, now known as the EF-S 18-55mm f/3.5-5.6 IS II, which also ships with the Rebel T3 and T2i. Compared to the earlier EF-S 18-55mm f/3.5-5.6 IS version, that lens has cosmetic changes and uprated stabilization algorithms said to be good for a four stop improvement, but we believe it to be optically similar to the earlier model. The lens has a 3.1x zoom ratio, and a 35mm equivalent focal range of 29-88mm due to the T3i's 1.6x "focal length crop" (see below). This lens is constructed of 11 elements in 9 groups, and extends during both focus and zoom operation. The EF-S 18-55mm II uses a micro DC motor for autofocus, instead of the ultra-sonic motor found on models with the USM designation, and includes both an AF/MF switch and a Stabilizer On/Off switch on the lens barrel. Other specifications include a 6-bladed (rounded) diaphragm, minimum aperture of f/22-f/32, maximum magnification ration of 0.28x (or 1:3.6), and 58mm filter threads. Dimensions are 84.5mm long with a 68.5mm diameter (3.3 x 2.7 inches), and weight is 200g (7.1 ounces). The lens has a MSRP of US$199.99 if bought separately, but costs significantly less when purchased bundled with the camera. A lens hood and soft case are optional accessories. While we've yet to run this newer version through our testing process over at SLRgear.com, the preceding lens was quite impressive when compared to those bundled with Rebel cameras preceding the XS, yielding improved sharpness and reduced chromatic aberration.
The second lens option is the Canon EF-S 18-135mm f/3.5-5.6 IS lens, which has a 7.5x zoom ratio, and a 35mm equivalent focal range of 29-216mm. The lens is constructed of 16 elements in 12 groups. Focusing is internal, and the 18-135mm uses a DC focus motor. An AF/MF switch is provided. The lens features built-in image stabilization (IS) that is capable of up to four stops of correction. A Stabilizer On/Off switch is also provided. Other specifications include a 6-bladed (rounded) diaphragm, minimum aperture of f/22-f/38 (or f/36 if using 1/3 stop increments), maximum magnification ration of 0.21x (or 1:4.8) at 135mm, and 67mm filter threads. Dimensions are 101mm long with a 75.4mm diameter (4.0 x 3.0 inches), and weight is 455g / 16.0 oz. The lens has a MSRP of US$499.99 if bought separately, and again, costs significantly less when purchased bundled with the camera. A lens hood and soft case are optional accessories. See below for our test results with this lens mounted on the Canon T3i, and see our full review of this lens on SLRgear.com.
The sub-frame sensor on the Canon Rebel T3i means that it has a smaller angle of view (by a factor of 1/1.6) than a full-frame camera with any given lens. While most properly called a "crop factor," the 1.6x ratio is more commonly referred to as the "focal length multiplier" since that's how it works in practice. Any lens used on the Canon T3i will have the same field of view as one with a 1.6x greater focal length would when attached to a 35mm camera. (For example, a 100mm lens on the T3i will show the same field of view as a 160mm lens on a camera with a 35mm frame size.) This means that the 18-55mm kit lens for the T3i has a coverage roughly equivalent to that of a 29-88mm lens on a 35mm camera, while the alternate 18-135mm kit lens has a coverage roughly equivalent to a 29-216mm lens on a 35mm camera.
The Canon T3i offers Lens Peripheral Illumination Correction, which corrects for lens shading (commonly called "vignetting"), producing uniform exposure across the frame by compensating for the light falloff seen with some lenses in the corners of the frame. Lens Peripheral Illumination Correction first appeared in the Canon 5D Mark II, and has since appeared across Canon's lineup, all the way from entry level to professional models. This setting is enabled by default, but can be disabled if desired.
The "IS" in both kit lenses' names stands for "Image Stabilization." This is a handy and increasingly common feature of both lenses and some camera bodies. The idea for lens-based IS systems is that a motion sensor, computer chip, and movable optical element are built into the lens barrel. The motion sensor detects camera movement that could lead to blurred images with long exposure times. This data is processed by the computer chip, which in turn moves the floating optical element in such a way as to counteract the motion of the lens, thereby keeping the image stationary on the camera's image sensor. The net result is that you can shoot at much slower shutter speeds than you'd otherwise be able to, without getting blurred images as a result.
Image stabilization technology generally works very well, and Canon says that either kit lens should be good for around a four-stop correction. The net result is that the Canon T3i's IS-enabled kit lens does a great job of delivering sharp photos under dim lighting, and you should be able to shoot at shutter speeds up to 16x slower than you can normally hand-hold without IS.
As mentioned above, some manufacturers have begun building sensor-shift image stabilization capability into their camera bodies, rather than their lenses. The advantage of this is obvious: Every lens you put on a camera with body-based stabilization is, effectively, an IS lens. A body-based IS system makes for a much less expensive lens collection, since you don't have to pay for IS technology in every lens you buy. There is a downside to body-based IS, though. Because their IS systems only affect the captured image, body-based systems don't stabilize the image seen in the optical viewfinder. (Of course, this limitation doesn't apply when using a Live View camera that captures its viewfinder image from the camera's main sensor.) In extreme cases, having a stabilized view through the viewfinder, like you get with the Canon T3i, can be a great aid to accurate framing and improving your own stability for sharper pictures.
So neither IS technology (lens-based or body-based) wins over the other on all points. If you plan on assembling a large collection of lenses, body-based IS will save you money, but at some possible cost in performance, and without the benefit of a stabilized view through the viewfinder. Lens-based IS can work better (not all IS systems are created equal), but will cost you more if you end up buying a lot of lenses. For the casual user who doesn't plan on acquiring a large lens collection, either approach will work, now that IS-enabled kit lenses are common as part of consumer-level SLR bundles.
Canon T3i Autofocus
SLR autofocus accuracy is governed in part by how far apart you can space the sensor elements for a single AF point from each other. The wider this "baseline," the more accurately the AF point can determine focus. What limits the AF baseline spacing in a camera system is the lens aperture. You can build sensors with wider baselines, but that also restricts the range of lenses they can be used with. By and large, camera manufacturers have set f/5.6 as the minimum aperture their AF systems will work with. Lenses with wide-open apertures smaller than f/5.6 just won't focus. But once the baseline spacing is set, using a faster lens doesn't improve focus accuracy any. That is, unless you add a larger baseline sensor, as is built into the Canon T2i's center AF point. (Note that only the center AF point shows this increased accuracy at f/2.8: The surrounding AF points are all conventional f/5.6 ones.)
Autofocus modes include One-shot (also known as single-shot), Predictive AI Servo AF (continuous), and AI Focus AF, which automatically selects between the One-shot and AI Servo modes. Of course, there is also a manual focus mode.
Like previous digital Rebels, the Canon T3i uses the built-in flash head as its AF-assist illuminator, rather than a bright light built into the camera's body. This works well because the flash is quite bright, and probably has a greater range than do typical on-body incandescent illuminator bulbs. Following the lead of the T1i, you can disable the internal flash, yet still have the benefit of the flash-based AF-assist illuminator. You do this via the Flash Control menu, but note that this AF-illuminator-only setting for the flash head means you lose flash exposure capability until you explicitly turn it back on. If you attach a 320EX, 430EX II, or 580EX II external flash unit to the Rebel T3i, their internal AF-assist illuminator can be used instead of the flash head itself, providing a good working range with a less obtrusive light source. For non-flash photography, Canon's ST-E2 wireless sync transmitter can also be used for AF assist, a handy trick. The ST-E2's AF-assist light has a useful range of about 25 feet. (Note though, that we haven't tested the ST-E2 ourselves, so we can't verify this performance independently.)
The second part of the cleaning system involves post processing with a compatible personal computer and the supplied Digital Photo Professional software. Here (via a menu option) the camera maps any spots that may remain on the sensor, saving it as Dust Delete Data and subsequently subtracting dust spots from the final image during post processing. A third option includes a manual sensor cleaning function which raises the mirror and allows users to clean dust that may have stuck to the low-pass filter.
We haven't yet seen an automatic system capable of removing all dust, but with the T3i lacking even a basic cleaning system, it's users are even more likely to have to either learn how to clean their sensor, or send the camera in for cleaning.
Everyone understands that lenses sometimes get dust on them and need to be cleaned, and there are a lot of lens-cleaning cloths, solutions and other accessories on the market that work well. But what do you do when your sensor gets dusty? Dust specks on the sensor tend to show up when shooting at very small apertures, appearing as dark blobs on your images. They're distracting at best, a terrible nuisance at worst, if you end up having to retouch every image to be rid of them.
Most of us are naturally leery of the idea of poking around inside the delicate innards of our DSLRs to wrestle with recalcitrant dust specks. Gently blowing the sensor surface (actually, the surface of the anti-aliasing filter) with compressed air gets rid of some dust, but there's invariably a lot that just stays stuck, no matter what. So what do you do?
If you've got dust specks on your sensor (and sooner or later you will), you're going to need to clean it. There are a lot of products out there intended to address this need, but a distressing number of them work poorly (if at all), and many are grossly overpriced. Advertising hype is rampant, with bogus pseudo-scientific jargon and absurd product claims. And prices - Did we mention prices? How about $100 for a simple synthetic-bristle brush?
So how do you know which product to use?
We don't pretend to have used everything currently on the market, we but can tell you about one solution that worked very well for us. The "Copper Hill" cleaning method is straightforward and safe, and in our routine usage here at Imaging Resource, very effective. Better yet, the products sold by Copper Hill Imaging are very reasonably priced. Best of all, Nicholas R (proprietor of Copper Hill) has put together an amazingly detailed tutorial on sensor cleaning, free for all.
Sensor cleaning is one of the last things people think about when buying a DSLR, but it's vital to capturing the best possible images. Take our advice and order a cleaning kit from Copper Hill right along with your DSLR, so you'll have it close at hand when you need it: You'll be glad you did!
(While they've advertised on our sister site SLRgear.com from time to time, we receive no promotional consideration from Copper Hill for this note. We just think their sensor cleaning products are among the best on the market, and like their way of doing business. -- We think you will too. Check them out.)
Canon EOS Rebel T3i Optical Test Results
The Canon Rebel T3i is available body-only, or bundled with either the Canon EF-S 18-55mm f/3.5-5.6 IS II lens, or the Canon EF-S 18-135mm f/3.5-5.6 IS lens. Below are the results of our optical tests with a Canon EF-S 18-135mm f/3.5-5.6 IS lens.
Kit Lens Test Results
The Canon EF-S 18-135mm IS (Image Stabilized) lens performed very well overall.
|18mm @ f/8||26mm @ f/8||135mm @ f/8|
The Canon EOS Rebel T3i is available bundled with the EF-S 18-135mm f/3.5-5.6 IS lens. This lens has a generous (for a kit lens) and versatile optical zoom ratio of 7.5x with a 35mm equivalent range is about 29-216mm, because of the T3i's ~1.6x crop factor. Sharpness and contrast were pretty good across most of the frame at 18mm and f/8, though there's moderately high chromatic aberration and some coma distortion visible in the corners and along the edges. Corners were also just a little soft. At 26mm and f/8, sharpness across much of the frame was superb, though extreme corners were still a touch soft and a moderate amount chromatic aberration was still visible. Sharpness at 135mm and f/8 was quite good, with very good detail and contrast across much of the frame. Chromatic aberration was still a little high in the extreme edges and corners, and some blurring was noticeable in the corners. However, results were still quite good overall for the type of lens, and the image stabilization will come in handy for handheld telephoto shots or in poor light.
A fairly large macro area with soft detail. Flash throttled down well.
|Macro with 18-135mm IS Lens
|Macro with Flash
The Canon EOS Rebel T3i's macro performance will of course depend entirely on the lens in use. With the 18-135mm IS lens set to 135mm, the Canon Rebel T3i captured a fairly large (even for an SLR lens) minimum area measuring 3.64 x 2.43 inches (93 x 62 millimeters). Details were somewhat soft in the center of the frame, and softer still in the corners and edges. (Most lenses have some softening in the corners at macro distances.) Some noticeable vignetting (corner shading) was also present. Both the softness and vignetting would likely improve by stopping down a bit more, though. (The above macro shots were taken at f/5.6.) The Canon T3i''s flash throttled down for the macro area very well. There was no detectable shadow from the lens barrel, only the same vignetting as in the non-flash exposure.
Higher than average barrel distortion at wide-angle and moderate pincushion distortion at telephoto with the 18-135mm IS kit lens.
|Barrel distortion at 18mm is 1.1 percent|
|Pincushion distortion at 135mm is 0.4 percent|
The Canon EF-S 18-135mm IS lens produced images with about 1.1 percent barrel distortion at wide-angle, which is higher than average and noticeable in some shots. At the telephoto end, there was about 0.4% pincushion distortion, which is also higher than average though not quite as noticeable. The Canon T3i does not appear to be correcting for any geometric distortion in its JPEGs, as uncorrected RAW files have identical amounts. Geometric Distortion is the tendency for the lens to bend straight lines outward (like a barrel -- usually at wide-angle) or inward (like a pincushion -- usually at telephoto).
Chromatic Aberration and Corner Sharpness
Moderately high chromatic aberration at wide-angle and telephoto with the 18-135mm IS lens. Some minor softening in the corners.
Chromatic Aberration. Chromatic aberration in the corners with the Canon 18-135mm IS lens is moderately high at both wide-angle (18mm) and telephoto (135mm) settings. The amount and intensity of the color fringing reduces as you move toward the center of the image, but is still slightly evident in the center at wide-angle. CA is much lower in the center at full telephoto. The Canon T3i does not appear to be correcting for CA in its JPEGs, as uncorrected RAW files exhibit similar amounts.
Corner Softness. The Canon Rebel T3i and 18-135mm lens produced some slightly soft corners in a few shots. At full wide-angle, corners on the right side of our test targets were somewhat softer than the center, but the blurring didn't extend very far into the frame. The left side, however, showed slightly less softening in the corners. The center of the image was quite sharp. At full telephoto, all four corners were only slightly soft with the top right being the softest. The image was pretty sharp in the center. Corner sharpness in general was pretty good for the type of lens, and somewhat better than expected compared to far-field (house) results.
Overall, a good performance here, especially for a wide-angle lens a 7.5x zoom ratio. Also keep in mind the above lab target shots are taken with the lens wide-open and sharpness and corner shading generally improve when a lens is stopped-down a couple of f-stops from maximum aperture.
Peripheral Illumination Correction
Like other recent Canon DSLRs, the T3i features Peripheral Illumination Correction feature to reduce vignetting or lens shading with Canon lenses.
|18mm @f/3.5||135mm @f/5.6|
|Peripheral Illumination Correction:||Off||On|
The Canon T3i provides what the company calls Lens Peripheral Illumination Correction, which corrects for lens shading (commonly called "vignetting"), producing more uniform exposure across the frame by compensating for the light fall-off seen with some lenses in the corners of the frame. Mouse over the Off and On links above to see the effect on the 18-135mm kit lens at wide-angle and telephoto at maximum aperture.
Peripheral Illumination Correction works with over 85 different Canon lens models, in both RAW and JPEG workflows. For JPEG shooting, the correction is made at capture time, while RAW shooters can access the function in Canon's Digital Photo Professional software, although Canon shooters should note that the latter approach offers the highest degree of correction. In-camera correction of JPEGs operates with somewhat reduced strength, especially when shooting at higher ISO sensitivities, given that the correction can make image noise more pronounced. From the factory, the T3i body ships with correction data for about 25 lens models. Canon's EOS Utility software allows correction data for lenses (including models as-yet unreleased) to be uploaded to the Canon T3i.
Canon EOS Rebel T3i Optical Viewfinder
Viewfinder Test Results
Fair accuracy from the optical viewfinder, excellent accuracy from the LCD in Live View mode.
|70mm, Optical||70mm, LCD Live View|
The Canon EOS Rebel T3i's optical viewfinder was a little tight, showing just under 94% coverage. The resulting image also appears to be vertically shifted slightly compared to the sensor, though there is no noticeable tilt which is unfortunately quite common with this type of optical viewfinder. Accuracy is a little lower than the 95% coverage that is typical for consumer digital SLRs. Live View mode coverage using the LCD monitor on the other hand was very accurate, at about 100%.
The images above were taken from our standardized test shots. For a collection of more pictorial photos, see our Canon EOS Rebel T3i (EOS 600D) Photo Gallery .
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