Canon EOS 650D/Rebel T4i In-Depth Review
Image Quality Tests
Curiously, when using flash with Auto ISO enabled, Canon has deliberately chosen to bias the sensitivity setting to ISO 400. Shooting in P mode the camera simply refuses to use a sensitivity below ISO 400, meaning that in bright conditions where you may want to use fill flash for a portrait, you can easily end up with a camera selected aperture of f/16 or f/22. In Av mode, the camera will drop down to lower ISO values in bright light. But there is still a clear preference for setting ISO 400. In every flash-enabled shooting mode we regularly encountered the bizarre situation in which the camera chooses a higher ISO with the flash enabled than it does when pointed at the same scene with the flash turned off.
The ability to successfully manage shadow noise on a per pixel level can be of interest, particularly when comparing cameras that use the same sensor size - in this case APS-C - but offer different resolutions. In the example below we're comparing the EOS 650D against the higher resolution 24MP Nikon D3200.
We've taken base ISO Raw shots of our studio test scene and processed them in Adobe Camera Raw with a +3.0EV exposure adjustment. We've then taken crops in the darkest areas of our scene to compare the amount of shadow noise between the two cameras.
|Canon 650D ISO 100: ACR +3EV, NR off||100% crop|
|Nikon D3200 ISO 100: ACR +3EV, NR off||100% crop|
Looking at the 100% crops above, it is clear that the 650D displays noticeably more chroma noise than the Nikon D3200, which manages very clean output despite having a pixel count that is 33% greater than that of the Canon.
Real world sample
While the results of our studio scene reveal interesting information about the sensor's maximum capabilities, it's important to place those results in the context of real-world photography. Below is an image shot outdoors under typical daylight conditions at ISO 100. We've taken the same raw file and converted it twice in ACR 7.1 - once at default exposure settings and again with three Basic Panel adjustments, detailed below.
|ACR 7.1: Default settings with NR off||ACR 7.1: Exposure +30, Shadows +30, Blacks +40 with NR off|
|100% crop||100% crop|
As you can see it is certainly possible to gain significant detail - while maintaining a reasonable overall exposure - by opening up the shadows in ACR. Yet this comes at the price of much more prominent chroma noise. It's important though to keep in mind that we're looking at 100% crops and that these noise levels will be far less objectionable at all but the largest print sizes.
The EOS 650D offers - as an additional option in the NR menu - the ability to capture four successive shots (presumably at 5fps) in a single burst and combine them into a single image. Because noise is a random event, the advantage of capturing multiple images and then merging them together is that you can average out the noise in the final processed image.
Multi Shot NR is a JPEG-only feature. You cannot select it in either of the 650D's raw-enabled modes. And once it is activated, switching the mode dial to any of the basic shooting modes, recording a movie, using the bulb setting, or powering off the camera will revert the NR setting back to its default, Standard setting.
The process of combining the separate images and averaging out the noise takes a bit of time. A 'busy' status is displayed for about 10 seconds after the final exposure. While you cannot take another image during this time you can access the camera's menu system.
Using the same lowlight scene in which we compared the EOS 650D against two of its peers on the high ISO comparison page of this review, we compare the 650D's new Multi Shot NR setting against both the default and 'high' NR settings.
|ISO 6400, 1/100 sec. @ f/7.1||Multi Shot NR 100% crop|
|NR Standard (default) 100% crop||NR High 100% crop|
Multi Shot NR mode does an extremely impressive job of minimizing noise and image artifacts while simultaneously offering greater fine-edged detail than either of the single shot NR modes. As you'd expect with any multi-shot mode, Canon cautions against excessive camera shake or shooting moving subjects, stating that the NR results will be 'less effective' in such situations.
To examine this we photographed the scene you see below. In the first image all of the objects are static. In the following shot we turned on the Elmo doll which vibrates and spins in a circle during the four exposures. As you can see, when the camera determines a subject has moved between exposures, noise is much more prominent. In fact this result below is nearly identical to what you'd get using 'NR Standard', suggesting that where the camera abandons its noise-averaging attempts it reverts to the default NR behavior.
|ISO 6400 static subject||ISO 6400 moving subject|
|100% crop||100% crop|
Interestingly though, even when movement between exposures is detected, it appears the 650D still attempts to average noise in areas of the scene it deems stable enough. Below you can see a slightly ghosted image along the edge of the mannequin. And in this area of the scene, the noise levels are significantly reduced compared to the camera's default NR setting. This suggests that the multi-shot noise-averaging is not an all or nothing affair; a very clever trick.
|Multi Shot NR: static subject||Multi Shot NR: moving subject (due to table vibration)|
|Default NR: static subject|
Lens correction settings
The 650D offers two built-in lens corrections, based on camera-stored lens profile data, which can be enabled via the shooting menu. You can use Canon's included EOS Utility to download current lens data to the camera. Note that neither of these corrections are baked into accompanying raw files. If you use Canon's own DPP raw conversion software, the corrections travel with the raw file as metadata, allowing you to adjust them to taste. Third party converters, like ACR and DxO, however, will not make use of this data, although both have their own tools for these types of corrections..
Peripheral illumination control is meant to counter corner vignetting effects. It is enabled by default. Below we've shot an evenly lit neutral area with Canon's new EF-S 18-135 f/3.5-5.6 IS STM lens at its widest aperture. As you can see, enabling the lens correction results in more even illumination, providing just over 1 stop EV of increased luminance in the farthest corners compared to the sample without the correction applied.
|Peripheral Illumination On 18mm @ f/3.5||Peripheral Illumination Off 18mm @ f/3.5|
The chromatic aberration (CA) setting seeks to minimize color fringing that is typically found along very high contrast edges. This feature is disabled by default because when active, the maximum image burst in continuous shooting mode is greatly reduced. The scene below, with dark leaves against a bright sky is a typical scenario in which you'd encounter color fringing. It was shot with the 18-135mm STM lens at 18mm. And as you can see, the in-camera software correction does an admirable job of reducing, if not eliminating CA.
|Chromatic aberration disabled||Chromatic aberration enabled|
The occurrence of CA varies of course from lens to lens, but it has been our experience in shooting with the 650D's kit zooms that CA occurs often enough in high contrast scenes - especially at their wider focal lengths - that it's generally worth enabling the automated correction except where you anticipate shooting bursts in continuous drive mode.
Overall Image Quality
The EOS 650D, much like the EOS 600D before it, offers very good image quality with default settings that produce pleasing JPEGs. The camera produces reasonably sharp images without introducing excessive edge halos, although you can easily improve on these by shooting Raw images and processing them yourself.
Color rendition and saturation will be familiar to users of previous Rebel series models and the camera's auto white balance yields generally pleasing, if not completely accurate colors in a wide range of lighting conditions. Exposures are typically well-judged in all but the most challenging of lighting scenarios. Dynamic range is perhaps a bit shy of some of the 650D's DSLR peers - as well as impressive mirrorless models like the Olympus E-M5 - requiring Highlight Tone Priority (HTP) to be enabled on bright sunny days for comparable results.
And although its pixel count remains the same, the noise levels of the 650D are slightly higher than we saw from its predecessor, the EOS 600D. What the 650D does have in its favor though is the new MultiShot NR setting which provides a genuinely useful method of controlling noise, albeit it in scenes that don't contain moving subjects. It also adds an additional stop of sensitivity (ISO 25600) for extreme situations.
Overall, there are few here surprises for users of previous Rebel models, and on balance we consider that to be a good thing. The ability to use in-camera lens profiles to correct for vignetting and chromatic aberration adds even more value to a camera line that has long been a solid performer.
Aug 17, 2015
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