Does full-frame really matter? (Sony Alpha 11 vs Canon EOS 5D Mark II)
The APS-C-sized sensor has changed dramatically over the past few years. Tim Coleman tests the image quality of the best APS-C sensor, used in the Sony Alpha 11, against the most popular full-frame model, the Canon EOS 5D Mark II
With the launch of the 21.1 -million-pixel Canon EOS 5D Mark II and the 24.6-million- pixel Sony Alpha 900 in 2008, high-pixel, full-frame DSLR cameras became more ‘affordable’ for enthusiasts At this point, the sensors in these cameras gave a degree of image quality that was superior to that of their smaller APS-C-format counterparts, through improvements in the areas of detail resolution, dynamic range, low-light performance and control of image noise.
Three years later, the 24.3-million-pixel resolution of Sony’s APS-C-sized sensor, which is found in its Alpha 65,77 and NEX-7 cameras, matches the pixel count of the best of these older-generation full-frame models.
However, while the number of pixels affects the size at which an image can be printed, large numbers of pixels do not guarantee good image quality. An APS-C sensor with the same resolution as a full-frame sensor will have smaller photosites than its full-frame equivalent. Generally, this means that the smaller APS-C sensor is more likely to perform poorly in low light, producing higher levels of noise, less accurate colour rendition and lower dynamic range.
What I hope to discover in this test is exactly how far the imaging sensor has progressed in just a few years. Does the best APS-C sensor – found in the AP Reader Product of the Year, the Sony Alpha 77 – outperform the most popular full-frame sensor, which features in the Canon EOS 5D Mark II, voted by our readers as the greatest camera of all time? This article will show how the image quality of each camera fares in bright and low-contrast light, looking at resolved detail, dynamic range, colour and noise levels.
Sensor test Canon EOS 5D Mark II vs Sony Alpha 77
There is a vast number of controls on both cameras, and many of the Alpha 77’s buttons are customisable
THE CAMERAS AND THEIR FEATURES
Before we look at image quality, let us consider how each camera handles and the features that affect their use.
Both the Canon EOS 5D Mark II and Sony Alpha 77 are high-end enthusiast- level cameras built to a high standard. A weather-sealed magnesium-alloy body protects each camera from the elements and the more demanding of environments. The LCD screen of the Alpha 77 can be viewed from a number of angles thanks to its dual-axis articulation, while the screen of the EOS 5D Mark II is fixed A greater degree of customisation is possible on the Alpha 77 via buttons on the camera, which can be set up for quick access to controls according to those most common used.
The greatest difference in the way the cameras operate is that the Alpha 77 has a fixed translucent mirror placed in front of the imaging sensor, while the EOS 5D Mark II uses a moving mirror. Without going into too much detail (for more information read the full Sony Alpha 77 test in AP 15 October 2011), the fixed translucent mirror allows approximately 70% of light entering the lens through to the imaging sensor, while reflecting the other 30% to the phase-detection AF sensor. A moving mirror, on the other hand, flips up during an exposure to allow all the light through to the imaging sensor.
One benefit offered by the translucent mirror technology is that it allows the camera to achieve higher frame rates.
Sony’s Alpha 77 boasts a fast processing engine capable of up to 12fps for full 24.3-million-pixel files, at a 13-frame burst in raw format or 18-frame burst in J PEG format. At 3.9fps, the EOS 5D Mark ll’s frame rates are much slower, although a J PEG burst can last for up to 130 frames depending on the card being used.
The video capabilities of both cameras have been a great success with consumers, with the EOS 5D Mark II breaking new ground at the time of its release through the use of live view and contrast-detection AF during capture. The translucent mirror technology used in the Alpha 77 gives huge benefits to video recording by offering full-time phase- detection AF with uninterrupted live view.
The Alpha 77 features sensor-based image stabilisation, so its lenses do not need to offer optical stabilisation. Canon has chosen to use lens-based image stabilisation in the EOS 5D Mark II, rather than in-camera stabilisation. There is little to distinguish one system from the other. With either type, up to 4.5EV slower shutter speeds are possible for blur-free handheld images, depending on the type of lens being used. This means there is extra control over which apertures and ISO ratings are selected when shooting handheld.
When each camera has a particular focal length and aperture set, the EOS 5DII produces shallower depth of field, as to get the same composition you’ll have to stand closer to the subject. This shallow depth of field is attractive for certain styles of portraiture, but for front-to-back focus the smaller sensor of the Alpha 77 will always have the advantage
While both cameras are great all-rounders, the use of a translucent mirror makes the Alpha 77 ideal for those interested in highspeed action photography and video capture. The camera’s access to its most used controls is perhaps a little quicker, too.
SENSOR SIZE AND PIXEL DIMENSIONS
THERE are several areas of performance to consider when discerning how good an imaging sensor is. First let us look at the sensors.
The diagram above shows the difference in size between the sensors. The surface area of the EOS 5D Mark II is 861mm2, while the Alpha 77 sensor has a surface area of 368mm2, making the EOS 5D Mark II sensor approximately 134% larger With its larger full-frame sensor, the Canon EOS 5D Mark II has an immediate advantage over the Sony Alpha 77 in the amount of light (number of photons) it collects, meaning it performs better in low light
The pixel count of the two cameras is similar, at 24.3 million pixels (Alpha 77) and 21.1 million pixels (EOS 5D Mark II). The Alpha 77 has therefore approximately 15.7% more pixels. As the sensor of the Alpha 77 is smaller and has a greater number of pixels than that found in the EOS 5D Mark II, each pixel is smaller, at 3 89 microns, as opposed to 6.39 microns in the EOS 5D Mark II (www. sensorgeninfo).
Given that the Alpha 77 has a smaller sensor and more pixels than the EOS 5D Mark II, it would be reasonable to assume that noise levels will be greater, especially as the Alpha 77 uses a fixed mirror, which prevents 30% of the available light being received by the sensor.
In real terms, the difference between 21.1 million pixels and 24.3 million pixels is the difference between a print at 16.1 xl 0.73in and one at 17.14x1143in at 350ppi (the print resolution recommended by Epson when using its printers). The landscape pnnts shown below are made on A3 paper and the border around the print shows how the print sizes differ when produced at 100% and 350ppi.
Sensor test Canon EOS 5D Mark II vs Sony Alpha 77
NOISE, RESOLUTION AND SENSITIVITY
There is little to choose between the noise levels of the two cameras at low ISOs, although the Alpha 77 shows a degree of luminance noise from ISO 100
THE EOS 5D Mark It’s native sensitivity range is ISO 100-6400, although this can be extended to ISO 50-25,600. There are no ‘Hi’ extended settings in the Alpha 77’s ISO 100-16,000 range, although it can be pulled down to ISO 50. This means that the EOS 5D Mark II has a 6EV ISO range that extends up to 9EV, white the Sony has a 71/iEV range extending up to 816EV.
In our resolution charts, the EOS 5D Mark II scores very well, resolving up to the 30 marker at ISO 100 with only a minor drop to the 26 marker at ISO 12,800 (Hil). With a higher pixel count, it comes as no surprise that the Alpha 77 edges the EOS 5D Mark II at lower ISO ratings, reaching the 32 marker at ISO 100
Both cameras maintain a high level of resolved detail right up to ISO 1600, beyond which the toll of the Alpha 77′s translucent mirror and smaller pixel pitch starts to show. The camera’s noise levels increase rapidly with each ISO rating and consequently the resolved detail drops. By ISO 3200, the EOS 5D Mark II outresolves the Alpha 77.
In the landscape image shown on page 50, which was taken with the same exposure settings of 1 /250sec at f/11 and ISO 100, the Alpha 77 produces a marginally better result than the EOS 5D Mark II. If your photography involves a lot of tripod work and the use of a shallow depth of field is not important, then the Alpha 77 is the better option.
There is little to choose between the noise levels of the two cameras at low ISO ratings, although the Alpha 77 does show a slight degree of luminance noise from ISO 100. Once beyond ISO 800, the Alpha 77 shows a more rapid rise in levels of noise as the ISO ratings increase. At ISO 3200 and beyond, luminance noise in the Alpha 77 is evident in the resolved detail and in other areas of image quality, which can be seen in the flower still life (see page 49). JPEG files at ISO 16,000 are badly smudged, with a loss of detail. The EOS 5D Mark II performs admirably up to ISO 3200, by which point luminance noise is evident.
Chroma (colour) noise gives an overall red hue in unedited raw files from the Alpha 77 at ISO 12,800, and there is green and blue speckled colour noise. White this chroma noise can be dealt with to some degree in raw editing software, for low-light handheld work the EOS 5D Mark II is the better option.
RAW AND JPEG
In unedited raw files, the images at higher ISO ratings beyond ISO 1600 are much noisier in the Alpha 77 than in the EOS 5D Mark II, both in luminance noise and (at IS012,800) in chroma (colour) noise. While the EOS 5D Mark II is also affected by luminance noise, its control of chroma noise is better. Only at its Hi2 setting (ISO 25,600) is green chroma noise truly evident.
Tonal compression in JPEG files applies noise reduction, which darkens shadow areas and hides noise artefacts. This process loses a degree of shadow information, which is more dramatic in low light and at high ISO ratings. Applying noise reduction manually to a raw file affords greater control. A simple application of colour and luminance noise reduction can reduce these artefacts without compromising image clarity too much.
JPEG files from each camera lack the level of detail found in raw files. Noise is controlled better in JPEGs at around the middle of the ISO range, but at higher ISO ratings there is both severe smudging of detail and noise, so sticking to raw capture is best. JPEGs from the EOS 5D Mark II are affected by this less than those from the Alpha 77, white the saturation is also better. Only at ISO 25,600 does the EOS 5D Mark II show red banding, blue patches and red flecks.
Canon EOS 5D Mark II vs Sony Alpha 77 Sensor test
DYNAMIC RANGE
Results from dynamic range tests (see www. dxomark.com) show that with each camera set to ISO 100, the dynamic range is 12.8EV in the Alpha 77 and 11 8EV in the EOS 5D Mark II, giving the Sony model an extra 1EV of light at this setting. The dynamic range of the EOS 5D Mark II holds its performance for longer, losing only ’/>EV all the way to ISO 800, while the Alpha 77 shows a steady decline By IS012,800, the tables have turned, with the EOS 5D Mark II having a dynamic range of 7.8EV and the Alpha 77 6.9EV. Tonal range at these higher ISO ratings is typically flatter. In low-light conditions the EOS 5D Mark II produces images with a wider tonal range.
The dynamic range of the Alpha 77 has the edge over the EOS 5D Mark II at ISO 100, while at ISO 200 and ISO 400 the cameras are pretty much on a par. At ISO 800 and above, the EOS 5D Mark II performs better. Across the entire ISO range, there is never a greater difference than 1.4EV.
Comparing IS0100 and IS012,800 JPEG files of the flower still life (see right and below), we can see that some details in highlight areas, such as the pin in the jug, are not visible at all at the ISO 12,800 setting. To keep a strong tonal range in images, it is best to stick to ISO 6400 and below in the EOS 5D Mark II and IS01600 in the Alpha 77.
Sensor test Canon EOS 5D Mark II vs Sony Alpha 77
QUANTUM EFFICIENCY
A camera’s ability to produce high-quality images with depth of tone, colour, resolved detail and low levels of noise is mostly down to its ability to collect light. The size of the sensor is the biggest factor in light collection, but there are other aspects involved.
Each camera is able to process (use) a percentage of light that reaches the imaging sensor. This is known as the sensor’s quantum efficiency (QE). For more on QE, see AP 4 February 2011.
The performance of the imaging sensor in the Sony Alpha 77 is at an immediate disadvantage, on account of the fixed translucent mirror. By reflecting around 30% of the incoming light away from the imaging sensor towards the AF sensor, the imaging sensor is receiving only around 70% of available light. What is impressive, though, is that despite this, the Alpha 77’s QE of 35% still edges the 33% of the Canon EOS 5D Mark II. A better insight into the full capability of the Sony sensor can be found by looking at the Sony Alpha NEX-7, which does not have a mirror, so reflects none of the light away in this manner The QE of the NEX-7 is 47%
Generally, the QE of cameras today is better than those of the last generation. This is one way in which smaller sensors are getting closer to the low-light performance of larger sensors. If the percentage difference in QE is greater than that in sensor size, then the smaller sensor returns less noise. It is rare for this to be the case, although it is true of the Nikon D3S and Hasselblad H3DII-50. The Nikon D3S has a QE of 57%, with that of the Hasselblad H3DII-50 measuring 16%, which makes a difference of 256%. The medium-format sensor of the Hasselblad has a surface area of 1,803mm2, which is approximately 110% larger than the 862mm2 surface area of the Nikon D3S. Although just over twice the size of the D3S, of all the light the H3DII-50 collects, it is only able to ‘use’ a quarter of that compared to the D3S, meaning that the Nikon camera returns less noise With a sensor 134% bigger and a QE difference of 6% lower, the EOS 5D Mark II is still able to collect 128% more light, giving it around a 1 ‘AEV advantage. A 42% increase in QE in the Alpha NEX-7 over the EOS 5D Mark II makes the difference just under 1EV.
COLOUR
There is little to choose between the colour sensitivities of the two cameras Both show a strong colour rendition at IS0100, as seen in this landscape image and the flower still life (see page 49). Blues and greens are punchy In the still-life, it is clear to see just how the colour range is limited further up the ISO range. The greens and purples of the flowers are much less vivid at ISO 6400 and above, with a flatter tonal range. Only the impact of noise at higher ISO ratings affects the colour more in the Alpha 77 Otherwise, as far as colour goes, the cameras are on a par.
Verdict
In use, the full benefit of the fixed mirror in the Sony Alpha 77 can be seen in faster frame rates and full-time phase-detection AF in video mode.
The performance of the Alpha 77 at ISO 100 is excellent at resolving detail and dynamic range, outperforming the Canon EOS 5D Mark II So, for those shooting landscapes and scenes in bright light, the Alpha 77 is a good choice.
In some ways, the comparison is a little unfair here. The sensor of the Alpha 77 is fronted by a fixed mirror, which means it can only perform to 70% of its potential This affects the camera’s ability in low-contrast light. In all areas of image quality, the Alpha 77 shows a more dramatic decline than the EOS 5D Mark II, and at the higher ISO ratings the Canon camera performs best. The potential of the Sony sensor is shown by the stats for the Sony NEX-7 (www.dxomark.com).
We can see that up to ISO 800 the best APS-C sensor is slightly better in image quality than the most popular full-frame camera. Beyond ISO 800, the EOS 5D Mark II has the edge.
Unless your photography involves a lot of shallow depth of field or low-light work, then the EOS 5D Mark II offers little benefit over the Alpha 77. Although conclusions here may suggest that the Alpha 77 is better than the EOS 5D Mark II in certain conditions, the latter is still a great camera and one that made excellent image quality more affordable when it was released. The fact that APS-C sensors have evolved to where they are today makes the potential of future full- frame models even more exciting. As cameras like the Canon EOS-1 D X, Nikon D800 and D4 are announced, as well as speculation around a possible Canon EOS 5D Mark III, we can expect full-frame sensors to up the bar again. Improved quantum efficiency and resolution capable of producing A2 prints without upscaling will make true exhibition-quality printing affordable.
