A Viewfinder Darkly

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Sony Alpha SLT A77 High Resolution Digital SLR Camera Review

September 30 2011

by Philip Northeast

The new Sony SLT-A77 excels in resolution and frame rate, while in other areas it is merely very good.

At a projected price of around $1400 US dollars for the body only, the Sony SLT A-77 offers performance that in many areas matches, or exceeds, more expensive full frame Digital SLRs.

Photography is a compromise where gains in one area are offset by losses in others. Advances in technology allowed Sony engineers to minimise losses while making significant gains in sensor performance for the smaller APS-C sensor. These sensors are sometimes called cropped sensors.  Sony’s recent creations are the current pace setters in the fast moving world of digital imaging and their performance challenges Digital SLRs with larger full frame sensors.

Sony SLT Alpha 77 camera

The Sony 16 megapixel APS-C sensor in the Pentax K-5 is a low light marvel, but the Sony SLT A77 presents another option with 24 megapixel resolution and it can capture an amazing 12 frames per second.

“We feel that these cameras are not only a significant evolution of our breakthrough Translucent Mirror Technology,” said Mike Kahn, director of the alpha camera business group for Sony Electronics. “They’re also a revolution in terms of redefining how this unique technology can be put to use by enthusiasts.”

The new technology presents a dilemma for photographers trying to choose a camera, but DxOMark can help by giving a realistic appreciation of the areas where the Alpha 77 is best suited.

DxOLMark sesnor score summary

In the overall DxOMark Sensor scores the Alpha 77 is just shaded due to the incredible low light capabilities of the Pentax K-5 with a Sony sensor.  Significantly both the Digital SLRs with Sony sensors earned a DxOMark score comparable with the Canon EOs 5D Mark II, a full frame sensor model.

Portrait Category Excellence

The Sony SLT Alpha 77 had the best score in the portrait category where its extra megapixels help in capturing subtle colour transitions and fine detail. Each pixel can only show one colour, with more pixels a greater range of delicate colour tones can appear in the image, particularly the transition between similar colour shades.

Colour sensitivity comaprison with Sony A77, Pentax K-5 and Canon 5D MkII (DxOMark)

The DxOMark tests show the Sony SLT A-77 is at its best in this area of imaging performance at low ISO settings compared to the other cameras.

Frame rate versus ISO noise conundrum

One of the contradictions of the Sony SLT-Alpha 77 is that it has a fast frame rate, but its noise performance lacks the same level of excellence. The frame rate is faster than that of the most expensive sports DSLRs from Nikon and Canon. One of the factors stopping from being the supreme sports DSLR is the image noise performance, especially at higher ISO settings often used in sports photography.

Image noise comparison for Sony A77, Pentax K-5 and Canon 5D MkII (DxOMark)

The Pentax K-5 shows the other side of the Sony design compromise for an APS-C with full frame challenging noise performance, but with a lower 16 megapixel resolution. The Sony SLT A77 has the same 24 megapixel resolution as the Nikon D3x only with more noise as the DxOMark noise comparison shows.

Video Autofocus versus Battery Life

With Sony’s Single Lens Translucent (SLT) technology the autofocus system uses the normal DSLR method of phase detection rather than the contrast detection system used in compact digital cameras. The separate sensor array for the phase detection system usually sits in the pentaprism housing on top of DSLRs and only works when a conventional mirror is in down position so photographers can use the optical viewfinder.  The SLT system reflects some light up into the autofocus array even while the A77 is in live view or movie mode. This gives fast accurate autofocus in these two modes of operation. Most DSLRS offer only contrast detection autofocus or rely entirely on manual focus in movie mode.

The functional cost of this is that the Sonly SLT cameras do not have optical viewfinders. Instead they have an electronic display in the same place as the conventional optical viewfinder. This addresses concerns over using the camera in bright light where the rear screen can be difficult to see when using Live View. Viewfinders also allow photographers to hold the camera more securely to minimise camera shake at slow shutter speeds. The Sony SLT-A77 has an image stabilisation system in the camera body, so holding it properly extends the shutter speed range for sharp photos while hand holding the camera.

This reliance on an electronic viewfinder, or rear screen, for composing reduces battery life, even just to look through the lens takes power.  Photographers using longer focal length telephoto lenses often use then to watch the scene when they compose or wait for the action to unfold so they can capture the decisive moment. Conventional optical DSLR viewfinders use no power to look through the lens. The facility to see the scene the same way as the lens is one of the major attractions of the DSLR system.

According to Sony, the SLT A-77 can take approximately 470 still photos using the viewfinder and 530 still photos using the LCD monitor, under CIPA standard test conditions.  Using the same battery Sony’s Alpha 900, with an optical viewfinder, can take 880 photos under CIPA test conditions.

Dynamic Range

This is a measurement of the camera’s ability to capture the range of light from dark shadows to bright whites. Digital cameras currently capture less of this range than the human eye. The result is usually a lack of detail in the black or bright white areas of a photo.

Dynamic range comparison Sony A77, Pentax K-5 and Canon 5D MkII (DxOMark)


The DxOMark dynamic range tests show the quest for more megapixels by Sony produces a smaller dynamic range than their 16 megapixel sensor in the Pentax K-5. Interestingly, at low ISO settings both these APS-C sensor cameras have a significant advantage over the full frame Canon 5D MkII.

Typically dynamic range limitations are a problem in situations where there is very bright light and the resultant deep dark shadows. In these situations ISO settings are usually towards the lower end of their range, where the Sony SLT A-77 has the edge over the Canon.

Specification  Summary
Sony SLT A-77 Pentax K-5 Canon 5D  MK11
Price (US Dollars ) body only $1,399.99 $1,499.95 $2,399.00
Sensor Size 23.5 X 15.6mm 23.7 x 15.7mm 36 x 24 mm
Crop Factor 1.5 1.5 1
ISO 100-12800 80-51200 50-25600
Dimensions (WxHxD) 142.6 x 104 x 80.9mm 132 x 96 x 73 mm 152.4 x 114.3 x 76.2 mm
Weight (no battery or lens) 653g 660.54 g 811 g
Image Stabilisation in camera yes yes no

Price and Availability

The Sony SLT Alpha 77 DSLR Camera is set for release in October  and can be pre-ordered at Adorama for the manufacturer’s recommended retail price of $US 1,399.99 for a the body only.




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