Sony Digital SLRs > SLT-A55 Features

Sony SLT-A55 Features

sony slt-a55
Release Date: October 2010
List Price (body only): $700 USD
List Price (with 18-55mm lens): $800 USD

Available at Amazon, Adorama and B&H Photo Video


The Sony SLT-A55 features an exterior that looks a lot like a traditional SLR and an interior that's fundamentally different.

Instead of a mirror that reflects light up to an optical viewfinder, the SLT-A55 has a partially transparent mirror: some of the light passes through to the camera's sensor and some is bounced up to a sensor for the electronic viewfinder.

I'll explain the benefit of this system in more detail below, but here's the quick overview: this camera is fast.

Whether you use the viewfinder or the LCD to compose images, autofocus will be equally snappy. Furthermore, you can capture consecutive images at a rate of 10 per second, a speed previously only available to very high end professional cameras.

In addition to speed, the SLT-A55 has a Full HD 1080i video mode and a flexible 3 inch LCD screen to help you compose pictures and videos from all sorts of odd angles.

This innovative feature set convinced me to pick the Sony SLT-A55 as the best digital SLR of 2010.

Feature List

StabilizationIn Body
Memory CardSD / SDHC / SDXC
Max. Shutter Speed1/4000
Max. Photo Capture10 per second
ISO Range100 to 12800
Movie ModesAVCHD
1920 x 1080i
Motion JPEG
1440 x 1080
640 x 480
LCDFlexible 3in (921,600 dots)
Autofocus15 point
Face Detect AFYes
Sensor Dimensions23.4 x 15.6 (1.5x crop factor)
HDMI PortYes
Live ViewYes
Built-in FlashYes
Compatible LensesAll Sony ALPHA
BatteryNP-FW50 LiIon
Dimensions4.8 x 3.6 x 3.3in
124 x 92 x 85mm
Weight15.3oz (433g)

New and Notable

sony slt-a55 no lens

Clearly, what's new and notable on the SLT-A55 is that translucent mirror. But what - exactly - does the translucent mirror do for you when you want to take pictures?

In a traditional SLR camera system, a mirror sits directly in front of the camera's digital sensor. This mirror reflects light up to the camera's optical viewfinder so when you look through it you see exactly what the lens sees.

Every time you take a picture, the mirror flips up out of the way of the digital sensor so that it can be exposed to light.

When the mirror flips up, it temporarily disables the camera's autofocus system (the autofocus mechanism is located in the direction of the viewfinder, which is blocked when the mirror is up).

The mirror is in the "up" position at three different times:

  • Every time you take a photo
  • When you use the live view mode
  • When you capture video

If you're just taking a picture, then the autofocus is only disabled for a split second. But what happens when the mirror is flipped up for a long time when you use live view mode or want to capture video?

In these cases, the camera resorts to a secondary autofocus system that's not nearly as fast as the primary one.

The primary autofocus in any DSLR is also called phase detection — it's this system that allows you to focus (even on moving subjects) in fractions of seconds. The secondary autofocus is called contrast detection and it's the type of autofocus used in compact digital cameras.

The main difference between the two: speed. Phase-detection autofocus systems are substantially faster than contrast-detection systems.

This means that on most digital SLRs, autofocus in live view mode and during video capture is MUCH slower than it is when you're just taking still pictures. The translucent mirror system is designed to address this limitation.

Since the translucent mirror both reflects light up to the viewfinder AND allows light to pass through to the sensor, the phase-detection autofocus can be used in both live view and video capture mode.

This should result in much better autofocus performance regardless of how you're trying to use the camera.

The second side benefit is that cameras with a system like this are capable of MUCH faster continuous shutter speeds.

The main drawback to a translucent mirror system is that you give up the optical viewfinder for an electronic one. Electronic viewfinders often don't have the same level of clarity as optical ones since they are really just tiny monitors stuck inside the camera's viewfinder.

The advantage that electronic viewfinders have over their optical counterparts is that camera settings (and other special displays like grids and horizon line levels) can be super-imposed on the viewfinder image.

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