Sony SLT-A77 In-depth Review
Like the NEX 5N and the SLT-A65 the Alpha SLT-A77 comes with optional in-camera optical corrections. Sony calls these tools 'lens compensation' and lens compensation comes in three flavors - 'shading', 'chromatic aberration' and 'distortion'. When these functions are activated (separately or en-masse) in the setup menu, the camera will attempt to reduce the respective effects based on Sony's profiles of current lenses. Sony has indicated that the number of profiles that the camera holds will be expanded via firmware updates as the system expands.
Even though CA and Distortion compensation will be applied to the JPEG file when shooting in raw+JPEG, the raw file will remain uncompensated. The story is slightly different for Shading compensation which is not only applied to the JPEG but also the raw file. In practice this means that, if the function is activated, Shading compensation will be applied to your output images when converting raw files in Adobe Camera Raw, Sony's IDC or any other raw converter.
It's also worth mentioning that Sony’s Image Data Converter software will apply CA and Distortion compensation if you have them activated in the camera at the time of shooting. You cannot manually turn them on and off in the software itself. The implication is that CA and Distortion compensation settings are stored in the raw file as metadata tags, and IDC applies them whenever it sees them. However Shading Compensation is applied directly to the data from the sensor before the camera writes the raw file, so it can’t be ‘undone’.
CA compensation is applied by default and in our tests does a good job of removing green and purple fringing as you can see in the the sample crop below. These images were taken with the DT 16-50mm F2.8 SSM kit lens but each lens will have its own particular CA characteristics. Therefore results may vary with the lens you use.
The rollover above shows a 100% crop. The click-through links to the full image.
As you can see in the images below, the auto distortion compensation does a very good job of keeping the image from showing the barrel distortion caused by the lens. This shot was taken with the kit 16-50mm F2.8 SSM lens at its widest focal length.
This feature is not enabled by default and we imagine most people will choost to enabled it as there is really no noticeable detriment to overall image quality or continuous shooting speed.
The following shading compensation analysis was shot using the 16-50mm F2.8 kit lens, at the widest focal length and F2.8. As you can see in the samples below the compensation function is quite effective at reducing vignetting.
With shading compensation set to 'auto' the far corners of the frame retain 69% (-0.6 EV) of the center brightness. When shading compensation is off the brightness drops to 43% (-1.2 EV) of center brightness. Although the compensation does not remove all of the vignetting caused by the lens, it will make a noticeable difference, especially in images with large areas of continuous tone, as you might find in skies. And even though Shading compensation works by essentially increasing the brightness in the corners of the image, we don't see a significant increase in visible noise in the compensated areas.
As we've mentioned above, Shading compensation is not only applied to out-of-camera JPEGs but also the A77's raw files.
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