The a7 has a distortion correction feature for use with E-mount lenses. Whether correction is applied depends on the lens. For the 28-70mm and 55mm FE lenses it's active, while it's off for the 35mm.
Below are examples of the distortion correction feature in action, first for the 28-70mm kit zoom. The corrected versions are straight-out-of-the-camera JPEGs, while the Raws were processed with ACR 8.3 with lens distortion correct turned off.
|28mm - corr. off||28mm - corr. on||70mm - corr. off||70mm - corr. on|
The 28-70mm kit lens has plenty of both barrel and pincushion distortion, which the correction feature dramatically reduces, without a significant hit in image quality. Up next, the 55mm prime:
|55mm - corr. off||55mm - corr. on|
The 55mm F1.8 prime needs a lot less correction than the 28-70, and again, the distortion correction feature does its job, with no ill effects.
Neither of these is necessarily problematic (it's not unusual for mirrorless lenses to be designed with correction as part of the concept), but the high price of the Sony lenses, combined with the differing results achieved by shooting in JPEG (where the correction cannot be turned-off), and Raw, where the correction parameters don't appear to be available to third-party converters, isn't ideal.
The Sony a7 (and a7R) use a content-sensitive noise reduction system that attempts to protect areas of fine detail while applying higher levels of noise reduction to smooth, featureless areas. The results are mixed.
|ISO 16,000, F1.8, 1/400, 55mm F1.8 lens||100% crop|
|Raw image, processed with 61% luminance noise reduction in ACR 8.3 beta||100% crop|
On the plus side, the JPEG has done a good job of preserving detail in the face, while smoothing the beige wall to the left. Our processed Raw file uses the same noise reduction over the entire image, meaning a balance has to be struck between smoothing the background and retaining detail. As such, our chosen settings, while appearing to retain more detail, have neither the well-defined edges or smooth background of the camera's JPEG.
Where the context-sensitive approach falls down is at transitions between areas it concludes to be smooth and those it considers detailed - leaving a pronounced 'halo' of noise at the edge of smooth regions. This, combined with the camera's tendency to sharpen edges, can leave a rather unpleasant result if you zoom in. Our test scene suggests the problem becomes visible around ISO 12,800.
We printed the central 19 x 13" of a similar image to the one shown above (such that the whole image would have been 30 x 20") and, although the effect was clearly visible, and the radical difference in noise levels across the image is slightly unusual, the results were pretty usable.
Heavy-handed noise suppression
Overall, the noise suppression is too aggressive in the JPEGs, making particularly the a7 images seem artificial at times. Naturally this can be turned down, but the default settings look way too much like a brush stroke filter has been applied. This gets worse as ISO rises.
|100% crop - Camera JPEG|
|ISO 640, F7.1, 1/250, 53mm w/28-70mm||100% crop - ACR conversion|
The birds in the above ISO 640 image look plastic, and the grass looks like a poor paint job, with very little definition. It's the opposite of what we'd expect from a 24.3MP camera, while the Raw looks noticeably better.
Overall image quality
Despite this two-page Image Quality section being full of little complaints, we were actually generally pretty impressed with the a7's image quality - particularly if you shoot Raw. The JPEGs are rather over-processed and prone to exhibit some or all of the above flaws and limitations, depending on the subject matter. Overall, they're not terrible, but we're disappointed to see such potentially limited and limiting files from a camera at this price.
In addition, despite having an anti-aliasing filter, the a7 can occasionally exhibit moiré, but it's something we only saw once or twice in the hundreds of images we shot.
One of the advantages of a full frame sensor is that its large surface area means it has the chance to receive more light, at any given set of exposure settings, than a smaller sensor. As expected, the Sony a7 performed well in low light (with the caveats we've already mentioned). Image quality from the a7 was very good in low light when detail was high, making shooting as high as ISO 6400 an easy choice.
|Sony a7 ISO 2500, F5.6, 1/80, -1EV 28-70mm lens @69mm|
Whether the degree of Raw compression concerns you is a decision for you to make for yourself. From a philosophical perspective, we're not at all happy to see this approach being taken in a camera at this level (and that becomes an even bigger concern in the a7R). As it is, the real-world impact is likely to be small, and will only have any effect from time-to-time. We're not sure buyers should have to tolerate that extra uncertainty from what is likely to be the camera they turn to for optimal results.
Raw files for download
Below are a few Raw images that you can download and tweak to your heart's content: