In-camera lens corrections
Like other recent Sony models, the NEX-7 comes with optional in-camera corrections for certain lens aberrations. Sony calls these tools 'lens compensation' and they come 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 profile of the lens in use. On the NEX-7 Shading and CA compensation are turned on by default - Distortion is turned off.
Lens corrections only work with native E-mount lenses - i.e. not with Alpha lenses on either of the LA-EA adapters. Sony's Image Data Converter software will silently apply whatever lens corrections were enabled at the time of shooting when it's converting RAW files, and there's no obvious option to disable this (so you're stuck with whatever options you selected at the time of shooting).
More interestingly, Shading Compensation affects RAW files converted using Adobe Camera Raw, suggesting it's been applied to the RAW data itself; neither Distortion nor CA compensation have any analogous effect.
In the examples below we compare four images - JPEG with compensation turned off, JPEG with compensation turned on, RAW with compensation turned on processed through IDC, and RAW shot with compensation turned on, then processed through ACR with its own profiled lens corrections turned off. Adobe tells us it applies no lens corrections automatically to NEX files, so the IDC/ACR comparison allows us to distinguish between corrections applied automatically by IDC, and those applied by the camera before the RAW file is written. (In normal use, of course, you'd probably turn profiled lens corrections on when using ACR whenever necessary.)
Chromatic Aberration compensation
Chromatic aberration compensation is applied by default, and in our tests does a good job of removing lateral CA (colour fringing towards the corners of the frame) as you can see in the the samples below. These images were taken with the E 18-55mm F3.5-5.6 OSS zoom, but each lens will have its own particular CA characteristics, so results may vary with the lens you use.
|Off||On (JPEG)||On (RAW + IDC)||On (RAW + ACR)|
The rollover above shows a 100% crop taken from the top corner of the frame. The click-through links to the full image. Setting CA compensation to 'On' not only corrects the out-of-camera JPEG, but also instructs IDC to apply the same correction. As we can see from the ACR conversion, the underlying RAW data is unaffected - exactly as we'd expect.
As you can see in the images below, the auto distortion compensation does a decent job of reducing lens distortion, which here is of the barrel type (this example was taken with the kit E 18-55mm F3.5-5.6 OSS zoom at 18mm). This will generally have an impact on corner sharpness, but you'll have to look closely to see it. Distortion compensation is disabled by default on the NEX-7, so if you're using JPEGs or IDC and like your straight lines to be genuinely straight, you may wish to turn it on (especially as the 18-55mm kit zoom shows unusually high levels of distortion). Note that this correction is not previewed live in the viewfinder.
|Off||On (JPEG)||On (IDC)||On (ACR)|
As with CA, setting Distortion compensation to 'On' instructs IDC to apply the same correction to its RAW conversions as the camera does to its JPEGs. Again, though, the 'straight' ACR conversion shows that the underlying RAW data is unaffected (as expected). This indicates that IDC is applying compensation on the instruction of a metadata tag encoded in the RAW file.
The following shading compensation analysis was shot using the 18-55mm F3.5-5.6 kit lens, at the widest focal length and F3.5. As you can see in the samples below the compensation function is quite effective at reducing vignetting. Unusually, though, it has exactly the same effect on RAW files converted using Adobe Camera Raw as it does on out-of-camera JPEGs. Adobe tells us that it's not applying any compensation of its own during raw conversion, which implies that shading compensation is written into the RAW data before the file is saved.
|Off||On (JPEG)||On (RAW + IDC)||On (RAW + ACR)||Off (RAW + ACR)|
Interestingly, from these tests we estimate falloff at 18mm F3.5 to be approximately 2 stops, falling to about 1 stop when compensation is enabled. This latter figure more closely matches what we originally measured for the lens using the NEX-5, suggesting that on older NEXs, shading compensation was applied automatically to RAW files all of the time. This has obvious knock-on implications for any lens tests conducted on these older bodies, including our own which we'll revisit in due course.
Our overall conclusion from these tests is that there's no obvious reason not to enable CA and Distortion compensation, as they'll improve the camera's JPEGs without affecting RAW. But RAW shooters may prefer to disable vignetting compensation, to keep the data as close as possible to what the sensor recorded. As usual, if in doubt it's best to do your own tests to see what better suits your personal needs.
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