Sony’s latest APS-C mirrorless features some remarkable technology, says Andy Westlake, but is let down by its out-dated body design.
Sony Alpha 6400: Image quality
Sony has fitted the A6400 with the same 24.2MP APS-C sensor as its predecessor, but teamed it up with a faster processor. Unlike the firm’s current full-frame and 1-inch type sensors, it doesn’t use a back-illuminated or stacked architecture. As a result, the A6400 is now technically surpassed by Fujifilm X-T30, with its 26.1MP back-illumimated X-Trans CMOS 4 sensor. But it’s still capable of excellent image quality, with good detail and dynamic range at low sensitivities, and strong performance at higher settings up to ISO 6400.
At ISO 100 in raw format the A6400 comes close to the maximum resolution its sensor could theoretically deliver, achieving approximately 3800 lines per picture height before false colour and maze-like aliasing creep in. This falls progressively as the sensitivity is raised, but the camera still maintains around 3000 l/ph at ISO 6400. At higher settings, noise has an increasing impact, with around 2800 l/ph resolved at ISO 25,600 and just 2000 l/ph at the top extended setting of ISO 102,400. Sony’s JPEG processing prioritises suppressing artefacts, resulting in slightly lower resolution compared to raw.
In the crops below, multiply the numbers beneath the line to calculate the resolution in lines per picture height.
ISO and noise
At low sensitivities the Alpha 6400 delivers finely-detailed images with barely any hint of noise. Increase the setting to ISO 800 and noise starts to impinge on even-toned areas when viewed closely onscreen, but you’d really struggle to see it in print. This gets more pronounced at ISO 1600 and ISO 3200, but I still wouldn’t hesitate to use these settings. Indeed it’s only really at ISO 6400 that there’s clearly a negative impact on fine, low-contrast detail and colour saturation, although image files still look quite usable, especially with a touch of luminance noise reduction applied. Beyond this things go downhill fast, and while ISO 12,800 images might still be OK when viewed at smaller sizes, the top three settings all suffer from muted colour and excessive noise that swamps all but the broadest details.