Up until last year the only way to auto-focus motorless A-mount lenses on the A7 and higher e-mount cameras was with the LA-EA4 adapter that Sony sold. And it had a translucent mirror built into the adapter to provide autofocus points to control the autofocus of the lens on the camera. This had several difficulties. One was the translucent mirror itself which acts as a beam splitter and wastes 30% of the image light to the autofocus function. And because it uses the adapter’s autofocus system instead of the camera’s, all the advances in autofocus that have accrued over the time that the E-mount cameras have evolved are unavailable when using the LA-EA4. In other words the autofocus is very limited.
But in 2020 Sony launched the LA-EA5 adapter with the ability to autofocus motorless lenses through the camera’s autofocus system and without the beam-splitter in the light path. This was a marvel when it was announced and there was great rejoicing among the owners of old but sharp Minolta and Sony A-mount glass. But because it is Sony we’re talking about, they had to make it a tragedy. They only programmed the adapter to provide this capability for three cameras, the A7R IV, the A1 and the APSC camera the A-6600. I have since attempted several times to contact Sony to determine if they will update their firmware to let this adapter work for my camera, the A7 III. Of course, they have completely ignored my requests.
But there is one other option. If you have an LA-EA4 adapter you can purchase a third-party kit from China to replace the firmware on this old adapter, remove the translucent mirror and use it to auto-focus these motorless lenses with any of the Sony E-mount cameras. Gary Friedman has been an E-mount expert user since the mount was invented and he writes how-to books about their cameras. He has produced a couple of YouTube videos on this subject. One demonstrates how to modify the LA-EA4 and install the Chinese autofocus firmware. The other demonstrates the way both the LA-EA5 and the hacked LA-EA4 focus with various Minolta lenses. It is valuable to know that even with the LA-EA5 and a compatible camera the speed of the autofocus is much slower than with E-mount lenses. And the autofocus with the Chinese firmware on the LA-EA4 is very uneven. It starts and stops several times to reach a focus point.
I have an LA-EA4 and after seeing the video I am considering doing the retrofit myself. It costs about $200 which is about the cost of the adapter I think but I am intrigued with the thought of being able to autofocus my Minolta 200mm f4 macro and Sony 135 f1.8 A-mount lenses. I guess that sort of makes me some kind of a fanatic but Sony leaves me no choice. When I buy and install the firmware, I’ll do some tests and post them for the curious.