Upgrading the Techart TA-GA3 Contax G - NEX adapter

The Techart TA-GA3 is a lens adapter made to fit the Sony NEX or α-series mirrorless cameras. It allows you to mount lenses made for Contax G, and the adapter includes its own autofocusing system for these lenses. Techart offers firmware updates to this adapter via an Android and iOS app called TECHART Update. The app communicates with the adapter via Bluetooth.

To upgrade the adapter, put the camera in manual mode, set the aperture on the camera to 𝑓/90, take a picture and finally turn off the camera. This will put the adapter in the “programming” mode, and it will turn on its Bluetooth connection. Some instructions online says you should also remove the lens, although in my experience this is not necessary.

In the app, you select the firmware version you want, and the app will then download the firmware, discover the adapter and then start updating the adapter with the new firmware. When everything works properly, this is a very nice way of handling firmware updates.

Inside the menu system of the Sony α7 camera, there is a field where the lens firmware version is shown. I’ve been experimenting with the firmware version but I’ve never seen it actually change from the value “2” for this adapter. So in a misguided attempt to see whether it showed, I decided to downgrade the TA-GA3 adapter to the oldest available firmware for it, firmware version 1.0.0.

While the downgrade went just fine, ever since then the TECHART Update app, neither on Android nor iOS, was able to discover the adapter to upgrade it again.

Adapter TA-GA3 not found, please try again

After a few months of not really bothering too much with it, I sat down yesterday to figure out what was actually going on. I tried to put the adapter in the firmware update mode, and I saw something called “EOS-iNEX II” show up as an available bluetooth device on my phone.

I quickly concluded that the TA-GA3 1.0.0 firmware makes the adapter identify as a EF mount to NEX adapter. It’s no wonder the TECHART Update app didn’t find any TA-GA3 adapters to update! Now that I had a good idea about the problem, how do I convince the Techart Update app to put a firmware for the TA-GA3 adapter onto an adapter that identifies itself as a EOS-iNEX II?

My first idea was to reverse engineer the TECHART Update app and patch it to allow it to patch any device with any firmware. I started looking at Techart Update app and I found the string http://www.techart-logic.com/g-nex/firmware/firmware.txt. This CSV file contains a list of firmwares for different models of lens adapters. The fields in the file were adapter, description, url, unknown.

Armed with that information, I created a copy of the firmware.txt file and modified it to apply a TA-GA3 firmware to a EOS-iNEX II adapter. I created a custom DNS zone for techart-logic.com on my own network, and pointed it to a web server that would serve the files as specified in the firmware file.

And… it worked! The TECHART Update app read my own firmware.txt file, presented me with the option to flash a TA-GA3 firmware on a EOS-iNEX II adapter, and once I selected it, the app found the adapter straight away and started updating it. A couple of minutes later, it was done.