E-mount electronic protocol reverse engineering

Is this far enough along to make a “dumb” adapter?

IE rather than translating between two protocols, just take output from an E mount body into an Arduino, and drive a stepper motor directly with a motor driver circuit? All that’s really needed would be “move back” “move forward” and “stop” or “off”.

I could fool a camera into detecting an emulated lens and then change the aperture values the camera was receiving. The focus commands are harder to interpret I never got to the point of deciphering the protocol to a fwd/stop/back. It's more complicated than that because the camera can command the lens to an absolute position not just a direction. In fact there are quite a few focusing modes. That said I don't think I was far off that I just haven't figured out that detail. I actually have a stepper motor attached to an old lens to do exactly what you were suggesting lol.

If you wanted to make a chip to talk to the camera and return the focal length of a lens for setting the image stabilizer that is possible with what I currently have.

bostwickenator wrote: I could fool a camera into detecting an emulated lens and then change the aperture values the camera was receiving. The focus commands are harder to interpret I never got to the point of deciphering the protocol to a fwd/stop/back. It's more complicated than that because the camera can command the lens to an absolute position not just a direction. In fact there are quite a few focusing modes. That said I don't think I was far off that I just haven't figured out that detail. I actually have a stepper motor attached to an old lens to do exactly what you were suggesting lol. If you wanted to make a chip to talk to the camera and return the focal length of a lens for setting the image stabilizer that is possible with what I currently have.

I don’t know if it helps but I still have an A7s I, which is CDAF only, I remember gen III coming out and Sony making adapters work way better then they do on previous gen. So I guess the adapters are buggy and gen III is more flexible and compensating for known problems, where as older gen is more ‘strict’ in the protocol

Hi. I'm an electrical & computer engineering professor at the University of Kentucky. Way back in 2014, I looked at making something like the TechArt pro LM-EA7... but I backed off when Sony refused my formal request for E mount details because I was afraid future protocol changes might break my device (a fear that has been confirmed). Anyway, I never got very far on the protocol and haven't looked at it again -- until now.

In the DPReview Adapted Lens forum, I recently brought-up the topic of Trap Focus for manual lenses. Trap focus normally means to pre-focus where your subject will be and delay shutter firing until something moves into focus -- however, for manual lenses, it can mean that the shutter doesn't fire until you've manually hit focus on your subject. That's really useful for various circumstances. On some Sony A-mount cameras, this could be done by using a chipped adapter, focus priority, and letting the screw drive (apparently harmlessly) spin while the shutter was depressed until focus was detected and the shutter fired.

So, I'm thinking again about making a custom adapter: this time, it would be one that simply tells the camera the lens is an autofocus lens with the appropriate focal length for IBIS, but it simply doesn't do anything -- thus allowing the above type of trap focus behavior (without a spinning screw drive) using the AF-S or AF-C Focus Priority setting on the A7RII and later E bodies. I've designed & made tons of dumb 3D-printed adapters (my things on Thingiverse), so the idea would be to make an adapter that did this and provided something like a thumbwheel and maybe a little OLED display to select EXIF data. It seems like something on the scale of an Arduino Nano should be able to do it (if it can be coaxed into doing 750K baud).

Any interest?

PS: Using an LA-EA2/4 with an AF lens on my A7RII does implement trap focus, but with the 3rd-party chip on a manual lens it didn't work. It's been a long time, and 3rd-party A-mount chips vary in what they say the lens can do, so I'm not sure if a different chip would have worked.

Edited by profhankd - 31 August 2020 at 15:48

bostwickenator wrote: You should pull my Teensy code. It does all the negotiation stages and enters the main message loop. From there it should be pretty easy to do what you are talking about. Also I have docs for the message sequence. Just please don't start from scratch again 3 of us have gotten to roughly this point before giving up. https://github.com/LexOptical/E-Mount

Seeing your teensy code (which I grabbed) is part of why I'm thinking this should be doable now... although I'm less fond of you board choice. Might try an ESP32 if it needs the power, but I was really hoping a 3.3V nano might be able to handle 750K baud....

bostwickenator wrote: I opted for something way too powerful because I wanted to eliminate that as a concern while in the POC phase. For building a product it would make sense to optimize and use something more appropriate. Best to prove it out first though IMO.

Well, your code definitely seems like the right starting point.... Do you have a diagram of your pin connections for the Teensy 3.5 posted?

I've been busy with other things, but I did open an extension tube and I'm thinking literally running your code on a Teensy 3.5 might be a safer first step than using one of the other chips. I hand't realized that the Teensy 3.5 is actually pretty different from other so-called Arduinos....

bostwickenator wrote: Pin assignments are https://github.com/LexOptical/E-Mount/blob/master/E-Mount.ino#L7 Teensy pinouts are here (make sure you are looking at the 3.5 I've made the mistake of referencing the wrong board before) https://www.pjrc.com/teensy/pinout.html Wiring is direct no need for voltage translation or anything.

I saw the 3 PIN_ constants in the code, and I see some magic constants in the code for things like pin 1 and 5. I was hoping there was a diagram somewhere just to be sure.

In particular, I was wondering about power & ground. I assume you powered the Teensy 3.5 off a USB supply, tied the grounds together, and probably didn't connect the E power pins to anything? Or did you use that to see when the camera is turned on?

Did you have to do any jumpers to play with 3.3v vs. 5V signaling? I've never used a Teensy before....