I'm trying to build remote follow focus and after some research I think that it is possible to build very accurate one. I know that there is Rack Focus option but it is very limited and not much accurate with my Canon 17-55 IS USM when focal is set to 55mm (when speed is set to 1 it has about 709 steps from shortest distance to infinity but 739 steps on the other way). Step size depends also on the selected focal so it's not much useful for me. I'm trying to build something that works like this:
1. you can use AF or manual focus to point to selected object
2. once focus is ok you can remember this position
3. you can select any remembered point and selecting one will always work and will be very accurate
It sounds to great to be possible but I discovered that there is some counter that shows relative position of the focus. When you change focus position using PROP_LV_LENS_DRIVE_REMOTE this counter is always accurate even when speed is set to 3. You can find it at 0x20-0x21 (Canon 60D) in structure given when handler for PROP_LV_LENS is executed. For my C17-55 it allows to distinct about 1500 positions, for C100mm it's about 3000!
Now it's time to describe the problem
Sometimes PROP_LV_LENS_DRIVE_REMOTE breaks some Canon code and some events are no longer sent (for example PROP_LV_LENS). To fix this you have to press shutter button or go to menu and go back to LiveView. I don't have any idea how to fix this from code so I thought that maybe I can find this counter in some other place. And after some memory scanning and disassembly of original firmware I can't find source of this value. I found some related values near 0x265FC and 0x549DC but there is only last step size (it's not correct when last step was shorter because of limit in focus range) and what's funny there is previous value of the counter I mentioned before (it's always one step behind). Even when PROP_LV_LENS is not sent and value of counter in structure related to this property is not updated the one step behind counter is always refreshed 
So now I can ask my questions Does anyone know:
- how to fix LV notifications from code when PROP_LV_LENS_DRIVE_REMOTE breaks them?
- where can I find the origin of this counter, I tried to find this in disassembled code but it's not so easy for me (Java guy ) because code related to this addresses has hundreds of subs and operates on SP with is hard to track for me (at least until someone will run original firmware in qemu )
1. you can use AF or manual focus to point to selected object
2. once focus is ok you can remember this position
3. you can select any remembered point and selecting one will always work and will be very accurate
It sounds to great to be possible but I discovered that there is some counter that shows relative position of the focus. When you change focus position using PROP_LV_LENS_DRIVE_REMOTE this counter is always accurate even when speed is set to 3. You can find it at 0x20-0x21 (Canon 60D) in structure given when handler for PROP_LV_LENS is executed. For my C17-55 it allows to distinct about 1500 positions, for C100mm it's about 3000!
Now it's time to describe the problem
Sometimes PROP_LV_LENS_DRIVE_REMOTE breaks some Canon code and some events are no longer sent (for example PROP_LV_LENS). To fix this you have to press shutter button or go to menu and go back to LiveView. I don't have any idea how to fix this from code so I thought that maybe I can find this counter in some other place. And after some memory scanning and disassembly of original firmware I can't find source of this value. I found some related values near 0x265FC and 0x549DC but there is only last step size (it's not correct when last step was shorter because of limit in focus range) and what's funny there is previous value of the counter I mentioned before (it's always one step behind). Even when PROP_LV_LENS is not sent and value of counter in structure related to this property is not updated the one step behind counter is always refreshed So now I can ask my questions
Does anyone know:- how to fix LV notifications from code when PROP_LV_LENS_DRIVE_REMOTE breaks them?
- where can I find the origin of this counter, I tried to find this in disassembled code but it's not so easy for me (Java guy
) because code related to this addresses has hundreds of subs and operates on SP with is hard to track for me (at least until someone will run original firmware in qemu )