Precision in this project is limited by rise time of the received signal. Meanwhile, this time is limited by rise time of laser's current. It is too long now - 10 ns.
Theoretical TDC resolution is ~13mm per BIN.
You could see real results here: https://github.com/iliasam/OpenTOFLidar/wiki/Resolution-of-t...
> "How did you calculate the appropriate laser lens and standoff"
I can't say that there was too much calculations.
The is some information here: http://www.ti.com/lit/ug/tiduc73b/tiduc73b.pdf (part 2.3.5)
and here: http://www.ti.com/lit/ug/tiducm1b/tiducm1b.pdf (part 2.3.2)
Laser's lens should have maximum possible focal length, but it must not crop light beam from the diode.
Photodiode's lens should have maximum Entrance pupil
> "Is the CS mount lens's focal length important, or is there no need for a sharp image at all distances?"
You need to have sharp image at big distances. At short distances it is not important - light signal is high enough.
> "Why use one CS-mount lens and one M12 lens, rather than two M12 lenses?"
I think that it is easier to find lens with big "Entrance pupil" with CS mount that with M12 mount. Bigger mount - bigger lens diameter, bigger "Entrance pupil".
> "Do you need any sort of dynamic gain"
I don't have any kind of electrical gain control. There is an ability to change APD gain, but I don't use it.
> "optical filtering on the received signal"
I don't have filter in my LIDAR, but it is necessary to have it if you are going to run LIDAR at sunlight. I give links to a several interference filters in "LidarTotalBOM.xlsx".
> "Did you need much fancy $$$$ test equipment to get the design working".
All that I have is Tektronix TDS540D oscilloscope (bought at the Ebay for $300) and multimeter.