dhenry:
TI ADS1115 16 bit
Let me be the first to say that unless you are a very good engineer, using a 16-bit adc can be quite a challenge. And unless you are some analog god, using a 24-bit adc can be downright impossible.
Rather than increasing the bits, you should think if you need that much resolution and if that high of a resolution makes sense for your application (for example, is it even that accurate?).
dhenry I think it will help if I clarify with a bit more context: The best scenario from the ratio of the 'image movement to ADC output' point of view is using the red light and comparing white with black marks. The technique used (so far) places the light half on one colour and half on the other colour, which provides the average greyscale as output. To move from fully on one colour to fully on the other the image needs to travel around 1.5mm which provides less and less resolution the lower the relative greyscale values get.
As mentioned, 0.01mm per integer from the ADC is adequate, but 0.1mm isn't. For example: If a small sheet (all sides are in centre vision) of paper has a black border of say 1mm, and a 0.1mm error occurs along one axis, one side will become 0.9mm and the other 1.1mm, meaning the smaller will be nearly 20% smaller which humans can see quite easily and may or may not hurt sensibilities (depending upon the nature of the onlooker!) and this assumes the conversion is accurate and doesn't suffer from noise etc.
It is also worth noting that my current quest is to measure any error rather than applying any correction (I'm treating subsequent correction as incidental).
You've got me worried though and I would appreciate some detail if you are in the position to do so...Thanks a lot