Could it help to have a point-like light source from a good angle that gives you a sharp shadow? Then it may be possible to judge distance based on the distance between the tip and its shadow.
Haven't thought of that. I will investigate, thanks for the tip!
> The bigger problem is with placing fine components on the board. It's just slow and irritating. I will position the component in its location and then slowly bring it down until it touches the paste.
Have you tried not using solder paste and instead using a "normal" thin solder wire (with jelly flux)? I prefer to use that over solder paste for everything up to 0402.
I would use dragging on larger components like QFP but 0402 is very tricky for me. I am happy to be able to place it at all.
Reflow seems to be much easier for me as I can take multiple tries at placing the flux paste and then the component and then once I'm happy with the placement I no longer have to touch it and instead hope surface tension and solder mask will do its job.
Takes more work but with my eyesight, no stereoscopic vision and limited motor skills I am pretty happy I can do it at all.
I am using a camera connected directly to a monitor to reduce lag. This allows me to see both the monitor and the board at the same time, without moving my head. I see the board an the tip at an angle allowing me to judge the height. When soldering, I will mostly look at the monitor and regularly scanning to see the height of the tip.
The bigger problem is with placing fine components on the board. It's just slow and irritating. I will position the component in its location and then slowly bring it down until it touches the paste.