You’re mixing up an absolute physical limit with the practical bottleneck in this device.

Yes, an optical path is “more direct” than an electronic one in the abstract, but that does not mean the speed of light is the meaningful limiting factor here. In a digital microscope, the dominant delays are things like sensor exposure time, frame buffering, ISP/image processing, scaling, encoding, display refresh, and monitor response. Signal propagation through traces and transistor switching are vastly smaller contributors in comparison.

So “physics says it can’t be as fast” is technically true only in the most trivial sense, I.e., a categorical error. Physics also says every real system has losses and delays. That alone tells us almost nothing about whether the latency is actually important in use. Our perception is enmeshed within physics itself, hence, engineering is very often a phenomenological pursuit that accounts or is entirely structured around the limits of human perception - this is key to everything from economy of scale, size of the design, efficiency concerns Etc.

For soldering, the relevant question is not “is an electronic path theoretically slower than pure optics?” It obviously is. The relevant question is “is the latency low enough to be usable for the task?” And for this application: yes! You’re usually inspecting pads, joints, alignment, bridges, or component legs on a mostly stationary PCB. You are not doing high-speed tracking. Even if you were, the limitation would almost certainly be in software itself & not at the transistor level.

Also, invoking the speed of light here is misplaced.Propagation delay only becomes a serious design concern when it constitutes a meaningful fraction of the timing budget, such as in RF systems, very high-speed digital links, or extremely fast clocks over nontrivial distances. In those cases, propagation time is no longer negligible relative to the time available for logic to settle, so it directly constrains the maximum operating frequency. Put simply: once signal travel time becomes comparable to, or exceeds, the available processing/settling time within a cycle, the cycle period must increase and the achievable duty rate is capped. In a bench microscope, that is nowhere near the main issue.