In a nutshell, my question is:
Why is the depth of field for endoscopic cameras so limited? It seems it is generally around 3 to 8cm (some are around 3 to 40cm). Why aren't they similar to automobile backup cameras that seem to have an "infinite" depth of field (or, at least, about 4cm to really far from the camera).
Out of the netshell:
First, it seems that my question could have aspects that may not be strictly photography related. If so, should it be posted on a different Stack?
Also, I am not a photographer, so my terms may not fit precise, strictly photographic (or other technical) usage. But, I think they're clear enough. However, just in case I'm not as clear as I think I am, here are a couple of terms and how I think of them:
"focal distance": The distance from the camera that is in focus. E.g., 8cm.
"depth of field": The range of distances from the camera that are in focus. E.g. 3 to 40 cm.
However, in product descriptions of the relativly inexpensive endoscopic cameras that attach to personal computers & smart phones, is seems that either term, "focal distance" or "depth of field", may be used to mean "depth of field" as I defined above.
Anyway, I ask because when I need to look in a wall or other tight spot, I don't want to have such a limited range of focus (the ~3 to 8cm that endoscopic cameras have). I've used my android device (an otherwise inactive Samsung S3) when the wall opening was large enough, and it provided really good images in focus over, if not infinity, most of the interior of the wall. But, it is also cumbersome at best for such an application (and usually not possible at all due to hole sizes). I've considered MacGyvering up a backup camera for endoscopic use, but they are quite a bit larger in diameter, and would again limit usage in tight spots. Plus, I'm no MacGyver...