Tim S wrote:
Limey Lurker coughed up some electrons that declared:





the lenses have some spherical aberration which causes
the lines to curve.


Really? How the Hell does that happen, then?

He means the line, along its width. Not its length.

No, I really did mean that the line is curved along its length on the
wall.

Apologies that "spherical aberration" wasn't the correct term for the
cause, but it's still in the cheap and nasty optics.

The laser diode initially creates a spot beam. The flat fan beam that
projects a line on the wall is created by a cylindrical diverging lens.
You'll only get a straight line if the axis of that cylinder is exactly
at right-angles to the beam. If the lens is tilted either forward or
back, the flat fan becomes slightly dished and the projected line will
be slightly curved.

I never considered that, but then I couldn't work that accurately anyway, so
it's fairly moot for me.

My cheapie laser level projects a very noticeable curve relative to a
plumbline. OK, we can't expect much better for a retail price of under
20 quid (which means the optics probably cost about tuppence) but even I
can hang wallpaper straighter than that.



--
Ian White