Re: Creating long straight edges

> With the lasers poor mode structure and fraunhofer difraction limit
> the spot diameter. Amazingly if you put a very small pinhole in the
> beam it will eventually cause the light to diverge more! The spot
> will have a central fuzzy area surrounded by concentric rings of
> intensity K (sin theta/theta)^2.

I had offered the idea of a laser in answer to just aligning the
rails. But that was some time ago. I think it was Jon who offered
that the laser not only diffuses over distance, but if you are using
a pocket pointer, the beam is not parellel to the axis of the housing.
Some even recomended rotating to remove the error.

And one can use a couple photo receptors or similar (LED's even) to
read the intensity, and with a cheap op-amp or comparator, design a
circuit to pick up the edge of the light.

That said, if you chose to try a laser you still have to move it
along and manually raise and lower some device like a micrometer.

And although it seems more fun than a level, it seems to me that it
adds more time and complexity and does not offer a higher accuracy
than the level.

If anyone chooses to do use a laser, blow smoke in the room and take
picutres. Those are one's I'd like to see.

Dave