Re: Laser light

[sample@lyon.edu (John D. Sample)]

At 11:47 AM on 12/12/96, <phys-l@mailer.uwf.edu> wrote:

> If the granular appearance of the laser light shone on a white card is what
> you are calling "speckle" keep in mind that the pattern you are seeing is
> being produced on your retina.  A film placed at the position of the paper
> would not record the pattern you are seeing.  To support this argument have
> two different people look at the same white surface.   If you can arrange it
> have one near-sighted person and one far sighted person.  Have both
> simultaneously move their heads from left to right.  As the near sighted
> person moves his/her head from left to right the he will see the pattern
> moving in a direction opposite the motion of the head and the far sighted
> person will see the pattern moving in the same direction as the head.  (It
> may be just the opposite, it's been a while since I have tried this.)  If
> you wear glasses try the same experiment with your glasses off and then on.
> With the glasses off you will see the dots move.   If the glasses totally
> correct your vision then when you put them on the pattern of dots, or
> speckle, will not move.  If your glasses over correct then the direction of
> motion will reverse when you put your glasses on.
>
>
> Jim Riley, Department of Physics
> Drury College
> 900 N Benton Ave.
> Springfield, MO 65802
> e-mail: jriley@lib.drury.edu
> Phone:  (407) 873 7233

This is interesting!  I've never heard mention of this effect before.  Do
you know of references?  Would this be an accurate way of determining the
correct prescripton for us blind people?  It sounds like it might be a more
sensitive test than the somewhat subjective decision of which lens "looks
best."

Chip