Re: fun things to try / laser pen questions

[P3D John W Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Thu, 14 Nov 1996 07:43:53 -0600
>From: P3D romney <romney@xxxxxxxxxxxxxxx>
>Subject: fun things to try

>3. Another fun thing is a little laser  like those pens lecturers use to
>point to vu-graphs and slides. Stick it in the eyepiece of your coupled RF.
>It makes two spots like the old Kalart Focus Spot but very  bright. At a
>correct infinity setting the spots are the base of the RF apart at ANY
>distance. The spots come together as one spot (or one above the other in
>split image RF's) at the distance the camera is focussed to.Best way to set
>a RF by far! Take pictures with it too. I made up one for my Speed Graphic
>KAlart RF to go in place of the old Focuspot. But don't use it on people,
>only on things. Laser light is dangerous. Surely there are many more
>interesting things to do with these little lasers. Any ideas??..

I've taken 3D photos at night, with the camera shutters open and a
(helium-neon) laser used to "scan" over a still scene in various patterns.
The result doesn't look like much in 2D, but in 3D much of the depth
information can be reconstructed. It's comparable to making a "wire mesh"
image by photographic means rather than by computer modeling.

It looks like I may have a legitimate use for a laser pen, and if I'm going
to buy one, I would be interested in getting one that can be used for
photographic/3D purposes as well. I'm told that He-Ne lasers put out light
at 632.8 nm. From a casual glance in the laser pen store, I notice that
most of the cheap laser pens put out light at 670 nm, and others are
available at 650, 640, and 635 nm. I presume the shorter wavelengths are
better for pointers, because they are further up the sensitivity curve
of the human eye.

My question: how well do typical color slide and negative films respond at
these wavelengths? The He-Ne laser worked pretty well with color negative
film. From a photographic standpoint, is paying a few tens of dollars more
for a 635 nm laser pen (compared to the cost of a 670 nm model) justified
by increased sensitivity of the film at that wavelength? (Further question -
anyone know the spectral sensitivity of typical consumer CCD video cameras?)

John R


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