Hi Forrest,

I think that you will have better luck with other types of filters.
Try looking for interference filters. These can easily have very sharp
responses since they work by diffraction, not the
absorption/transmission spectrum of chemicals. Their biggest
disadvantage is that they only work properly when the light going
through them is within a certain range of angles relative to the
surfaces of the filter.

You may also be able to find very sharp filters in laser safety
glasses. Sometimes these are intended for one particular laser
wavelength and they will pass the light from one red laser and not
from another - even though those two lasers look identical to the
naked eye.

Sean


On Sun, Aug 31, 2008 at 7:04 AM, Forrest W Christian <forrestc@imach.com> wrote:
> I am working on a presentation related to a RF technology.   As part of
> this, I'd like to purchase some sheets of transparent color filters
> which are of different colors to provide the audience with a visual
> impression of how filtering and/or frequency selection works.   That is,
> I would like to be able to give the audience several different filters
> of the same basic color - for instance, several different green filters
> which would differ in their peak transmission wavelength -say every 20nm
> from 500 to 560nm.   Then I would provide a light source of the same
> wavelength of light as one of the filters and show how a filter cuts out
> much of the light energy outside it's bandpass.   (I.E. a 520 nm filter
> cuts out some at 540nm, more at 560, and even more at 580 or 600 or beyond)
>
> Having some A/V background, I figured I'd just go and get some color
> gels of different colors - but looking at the transmission charts of
> commonly available gels makes me realize that most of the gels available
> are just like paint colors - that is, a mixture of multiple wavelengths
> and it's not going to be easy to find a set that will work for my
> application.  Note I didn't say impossible, since it looks like I might
> be able to come up with a suitable set color-wise.   However, getting a
> balanced set where the transmissivity on each color is consistent across
> the filter set is even going to add to the complexity (and *may* be
> impossible).
>
> So before I spent hours and hours trying to come up with an appropriate
> set of commonly available filters, I figured I'd also look around and
> see if someone made a set of gels which were optimized for light
> filtering and weren't that bad cost wise.    I have come up with a
> couple of sources, but most of them are typical red/green/blue filters -
> which would probably work, but I'd really like to be able to .   So far,
> nothing which will fit my application neatly.
>
> What I'd like to find is someone who makes fairly inexpensive gels which
> are available in different colors which correspond to say every 20nm of
> the light spectrum, and which are fairly consistent in transmission and
> "bandwidth".
>
> Ideas?
>
> -forrest
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