T3D Re: TECH-3D digest 552 ; interference filters

[lunazzi <lunazzi@xxxx>]

> Peter Abrahams wrote:
> Subject: T3D interference filters at Lindau

........

> - No ghosting!

Good!

>
> - Bright images

Interesting. Let me calculate: you use only a limited part of the spectrum of
your white light lamp.  20 nm x 3 = 60 nm (one eye) and similarlly, 60 nm for
the other.  You lost about 60 nm, you need that for separation, O.K? So you had

lost less than by using plastic polarizers, which is more than 50 % lost.  But
even interference filter may have losses, I mean, not 100 % at the
transmission peek.


>
> - No silver screen necessary

Great!

>
> - Glass filters -> higher quality, longer lifetime

If not broken or lost or stolen  8-)@

>
> - It does not matter how the filters are orientated
>

In multiple coating the angular dependence is of some consideration, you would
not have a large angular  field of view. For the interfencially made filters  I

comment below the angular dependence would be too strong.

>
> Disadvantages:
> - You cannot buy these filters

> - A filter pair would cost about 300$, that means you have to invest
> 300$ for every person!!
>

Interference filters are usually made by multiple  coating, but can also be
made by photographing interference gratings in photoresists.  These are usually

named "holographic", although the term is rather confusing. In some cases they
are succesfull in reflection, as in displaying monochromatically the control
panel of an airplane, so that the pilot can see the information through the
cokpit window, not needing to move his head.  It is just one reflection peek,
but it could  be three, if color were important.
In other case, it was possible to make an antireflection filter, in a plastic
foil.  That means that it can be cheap. But it seems not possible to obtain
three transmission peaks.


> - One image had a slightly red the other a slightly blue tendency, maybe
> this can be reduced in the future
> Andreas Petersik    A.Petersik@xxxxxxxx
> =======================================
> Anyone else know about these?
> _______________________________________
> Peter Abrahams   telscope@xxxxxxxxxx
>
> ------------------------------

Yours,

                 José
<lunazzi@xxxx> <http://i.am/lunazzi>