Re: [ATM] Betr.: Re: cutting a big piece of plate glass - Polarizer

[Dominic-Luc Webb <dlwebb@canit.se>]

On Fri, 13 Jul 2007, Richard wrote:

> Hi Dominic-Luc,
>
> Friday, July 13, 2007, 6:14:10 PM, you wrote:
>
> DLW> On Fri, 13 Jul 2007, Richard wrote:
>
>
> DLW> I never found one that was purely 2 linear polarizers.
>
> OK, having dredged the deeper darker brain cells, I recall circular
> polarisers are used in photography, as are linear.
>
> No, they are not two linear polarisers, they are just one linear
> polariser or one circular polariser. The purpose is not to act as a
> variable neutral density filter, it is to act as a filter to
> selectively block out strongly polarised light, like sunlight
> reflected off water for example. If the filter is marked PL it is
> linear polarised and if it is marked PL-CIR it is circularly
> polarised. Both have there uses, but I believe one is better for auto
> focus and one is better for manual focus camera, and no, I can't
> remember which. Never seen a pair in one cell though Dominic.

I agree. When I wrote 2 linear polarizers, I meant the third and
last type that you have not seen. While uncommon, I have encountered
them. As you can guess, in this case, it is adjustable with one
linear polarizer that rotates relative a second linear polarizer.
For my application, I would have to have them as two separate disks.
I reckoned it might be possible to take apart a commercial pair.
Pricing out two decent quality camera polarizers, I ended up asking
Polaroid for some samples of their production line stocks. I do not
think this was especially good optical quality, but it had a
transmission/polarization peak exactly where I needed it. My
application was fluorescence polarization in drug-receptor binding
studies, using a fluorophore labelled drug. The massive size was
convenient for checking large glass disks for fractures. Maybe
this brings up a useful point. Polarizers, as I learned, are
manufactured to polarize only within specific wavelength ranges.
Outside this, they may act as simple neutral density filters, etc.

Dominic

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