Re: polarizer?

["David J. Romano" <romano@xxxxxxxx>]

Paul,
Some rules regarding filters do not apply to IR film. The polarizing filter
probably will not work well, as you said. It will act as a neutral density
filter, but not as much as it would for visible light photography. The filter
factor of 2.5 would probably be less, maybe 1.5 or 2. For IR light you really
need an IR polarizer.  If you want to splurge, you can get a 3x3 inch infrared
polarizing filter for $210 from Edmund Scientific. It transmits a maximum of
only about 37% at 900 nm, 30% at 800 nm and 15% at 740 nm so it would double as
your normal IR filter.

The filter factor for red filter used with IR film would be nearly zero. Since
it would nomally be there to get the IR effcts with the film, it is moot issue.
Also, it does not matter what order you put the filters on the lens.

Dave

paul schuster wrote:

> hello list!
>
> I recently received the maco IR 4x5.
> I have only exposed a couple of sheets.
>
> my question is:  are there any special considerations when using a polarizer
> and IR.  I stacked the filters (#25 red and the ploarizer).  I had heard it
> would only act as a neutral density filter when using IR (what I was going
> for).  I had the red on first and then the polarizer.  now normally, I would
> turn the ploarizer until I got the desired effect.  but I was unable to see
> much change through the red.  I guess next time I will put the polarizer on
> first and red last.
>
> the day was a bit hazy.  I had figured that if the polarizer did do anything
> it would naturally make my usually dark/black (actual blue) skies even
> darker.  but they are white on the resulting image?  could be the haze?
>
> also!:  is my math correct in my filter factor of 5.5?  a filter factor of 3
> for the 25 red, and 2.5 for the polarizer.  bringing my maco ISO 100 to
> around 3 or less ?
>
> this 4x5 IR ain't cheap!  I'm just trying to save some head ache and much
> needed $
>
> any suggestions would be much appreciated
>
> p.s. YES, I am trying to slow down the film as much as possible.  I am
> hoping for 3+ second exposures to blur all ambient movement, waves mostly
>
> paul schuster
> www.schusterphoto.com
>
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