Using Circular Polarizing Filters for Digital Infrared Photography

Using Circular Polarizing Filters for Digital Infrared Photography

Hi All,

I've been experimenting with using a circular polarizing filter when
shooting digital infrared images:
* w w w .dimagemaker . com /article.php?articleID=1053

Cheers,

Wayne
--
Wayne J. Cosshall
Publisher, The Digital ImageMaker, * w w w .dimagemaker . com /
Blog * w w w .digitalimagemakerworld . com /
Publisher, Experimental Digital Photography
* w w w .experimentaldigitalphotography . com
Personal art site * w w w .cosshall . com /

Re: Using Circular Polarizing Filters for Digital Infrared Photography

Wayne J. Cosshall wrote:
> Hi All,
>
> I've been experimenting with using a circular polarizing filter when
> shooting digital infrared images:
> * w w w .dimagemaker . com /article.php?articleID=1053
>

Can Digital HDRIR be far behind?

Ever tried using a pair of crossed linear polarizers? As you approach 90
degrees, the spectrum of light that makes it through apparently gets
weighted toward the red and IR. Not an appealing prospect to add these
to a filter stack, and the pair didn't substitute well for the IR pass
filter, but I was amused anyway.

Observed with unmodded Sony F828 in "nightshot" mode. Crossed linear
polarizers stacked with IR pass filter, in an attempt to reduce the need
for additional ND filters. (Yeah I know, I should just go get the thing
modded)

Imagine my surprise when I saw the IR target scene not fade at all as I
approached 90 degrees.

Several filters have unexpected effects when used outside their intended
spectra. A Hoya X1 *green* filter is more effective at attenuating IR
than yer basic 2 or 3 stop ND filter.

YMMV. HTH. HAND.
C.

--
It Came From Corry Lee Smith's Unclaimed Mysteries.
* w w w .unclaimedmysteries . net

In a time of deception telling the truth is a revolutionary act. -
George Orwell

Re: Using Circular Polarizing Filters for Digital Infrared Photography

On Aug 4, 1:30 am, Unclaimed Mysteries
<theletter_k_andthenumeral_4_...@unclaimedmysteries . net > wrote:
> Wayne J. Cosshall wrote:
> > Hi All,
>
> > I've been experimenting with using a circular polarizing filter when
> > shooting digital infrared images:
> > * w w w .dimagemaker . com /article.php?articleID=1053
>
> Can Digital HDRIR be far behind?
>
> Ever tried using a pair of crossed linear polarizers? As you approach 90
> degrees, the spectrum of light that makes it through apparently gets
> weighted toward the red and IR. Not an appealing prospect to add these
> to a filter stack, and the pair didn't substitute well for the IR pass
> filter, but I was amused anyway.
>
> Observed with unmodded Sony F828 in "nightshot" mode. Crossed linear
> polarizers stacked with IR pass filter, in an attempt to reduce the need
> for additional ND filters. (Yeah I know, I should just go get the thing
> modded)
>
> Imagine my surprise when I saw the IR target scene not fade at all as I
> approached 90 degrees.
>
> Several filters have unexpected effects when used outside their intended
> spectra. A Hoya X1 *green* filter is more effective at attenuating IR
> than yer basic 2 or 3 stop ND filter.

Why use any of that junk when you can buy interference filters that
have almost dead-stop cutoffs at any wavelength you'd like? You can
get cutoff filters, narrow band filters or even notch filters, all
with steep attenuation and throughput.

>
> YMMV. HTH. HAND.
> C.
>
> --
> It Came From Corry Lee Smith's Unclaimed Mysteries. * w w w .unclaimedmysteries . net
>
> In a time of deception telling the truth is a revolutionary act. -
> George Orwell

Re: Using Circular Polarizing Filters for Digital Infrared Photography




"Wayne J. Cosshall" <wayne@dimagemaker . com > wrote in message news:46b4066b$0$30511$afc38c87@news.optusnet . com .au...

> I've been experimenting with using a circular polarizing filter when shooting digital infrared images:
> * w w w .dimagemaker . com /article.php?articleID=1053
> Wayne

Interesting results. When I use my old Sony TRV9 (FS, BTW,
in very nice low-use condition...) Mini-DV camcorder (mine is
daylight IR enabled) with an IR filter, I also generally add a
circular polarizer, which gives a little more control over the
image, as you found. Some samples shot from a car are at
w w w .donferrario . com /ruether/ir.htm
--
David Ruether
d_ruether@hotmail . com
* w w w .donferrario . com /ruether

(see our "restaurant menu", at w w w .donferrario . com /ruether/menu.htm)

Re: Using Circular Polarizing Filters for Digital Infrared Photography

Good shots. I have a TRV9, I have to look into getting it converted or
modified.

Cheers,

Wayne

Wayne J. Cosshall
Publisher, The Digital ImageMaker, * w w w .dimagemaker . com /
Blog * w w w .digitalimagemakerworld . com /
Publisher, Experimental Digital Photography
* w w w .experimentaldigitalphotography . com
Personal art site * w w w .cosshall . com /



David Ruether wrote:
> "Wayne J. Cosshall" <wayne@dimagemaker . com > wrote in message news:46b4066b$0$30511$afc38c87@news.optusnet . com .au...
>
>> I've been experimenting with using a circular polarizing filter when shooting digital infrared images:
>> * w w w .dimagemaker . com /article.php?articleID=1053
>> Wayne
>
> Interesting results. When I use my old Sony TRV9 (FS, BTW,
> in very nice low-use condition...) Mini-DV camcorder (mine is
> daylight IR enabled) with an IR filter, I also generally add a
> circular polarizer, which gives a little more control over the
> image, as you found. Some samples shot from a car are at
> w w w .donferrario . com /ruether/ir.htm

Re: Using Circular Polarizing Filters for Digital Infrared Photography



>> "Wayne J. Cosshall" <wayne@dimagemaker . com > wrote in message news:46b4066b$0$30511$afc38c87@news.optusnet . com .au...
> David Ruether wrote:
"Wayne J. Cosshall" <wayne@dimagemaker . com > wrote in message news:46b5130f$0$15276$afc38c87@news.optusnet . com .au...

>>> I've been experimenting with using a circular polarizing filter when shooting digital infrared images:
>>> * w w w .dimagemaker . com /article.php?articleID=1053
>>> Wayne

>> Interesting results. When I use my old Sony TRV9 (FS, BTW,
>> in very nice low-use condition...) Mini-DV camcorder (mine is
>> daylight IR enabled) with an IR filter, I also generally add a
>> circular polarizer, which gives a little more control over the
>> image, as you found. Some samples shot from a car are at
>> w w w .donferrario . com /ruether/ir.htm
>> --David Ruether

> Good shots. I have a TRV9, I have to look into getting it converted or modified.
>
> Wayne

Any of the Sony 1-CCD camcorders can be modified to prevent the
IR switch from also forcing the camera to widest aperture and too
slow a shutter speed for daylight IR video (first installed in late TRV9s
due to Sony's silly prudery and the myth of "x-ray" vision for the
camera - but fortunately, mine is an earlier version, and not hobbled
by this nonsense). One day I tried it outdoors, and it worked fairly
well, so I added a red filter, and it worked better yet. A polarizer
improved the results further, and finally replacing the red with an IR
filter worked very well. I use the camera in B&W mode to lose the
"tooth paste green" look...;-) BTW, I prefer IR in motion to stills
(it is just plain more fun - and somehow less "hokey" looking...).
--
David Ruether
d_ruether@hotmail . com
* w w w .donferrario . com /ruether

Re: Using Circular Polarizing Filters for Digital Infrared Photography

Wayne J. Cosshall wrote:
>
>> "Wayne J. Cosshall" <wayne@dimagemaker . com > wrote in message
>> news:46b4066b$0$30511$afc38c87@news.optusnet . com .au...
>>
>>> I've been experimenting with using a circular polarizing filter when
>>> shooting digital infrared images:
>>> * w w w .dimagemaker . com /article.php?articleID=1053
>>> Wayne
>>

A few remarks, FWTW. There are two different influences affecting the
final results in your IR pictures. A circular polarizer consists of two
filters: a linear polarizer followed by a quarter-wave retarder. Neither
of these is fully achromatic, that is, they only have a limited
wavelength range over which they are fully effective. Outside its range
the linear polarizer will have decreasing effect in polarizing light,
and outside its range the retarder will convert less of the lineraly
polarized light to circular. Both tend to start failing rather badly as
you go into the IR, so I would expect diminished affect by rotating the
filter in the IR. How much depends on the specific polarizer and could
change with maker.

For my research I had achromatic polarizers and retarders fabricated
that worked from the UV to the IR, but they were very expensive. Normal
ones made for cameras start losing there effectiveness in the blue and
the red, only working well in between.

Joe

Re: Using Circular Polarizing Filters for Digital Infrared Photography

Hi Joe,

Thanks for that input. Makes perfect sense and With my Hoya filters I
was seeing more effect visually than the camera was.

Where do you go to get these custom filters made?

Cheers,

Wayne

Wayne J. Cosshall
Publisher, The Digital ImageMaker, * w w w .dimagemaker . com /
Blog * w w w .digitalimagemakerworld . com /
Publisher, Experimental Digital Photography
* w w w .experimentaldigitalphotography . com
Personal art site * w w w .cosshall . com /



Joseph Miller wrote:
> Wayne J. Cosshall wrote:
>>
>>> "Wayne J. Cosshall" <wayne@dimagemaker . com > wrote in message
>>> news:46b4066b$0$30511$afc38c87@news.optusnet . com .au...
>>>
>>>> I've been experimenting with using a circular polarizing filter when
>>>> shooting digital infrared images:
>>>> * w w w .dimagemaker . com /article.php?articleID=1053
>>>> Wayne
>>>
>
> A few remarks, FWTW. There are two different influences affecting the
> final results in your IR pictures. A circular polarizer consists of two
> filters: a linear polarizer followed by a quarter-wave retarder. Neither
> of these is fully achromatic, that is, they only have a limited
> wavelength range over which they are fully effective. Outside its range
> the linear polarizer will have decreasing effect in polarizing light,
> and outside its range the retarder will convert less of the lineraly
> polarized light to circular. Both tend to start failing rather badly as
> you go into the IR, so I would expect diminished affect by rotating the
> filter in the IR. How much depends on the specific polarizer and could
> change with maker.
>
> For my research I had achromatic polarizers and retarders fabricated
> that worked from the UV to the IR, but they were very expensive. Normal
> ones made for cameras start losing there effectiveness in the blue and
> the red, only working well in between.
>
> Joe

Re: Using Circular Polarizing Filters for Digital Infrared Photography

Wayne J. Cosshall wrote:
> Hi Joe,
>
> Thanks for that input. Makes perfect sense and With my Hoya filters I
> was seeing more effect visually than the camera was.
>
> Where do you go to get these custom filters made?
>
> Cheers,
>
> Wayne
>
> Wayne J. Cosshall
> Publisher, The Digital ImageMaker, * w w w .dimagemaker . com /
> Blog * w w w .digitalimagemakerworld . com /
> Publisher, Experimental Digital Photography
> * w w w .experimentaldigitalphotography . com
> Personal art site * w w w .cosshall . com /
>

The custom filters would not work with normal cameras. They are quite
bulky, fragile, and can require careful alignment. I'm an astronomer and
use them on very big telescopes (e.g., the Keck Telescopes) to measure
polarization of faint astronomical objects.

Joe

Re: Using Circular Polarizing Filters for Digital Infrared Photography

Ah, so you are a professional photographer. You should have said. I
almost went into astrophysics but went into computer science instead.

Cheers,

Wayne

Wayne J. Cosshall
Publisher, The Digital ImageMaker, * w w w .dimagemaker . com /
Blog * w w w .digitalimagemakerworld . com /
Publisher, Experimental Digital Photography
* w w w .experimentaldigitalphotography . com
Personal art site * w w w .cosshall . com /



Joseph Miller wrote:
> Wayne J. Cosshall wrote:
>> Hi Joe,
>>
>> Thanks for that input. Makes perfect sense and With my Hoya filters I
>> was seeing more effect visually than the camera was.
>>
>> Where do you go to get these custom filters made?
>>
>> Cheers,
>>
>> Wayne
>>
>> Wayne J. Cosshall
>> Publisher, The Digital ImageMaker, * w w w .dimagemaker . com /
>> Blog * w w w .digitalimagemakerworld . com /
>> Publisher, Experimental Digital Photography
>> * w w w .experimentaldigitalphotography . com
>> Personal art site * w w w .cosshall . com /
>>
>
> The custom filters would not work with normal cameras. They are quite
> bulky, fragile, and can require careful alignment. I'm an astronomer and
> use them on very big telescopes (e.g., the Keck Telescopes) to measure
> polarization of faint astronomical objects.
>
> Joe

Re: Using Circular Polarizing Filters for Digital Infrared Photography

Wayne J. Cosshall wrote:
> Ah, so you are a professional photographer. You should have said. I
> almost went into astrophysics but went into computer science instead.
>
> Cheers,
>
> Wayne
>
> Wayne J. Cosshall
> Publisher, The Digital ImageMaker, * w w w .dimagemaker . com /
> Blog * w w w .digitalimagemakerworld . com /
> Publisher, Experimental Digital Photography
> * w w w .experimentaldigitalphotography . com
> Personal art site * w w w .cosshall . com /
>

I actually did partly work my way through college as a professional
photographer in an observatory, but with film and and a large darkroom.
I'll take digital any day. We closed all the darkrooms in our
observatory many years ago. I don't do much, if any, direct imaging, but
primarily spectroscopy, which is of course taking images of spectra. We
have our own CCD fabrication lab and are now working on a 4K x 4K device
with 15 micron pixels- it's big. We have made mosaics of 8 2K x 4K
devices that work very well (64 mp!), but each CCD cost around $100K.
Even the CCD controllers we build can cost upwards of $100K, but that's
part of the price of getting below 2 electrons read noise with a fast
read out. I say all this as background to how impressed I am by what you
can buy for a few hundred dollars. The technology in even an inexpensive
P&S still amazes me, maybe because I know how hard to do this stuff can
be. There's nothing like mass production to bring the cost down. Our
problem is that almost everything we build is a one-off. There are
probably less than 100 CCDs in the entire world, maybe less than 10,
that we would consider suitable for a recent instrument we delivered.

Joe