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Lee Polyester Filter, Problems


andre_noble3

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I am having problems with the Lee polyester filters. I am getting

weird circular rainbow/banding/interference type patterns across my

images when using them with wide angle lenses.

I was able to isolate this problem to the polyester type filters

themselves. For example, I get banding in both the 4x5 Polaroid and

4x5 traditional negatives when using the Lee 23A Red and Lee 21

Orange, but not in an identical scene taken with corresponding B&W

glass filters shot at the same moment. Furthermore, the polyester

filters where used singly - not in conjunction with a polarizer or

any other filter.

 

The problem appears limited to use with wide angle lenses.

(Unfortunately, much of my own photography involves these

parameters). At time of use, there was no direct sunlight striking

either the filter or the filter holder which my have caused unwanted

reflections. Furthermore, the problem seems to relate to the angle in

relation to the sun at which the image is taken. The camera was

pointed appx. 180° away from the sun in the 35mm slides using a 20mm

lens, and approximately 90° away from the sun in the large format

images using a 90mm Nikkor f/8 lens and front rise. Finally, rotating

only the filter caused the �interference pattern� to rotate around

inside the viewfinder in kind.

 

I also visualized the same problem with other Lee Polyester filters

such as the Colour Temperature set.

 

After a couple phone calls to Lee Filters in England, they deny

having ever experienced such problems before despite possible

evidence such as this thread on Photonet:

 

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=005bh7

 

Anyone else have a similar experience with these (or their Calumet

equivalents)? Note: I am specifically referring to the thin Lee

Polyester filters. I do not mean the thicker Lee resin filters, nor

am I referring to the thin Kodak gel filters, which are both

manufactured using a different technology than the polyester type

filters.

 

Thanks in advance for any input you can share.

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<p>My memory of the instructions that come with the Lee thin polyester filters is that the instructions warn against using the filters on one side of a polarizing filter. Of course, you aren't using a polarizing filter, but this warning is a clue that the polyester filters can be birefringent. When certain plastics are stressed, or from stress created in the plastic when the item was made, they become birefringent, which means that two polarizations of light have different refractive indices in the glass.</p>

 

<p>Skylight is naturally polarized in some directions. In fact, the two directions that you describe are consistent with directions of maximum polarization. It is normally stated that the polarization is maximum at 90 degrees from the sun -- this could be 90 degrees to the side -- this could be one of your cases. Maximum polarization can also occur at 180 degrees in azimuth from the sun, but above the horizon by an angle that makes the patch of sky 90 degrees from the sun -- this could be your second case. See <a href="http://www.polarization.com/compass/compass2.html">http://www.polarization.com/compass/compass2.html</a>.

So I think this is a second clue that your colors are from some polarization phenomena.</p>

 

<p>The phenomena of birefringence in plastics is best observed with two polarizers, one in front of the plastic to polarize the light transmitted through the plastic, and a second after the object to analyze the light. In your case, the partially polarized skylight may take the role of the first polarizer. I can't explain why you are seeing the effect without a polarizer after the polyester filter, nevertheless, from the clues I suspect that polarization and birefrigence is involved.</p>

 

<p>Here are some explanations and example photos of stress birefrigence in plastics observed with polarized light: <a href="http://www.oberlin.edu/physics/catalog/demonstrations/optics/birefringence.html">http://www.oberlin.edu/physics/catalog/demonstrations/optics/birefringence.html</a>, <a href="http://www.devicelink.com/mddi/archive/99/03/008.html">http://www.devicelink.com/mddi/archive/99/03/008.html</a>, <a href="http://www.devicelink.com/mpb/archive/97/01/001.html">http://www.devicelink.com/mpb/archive/97/01/001.html</a> and <a href="http://www.fas.harvard.edu/~scdiroff/lds/LightOptics/Photoelasticity/Photoelasticity.html">http://www.fas.harvard.edu/~scdiroff/lds/LightOptics/Photoelasticity/Photoelasticity.html</a>.

Does the effect you see look similar?</p>

 

<p>From this analysis, one shouldn't use a polyester filter in front of polarizing filter, because skylight could act as a source of polarized light and the polarizing filter could act as the analyzer, producing a colorful display of birefrigence.</p>

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This is exactly what is happening with my Lee polyester filters. The patterns in my photos look VERY simlar to the patterns in the protractor below. I will develop my remaining roll and post some actual examples later.

 

A key quote from the Oberlin page states, "The protractor shows colored bands without being deformed because anisotropies arise when the plastic solidifies when manufactured. The colored patterns

reveal internal stresses."

 

Thank you Michael for taking the time to research the issue.

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