Weird Interference Patterns Using Lee Polyester Filters

[Andre Noble]

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

[Philippe Gauthier]

I never used these filters and therefore, never encountered the same problem, but when you described the interference patterns you got, it just sounded as Newton rings to me. OK, Newton rings normally occur when two flat surfaces are in close contact, but how far is your filter from your lens anyway? Given that polyester is quite flexible, is it possible that some wind could cause contact?

Just a thought...

[Michael S. Briggs]

My memory is that the directions that come with the Lee/Calumet thin polyester filters instruct one not to use them behind a polarizing filter. This is because some plastics partially polarize transmitted light, especially when stressed. If you view these plastics when stressed (e.g., stretched) with polarized light you can see interesting colored patterns because the polarization varies with the wavelength of the light. This is sometimes used to study stress patterns in engineering models. Of course, you are not using a polarizing filter. However, the directions that you describe relative to the sun are directions in which the natural polarization of skylight is near its maximum (e.g., see http://www.polarization.com/compass/compass2.html). Perhaps this partial natual polarization of skylight is sufficient to interact with the small degree of polarization created by polyester to show up in your photos. If so, the mystery is why you have this problem and so few other people do. I have used these thin polyester filters and never had a problem. Does your method of holding the filters stretch them or otherwise introduce stresses?

[Ernest Purdum]

I also thought of polarization as I read the question. Cellophane has a crystal-like structure which derives, I think, from being rolled under pressure during the process by which it is made. Maybe something in the manufacture of the polyester filters is causing a similar result.

[Andre Noble]

Thanks Philippe and Michael.

Phillipe, you are correct in that the images does look exactly like a Newton ring type phenomenon, despite there being no physical contact of the filter with any other surface whatsoever.

Michael, I suspect the reason I am getting the problem and few (but some) others have, relates to the angle of light as it passes through the filter. The problem is apparent when shooting my super wide 20mm lens in the 35mm format, or when using my 90mm Nikkor on the 4x5 for architecture when the image circle is shifted in order to take in the scene of a tall building, for example.

Unfortunately, architectural shots requiring shift , or expansive wide angle landscapes is not a special circumstance with the type of photography I do.

P.S., I have also ruled out mechanical deformation as the problem because it occured on numerous new Lee polyesters- while mounted in Lee filter holders displaying no physical deformations.

Furthermore, the interfernce pattern was very similar in the 5 Lee polyester filters I tried such as 05CC Green, 85B Color Temperature, and Magenta CC filters.

Specifically, on the 20mm Nikkor shots, it appeared as two multicolored/multiconcentric circles about 15 or 20 mm apart from each other in the upper 1/3 of the frame. These circles rotated around the frame as I rotated the filter.

In the 90mm Nikkor shots, it appeared somewhat differently: The interference pattern appeared as an inverted rainbow, swooping down the upper quater portion of architectural shots. The pattern was very similar as well using 3 different Lee Polyester filters for black and white film.

[Struan Gray]

Polyester film is usually birefringent, so using polyester filters with polarised skylight could well produce these effects. It is similar to how you can sometimes see the stress patterns in a car's windscreen even when not wearing polarised sunglasses.

Working at large angles makes it more likely that you will include a bit of the sky with a high degree of linear polarisation, and enhances the effects of multiple reflections back and forth inside the film.

You can confirm that this is your problem by putting a linear polariser in front of the polyester filter and pointing it at a diffuse lightsource like a light box or a white wall. You should see the same patterns. If you have a circular polariser, hold it reversed or the patterns will be almost certainly be different to the ones you see with skylight.

If the filter's response to polarised light is the problem, your only hope is to switch to resin or gel filters.

[Steve Lewis]

so using polyester filters with polarised skylight could well produce these effects

I had exactly the same problem a few years ago, and, after consulting with Lee, they confirmed that using polyester filters with a polariser is likely to produce these effects. HTH

Steve Lewis

www.landscapesofwales.co.uk

[Philippe Gauthier]

Your theories about the PL filter being the problem are very interesting (good thing to know) but please André's question carefully: he says he gets the problem even when he uses the filters alone, not in conjunction with a PL or anything else.

My feeling, if there's no contact even in windy conditions, is that the problem is somehow refraction related. Must be a problem with the high angles between the wide glass and the filter, and the different refraction indexes of both. But it's just a guess and someone better versed in optics will probably know better.

[John O'Connell]

I use these same filters, and I remember there being specific instructions with them not to use them with a polarizer or some kind of ugly pattern would appear. I have, however, taken an awful lot of exposures with the yellow polyester filter on the Nikon 20mm which included large expanses of blue sky, and have never noticed this. I assume I've merely been lucky.

Are you using a holder that puts them under a lot of tension? Are these recently purchased filters, or fairly old? (Mine are about three years old).

Best of luck, and I'm sorry to hear that I may have three problem sheets of film waiting to be developed...

[Andre Noble]

Thank you Phillipe for helping to clarify! And also thank you to everyone else for taking your best stab at it too.

1) I am NOT using a Polarizing filter of ANY kind.

2)There is no filter contact with lens surface. There is no mechanical stresses. (Filter taught and smooth as a drum). Problem observed whether filter in Lee holder or held by hand in front of lens.

3) Interference patterns were of a very, very similar type and location across filter types on a given lens. (This helps to rule out (2) as cause). They rotate around as I rotate the filter around.

4) They are not due to simple internal reflection of skylight of filter surface and lens element because the bulleye's rotate in perfect unison as you rotate the filter while keeping lens steady.

Technically, I find it very interesting because of the uniformity of the patterns - on the Nikon 20mm, they look like 2 multicolored bull's eyes across 5 different Lee polyester filter types, for example.

In my haste, I sent all sample slides and negs to Lee Filters in U.K. (They have not gotten back to me with a satisfactory response yet.) So I don't have scans to post. Anyway, I know it's 'no more' polyester filters for me. Too bad because they're a lot less expensive than the Kodak gels.