Polar filter

[Stephen Hunter]

Hi, I never have problems when shooting 5x4 transparency without my polar filter but every shot I have done with the filter on I have had dark areas on the film , these dark areas normally come from only one corner and fade as they come to t he centre of the film, even without camera movement. I bought a new polar filter last week as I thought it was that filter at fault but the problem is still the re though not as bad. Like I say there is never a problem when I dont use the po lar filter. this has puzzled everyone from the lab, fellow photographers and other professio nals.... any ideas?

[Wayne_6692]

What focal length lens are you using? Since the polarizing effect is dependend upon the angle at which the light is striking the subject, and with a shorter focal length lens this angle will vary greatly across the field, uneven densities are to be expected with shorter focal length lenses. Either that, or vignetting has to be the culprit.

[Stephen Hunter]

I use a 150mm & 90mm, I have even used an oversized filter held infront and against the lens, still the same......I have looked through these pages and see others have had the same problem, I thought it may be the way a polar filter works and it appears that is it really, smaller formats no problem but 5x4 uneven exposurer problems

[Ellis Vener]

You are probably seeing the fall off mostly with the 90mm , right? If this is the case then you need to understand that the the physics of polarization mean that the light coming into the lens can only be completely polarized over a certain angle. theangles that are completely or mostly polarized will be darker than the other areas. I assume you are rotating the filterto get the best effect for the photograph you are making.

My opinion is that polarizing filters are the most over used and least understood filters photographers use. I have over $500.00 tied up in some very high grade polarizers and very rarely use any of them.

[Jorge Gasteazoro]

It seems to me you dont have your front or back standard centered. If the dark area was in all four corners then your lens did not have enough coverage or the filter'r rim was blocking the image, but since you have it only in one area, I think it is the problems I mentioned before. SInce you don't mention what camera you use, you will have to go check. Take care and good luck.

[Stephen Hunter]

Thank's for your replies, conclusion is as pointed out that the polar filter only allows light to enter at a certain angle so as not covering the whole sheet of film evenly when using a 90mm or 150mm lens especially if if the front plate is moved or tilted, solution is now I dont bother with polar filters for transparenies, if i want dramatic sky's I use print film & hand print or red/orange filters with B&W transpareny or negative film. I could always use photoshop but when it comes to 5x4 I am a purist. Cheers