View Full Version : Polarizer - Effect on Negative Density

Brian Ellis
19-Oct-2005, 15:10
This is one of those elementary things I think I knew at one time but have since forgotten. I recently made some color photographs in Oregon with a lot of sky in the scene. I used a polarizer on all the exposures with three different lenses, 150, 210, and 300. A lab developed the negatives. On all of the negatives the sky is almost a full stop darker on one side than on the other. I am reasonably certain that the polarizer caused this but I wasn't using a wide angle lens and I can't remember why just using a poarizer on lenses this long had that effect. Could someone please refresh my memory?

Brian Vuillemenot
19-Oct-2005, 16:44
If you are shooting at a right angle to the sun, you will get uneven polarization of the sky if you are not careful. Although the effect is most pronounced for wide angle lenses, it is present in all lenses you use a polarizer on.

19-Oct-2005, 19:15
It helps to previsualize the polarizing effect by looking through the polarizer in various positions before placing it on the lens. FWIW, one does not need to use the GG for previsualization of polarization. Look at the view through the filter from beside the lens, note the position marking, place it on the lens in accord - or NOT. There's a whole lot you DON'T need to see on the glass, if you have the experience or confidence, but that's a different thread.

ronald moravec
20-Oct-2005, 00:45
I`m told it happens specially with wides, but I never noticed it.

Polorization is strongest when you are at right angle to the sun`s rays, even if the sun is directly overhead. When a larger angle is photographed, the difference shows.

Struan Gray
20-Oct-2005, 01:13
If you have a full stop difference for the 150 shot, and you simply replaced lenses without re-framing, then the photos with longer lenses should have less falloff. If you changed the direction of the camera's axis (i.e. the centre of the photos) the falloff won't necessarily change by as much, but is should still get less.

I would't rule out vignetting.

Brian Ellis
20-Oct-2005, 09:36
Thanks for the responses, the change in polarization when at a right angle to the sun is what I was trying to remember. Just to clarify, I wasn't standing in the same spot and using different lenses, I was using the different lenses in the same general area but at different spots. The subject, BTW, was the Painted Hills section of the John Day Fossil Monument in central Oregon, which I learned about from this group. Thanks to whoever mentioned it to me, it was a great location for color photography.