I’ve written before that it’s generally a bad idea to use a polarizer filter when shooting for stitched panoramas. I thought I’d put together some practical examples to illustrate why. It’s basically the same problem you can face when using a polarizer on a very wide angle lens, but amplified.
The gist of the problem is that a polarizer filter acts in a very specific way to the angle of light. Change the angle by a few degrees and you can get a dramatically different polarizing effect. Across the span of a panorama, that can create very distinct banding in the sky, with dramatic differences between light and dark areas where we’d normally expect smooth tones. And it’s something that’s very, very hard to clean up in a convincing way after the fact.This is most obvious on areas that we normally expect to be smooth gradations. Clear blue skies, for example. Or expanses of still water. You can still get the same effect without those elements in the frame, but it can be far less noticeable. So it’s not necessarily a hard and fast rule that you can’t use a polarizer when shooting panoramas–just that there’s a risk work recognizing before you get home and try to stitch the images together.
Here are a couple of examples of what I mean. The effect isn’t the result of a low quality filter–these are all shot with a high-quality B+W Kaesemann Circular Polarizer. And it’s not a problem of different exposures between frames–all of the frames that make up each stitched panorama used exactly the same exposure settings. It’s simply from the way that these filters work in relation to the angle of light.
To highlight the problem, I’ve deliberately shot this on a day with clear blue skies. So these are kind of worst-case examples, but they give a good illustration of what to avoid.
None of this is to say that polarizer filters can’t be exceptionally useful–just that they’re not well suited to shooting panoramas in many situations.
What About Graduated Neutral Density Filters?
If you’re looking to darken the skies when shooting a panorama, one option is to use a graduated neutral density filter (also known as grad ND filter). These are darker at the top than the bottom (or the other way around, if you prefer). These can be used successfully when shooting panoramas, but it’s quite critical that you make sure that the filter is level and that the camera’s rotation is equally square. Otherwise you can end up with ugly mismatches when you go to stitch the images together.