I photograph paintings.What is the difference between circular and standard pola

Question:

I photograph paintings.What is the difference between circular and standard polarizing filters?

I use a standard polarizing filter on my film camera and a circular polarizer on the digital camera. The specular highlights and flair are always grreater on the digital images. PS. I also polarize my lights.

Best Answer - Chosen by Asker: I think the first thing you need to know is what a polarizing filter does. A polarized lens basically has microscopic lines that filter extraneous light. This is why you can get rid of glare and reflections because the lens only allows only a set direction of light (for instance only allows vertical or horizontal light through). But unlike a neutral density filter, you lose only extraneous light and not a lot of desired light.

Now the difference between a regular polarizing filter and a circular polarizing filter is that the regular has the microscopic lines going in one direction (again, like vertical or horizontal stripes). The circular polarizing filter has concentric circles of lines. This is only important for auto-focus lenses. If you used a regular polarizing filter, the moment the lens shifted (circular motion) for focus, the light-waves have changed and now the auto-focus is lost. However, with a circular polarizing filter, regardless of how much the focus ring turns, the light is always the same and this allows the auto-focus to continually function.

Here's the fun part. You can see for yourself what a polarizing filter does. Take 2 REGULAR polarizing filters and place one on top of each other. If you twist one of them, you should be able to see clearly through both of them. Now continue to twist and soon you won't be able to see through at all. This is because one filter is filtering one direction of light and the other is filtering out another. So when they are aligned, you can see through. But when they're opposing, they're blocking all directions (both horizontal and vertical). If you use 2 circular polarizing filters, you won't get the opacity because they're always aligned when on top of each other.

If you polarize your lights, you're already filtering one direction of the light. That's probably why when you use your circular polarizer, less of the extraneous light is being filtered. With the regular polarizing filter, most of the time you're probably filtering multiple directions of light; hence reducing more glare.