Vadnais Engineering

I posted an example earlier illustrating the effects of using a polarizer and a fill flash on a car in a junk yard. In this post, you’ll see the effect of a polarizer on a large, slab-sided vehicle like a trailer or an RV.

Many people believe that polarizers are only effective on sunny days, and when the sun is at a 90° to the camera lens. But as these examples will show, a polarizer is just as effective in multiple directions on a heavy overcast day.

These images will also show that, just as on sunny days, the polarizer eliminated different amounts of reflected glare depending on the angle of the camera to the RV. As you will see when you look through and rotate a polarizer, the glare effectively moves around the scene. It’s up to you to decide what is the most important part of your image, and to rotate the polarizer until you eliminate the glare or get it just where you want it.

I inspected this RV in a salvage yard in Florida on a very cloudy day. [Click on the image to enlarge it, then click on the back arrow to return to the post.]

As with all of my vehicle photos, I used both a polarizer and a fill flash. In this image, you can see the thick overcast sky and the bright glare reflected on the side of the RV. I had the polarizer on my lens, but for illustration, I rotated it to minimize its effect. That’s what the RV looked like to the naked eye.

Keeping the camera and fill flash settings the same, I rotated the polarizer while looking through the viewfinder until I reduced the glare as I wanted. [Click on the image to enlarge it, then click on the back arrow to return to the post.]

As you can see, there was very little glare left along the side of the RV, which allowed its true colors to show through.

Moving around toward the 3/4 right rear position, I made another pair of photographs to illustrate the effect from a different angle. First the polarizer is minimized. Again, notice the reflections and the glare. [Click on the image to enlarge it, then click on the back arrow to return to the post.]

From this angle, I could not completely eliminate the glare regardless of how much I rotated the polarizer, so I chose the area where I wanted to eliminate the glare, and set it there. [Click on the image to enlarge it, then click on the back arrow to return to the post.]

From the right front, the side of the RV was again partially obscured by glare. [Click on the image to enlarge it, then click on the back arrow to return to the post.]

From this angle, I was able to rotate the polarizer into a position that eliminated the glare on both the right side and the front end. Notice how you can even see through the side windows now. [Click on the image to enlarge it, then click on the back arrow to return to the post.]

Here are the takeaways:

-1- Use a polarizer when you want to eliminate reflected glare off of vehicles.

-2- Use fill flash with a polarizer to bring out detail in vehicle photos.

-3- Polarizers are effective on overcast days when light is scattered everywhere. Polarizers are not just for sunny days.

-4- Polarizers can be effective at angles other than 90° to the light source.

-5- The only way to determine the best setting for a polarizer is to rotate it until it gives you the effect you want.

-6- Last but most important, you MUST rotate your polarizer before each shot to get the desired effects.

Except when making night photographs, I almost always use a polarizing filter (polarizer) when photographing accident sites. Rotating a polarizing filter removes glare and increases saturation relative to the angle of rotation.

Fortunately, to determine the amount of rotation you need for the effect you want, simply look through the polarizer (through the threaded side if you’re holding it, or through the viewfinder or rear LCD once it’s mounted on your lens) as you turn the outside ring. There are no settings or calculations or other analysis you have to do to get the effect you want. But, like polarized sunglasses, polarizing filters decrease the light, so you will have to adjust your exposure accordingly. Most polarizers require an additional one-to-two stops of exposure to compensate.

Speaking of sunglasses, make sure you remove your sunglasses—especially if they are polarized—before looking through your polarizer. Otherwise, you won’t be seeing the actual effect of your filter. In fact, if they line up, you won’t see anything; it will all go black.

While a polarizer will take the glare off of roads, grass, and trees at accident sites, it has its greatest effect on tire marks. In this first image, you can tell there are multiple tire marks on the road, but they lack definition. The photograph is properly exposed, but glare obscures any detail. (Click on an image to enlarge. Click on back arrow to return to this post.)

For this second image, I attached a polarizer to the front of the lens, and rotated it until I got the maximum detail in the tire marks. I had to brighten the exposure to compensate for the light lost with the polarizer. This is rarely an issue when your camera is on a tripod, but if your polarizer loses two stops of light, it might be difficult to keep the shutter speed high enough to handhold the camera.

This photograph obviously shows much more detail than you could ever extract from the first image. This increase in detail from reduction of glare is what makes a polarizer one of the three most important accessories for automotive forensic photography, along with flash and a tripod.

It’s important to remember to rotate the polarizer between each shot, and to compensate for any light loss by adjusting your exposure. It is also important to remember that a polarizer is the only filter whose effects you can’t replicate in post-processing.