Teotihuacan and using a CPL/Polarization

[manual_focus]

I recently toured the great pyramids north of Mexico City on a high overcast sunny day. I almost always use a CPL outdoors and tried shooting the same scene with no/little polarization (resulted in a more homogeneous light blue sky) and full polarization (which gave me better colors overall and a bluer sky with clouds).

I thought it might be informative to see the differences of reducing the stray, mostly blue light (full polarization) from the normal light (no polarization) produces.

I've combined the images into one with the no polarization on top and the full polarization on the bottom. Both shots were with a high quality CPL but the polarization was 90 degrees to each other. This eliminates any color shift introduced from the CPL which is minimal. The images were shot with the DA* 16-50mm f/2.8 PLM lens on a K3III. Both images were brought into SilkyPix 11 so that I could get an accurate histogram along with the color temperature of the original camera Auto White Balance used. The color temperature was almost the same for both. No polarization had a temperature of 5,255oK and with full polarization a color temperature of 5,149oK. The only difference between the two images was the exposure as the full polarization resulted in much less blue light. No Polarization exposure was 1/1600 sec and full polarization was 1/800 sec. I made almost no changes to the RAW images except to keep from reaching a RGB value of 255 in any part of the scene. A minor (-0.2) decrease in exposure for each.

The images speak for themselves.

View attachment 0f5ddd43e0b24ea0a38100433b5ca47a.jpg
Taken with DA* 16-50,, f/2.8 PLM . [Exposure: Top 1/1600 sec. Bottom: 1/800 sec]

Here's where it gets interesting. I screen captured the Histograms from each original image and combined them the same as the actual images. The histogram with no polarization (Top) has a very pronounced blue component of 246 which shows up in the image as the blue sky right above the pyramid. With full polarization all the RGB values in the sky are reduced significantly and the highlights that set the exposure are the whites in the scene. These are the mostly the plaster on the walls of the rooms on the lower left and the grout lines of the stonework.

I thought this might help people visualize what a CPL does and how it influences a scene when it greatly reduces the scattered and blue light from the sky.

Enjoy!





From the RAW images using SilkyPix 11 [Top: No polarization. bottom: Full Polarization]

 

[RBIV]

Interesting comparison. I notice the foreground (pavement, monument, and shaded areas) are slightly lighter in the polarized version. Is that caused by the polarizer, or maybe the slight difference in exposure, or PP?

Whatever, it certainly renders the sky better imo.

 

[manual_focus]

Interesting comparison. I notice the foreground (pavement, monument, and shaded areas) are slightly lighter in the polarized version. Is that caused by the polarizer, or maybe the slight difference in exposure, or PP?

Whatever, it certainly renders the sky better imo.

No PP was used. I would say it is a combination of both polarization and exposure used.

I took the image with no polarization and increased the exposure so that the grass etc had the same RGB values. This required about a +0.8 exposure (f stop) increase. When you look at the three histograms you can see that adjusting the exposure of the top image simply moves the RGB values to the right on the histogram. It does not result in the same histogram as with full polarization (bottom image). The blue channel in the sky goes to 254 and beyond. While the overall exposure is closer its still not the same. The elimination of stray and blue light from the use of full polarization is more than just exposure, i.e., it would be difficult to impossible to adjust an image with no polarization to make it look like one with full polarization.

Functionally, you have a high contrast scene with a slight blue cast as a result of having all that stray non-polarized light bouncing around, especially in the sky. It results in a scene that is just beyond the sensors ability to fully capture it. The use of a CPL significantly reduces the contrast giving what I believe is a better balance to the entire scene. YMMV.

Thanks for the comments.




Top: No polarization and camera exposure:: Middle: No polarization with +0.8 exposure:: Bottom: Full polarization