Just like most serious (and some semi-serious) photographers I own a few filters. Sure, it is quite easy these days to “fix” a lot of problems in Photoshop, Lightroom, etc. but still there are things that can’t be quite simulated in software. Or they can but it is sometimes easier/faster to do everything “in camera”. So, what do I have in my bag: a bunch of neutral, graduated Singh-Ray filters (both: hard- and soft- edge), a few polarizers and a 10 stop filter. What I noticed (along with many fellow photographers) was that some of them are not exactly “neutral”. In other words, they introduce some color cast, which in most cases needs to be “fixed” in post.
With that in mind, I decided to do a simple experiment. I shot a mid-gray target (Lastolite EzyBalance 18%) using various filters in two different light environments (shade and sunlight). As a point of reference, I also included a shot of the target without any filter. All photos were taken using fixed White Temperature of 5500 K. Once the images were uploaded into Lightroom, I used White Balance Picker to correct the cast. The filters that were used in this test were: Singh-Ray Gold/Blue Polarizer, B+W 10 Stop Neutral, Heliopan SH-PMC Polarizer and B+W Slim Kassman Polarizer. The spreadsheet below summarizes the results:
“Delta” that you see in the table is a straight difference between a given filter and “no filter” shot. “G/B Yellow” means that the polarizer was turned to render highlights Gold. Similarly, “G/B Blue” means that it was turned to render highlights Blue.
So, what do we see here ? First of all, as expected both Heliopan and B+W “Grey” Polarizers are indeed fairly neutral. The amount of correction is rather small. Some of the differences that you see, can be attributed to some variability in how I conducted this “quick and dirty” test. For example, I didn’t pay much attention to the exact location of my target when I was moving between shade and sunlight. I also didn’t do any validation if the degree of polarization would affect my results. The intent was to have a general idea of how these filters would compare.
Surprisingly, the 10 Stop B+W filter was not quite neutral. Both Tint and Temperature needed correction with Temperature being very different in Shade and Sunshine. This was definitely something I didn’t expect. Approximately -17 Tint correction was more in line of what I expected.
Similarly, Gold/Blue Singh-Ray Polarizer showed reasonably consistent Tint corrections between Shade and Sunlight with very different Temperature adjustments. Again, not quite what I expected. I don’t have any reasonable explanation why we are seeing such differences. If you have any suggestions please drop me a line.
So, what does it mean for us, photographers ? Well, I guess we can use “Gray” polarizers without much fear that they would introduce any color cast. On the other hand, more “exotic” filters like Gold/Blue Singh-Ray and 10 Stop B+W need to be handled with caution. The best strategy is to shoot one extra frame with Mid-gray target in the scene and use it to determine the amount of Temperature and Tint correction in post processing. Alternatively, you can try to find a spot in your image that approximates mid-gray (a grayish rock for example) and use that as a target.
About today’s image at the top: it was taken last Summer in the Jasper National Park. I got up in the morning to shoot a little bit north of Jasper town, around Pyramid Lake. That morning it was quite foggy so I decided to shoot in the forest. After an hour or so, the fog dissipated and this was when I took this photo. It was late in the Summer and you could feel that the Autumn was just around the corner.