The whole square filters subject has inspired a lot in my interest in filters in general. The main reason I would use filters on my lenses would be to either protected them with a MC UV filter, or to make the colors pop-up with the CPL filter.
Small intermission in my discussion about filters in general to talk about CPL.
I love the way the CPL filters make the colors pop-out and help organize better certain elements in a photo (such as eliminating non-metallic reflections). But that filter comes with its downsides. Which ones?
Well, it is not a filter specific downside, but the filter does increase the intensity and frequency it happens. In Lightroom, when I’m developing a photo, I generally start the development with screens in mind. Screens are the medium that most people (myself included) will consume the image. I adjust the photo as best as I think it can/will look on screen, sometimes adding a flare of drama/creativity to the image. Some of those photos I edit for screen will end up being printed on my photo printer as well. This is where CPL isn’t great.
I don’t know what the image color translation is between the screen and my printer that SOME colors don’t turn out the same way printed if there is no adjustment to the photo. This happens a lot with blue… that color you often see in the sky… the object/element that people generally use CPL to make the color pop-up more. I love CPL, but using that filter often gives me more work for the printed photos. It’s not difficult to change it, I often have to create snapshot/version of my photos specifically for print. The image below shows the blues in one of my photos: the photo under the “Current” panel is the screen version and the photo with “Proof Preview” is the version for my printer.
In the photo above, the left panel contains the original exported photo for screen consumption and the right panel contains how it will be printed. It might not seem like a huge difference in the background blue that is on the left part of the photo. But when you are working with photo printing and/or fine art, the slight change of color may change the intension of the photo. When these differences occur in the soft proofing for my printer, I have to adjust the blues in the HSL/Color tab in Lightroom and create a print specific snapshot/version.
There is one more item in the CPL filter that I will not discuss in this post, which is how it increases the f-stops required for the right light.A really good (pro grade) filters will interfere very little with the metering.
Note: The image above is a screenshot of me working in Adobe Lightroom Classic.
Now, back to Vignetting and round filters. One of the problems that round filters have that the square filters seem to generally fix, is vignettes on the photos. When stacking round filters, depending on the angle of the lens and the thickness of the filters’ frame, it can start to capture some of the metal on the filter as part of the image, thus creating a vignette.
As an exercise to help me understand better my work options, I decided to start stacking filters on my lenses. Each filters/lenses combination will produce a different result. The three major factors that come into play are: viewing angle of the lens, number of filters, and thickness of the filter rim.
As an example, below I have used my Nikkor 24-85mm with a CPL and the Warming filters. At 24mm there is a vignette, at 35mm just a tiny piece of the filter can be seen, but only at 50mm the vignette isn’t there anymore. The Polaroid Warming filter that I have is very slim, but the Polaroid CPL filter I have for that lens is a bulky (bulkier than my Hoya NXT Plus CPL for my Nikkor 50mm lens). Again, the vignette is only visible below the 50mm focal length, which means that at wider angles, stacking filters becomes a problem.
The photos above were not taken in raw/NEF format. For THIS exercise I configured the camera to do all the adjustments and generate a jpg file by itself. This is to help focus on the subject at hand, which is the vignetting when stacking filters.
When I tried to stack the Hoya CPL and my Polaroid MC UV on my Nikkor 50mm lens, I got no vignetting at all. I know the combination I used is not really a combination that would be used, but this is for comparative purposes only. I would more likely stack a CPL and a Warming filter as I did with the 24-85mm lens.
So, it will be a very good exercise to do this with my wide angle lens (Nikkor 18-24mm) once the warming filter arrives. I will need to make sure that if I want to stack a CPL filter on it, that it won’t vignette with the focal distances I want to use.