Polarising Filter for Lee 100mm System

[Update: if you’re wondering about the initial choice of filter system, I wrote something about this in a much earlier post.]

A rather technical post today, about a problem that is likely to be of interest to others, in particular to those interested in landscape photography. Specifically, this is about the use of a polarising filter with the Lee 100mm system of square and rectangular filters. It’s only an issue with ultra-wide angle lenses, with vignetting and intrusion of the filter edge into the visible frame.

Followers of this blog will know I don’t often write about gear. I took a decision some time ago to not even mention the equipment I use to take specific photos. Well, at least not beyond very generic statements where the type of lens etc is critical to achieve a specific image. I do this not because the equipment used is unimportant, but simply because it’s far from the most important issue. However, photography remains (so far) a rather technical subject. This is, for me, part of my fascination with the subject. Every so often some technical problems do crop up, and it’s not always easy to find the necessary information on the web.

In the following I will assume that the reader already knows about the Lee 100mm system of filters. The experiments in this article are all with my Canon EOS 6D and my wider lenses: the ‘kit’ EF 24-105mm f/4L and the EF 17-40mm f/4L. I would expect results to be similar with other full-frame camera bodies (film or digital); results with other lenses are more likely to vary. Caveat emptor.

I researched what I could, but it was hard to find specific and substantiated information. On the web, I think the most useful article I read was one by Tung Chung. I also discussed this with a friend from the Photo Society who had just been through the same decision process. In the end, I chose to go with the Heliopan 105mm slim circular SH-PMC multi-coated polariser. This has the advantage of having a lower profile than Lee’s (and many others’) offering, and the multi-coating should help keep internal reflections down. This is mounted on the Lee 105mm front ring, which in turn fits on the Lee foundation kit holder. Keeping in mind the expected vignetting problems, I keep this mounted with a two-slot setup. I generally use at least one ND grad, and should I want to use a solid ND for longer exposures, another slot is very useful. For both lenses I use the Lee Wide-Angle 77mm Adapter.

So here I am, finally, writing the information I would have liked to find when I was researching this. Let’s hope someone else finds it useful. The experiment I set up was very simple: I shot a translucent diffuser that was backlit by daylight through a window, with various lens and filter configurations. The lens was always manually focused at infinity, though with both lenses having an internal focus lens group it should not matter. The images were not post-processed, though I did keep the in-camera lens aberration correction (which corrects for vignetting). RAW images were converted to JPEG using Canon’s Digital Photo Professional. The idea is to simulate (and visualize) the vignetting one would get with the given configuration. In all cases below, click on the image for a larger version.

First I took a picture with the 17-40mm at 17mm without the filter holder on, as a basis for comparison. Next I added the filter holder with two slots and the front ring, but no filters (#1088). There is no discernable difference caused by the holder on its own. _MG_1088
Next, I added the polariser (#1090). As you can see, when used with two filter slots, at 17mm the filter does intrude into the frame at the corners. I have used this successfully on frames where I meant to crop to a more panoramic aspect ratio. _MG_1090
At this point I slowly increased the focal length until the filter edge was barely visible in live view (#1091). The EXIF data read this at 19mm. _MG_1091
I then increased the focal length further, until the edge was no longer visible on live view (#1092). Comparing with the next image you can see there is a little vignetting but this does not seem objectionable. The EXIF data read this at 20mm. _MG_1092
A further increase and even the vignetting seems to have gone away (#1093). The EXIF data reads this at 22mm. _MG_1093
Seeing that vignetting was gone by 24mm, I wanted to see whether the two-slot setup worked with the 24-105mm lens. However, at 24mm there is some vignetting (#1095). While this is a very capable general purpose lens, planned wide angle shots are better done with the 17-40mm. _MG_1095
Finally, setting up the 17-40mm lens again, I reconfigured the holder to a single slot (plus polariser). At 17mm there is some vignetting visible (#1098), but may just be usable depending on other conditions. _MG_1098
Increasing focal length very slightly, the vignetting is gone on the single-slot setup (#1099). The EXIF data reads this at 19mm. _MG_1099

If you’ve read this far, I hope you’ve found this useful. Comments welcome, as always, and feel free to get in touch if you have any specific questions about this setup.

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