Are all polarising filters equal? Part 1

The question in the title is one we probably all ask ourselves when faced with an array of similar filters at different price points.
Is there really a difference in quality?
This is something we hoped to reveal with our test.

For the purpose of this test we used a range of 77mm circular polarising filters at various price points.
Prices range from £15 for the budget end JYC, mid range £50, represented by Haida, Hoya and Kenko and £130 for the premium end STC CPL M ND16 (4 stop polariser) and STC Hybrid CPL. More about these two filters later.

All test images were taken on a Nikon D800 with a 24-85mm Nikkor lens, in aperture priority set a f11, auto focus enabled, white balance set to Daylight, using NEF images converted in Adobe Camera Raw into Jpeg format.
Images were then compared side by side on a colour calibrated monitor.

What is the purpose of a polarising filter?
Put simply it polarises light. That is, it cuts reflections shining off any non metallic surface. Additionally a polarising filter gives better colour saturation and contrast.
The making of a good filter starts with quality glass. JYC claim to use Japanese glass, Haida state they use German Schott glass, Hoya and Kenko (actually the same filter) use Hoya glass, both the STC filters are made using German Schott glass combined with Japanese polarising film.

In this first part of our test we are looking at sharpness, colour balance and exposure. Polarising filters can impact image quality to one degree or another, but which ones do and by how much?

What did we discover?

Image taken without filter – Red circle denotes area camera was focused on

Cropped area comparisons

Without filter

JYC

Haida

Hoya

Kenko

STC ND16

STC Hybrid

How we rated the filters from worst to best

The JYC filter displayed a noticeable loss of sharpness, combined with a yellow/ green colour cast, next came the Haida with some loss of sharpness, (not as severe as JYC), but still exhibited a yellow cast, Hoya and Kenko both had a similar slight loss of sharpness, but surprisingly differed in the fact that the Hoya filter gave a cooler image, whilst the Kenko filter was relatively neutral, but marginally darker overall. Both STC filters showed negligible loss of sharpness, whilst the ND16 polarising filter showed the slightest yellow shift, the hybrid polarising filter was very slightly cooler.

What makes the STC filters different from the rest of the pack? Whilst the other filters typically have a density of between one and a half and two stops. The STC ND16 filter has a light cutting capability of four stops and being a true neutral density filter, is ideal for reducing shutter speeds and or using a wider aperture.
The STC hybrid filter on the other hand only looses two thirds of a stop of light, meaning it can be left on the lens in most situations and used for its polarising abilities as required.

Conclusion

The JYC filter is cheap and cheerful. If you are planning to create a print up to A4, one of the midrange filters will suffice. However, if like us, you are serious about your photography, don’t cut corners, buy a STC polarising filter.

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