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Variable ND Blue 'X' Explained

RevoRing - Journey to Market

We are thrilled with the overall feedback we have received since the initial RevoRing Kickstarter launch campaign and the H&Y R&D team has been working tirelessly with revisions and updates based on expert feedback ever since. All of this has ensured the RevoRing 1.0 market version is the best it can possibly be.

We’re extremely proud of the products that are being sent to our early backers. They have been manufactured to the utmost quality and deliver on the promises made throughout our launch; to deliver a unique filter adapter with a twist!

The X-Factor

The X-factor is often referred to in a positive light and we believe the H&Y RevoRing is such an innovative, high-quality and great value imaging accessory, it truly has the ‘X-Factor’!

However, as is the case with every variable ND filter in the market, there is another kind of ‘X’ to consider and this is no different with the H&Y RevoRing VND/CPL version.

Example: The following image is an example of what the blue cross looks like and was shot on a Fujifilm X-T2 with a 16-55mm lens using the RevoRing VND+CPL. The setting used on the filter was set to maximum, forcing the X effect to show in the image.

Why Does the ‘X’ Appear?

Variable ND filters have been around for well over 10 years. Used by many in both stills photography and video production, variable ND filters are made up of two polarising filters, usually one linear and one circular polariser. When the polarisers are aligned correctly, which is done by hand, and using the highest quality glass and polarising film, this helps determine the level of attenuation and makes sure auto focus and sharpness are unaffected, especially when shooting with telephoto lenses up to 400mm. As you rotate one polarising filter against the other, you create the level of neutral density that is required for your shot.

There is an inherent physical characteristic in every polarising filter, when turning against another, called cross polarisation. This is commonly referred to as the ‘X-Cross’ or ‘Extinguishing Cross'. It’s a known physical factor with variable NDs and manifests itself as a visible ‘X’ within the frame. In essence, the number of stops achievable by a variable ND using two polarisers is governed by the focal length of the lens being used.

n.b. the relationship between lens focal length and VND is consistent, in that it does not make any difference which camera brand/sensor crop you are shooting with or which make of lens.

This X-Cross will appear at different focal points, depending on the focal length of the lens being used and wide focal lengths will generate an X-Cross as the user increases the level of neutral density/ light stops.

The X-Cross appears due to the lens accepting light from a wider area of the paired polarisers than from the concentrated centre of the glass. For example, at 70mm focal length, users can go right the way through to the RevoRing’s ‘MAX’ setting, (on the Variable ND filter) without the X-Cross appearing. However, as the width on the focal length increases, the X-Cross will appear. This is why H&Y opted for numbered markers on the RevoRing CPL/VND.

Whilst many people using variable neutral density filters will be familiar with cross-polarisation, those working with the RevoRing will find the phenomenon more apparent. This is not due to any malfunction or flaw with the product. Quite simply, the RevoRing CPL/VND has a much broader range than many other products in the market.

Quality & Value

When producing our RevoRing variable neutral density filter we wanted to offer customers a single filter with a stop range between 2 - 10 stops as well as benefit from not having to buy multiple size VND filters and step rings. Our goal is to use the highest quality glass and polarising film so that we offer best in class sharpness and color neutrality. The majority of this process is within our control, apart from the 'X' effect which is left to physics and one that has yet to be resolved when making an all-in-one VND. In fact, some brands have opted to break up the VND filter into 2 products that offer 2-5 stops and 6-9 stops and while this is a great option, it means having to buy an extra filter to match our 2-10 stops, resulting in a single purchase that can exceed $400.

With all of that said, the trade off of making a product that is great value and packed with high quality features meant that the 'X' factor would remain. For this reason, we have produced a simple guide to simplify the RevoRing experience. Use this chart as a guide for use across all common focal lengths to get the very best from your RevoRing CPL/VND.

RevoRing Variable Neutral Density Marker Guide 

VND Number Mark 16mm Focal Length 24mm Focal Length 35mm Focal Length 50mm Focal Length 70mm Focal Length
Marker 1 No Blue X No Blue X No Blue X No Blue X No Blue X
Marker 2 No Blue X No Blue X No Blue X No Blue X No Blue X
Marker 3 No Blue X No Blue X No Blue X No Blue X No Blue X
Marker 4 Blue X Appears Blue X Appears No Blue X No Blue X No Blue X
Marker 5 Blue X Appears Blue X Appears Blue X Appears No Blue X No Blue X
Max Setting Blue X Appears Blue X Appears Blue X Appears Blue X Appears Blue X Appears

Note: The above test was completed using Sony APS-C and Full Frame cameras and do not represent every single camera and lens setup. This information should be used as a guide. 

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