Aurora CR Format Filters for Canon Ultrawide Lenses

If you own a wide angle lens, especially ultrawide lenses like the Canon 11-24mm F/4 L USM you will understand the challenges of finding a good filter solution that delivers minimal colour shift, is fast to set up and affordable.

Because of the large field of view and large front elements, you need to use large filters to avoid vignetting as well as a specific filter holder. The filter holders are generally custom designed to suit a specific lens like the LEE SW150 and NiSi’s S5 for the Nikon 14-24mm to use 150mm square filters.

NiSi 180mm Filter holder for the Canon 11-24

Before digital imaging came about, a lot of the lenses produced had a rear gelatin filter holder. Rosco & Lee make gels in a wide range of colours and neutral density values. These gels come in a range of colours and ND values. CTO or CTB filters were commonly used to correct the white balance of the image. Now with digital imaging, it’s much easier to adjust the white balance in post.

Just one of the colour ranges of Rosco gels

Today, the mount is still used by many to add ND gels for long exposure photography. While it is a cheaper option to use ND gels instead of a front-mounted filter system, it does have its disadvantages such as causing ghosting or flares in the image.

Framing your subject is also an issue when using strong ND with an optical viewfinder as you need to remove the filter to see the frame and then place it back when taking the shot. With current cameras, using live view on an EVF or LCD, you can get around this issue to a certain degree.

Industry First Aurora CR format

Aurora Aperture has taken the concept of adding a rear mounted filter and developed their own Aurora CR format filter along with a new metal mount to replace the original plastic mounts. The filters use Gorilla Glass and are much smaller and lower in cost compared to the 180mm square filters required for the Canon 11-24mm lens.

The Aurora CR format is part of the PowerND family which has three ratings of light reduction capability:

ND8 (3 stops) – Aurora CR format only
ND64 (6 stops),
ND4000 (12 stops),
ND65000 (16 stops).

Along with the new filter format, they also create the ND filters in

circular filters from 37mm to 95mm
100 x 100mm square filters compatible with popular square filter adapters,
150mm circular filters with an adapter for the Nikon AF-S 14-24mm f/2.8G ED lens

Installing the Aurora CR format mount

Just like the gelatin filters, the CR format is designed to be mounted on the rear of the lens.

Replacing the mount is easily done by removing three screws.

Once the new mount is installed, it can securely hold the glass filter in place.

Size Matters

You can see the massive difference in size between the Aurora CR format and a 186mm round filter.

Compatability

The Aurora CR format filter kit can also be used with these other lenses:

EF 8-15mm f/4L Fisheye
EF 11-24mm F4L USM
EF 14mm f/2.8L USM
EF 15mm f/2.8 Fisheye
EF 16-35mm f/2.8L USM
EF 17-35mm f/2.8L USM
EF 17-40mm f/4L USM

Since release, there is now also a version to use with the Irix 11mm f4 & Irix 15mm f2.4 EF wide angle lenses.

Composition & back focus?

Framing your subject when using an ND filter with a high value can bring its own set of challenges. Using square filters, the filter holder can be removed from the lens allowing the user to set up their frame and then place the filters back. With the Aurora CR mount, it does make it a bit more finicky having to do this as you have to remove the lens, place in the filter and then re-mount the lens, during this whole time your gear would be exposed to the environment even if you were careful to place body & lens caps on. If you were using the lower ND values, you may be able to get away by using live view to compose your shot.

Adding a glass filter between the lens & camera can also cause a shift in the focus. Since you can’t focus with the ND filter in place (since it’s so dark), you normally focus without the filter in place. The issue here could be that once you place the filter in, it has now changed the focus and you end up with a soft image after waiting a few minutes for the exposure.