As part of our PowerND product family, the Aurora CR filter set comes with a CR filter holder and four CR format ND filters in the rating of ND 8 (3 stops), ND64 (6 stops), ND 4000 (12 stops), and ND 65000 (16 stops).
Aurora CR filter
We take advantage of some Canon wide angle lenses having a rear mount filter holder for gel filters and have designed a replacement of filter holder for glass filters.
The CR filter holders are CNC machined with utmost precision. Not only it allows the Aurora CR format glass filters to be used, but they are also much stronger than the original factory built in plastic holding mechanism.
Left: Aurora CR filter, Right: 186mm front mount filter
The reason for using the rear mount filter over the front one is primary the size of filters. Based on our simulation, if we were to make a front mount filter for the Canon EF 11-24mm F4L USM, a lens that is very popular among the Canon landscape shooters, a front mount filter size would be at least 185mm or larger, either in circular or square format. Filters of such size are not only inconvenient to carry and use, but also very expensive.
Another reason for using our rear mount glass filters is that gel filters are optically inferior with significant resolution degradation and strong color cast. In order to achieve accurate color reproduction and high resolution, we apply multi-layer nano-coating to both sides of the PowerND 4000 and PowerND 65000 filters. The end result is that we achieve excellent result in resolution and color rendition.
One of the additional benefits of having a filter between a lens and a camera is zero vignetting and ghosting effects often seen in front mount filter.
The CR filters are coated with the same multi-layer nanocoatings for surface protection against water, oil, dust, and dirt. Perfluoropolyethers (PFPE) are used as hydrophobic and oleophobic coating agent. With such a coating, we are able to achieve a static contact angle of 110 degrees with water droplets on the surface of the filter.
Untreated glass can barely maintain 15 degrees or less. Even a well-known brand’s 10 stop filter keeps less than 40 degrees of static contact angle and their 6 and 15 stop filters do not even have water repel coating.
Gorilla Glass® is used for the CR filters to provide rigidity and durability for such small size filter. It’s the same type of glass used in modern smartphone screens.
Auto and manual focus is possible when using the 3 and 6 stop filters with the camera’s liveview function.
The CR filters may cause a slight focus shift so pre-focusing without a filter then adding a filter may not result in a precise focus shot.
When using the 12 and 16 stop filters, users may use techniques of DOF or smaller aperture to overcome this. Or use a 3 stop filter to prefocus first and lock the focus manually or carefully not touching the focus ring, then swap the 3 stop filter with the 12 or 16 stop filter.
Canon lenses that can use the CR filters include:
- 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
- CR format PowerND 8 (ND 0.9) – 3 stops
- CR format PowerND 64 (ND 1.8) – 6 stops
- CR format PowerND 4000 (ND 3.6) – 12 stops
- CR format PowerND 65000 (ND 4.8) – 16 stops
- CR filter replacement adapter
- CR Adapter Installation Guide
* Patent pending
Additional CR filter replacement adapter is also sold independently.