The circular polarizer filter is, by far, my favorite filter type. These filters are most commonly threaded onto the end of a lens. Because Canon's big white lenses have a huge front objective lens size, these threaded filters are not practical. Therefore, Canon provides a different type of circular polarizer filter option, the Canon 52mm Drop-In Circular Polarizer Filter.
Read the circular polarizing filter review to learn how circular polarizing filters work. The Canon drop-in filter will provide the same effect, but it of course installs and functions differently.
To install the drop-in filter, the standard filter holder must first be removed. A simple pinch of the drop-in filter release allows removal of the filter holder. The drop-in circular polarizer filter slides into the same slot and clicks into place. The process is very simple, though you will want to avoid getting dust and moisture into the filter opening or lens mount while no filter is in place.
A small wheel exposed at the top of the filter allows easy rotation adjustment of the CP filter.
This filter is compatible with Canon's big white IS and IS II lenses, including the Canon 300mm f/2.8 L IS II Lens, Canon 400mm f/2.8 L IS II Lens, Canon 500mm f/4 L IS II Lens, Canon 600mm f/4 L IS II Lens and Canon 800mm f/5.6 L IS Lens. Note that some earlier Canon non-IS lens models utilized a different filter size.
Also note that this filter is available in version "I" and "II" models. According to Chuck Westfall (Canon USA), "The paint color is the only difference. The "II" version was introduced specifically to match the new color tone of the IS II series super-telephoto EF primes from 300mm to 600mm that were announced in 2010." The version "I" model of course matches the older lens paint color.
CP filters can, in some circumstances, dramatically improve the quality of your images. The Canon 52mm Drop-In Circular Polarizer Filter is your only option for getting this benefit from Canon's big white super telephoto lenses.
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