I designed an adapter that allows you to fit a MagFilter CPL to the DR500 and to the front cam of the DR550. The adapters are available through Shapeways and Sculpteo. 126 of the adapters have sold through Shapeways, but I cannot track sales through Sculpteo since I have no markup on the adapters, and Sculpteo does not report on sales with no royalties.
The lens barrel of the DR650 apparently extends farther out from the side of the cam body than does the lens barrel of the DR500/550. I redesigned an adapter to fit the front cam of the DR650, based on measurements reported to me by a DR650 owner. The DR650 adapter is available at Shapeways and there have been several sales, but nobody has yet reported if it works or not.
The most popular adapter is on the left. I moved surface S1 to position S2 (on the right) for an adapter for the DR650.
Yes, the CPL will cut down on light, and I take it off (
very easy to do) when I drive at night. I do not drive fast enough during the day (with the CPL mounted) to experience "motion blur" mentioned in an earlier append.
There are definite advantages to the CPL.
(1) Far more light is blocked from the sky than from the rest of the outside. Therefore, the non-sky parts of the image are opened up more and you can see more detail in the darker areas - detail that would otherwise have been obscured.
(2) The reflections in the windshield are greatly reduced. Windshield reflections can also hide detail, but the CPL almost eliminates the problem.
A typical before/after comparison:
An extreme before/after example (dash reflections are still present, but greatly reduced, and you can see more detail):