The Hoya RM100
Stunning results from this filter.
This filter is unusual because it is not a standard production part. Hoya currently do not make RM100 camera filters in any size. Hoya only supply RM100 glass in sheets for industrial uses now so there is little point trying to buy one from a photography shop.
The only people who can supply this filter are those who are buying the glass by the sheet, cutting it to size and fitting it in filter rings (as pictured above).
These filters are usually only found in 37mm.
The filter begins transmission at around 1000nm which means it out-performs many of the other filters available. Infrared "x-ray" pictures taken with the RM100 are very impressive.
The filter sometimes comes in a poor quality paper or card envelope or simply wrapped in tissue. If this is the case, I can recommend buying any proper filter from a company such as Hoya, Tiffen or B&W and using the plastic case to store your RM100. Hoya's RM100 glass is quite resistant to scratching and appears to be of similar quality to their camera filters.
Testing has shown that this filter combats Sony's modification and can be used to film in sunny conditions without further work-arounds or modifications.
If you choose to buy an RM100, exercise caution. There are many places advertising them for sale on the internet and you run the risk of acquiring a fake or nothing at all. Opt for a larger company if you can.
Fortunately there is a way to spot a fake. See Checking your filter for more information.