[Leica] Series VII IR cut filters?

[leica at web-options.com (Bob W)]

Thanks - that's very useful information that I did not know before. 

> >One of my lenses is a Summilulux-M 35/1.4, which takes Series VII 
> >filters held in the lens hood. Do you know if IR cut filters are 
> >available in this size for the M8? I haven't been able to 
> find any reference to them.
[...]

> Heliopan has them; you just have to find someone willing to 
> order them for you. I managed to find a shop in Germany that 
> would do it for me and ship them to me; it cost a lot less 
> than ordering them through a store here.
> 
> The other option is to use a 49mm filter, drop it in and shoot away. 
> Series filters go by a simple formula: square the series 
> number, and you're pretty close to the filter diameter in 
> millimeters. Well actually, it only works for a couple of 
> sizes, but the others are close. Series 7 is one that works.
>