[Aavso-photometry] Question about "R" and "I" filters

[George Sjoberg]

I'm just begining to try some photometry and have a question about I and R photometry filters. I've noticd that many AAVSO Field Photometry Tables  refer to Ic and Rc (Cousins) whereas Astrodon refers to their filters as Is and Rs (Schuler). Is there a significant difference in these filters or are they different names for the same things? 

Thanks

..george