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

[robertjmodic at att.net]

Arne,

Regarding the Schuler/Bessell prescription for the Ic filter, you've mentioned
before that this has a red tail that can cause very red stars (like Mira's) to
appear too bright compared to true Cousins I.  You suggested that ideally the Ic
filter should be an interference type to better control the bandpass.  Do you
know of a supplier that stocks these or is this something that has to be custom
ordered ($$$$$)?  I know that SBIG has one as part of the BVI set for their
ST-402 filter wheel but these filters are rather small (~21mm diameter).

Bob


> Date: Fri, 20 Jun 2008 01:15:47 -0400
> From: "Arne Henden" <arne at aavso.org>
> Subject: Re: [Aavso-photometry] Question about "R" and "I" filters
> To: "George Sjoberg" <george_sjoberg at yahoo.com>
> Cc: aavso-photometry at mira.aavso.org
> Message-ID:
> <9c3d14ae0806192215g507284fdp8161733ffbff07cc at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Different names for the same thing, for the most part.  The big difference
> is between Johnson R,I and Cousins R,I; the Cousins filters are recommended.
> Cousins filter bandpasses are detailed carefully in various papers, and then
> there have been a couple of papers that give filter glass
> prescriptions to closely
> match (with CCDs) the Cousins filter bandpasses.   Most vendors follow the
> prescription given by Mike Bessell (the so-called "Bessell"
> prescription), including
> Astrodon.  The "s" subscript on Astrodon/Schuler filters just refers
> to "standard".
> Arne
>
> On Thu, Jun 19, 2008 at 9:23 PM, George Sjoberg
> <george_sjoberg at yahoo.com> wrote:
>> 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
****