[Aavso-photometry] Filters

[Thomas Rutherford]

Gentlemen:

I have a few questions that are a little more fundamental than most of 
the postings that I have been reading on this list so please bear with me.

How does a modern "V" filter for CCD work compare to a "V" filter used 
for photometry back in the 60's and 70's?  I ask this because an old 
photometry filter is what I have.  While researching this question, I am 
finding contradictory answers.  Some sources indicate that the old 
filters do not stop the red and IR end of the spectrum since the old 
photometers were not very sensitive at those wavelengths.  Other sources 
indicate that for a "V" filter, this doesn't matter-- the old filters 
are the equivalent of the newer ones.  Also, the camera has an 
IR-blocking filter already-- should I keep this in place or remove it?   
In addition, my filter is yellowish, while I always see V filters 
referred to as being green.  Should I order a new "V" filter or use the 
old one? 

Also, if I were to add one additional filter (a modern one), what should 
it be?  I am using a Meade DSI camera and a Meade ETX 70 telescope (a 
refractor).  This is for a high school astronomy class project that I 
started last year and those are the items that we have to work with, 
although I know now that they are not the best choices and if I were 
starting over I would select different equipment (I do like the wide 
field of the ETX, though).

Thanks for your time-- any input that you can give is appreciated.


Tom Rutherford