[Aavso-photometry] Transformation equaions for only B, V and I filters.

[arne]

arne wrote:
> Lionel Catalan wrote:
>> Transformation equations are usually written as 4 equations involving the
>> terms V, B-V, V-R, and R-I. Hence, they assume that one uses the set of
>> B,V,R, and I filters. However, when I use only 3 filters (B, V and I), it
>> would seem logical to use only 3 equations giving V, B-V and V-I to
>> calculate the transformation coefficients. Is this permissible? If so, is
>> there more uncertainty on the transformed I magnitudes than if the R filter
>> was also used? 
>>  
> V, (B-V), (V-Ic) are fine for transformation coefficients; you don't need
> Rc.  In most cases, you will get superior results for Ic if you solve
> directly for Ic using your instrumental magnitude and (V-Ic) than by
> solving for V, (V-Rc), (Rc-Ic) and obtaining Ic from
>    Ic = V + (V-Rc) + (Rc-Ic)
> 
ok, let me try again!
Ic = V - (V-Rc) - (Rc-Ic)

Arne