We calculate theoretical isochrones in a consistent way for five filter pairs near the J and K band atmospheric windows ( J – K , J – K ^ { \prime } , J – K _ { s } , F110W–F205W , and F110W–F222M ) using the Padova stellar evolutionary models of Girardi et al .
We present magnitude transformations between various K -band filters as a function of color .
Isochrones with extinction of up to 6 mag in the K band are also presented .
As found for the filter pairs composed of H & K band filters , we find that the reddened isochrones of different filter pairs behave as if they follow different extinction laws , and that the extinction curves of Hubble Space Telescope NICMOS filter pairs in the color-magnitude diagram are considerably nonlinear .
Because of these problems , extinction values estimated with NICMOS filters can be in error by up to 1.3 mag .
Our calculation suggests that the extinction law implied by the observations of Rieke et al for wavelengths between the J and K bands is better described by a power-law function with an exponent of 1.66 instead of 1.59 , which is commonly used with an assumption that the transmission functions of J and K filters are Dirac delta functions .