I am looking at several galactic sources in the $I$, $R$ and $V$ bands and I want to calculate their absolute magnitudes. I can get the apparent magnitude and I know the distance so I just need to account for extinction to acquire the absolute magnitude. I first used the NED Coordinate Transformation & Galactic Extinction Calculator but the calculated extinction values are too high. I figured that this is probably due to the fact that my sources are relatively close ($\sim 100\,\text{pc}$) and I am thus only looking through a fraction of the dust that these coefficients were calculated for.
If I lower the extinction coefficients to a certain fraction of NED's value (say 60% in a particular case) then I get the expected answer but I'm looking for an accurate way to choose this fraction. I've looked for a method to calculate the extinction coefficients as a function of distance but haven't been able to find anything. Does there exist a map of extinction as a function of distance (and galactic coordinates) in the galaxy from which I can extrapolate the information required? Is there a way to calculate the extinction coefficients ($A_I$, $A_R$ and $A_V$) for an object in the galaxy a known distance away? I found IPHAS which seems to be the right idea but I'm not sure if I can use it to get what I want (or how).