[Aavso-photometry] Calculation of Transforms, K' and ZP

[Steven Orlando]

Hello All,
 
A couple of nights ago, I imaged two Landolt fields at different airmasses. I took 5X1 min of BVRI, for the two fields. I used MPO PhotoRed to analyze the data. This are the results:
 
V-R:
B: Transform = 0.328, k' = 0.458, ZP = 17.724
V: Transform = -0.145, k' = 0.525, ZP = 19.062
R: Transform = -0.196, k' = 0.635, ZP = 19.266
I: Transform = 0.007, k' = 0.411, ZP = 18.406
 
B-V:
B: Transform = 0.173, k' = 0.428, ZP = 17.567
V: Transform = -0.078, k' = 0.538, ZP = 19.132
R: Transform = -0.105, k' = 0.383, ZP = 19.361
I: Transform = 0.002, k' = 0.410, ZP = 18.403
 
V-I:
B: Transform = 0.17, k' = 0.421, ZP = 17.531
V: Transform = -0.073, k' = 0.541, ZP = 19.148
R: Transform = -0.101, k' = 0.387, ZP = 19.383
I: Transform = 0.005, k' = 0.410, ZP = 18.402
 
Are these good ballpark figures, I think the k' are way too high. I really don't know about the trans and the ZP.
 
If you're capturing a timed event like an exoplanet transit, how do you transform the mags if you only shot the transit with one filter. Do I just take some images of the transit star with another filter, like R for example? I ask this because I don't understand how you can calculate k' and ZP each night, if you are using one filter.
 
Steve