changed filter docs

docs/instrument_response.rst

@@ -9,4 +9,6 @@ When calculating broadband phase curves, either for observations through a filte
 
 This filter file must be a plain text file that consists of two columns, the wavelength in metres and the corresponding instument response value (typically a number between 0 and 1) and must be in units of counts per photon. The code will then convolve the given filter function with the fluxes when calculating physical models with grids of blackbodies or stellar model spectra. Spiderman will linearly interpolate between the provided wavelength points. 
 
-If the filter function is too course, or if it contains a very sharply varying response then the results may not be accurate. In these cases it may be necessary to modify the "n_bb_seg" parameter in the lightcurve function, for which the default is 100.
+If the filter function is too course, or if it contains a very sharply varying response then the results may not be accurate. In these cases it may be necessary to modify the "n_bb_seg" parameter in the lightcurve function, for which the default is 100.
+
+.. warning:: SPIDERMAN normally calculates ratios in flux density assuming a uniform *energy flux* response - a uniform counts / photon response function will be different by a factor of hc / lambda, therefore it is possible to recover a different result with a uniform response function than you would get by setting the upper and lower bounds of the integration with l1 and l2.

docs/quickstart.rst

@@ -57,6 +57,7 @@ Since this uses model spectra, it is necessary to specify the bandpass with thes
 	spider_params.l1 = 1.1e-6	# The starting wavelength in meters
 	spider_params.l2 = 1.7e-6	# The ending wavelength in meters
 
+.. warning:: SPIDERMAN calculates ratios in flux density assuming a response function that is uniform in *energy flux*. If you want a response uniform in photon counts you must define a instrument response function (see Instrument Response section).
 
 Now, define the times you wish the model to be evaluated at, let's do a single full orbit: