This section is for performing the film calculations of Exposure, Reciprocity, Speed Correction and ISO/ASA to/from DIN conversion. This section uses formulas from “Astrophotography for the Amateur”. See bibliography for more information. This section based mostly on Michael Covington’s book “Astrophotography for the Amateur”. Covington Innovations Note that I have added combo boxes to make entry for some variables easier. Just select the check box next to variable and then pull down the desired value.


For the Exposure Calculations enter the film ISO/ASA, the lens f ratio f/, the Brightness Coefficient and the Schwartzschild Exposure Coefficient. Press “Calculate” to compute the Time and Actual Time of the film. “Clear” to erase and try again. The Schwartzschild Exposure Coefficient is film dependant and can range 0.6 to 1.0 for most films. Check with your film supplier/manufacturer. Typical values are 0.65 for most 400 ISO films, 0.75 to0.8 for Technical Pan 2415 and Panatomic-X and 0.95 to 1.0 for a film that shows little reciprocity failure (such as spectroscopic or gas-hypersensitized films).


For the Reciprocity Calculations enter the time in seconds, p the film Schwartzschild Exposure Coefficient and the Rated filmISO/ASA. Press “Calculate” to compute the Actual Time or Actual Speed of the film corrected for reciprocity. “Clear” to erase and try again.


For the Speed Correction enter either the Uncorrected or Corrected ISO/ASA setting for the selected Filter setting number and it will convert to the other. Press “Calculate” to compute or “Clear” to erase and try again. Filter settings are based on Transmissibility Factors and can range 1.0 for clear, 1.2 to 2.0 for light filters, 8-10 solid colors, 16 for dark blue to 20 for dark red or dark green. See Covington's "Astrophotography for the Amateur" page 83-83 for the color filer table.


For the ISO/ASA<>DIN conversion enter either the ISO/ASA or DIN number and it will convert to the other. Press “Calculate” to compute or “Clear” to erase and try again.  

Check this site for more information about these film standards. ASA, ISO, DIN