## Prerequisites

Needs both astrometry and instrumental photometry of frames.

Headers would contain all the exposure time, filter, telescope area and photometry system keywords.

Specify photometric system (a conventional set of filters). Default is used value from frame header, use it when value is missing or needs correction. The option is important while determining of photometry calibration.

Specify filter. Default is used value from frame header, use it when value is missing or needs correction. The filter is important while determining of photometry calibration.

When calibrated frame contains FWHM parameter, the first aperture larger then the radius is used. When the parameter missing, the first aperture or user provided aperture is used.

Important.

The exposure time, filter, gain, area and an instrumental photometry system are absolutely necessory for calibration and none of them can not be omitted. At first, all values are obtained by reading of headers of FITS files. If at least one is not found, the calibration process is stopped (a wrong calibration which looks as valid is much more worse than any fail).

The situation can be solved by the ways:

- The values can be provided by editing of input files with help of `fits` module:

      $ munipack fits --key-update AREA=1,'[m] telescope area' huge.fits

  for all missing parameters.
- Also convenience options for most frequent missing parameters are provided: area and instrumental photosystem:

      $ munipack phcal ... --area 1 --photsys-instr 'MONTEBOO' ... frames.fits

  The convenience options doesn't supply common keywords (exptime, filter and gain) which can be usually found in frames.

While common values of exposure times, filters etc. are included to every header, the keywords can differ from Munipack's defaults. In the case, set ones via environment variables.