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V. Strelnitski (Maria Mitchell Obs.), C. Springob (U. of Minnesota \& Maria Mitchell Obs.), F. Tam (Stanford U. \& Maria Mitchell Obs.)
We have investigated the accuracy of three methods of photographic plate photometry for stars: (1) eye estimates, (2) measurement of the plates with an iris microphotometer; and (3) digitizing the plate image with the aid of a Kodak DCS200 CCD camera and processing the image file with the NOAO's IRAF software. Thirteen standard stars in the open cluster M25 were measured, using each of the three methods, on seven typical plates from the Maria Mitchell Observatory collection. Plotting the measured, ``instrumental'' magnitudes of the stars against their standard magnitudes allowed us to determine the accuracy (rms deviations) of each method in the same units of standard stellar magnitudes. All the eye and microphotometer measurements were done independently by two of the authors (F.T. and C.S.). Somewhat surprisingly, eye estimates were found to be, on average, more precise than the two other, ``objective'' methods. However, the differences are not large: for all three methods rms deviations lie in the range 0.1 - 0.2 magnitudes, eye estimates being closer to the lower value and microphotometer measurements to the upper value of this range. Thus, accuracy should not be a decisive criterion in the choice between these methods. We discuss other criteria that would be more useful in choosing a method --- speed, the available field of view, accessibility of the required hardware.
The author(s) of this abstract have provided an email address for comments about the abstract: vladimir@mmo.org