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> The main intention of my analysis at that time was to better illustrate > the wide range of visual color sensitivities (with unspecified measuring > techniques), but not to discuss the deviation from the "true" V band. > Such an experiment can be better done with the "reddest" objects, for > which I selected an extremely red star R Lep. > > This experiment was originally intended for two special reasons: > > (1) There is a widespread belief that the visual sensitivity can be > well expressed with a nearly single "transformation coefficient", and > there was a movement to "correct" comparison star magnitudes on visual > charts, rather than using V magnitudes. I had to repeatedly express > a worry about this oversimplified treatment. I understand that this > approach was overthrown, and was taken over by a better and rational > approach to limit the color indices of the comparison stars. Of course there is no such a transformation coeficcient that can be applied even for a single person because there are too many factors affecting every individual estimate. The very best example is the different results for the same star when aperture or power are changed (star color is the same but the response is different). And also the deviation from V for a given star changes if the star is at maximum or at minimum, since different cells are involved in any case. So a single coefficient only makes things worse. > (2) There was an AAVSO experiment to determine this "coefficient" > using the SS Cyg field (and I remember that this field selection was > a target of complaints from southern observers...). I simply tried to > show that such a coefficient (if any) can be determined from the existing > data with a smaller bias (from the observer's degree knowledge in the > experiment prescription), and probably a better accuracy. I don't think > the field of SS Cyg is particularly suited for this kind of experiment. My experiments have given better results using a self-calibration technique beforehand than applying any coeficcient to the results made with a single observing way such as using averted vision or direct vision. Scatter was always higher when you observe everything the same way, because stars are not the same and eye cells are stimulated in different ways. I can compare the application of a formula to the results with the transformation between photometic systems: no matter how good is the transformation, the original data will always be of higher quality. Calibration to V allows an observer to get into to a system rather than trying to force him inside it later. Regards, Sebastian.
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