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Re: vsnet-obs 45730 Confusion SS UMI > Telescope 20cm+CCDST9E unfiltered CCD observations calibrated > on V-magnitude sequence(=CV), > Chart AAVSO sequence V This description seems to explain my long-lasting question why people want to use "CV" (unfiltered CCD observations calibrated on V-magnitude scale), rather than to choose the best matching system. Is the AAVSO recommending to use visual charts for unfiltered CCD works? Are these "V-band" comparison stars carefully chosen to produce adequate results even if they are used in unfiltered CCD works? As I stated earlier, the application of "CV" system (not cataclysmic variable ;-) is limited. See: http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/docs/unfilteredccd.html In heavily reddend regions, this application is mostly useless, unless there is fortunate presence of an unreddened blue star which can be used as a comparison star. In most other cases, "CV" magnitudes would give systematically fainter magnitudes -- this sometimes gives an illusory impression that "my system can go as faint as xx.x mag". If one would apply this "experimental" limiting magnitude to deduce upper limits of other objects (e.g. supernovae), this would even yield a wrong result. I have seen suspicious cases in several past occasions, and they could have been a result of such (wrong) application. Regards, Taichi Kato
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