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Dear Jan and Doug, > This problem has been widely discussed probably a year ago. Sebastian > Otero gave us an overview of his arguments, which ilustrated his > opinion that the transformation of visual data is not possible. But > in the past there were published several papers which shows some > attempts to do it. I cannot give you exact references now but I > remember names Stanton, Howarth and some others... I can post them to > you later. I have proposed my own method how to do the > transformation, but I haven't meet any serious interest yet. It is and it will always be a very interesting issue. Actually I think it is possible but not in the present circumstances. A new culture on how to observe will have to be established before attempting a successful transformation. Brightness of the star, sky background, aperture and type of vision used they all play a role in an observation, but all these things are not taught to the visual observer. Maybe this is just to avoid overwhelming him/her with something to difficult that could cause him/her to give up. I don't know, but even using the same type of vision or observing technique (which most experimented observers do), if some of the other variables change, the results will be totally different. So a proper calibration won't be a fixed thing but will change according to the circumstances. This is what makes it too difficult for most people even to try it. A red star is the best example: if it's bright will give a completely different result than if its' very dim. A completely different result in a polluted sky or in a country sky. A completely different result for observers watching it with different apertures and above all, a completely different result for the same observer by a simple eyepiece change. It has been widely discussed in these lists. I remember a faint red star in Cygnus started the debate. What aperture to use, which results to trust and how to make this calibration is a question of experience. And it takes time. But making lots of practices and experiments, I found that the consistent-averted vision method and subsequent calibration based on a fixed personal color term never gave me results as good as those from a calibration made during the observation (not applying a formula after that) and mostly based on direct vision. I have the numbers here: I used over 30 stars between 5 and 8th magnitude with 7x50 binoculars. 1) Consistent observation with averted vision: mean error= 0.059 with outliers up to 0.15 mag. off (personal coefficient used: v-V= 0.1125*(B-V) + 0.0125 2) Consistent observation with direct vision: mean error= 0.040 with outliers up to 0.10 mag. off (personal coeffcient used: v-V= -0.002*(B-V)= 0.0175 3) Previously calibraed observations based on star's colour, no follow-up transformations: mean error= 0.034 wit ouliers up to 0.08 mag. Some people may have a different color-response and that wouldn't be a problem if a linear transformation could be done. But there are a lot more than a color problem in visual observations. The main differences lie on how every factor influences an observation, and they are not taken in account. Best wishes, Sebastian. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://vsnet.grisoft.com). Version: 6.0.518 / Virus Database: 316 - Release Date: 11/09/03
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