[vsnet-chat 4046] Re: Visual estimates accuracy

["Berto Monard" <Lagmonar@csir.co.za>]

Sebastian,

Direct vision is only possible if stars are bright enough, ie well within 1 magnitude of the telescope limit at the observing time.
But then, direct vision can result in staring, which will cause especially red stars to 'become' brighter. 

Observer's color (intensity) vision differ, which will cause more estimate scattering on stars with extreme colours, especially those red. 

Most often, differences in estimates are due to differences in the sequences used, or even different stars of the same sequence. The latter even with differences in the angle position errors.

There are so many factors as you have refered to. I want to read your article.


Yes, I use mostly averted vision since my targets are often faint and I have a hard and impossible time to reach the magnitudes seen by the Aussies (but wait another two weeks!).  
For eta Car and other brighter stars I use out-of-focus comparison.  

My opinion: it really would help visual observing if v (visual) magnitudes were tabled for a typical (30' +) darkadapted vision in stead of V (photopic). Extreme darkadaptation seems to render vision closer to B than V.... 


Mosters, he? What is that? 

Regards,


Berto

>>> "Sebastian Otero" <varsao@fullzero.com.ar> 02/02/01 05:39AM >>>

My articles are all about the technics used in visually vsoing, specially
when we observe stars of different colors.
My point is that a subtle change in HOW we observe the stars may be
reflected in several tenths of a magnitude discrepancies.
"HOW" means if we used averted, parafoveal (intermediate type, se Hallett,
1998, JAAVSO vol 26, 139) or direct vision.
If we are not aware of these different responses of the eye and randomly
observe with one vision or another, without taking care, results may be
dissapointing, specially for stars like R Lep, that are very red and may
completely disappear if we used averted vision for observing them. (I've
noticed 1.4 mag. differences for that star, which is saying we are observing
it in different ways).

If Stan agrees I will send a copy or parts of the article to vsnet-preprint
or vsnet-chat. And I think it would be interesting to exchange our technics
and experiences on this matter.
I believe that most of the discrepancies can be explained easily by the
different types of vision used.
And now that Johnson V is being accepted as a standard for visual
comparisons and charts are being converted to that system, I think observing
technics ought to be revised.
Furthermore, most of the charts that supposedly show "v" magnitudes have
values that are a mix between V and v.

I've realized that most observers use averted vision for all their
estimates. That would mean that red stars are always fainter in telescopic
estimates. And blue stars are always brighter.
If stars are not the same color and if it's not made for detection at the
limitting magnitude, I always try to avoid averted vision for all those
problems.

I wait for comments from all observers. It would be great to hear what
technics are used by Monard, Stubbings, Granslo, Comello, Pearce and all
that "mosters" (;-)) that report to vsnet.

Cheers for all,
Sebastian.




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