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Re: (IAAC) [amastro] Re: limiting magnitude at WSP



I concur with you comments about seeing objects (images) after one's 
attention is directed to the subject. A prime example is some star field 
photos that I have been examining with a low power microscope. Many of the 
deep sky objects were missed until reference was made to an atlas. They were 
definitely there at first pass, because I can see them now that I know they 
are there. There is nothing imaginary about the images on the photos. As you 
mentioned about the way the optics are wired to the brain results in 
misrecognition. The skill gained in repeated observation is another good 
example of expectations overcoming the nonrecognition/misrecognition 
phenomenion.  It is long established that there is a real difference in the 
way we individually see or interpret vision. It's referred to as the personal 
equation.
Dan Duriscoe wrote:
The National Park Service is beginning a program of night sky brightness 
monitoring
 with the objective of protecting dark sites in national parks.  One of the 
methods
 we propose to use is limiting magnitude estimates by human observers.  We are
 particularly interested in any information and/or previous research that has 
been
 done on this method.  I personally find that I do indeed find a few more 
stars in
 any given field if I know where to look for them.  However, I have never 
considered
 this as "bias", merely a physiological peculiarity of the human brain/eye
 interface.  If you know what and where to look for something you're chances 
of
 finding it are much improved.  I don't think it means that you are actually
 "imagining" that it is there.  Am I wrong?
 Dan Duriscoe
 Sequoia and Kings Canyon National Parks
 Lew Gramer wrote:
 > Alex Langoussis writes:
 > >Your mileage may vary.  When comparing skies at different observing
 > >sites, I would think the best results would be obtained by  the same
 > >observers using the same scopes at the different sites.
 >
 > This is key, Alex: using unaided-eye Limiting Magnitude as an analog, two
 > observers on the same night at the same location, with the same full (40+ 
min)
 > dark adaptation, can differ in their LM as much as a full magnitude.
 >
 > And in fact, for the same INSTRUMENT and conditions, I'd be interested to 
hear
 > what relationship holds between unaided and telescopic LMs across a sample 
of
 > several different observers. With all-important individual variations 
accounted
 > for, I suspect these two numbers are pretty well linked.
 >
 > BTW there is one problem with the sorts of charts published in S&T, and in 
the
 > excellent guidebooks of some of our 'amastro' participants: unintentional 
bias.
 > Particularly with estimates using intermittent averted vision, there seems 
to be
 > a tendency for HONEST and EXPERIENCED observers to "see" what they know is
 > there, even if strictly speaking it is not really visible.
 >
 > To completely avoid this, you have to sample multiple preselected, 
well-defined
 > star fields in a session, and to do "double-blind" estimates: either 
plotting of
 > the field without prior knowledge, or simply counting stars in the field.
 >
 > Lew Gramer
 >
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