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Message: <blockquote data-quote="elkcub" data-source="post: 1530704" data-attributes="member: 14473">Actually, I really don't disagree with anything you've said by way of instrument evaluation on an optical basis, except that in a few instances the presence of an aberration may be arguably beneficial for the user.  One example is distortion, for reasons that Holger Merlitz (and Jean-Charles) has articulated.  The value of moderate field curvature has been debated, and I tend to side with the moderates on that one.  Although not an aberration, the optimum intensity/frequency distribution at the retina would argue for some kind of filtering, and not simply a total brightness criterion to identify what's "good" vs "bad."  The article in my previous post should expose that elephant in the examining room.   Henry, even you must have realized the complete ambiguity of that precious statement.  Go to the head of the class!  :-OThe human visual process is concerned with creating a valid internal (mental, if you will) representation of the physical, 3-D world around us.  That is so obvious we are functionally blind to it, unless something goes wrong with our eyes.  At that point, the criterion for goodness quickly becomes the quality of that "internal representation."  So, perhaps we differ in that I orient to the manner in which the instrument manages to retain important qualities of the normal internal mapping.  Relative distance perception is high on the list.  The horopter is a theory of how the brain utilizes information on the two retinas, and concerns the mathematically complex determination of retinal correspondence.  Most modern work goes back to the German genius H. von Hemholtz (1867).  That it is a theory makes it no less valid (factual) than concepts of mass, gravity, or evolution, and like them it is under constant scientific debate.  The recent theory has been expanded to what is called the "extended horopter" and is very complicated.  Apparently, after 150 yrs., they have finally proved a conclusion by Hemholtz, whose analysis was too "dense" to comprehend.   Although I could make an effort to come up with a simple definition, the Internet is full of them (not always in agreement).  But, in my view it would be like jumping into the middle of optics with a definition of wave front aberrations.  For starters, a full-text .pdf file of Kenneth Ogel's 1962 lecture can be downloaded here: <a href="http://www.iovs.org/cgi/content/abstract/1/4/446" target="_blank">http://www.iovs.org/cgi/content/abstract/1/4/446</a>.  It summarizes the field up to that point.  His last sentence is "...Mathematics has been avoided!"  Ed</blockquote>

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