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Message: <blockquote data-quote="WJC" data-source="post: 3310382" data-attributes="member: 25191">Hi kkokkolis, et al.:Transverse Chromatic Aberration AND Longitudinal Chromatic Aberration can and ARE described mathematically. Yet, without some classical knowledge of optics in general, it may mean very little. Longitudinal CA in the easiest to measure, even with the computer models such as Zemax or Code-V can provide. However, it is the transverse (lateral color) that most observers speak of.It should not be thought of as “false color,” for the color may be a nearly perfect representation of reality. Yet, it is often described as such because it can be annoying to some.The elimination of aberrations is often misunderstood. There is no doubt many on this list have a pretty good handle on what is required. It is also certain some curious folk don’t.The most important thing to note is that ALL aberrations are interconnected, and that it is rare to be able to correct one without adversely affecting others. But, whose needs are more important? Let’s take Barrel Distortion for instance. In astronomy, Distortion that would drive an architectural inspector nuts, would probably not even be noticed. Why? Because the image might be might be as sharp as can be, just “bending” that sharp image a bit. Optical engineers seek “degrees of freedom” to give their employers what they want. These involve glass types, curvatures, spacings, and even the size and position of the Field Stop. I watched the manual iterations of Zemax when I was designing my Houghton telescope. By so doing, I allowed the computer to teach me. With the basic design being so forgiving of EVERYTHING, I learned a lot. I had a design that placed the whole visible spectrum in such a tight blur, the spot diagram made the blur to the Airy Disc look like a pea lying in the center of a platter. Choosing the secondary as my Field Stop, it formed about a 30% obstruction. With many PROFESSIONALS shooting for 33-35% obstructions, I thought I had done well. But, simply by changing where I wanted that stop (this time making it the corrector), I found I could make the blur become a FRACTION of the first (I optimize using OPD plots and use spots for just getting a design in the ball park). But, it was NOT without a downside. Just changing where I wanted the Field Stop (nothing tangible) caused the secondary to grow to 35% or more. Thus, causing the system to scatter more light and slightly reduce Contrast. In optics, there is no free lunch: “’Da head bone connected to da foot bone!”I think it is important to note that even the worst of the designs was many times tighter than the most critical observer could differentiate. So, was there any need to go beyond that mark—other than for learning purposes? There was NOT! Manufacturers know this and don’t cater to the handful of folks who sit around the computer looking for something to fuss about; they have to cater to the millions who need a magnified image of something and haven’t a clue what chromatic aberration is.It is also important to note that comparing ONE Zeiss, to ONE Leica, to ONE Nikon, to ONE Swarovski is an effort in futility! Such observations need to be taken as groups of instrument. Even then, we’re splitting hairs with an ax! Each bino is made of several elements with curvatures, thicknesses, and spacing often measured in MICRONS! In this environment, the thickness of a flyspeck—anywhere in the chain—can throw a design for a loop. With the best that can be done, there will be minuscule differences in two binos leaving the assembly line seconds apart.Now, take into consideration differences in glass melts, condition in the tools used for coring and edging, calibration variance in test equipment, visual acuity of the test technician, and more, and it should be easy for the bino enthusiast to see that comparing the BEST to the BEST is really a lost cause.The world is not perfect and the best binoculars may not be when compared to next week’s model of the same name, or the one that came out of production directly after it. This is especially true when considering the visual acuity and preferences of the many observers. I’ll crawl back in my hole, now. :cat:Cheers,Bill</blockquote>

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