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Message: <blockquote data-quote="Surveyor" data-source="post: 1280841" data-attributes="member: 50720">Ronh; Ed is correct. When resolution is being discussed in terms of line pairs, only one color bar is counted. I have attached a jpg of the ISO description of a bar, a line in our jargon. ISO uses a negative target so their primary bar is the bright bar. I do not have a problem with the line pair’s concept; it is far easier to measure by automated analysis means than other methods. I was just pointing out, that in surveying and engineering, both the black and white widths contain sub dividable information that are identified and measured separately, so they have to be resolved and counted individually. I hope the following will make sense and help you, but may confuse the issue even more. The real image formed by the objective train has to have an object to image. If we assume that the 168 mm is the focal length then it is easy to assume the objective was focused on a 1 mm object 1680 mm in front of it (about the size of the cluster containing group 4 and 5). The resulting real image would be .111mm so the 40 lp/mm would be compressed to 360 lp/mm at the focal point and your assessment of 60 lp/mm is in line with the perfect MTF curve. The lens and prism are probably not perfect so the 400-420 lp/mm seem like a reasonable extinction value. These numbers seem consistent with what one would expect from a good 42 mm objective. Since the text stated that the MTF curves were in general agreement with the (and not generated by the) interferograms, I assume (maybe a very bad assumption) that the MTF were done by the generally accepted method of using a target of a sine wave pattern or, more common, a standard bar pattern target. I will leave it at that and not get into the Ronchi test (I am not qualified) were the grating is inserted at the focal plane since, as far as I am concerned, that test is more about aberrations than resolution and contrast. For more information about choosing the grating and relay lens dimensions see <a href="http://www.mmresearch.com/articles/article1/index.htm" target="_blank">http://www.mmresearch.com/articles/article1/index.htm</a> In my own opinion and from what I have seen, small enclosed telescopes and binoculars and other optics that have a generally inaccessible real image are defined by the resolution of an object where photographic optics have either film or a sensor that capture the real image and can be analyzed separately.  Have a good day.Ron</blockquote>

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