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Message: <blockquote data-quote="Surveyor" data-source="post: 3172332" data-attributes="member: 50720">Hi Kimmo,I, of course, agree with you and Henry on this. In order to simplify and make MTF plots more useful for general comparisons I will relate some shortcuts I have found useful over the years.First, a general premise or assumption or two that I regard as accepted. Any aberration present results in a defocus of part or the entire image. The various lumps, bumps and bulges and other displacements are the result of these accumulated errors.For the sake of simply comparing one instrument to another and keeping track of them in the same terms for consistency I just compare my plots to the general defocus chart instead of trying to rate each by SA, astigmatism or whatever.I think you understated the importance of proper manual focus; this is the most common and largest source of error in a lot of the plots.When I do a test I first focus the instrument with a highly boosted image and have a micrometer drive attached to the focus control, leave the optic at that setting while positioning the imaging system. The target is at the focus of a collimator that is pretty close to ISO standards. Once I have the IS in place I then take images at 1, 2 and 3 mm either side of my starting focus point. Without disturbing the IS as much as I can, I take the files to the computer and run a rough curve reduction using the assumption that the best focus results in the best curves, If there is to great a spread in the curves I go back at start at the best point and go in 0.1 mm steps either side and repeat the process. Once I am satisfied I have the best manual focus I then image at vertical, horizontal and 45° and take the middle curve as average. Although I have a very stable imaging platform it is not unusual for different setups to be off infinity focus by several tenths of a diopter, worse with wide lenses. Occasionally even this procedure is inadequate.I have attached a pdf from the book Henry mentioned for those interested to look at. Also attached a file of some of my older tests.</blockquote>

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