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Message: <blockquote data-quote="Surveyor" data-source="post: 3173725" data-attributes="member: 50720">Thanks Kimmo, Henry;KimmoThat is sort of what I was getting at. It is very hard to get very good focus on a bench with effort. Focusing a hand held instrument in the field could be very hit or miss. I could easily envision someone looking at a scene a couple of times, refocusing between views and getting different perceptions of the same view at the edges, especially if he is of my vintage with poor accommodation.Ed,I'm really interested to understand your approach. Would you mind expanding on a few things I'm not quite following:•    The meaning of "IS." (I don't get the acronym.)In this case I am referring to the imaging system, a digital camera but without autofocus. A screw type focus is used. Focus is too critical for autofocus. Usually short focal lengths to the sensor, 70 to 150 mm common to get proper image size. I also use "IS" for integrating sphere, part of the lighting system.•    Computerized "curve reduction." (Data fitting, curve smoothing?)I have emailed you a document I did 8 or 9 years ago giving basics (not exactly technically correct, simplified to highlight the main principles). Since then I have changed my method to the ISO standard method of SFR (spatial frequency response method). This method uses a computer program to read and process the pixel data.•    Bench setup to measure MTF. (Photo/sketch how the instruments are positioned relative to the binoculars, etc.)Basically the same setup as a resolution test. A diffuse light source, a collimator with the target at the focal point, the optic under test then the imaging system (replaces the usual booster). Note: a dioptometer with crosshair is used for focus, discussed above, and to align the axis of the optic with the collimator to get the collimator and optic on the same axis. Collimator used to make sure you are always working with infinity focus.•    Chart coordinates. (Ordinate = MT, Abscissa = ?? frequency units)The chart x and y are direct out put of the program data for each pixel. The y axis is the computed contrast at that pixel location, the x axis angular location along the x axis as determined by the pixel location for its angular size. In the case above shown as degrees/cycle. To get to seconds, {1/(c/d)}*3600/magnification.•    The LXL tubes seem quite different. (Comment??)These are my hand picked 8x20’s that I carried when working. They are very good results and differences between tubes is very common and by considerably more than the ones shown. A large percentage of the binos I have tested are greater than 2 waves total error. Attached are computer generated plots, one shows a MTF with SA of 1/2 wave and astigmatism of 1/2 wave, the other plot is just 1/2 wave of simple defocus and a couple of 2 wave plots for reference.Sorry to be a bother, but when I get interested I ask questions.  Regards,Ed</blockquote>

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