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Message: <blockquote data-quote="Surveyor" data-source="post: 1280020" data-attributes="member: 50720">Ronh;Sounds good to me. I had got stuck on the object/target side of the objective, neglecting the image side. Strange for me to overlook this since my collimator has a USAF 1951 target at the focal plane, duh. Henry/Ed;I hope you carry this topic on awhile. I have trouble sometimes figuring out just what format people are using. In most situations, engineers and surveyors use lines per mm (each black bar and white bar are counted) most of the time. I only converted to line pairs/mm when I started viewing the BF. There are a lot of examples that I can bring up but will keep to a minimum for now. Attached is a picture of a typical level/stadia rod, a device that is mimicked for a lot of different fixtures and procedures. Notice that a black bar counts as one unit and a white bar is another unit. Between 10.6’ and 11’ there are 40 divisions, 20 black and 20 white, each being .01’ increments (50 line pairs/foot or 100 lines/foot). These spaces, both black and white, are often further subdivided by 10 by use of a vernier attachment. I refer to the two standards frequently. Most of my work related figures are what I call detectable resolution. For instance, a lot of our cheaper instruments are only capable of 2.4 arc seconds RMS so I have to be careful that the target should at least be that size, whether it is a plumb bob string (1.5mm @ 100m=3.1” and you can see it a lot further out), a 30 mm range rod @ 2km=3.1” (easily seen at 3km), triangulation lights used at night that are 400mm diameter that we try to stay within 25km of and larger targets from mountain top to mountain top. Over the last 20 or 30 years some lp/mm requirements have come into surveying practice. The point of the above is that we can detect antennas, wires and other objects considerable smaller than Dawes would indicate and measure them but if two are close together; we may not be able to separate them. NGS and USGS, when they require instrument calibration/verification, you report resolving power in lp/mm and the angle split accuracy (the 2.4” above) is the RMS value of a number of direct and reversed observations to a single bar to measure the pointing accuracy. Some agencies still want the USAF measurements in lines/mm. There are a lot of other applications where single line resolution is needed. A typical IR thermometer or FLIR thermograph with specifications stated in mrad have to be computed to make sure the sensitive area is completely contained on the target face to keep from mixing the background temperatures with the target value. Distance measuring equipment has the same limitations. So as you can see, as far as I am concerned, there is a difference between lp/mm and l/mm. Until I came to BF the only time I ran into line pairs were in photography or printing applications, with an occasional pixels/mm thrown in to really confuse the issue. Still, the only time I think in lp/mm is here on BF and I try to stay with that convention. I guess the biggest difference in my optics is that most are measuring optics instead of just viewing optics. I look forward to more clarification and standardization on the subject. Best to all.Ron Also attached a copy of my worksheet for resolution that I have inserted columns for line pairs.</blockquote>

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