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Message: <blockquote data-quote="Surveyor" data-source="post: 3569464" data-attributes="member: 50720">Hi Binastro,This information is probably already somewhere on the forum so I will give an abbreviated overview of simple collimators.A collimator is nothing more than lens (better quality lens give better results) with an image or reticule at the prime focus.See the pictures attached. The simplest form for most is the 50 mm diameter lens with a 200 mm focal length set on top of the TV. The two pictures are of two different USAF targets. The glass target you can see group 5 element 2 or 3 pretty well. Element 3 at this focal length would be about 26 arc seconds per line pair. This is not the most accurate/stable setup, but good enough for comparing a couple of cameras or binoculars in a hurry without going outside.The picture of my messy optics bench shows my 5” multi element lens at the top of the picture. It has about a 450 mm focal length and to the right of it, mounted on the optics rail is the target shown earlier. I use this open setup because I change the targets for different measurements. On the table you can see other collimator tubes of various purposes.The picture of the collimator tube is my resolution collimator. For stable accurate results the elements have to very solidly mounted and accurately adjustable. The objective on this tube has very fine threads to adjust to the focal length of the objective.There are many advantages to collimators over outside work, light control, temperature control, wind currents, etc. Plus you can do all the measurements on a table top instead of wandering all over the yard and trying to measure things off. For the example we are discussing, if I put a paper with a grid with lines spaced 3.49 mm at a 200 mm focal length then each grid square would represent 1 degree.The big advantage of a collimator is that all measurements are made a infinity focus, the optics design point.</blockquote>

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