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Message: <blockquote data-quote="Binastro" data-source="post: 3164837" data-attributes="member: 111403">. No,. The Yukon 30×50 that I have is essentially perfectly collimated and gives very nice star images. So it is apparently fairly easy for the maker to achieve collimation that is fixed. I suppose there may be collimation screws but I haven't seen them.Additionally, the Yukon 6x to 100×100 mm spotting scope that I have also gives very nice star images. I definitely would not want to drop this lightweight spotting scope. Also I don't think that I would like to drop the 30×50 binocular, although this seems to be more sturdy than the spotting scope.The alignment problems, relate to Maksutov telescopes. The classic design has the secondary mirror as part of the correcter shell. So there is no adjustment needed for this, although the positioning is critical in these designs.These are usually F/12.5 or slower.I do have a 150 mm F/10 Maksutov, but this needs a separate secondary which has collimation screws. I used this for years without problems, without having to adjust it, but the initial alignment has to be very good.Also Schmidt Cassegrains needs very careful alignment.So having  two of these instruments mounted as a high magnification binocular, using relay lenses would be extremely tricky, may be outside the capabilities of ordinary folk to align.I have a 5.3 inch approximately, Maksutov that had a triplet relay lens made by the person who made all the fast compound instruments mentioned earlier. He was able to figure lenses to give good results. This triplet was broken and replaced by a doublet, and lesser folks simply have been unable to make this instrument work. So basically, for some of these instruments you do need a master optician.Having said that, it is quite clear that large numbers of compound instruments with fast primaries, both telescopes, and mirror lenses for cameras, are being successfully made.I would mention that I have a Samyang 800 mm mirror lenses and the one I have is awful. It is very soft, the contrast is low and the resolution is not very good and the image is mushy.I've also had some of the older mirror lenses, which display bad astigmatism and generally poor images. So it is quite possible to make bad mirror lenses, both custom-made and factory made.I'm not disputing that most people would have trouble making these fast systems. However, there are people who can make them repeatedly to high standards, both custom-made and factory made.I have a 1000 mm F/10 very early Soviet MTO that is unbelievably good. The serial number is in low single digits.Also I've seen and tested another unbelievably good Dutch military mirror lens about 5 1/2 inches aperture.The Mirador 70 mm Maksutov spotting scope that I have has a standard zoom lens of 30 times to 120 times, plus an additional, I think 25 times eyepiece, and will take any Astro eyepiece. I think that this mirror spotting scope probably resolves as well or better at 120x than any 65 mm refractor spotting scope including fluorite models.It is thought that a 70 mm mirror scope like this resolves as well as the best 53 mm refractor. This is because normally the resolution is thought to be equivalent to the full aperture minus the diameter of the obstructing secondary mirror. But spotting scopes use fast objectives and have prisms though, and even exotic ones are not as good as the best long focus refractorsSome people don't like mirror scopes, but others do. The fantastic planetary images taken by Astro imagers are often taken with Schmidt Cassegrains, which have very large secondary mirrors.</blockquote>

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