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Message: <blockquote data-quote="Binastro" data-source="post: 3164609" data-attributes="member: 111403">. I said that there is nothing very difficult about making F/2 mirrors if the design requires it.I have been trying to find out the full specification of the large Maksutov binocular. I remember being told by the maker that the primaries were 12 inch, but I see reference to the binocular being 11 inch aperture. I think both of these can be true as Maksutovs may have oversize primaries. I have not yet established whether the primaries were F/1 or possibly a bit slower. The final F ratio may have been about F/4 or F/5 although I'm not sure of this. His telescopes usually had beautifully made secondaries and relay lenses.As to the comment about my having read about optics and not having made telescopes.I am not a telescope maker, I am a telescope user.I have used over 30 compound mirror telescopes and mirror lenses that have primaries of F/2 to F/2.5.In addition, my main telescope had the relatively slow F/3.5 12.5 inch thin edge main mirror, with a final ratio of f/14.7. Its larger brother, which is still being used has I think an F/3 primary. It is 16.3 inches aperture.Unfortunately, the gentleman making the the large Maksutov binocular was in his 80s and was unable to complete the instrument.. When I say that there's nothing very difficult about making F/2 mirrors, I mean that it is not difficult to somebody or to an organisation that makes these things.The gentleman making the large binocular made dozens of beautiful compound mirror scopes with primaries of F/2 to F/2.5. I have used some of these.I would estimate that there are more than 100,000 compound mirror telescopes and mirror lenses that have primaries of f/2 to F/2.5. For the people who make these mirror telescopes and mirror lenses it is not that difficult as they would not be making them and selling them for relatively low pricesNowadays, you can buy a good quality mirror telescope for about £100 or £200 and mirror lens for £100 or less.The Japanese mirror lenses in particular are very good.I have an Optomax 500 mm F/8 mirror lenses that splits both components of Epsilon Lyra using a three times teleconverter and a 10 mm monocular converter. That is, it is cleanly splits real stars of about 2.3 arc seconds separation, and on a normal photographic tripod.The Nikon, Minolta and Canon 500 mm F/8 mirror lenses are of similar quality.Similar mirror telescopes are of even better quality.I also find out now that a British worker was regularly making small optical units with top quality F/1 mirrors for industrial use.I am not recommending that Maksutov binoculars are a good idea. I was only replying to the question whether such binoculars have been made. The only one that I have seen is the large one mentioned, which was not completed because of old age.They are not a good idea for normal binoculars because of the complication and the fact that they have narrow fields. They might be interesting as a high-powered binocular, but even then they have to be made to extremely fine tolerances and they are critical as to alignment individually and as a pair.Neither am I advocating off axis designs.But discussion of different designs should in my opinion be allowed without personal attacks.As it happens, I think that the Yukon 30×50 is a magnificent effort. It is a pity that it doesn't have full multi coating and enhanced mirror coatings. It is the most usable 30 times binocular that I have seen.</blockquote>

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