Post by kp3ft on Apr 7, 2013 9:34:48 GMT -5
Hi,
Is there any chance of Istar producing planetary folded-refractors in the future? I don't think there are any commercially-made folded refractors produced anymore. There was in the past; I believe Unitron and others made some. The advantage is obviously the shorter physical length of the tube assembly, particularly for long f/15 (or longer) planetary scopes, although I'm not sure if there is enough demand to justify production. I once had a very nice picture of what must have been a commercial scope with a "single-fold", but unfortunately can't find it. It was a round tube assembly with the the single "fold" at about 2/3 of the length, pointing back in the direction of the main lens, and angled out perhaps 30-degrees. It also was angled up around 30-degrees or so, and did not have a diagonal. A diagonal isn't necessary in this case because the "fold" and angle provide the same convenience of a diagonal. I'm guessing that a "single-folded" refractor without a diagonal is optically the same as a conventional refractor with a diagonal. There are quite a few "multi-fold" scopes that amateurs have made, but obviously the more "folds" (i.e., mirrors), that are introduced increases optical errors, so a single-fold would make the most sense. I imagine collimation of multi-fold refractors are probably a real test of patience
A single-fold f/15 (or longer, f/20, etc.) scope might be attractive for people who want a dedicated planetary achromatic telescope without the extreme physical length of a normal conventional scope.
In summary, with my limited knowledge, a single-fold long-focus telescope at f/15, f/20, or longer, without a diagonal, might be attractive to people who are primarily interested in planetary/lunar observation, which would conveniently have shorter overall length but the same optical quality as a normal scope equipped with a diagonal.
Is there any chance of Istar producing planetary folded-refractors in the future? I don't think there are any commercially-made folded refractors produced anymore. There was in the past; I believe Unitron and others made some. The advantage is obviously the shorter physical length of the tube assembly, particularly for long f/15 (or longer) planetary scopes, although I'm not sure if there is enough demand to justify production. I once had a very nice picture of what must have been a commercial scope with a "single-fold", but unfortunately can't find it. It was a round tube assembly with the the single "fold" at about 2/3 of the length, pointing back in the direction of the main lens, and angled out perhaps 30-degrees. It also was angled up around 30-degrees or so, and did not have a diagonal. A diagonal isn't necessary in this case because the "fold" and angle provide the same convenience of a diagonal. I'm guessing that a "single-folded" refractor without a diagonal is optically the same as a conventional refractor with a diagonal. There are quite a few "multi-fold" scopes that amateurs have made, but obviously the more "folds" (i.e., mirrors), that are introduced increases optical errors, so a single-fold would make the most sense. I imagine collimation of multi-fold refractors are probably a real test of patience
A single-fold f/15 (or longer, f/20, etc.) scope might be attractive for people who want a dedicated planetary achromatic telescope without the extreme physical length of a normal conventional scope. In summary, with my limited knowledge, a single-fold long-focus telescope at f/15, f/20, or longer, without a diagonal, might be attractive to people who are primarily interested in planetary/lunar observation, which would conveniently have shorter overall length but the same optical quality as a normal scope equipped with a diagonal.