I suspect that the problem of the narrow field of view is often mis-attributed wholly to the inherent properties of the long focal length, when a surprising amount of it is actually due to a killer-narrow baffle in the draw tube. For my honorable, but not not valuable, f/15 Jason 313, I removed that baffle. For my collectable f/16.7 Tasco 7te-5, I stored the original draw tube in the cabinet, and replaced it with a new one without a baffle. Both draw tubes were then flocked and converted to accept 1.25" diagonals and oculars, resulting in notably wider fields of view and brighter images.Yes, the inherent flaw of slow refractors is difficulty getting low-power views. With 1.25" you can use up to a 40mm Plossl with a AFOV that maxes out the barrel, about 45 degrees. Still it is fun to use these scopes in period context. Also fun to run them up to maximum tripod height and look straight through, UP at the sky, no diagonal.
-drl
Note that the success with the Jason 313 occurred despite its draw tube being an odd, narrow size that I could not replace, because a 1.25" draw tube would not fit into the focuser. Furthermore, in the first iteration of its conversion to 1.25" when its narrow baffle was not removed, the scope was not improved so much as it became the King of Kidney-Beaning. The wider field of the 1.25" diagonal and ocular were simply allowing them to see the baffle! This illustrates the importance of eliminating the choke point of that narrow baffle.
Neither scope shows as wide an image as a faster scope would allow, but long focus scopes are capable of wider views than they were originally designed to show.
Edited by Joe Cepleur, 06 March 2024 - 09:04 AM.
