I'm designing my first Newtonian telescope around a 160mm/1300mm f/8.1 primary and a 35 mm secondary.
I need help understanding the mechanics and requirements of the focuser. I'm trying to figure out the distance between the primary and secondary: from the focal length I should subtract the outside diameter of the tube plus the height of the focuser.
Most references (e.g. The Dobsonian Telescope) recommend a "low profile focuser" that stands at about 50-75mm (2-3 in) when fully racked in. These references rarely go into much detail into the focuser, I imagine because they suppose some prior knowledge of them (which I don't have).
My questions are multiple and some may be simple in nature. I have already played around with some helpful tools (e.g. Newt) as suggested by other users but I haven't found all the answers I was looking for. Thanks to everyone in advance.
- How much "travel" (that is, the difference between the fully racked in and out heights) should I aim for? Does it depend on the type of eyepieces I will use?
- When calculating the distance between the primary and secondary, should I consider the average travel height of the focuser? Again, does it depend on the eyepieces?
- It seems very simple to build a "primitive" focuser that just works (some even use only an appropriate tube of cardboard/brass). Are there any cheap commercially available alternatives? Does it make sense to buy them?
- What's the con of using a relatively taller focuser to shorten a bit the distance between the primary and secondary?
Edited by blundered_bishop, 26 September 2021 - 09:27 AM.