Interesting but why? In the relatively short time since taking an interest in telescopes I've come to these conclusions: The purpose of any scope is to magnify. To bring something that cant be seen with the naked eye up to an image that can be observed. Magnification has two requirements; lots of light and a high resolution image. Making a scope with big aperture to gather plenty of light and a long focal length to preserve image quality means making a really big scope. Everything commercially available sacrifices one or the other, or a little of each in order to be compact enough to be marketable to the general public. I dont like to sacrifice. I want to build a scope that has both and can handle a high magnification eyepiece and still produce a beautiful image. This means I sacrifice portability and I'm ok with that. The 9 foot tube allows me to minimize the diameter of the secondary thus preserving aperture. I think this might also help with light pollution, maybe? I have no plans to use a glass window, just going to leave the top open unless that is problem. Also, if it works as planned I will at some point pay the extra cost (assuming I can afford it, I haven't looked at prices yet) to coat the secondary and tertiary mirrors with the silver stuff...supposed to have better than 99% reflectivity. And I do intend to purchase, not make, the flat mirrors.
Hi everyone. So I'm interested in grinding my first mirror and building my first telescope. I've been reading all that I can about telescopes and watching videos on YouTube. What I want to make is what would probably be best described as a Nasmyth Cassegrain style telescope. My initial idea is to use a 12 inch parabolic primary ground to a focal ratio of 15 and a flat secondary. With a 15 foot focal length the end result will be approximately a 9 foot tube, which is fine, that's actually what I want. I don't care that it won't fit in the trunk of my car, it's not an issue. After reading some articles I've learned that most Cassegrain style telescopes use a convex secondary and a steeper curvature on the primary. Would this be better? Would aberrations be worse with a flat secondary? I want as sharp of an image as I can get without sacrificing either aperture or focal length. It seems intuitive to me that a faster primary would result in a poorer image than using an f15 with a flat secondary...thoughts?