*NOTE - I used these mirrors for this version of the ABSDBS-8"
Primary mirror diameter: 203mm (8")
Focal length: 800mm (31.5")
Focal ratio: f/4
-=HOWEVER=- I have since learned that they are spherical mirrors, not parabolic. And at such a low f-ratio, this causes a large amount of aberration! In short, I do NOT recommend these mirrors. I suggest looking for different - parabolic, if possible - mirrors. (Although, parabolic mirrors are more expensive.) Here is a bit of helpful info:
-The distance from your primary mirror to your secondary mirror is determined by the focal length. These mirrors have a short focal length (and FAST focal ratio) so this version of the ABSDBS-8" is physically much shorter than the original design.
The images illustrate the process I took to determine the optimal length and position of my truss tubes. I wanted the focuser to be in the middle of its range of motion (travel) when the image in the eyepiece is focused. I found that the truss tube length should be 59-60cm long when measured from the bottom of the tube clamp to the top of the opposite tube clamp.
The nice thing about the shorter telescope is that one, it's smaller and easier to move. And two, it's lighter... which also means I didn't need a counterweight underneath the primary mirror. (However, depending on what's mounted to the focuser end - finder scope/laser pointer, etc. - a small counterweight might be needed on that end instead.)
I did a quick collimation and got a decent view of the top of the radio tower out back, but unfortunately it's not nearly good enough for actual astronomy as illustrated by the poor image of Jupiter (and moons). It seems a lot of time and precise adjustments will be needed to get this scope perfectly aligned and collimated.
I also used the following designs/makes for this telescope project:
1) Spider and secondary mirror holder: https://www.thingiverse.com/thing:2837604
2) Focuser: https://www.thingiverse.com/thing:2658607
3) Thumbscrew: https://www.thingiverse.com/thing:2424613
A HUGE thanks to:
They helped me tremendously throughout my build process.
And of course, to:
I've always wanted to build my own telescope, and I couldn't have done it without him!
Find me here: