Jims Mobile make these types of telescopes, the only problem I see other than having three mirrors (excess cost) on one of the folded newt designs is that you have a large Secondary obstruction with the three mirror system and the two. The two mirror system is the same as a typical newt but the mirror is angled less to allow the focuser to be bought further down the tube, but in some cases at a awkward angle. In any case the secondary mirror would be much bigger so the light cone will fit onto it, as the distance from Focuser to secondary is somewhat larger. Its a hit and miss game. I would say the design would be more benificial in a Larger newt 18" and above, rather than a small diameter telescope that does not need the restricted heights. Anyway check out this page, tells you a little.
You could also work with instead of a flat secondary, have a convex secondary to magnify the image before hitting the third mirror. (I think thats how it works.) But then it would be a folded cassergrain
All folded scopes have a compromise. For the same eypiece fold outside the tube, two mirror Newts have a lesser obstruction than three mirror folds but th eyepice points up at typically 45 degrees. The problem with all folded scopes is in th ebaffling.
Heres a link to Dan Grays folded 28". Gives you an idea of complexity in baffling the secondary mirror.
Another thing to remember is that the light baffle will have to extend way beyond the telescope around two metres from the secondary for a 24" having a flat secondary.
I was going to point you to Dan Grays web site but Mark beat me to it. To me the inclined eyepiece axis 2 mirror concept is probably preferable to the 3 mirror concept due to simplicity, although I assume you can get a much lower EP height with the 3 mirror option.
I have to say, I rather like Dan's 28" scope design (I know I am biased , but even ignoring it has a string truss).
To me the inclined eyepiece axis 2 mirror concept is probably preferable to the 3 mirror concept due to simplicity, although I assume you can get a much lower EP height with the 3 mirror option.
No, the two mirror option gives lower eyepiece position for the same central obstruction as a 3 mirror system. . The third mirror moves the eyepiece back up the tube with the 90 degree reflection ( as compared to 45 degree angle in the two mirror system) , but is much easier to baffle than the two mirror system. Private communications I've had with Dan suggest he is still battling with skylight flooding the field, in his two mirror system despite the complex baffle he has .
My personal option would be a faster mirror and a coma corrector ,rather than folding.
A fast mirror with a corrector would be the way to go making a shorter telescope without mucking around baffling light.
But if using a folded design a convex secondary (as Andrew mentioned) would bring the eyepiece down even lower and maybe reduce the baffling.
A "can" or round "shroud" around the secondary and tertiary mirrors might do the trick. I'll have to draw it up on the CAD to see.
Folded Newtonian
, but even ignoring it has a string truss).
