I have a 10" mirror f/5 and a 2.5 inch secondary. How far away is my eyepiece supposed to be from the secondary? and What size eyepiece would be good for my scope. thanks in advance.
2007-05-14 02:01:32 · 5 answers · asked by Anonymous in Science & Mathematics ➔ Astronomy & Space
It will be about 4-6 inches from the secondary mirror.
2007-05-14 02:09:48 · answer #1 · answered by Feeling Mutual 7 · 0⤊ 1⤋
You want the diagonal as close the the eyepiece as possible, but since it has to be pretty much centered in the tube, it can't ever be closer than than half the tube diameter away. A 10 inch mirror would probably go in a 12 inch tube, and allowing another inch or two for the focuser height, that makes the distance from the diagonal to the Eyepiece 7 or 8 inches. That also makes the distance between the diagonal and main mirror 43 or 42 inches (10*5-7 or 8). Which eyepiece depends on what you want to see. For general use I would just go for the standard 1.25 inch barrel and some medium focal length, like 15-20 mm or so. Most people have a whole set.
2007-05-14 09:15:06 · answer #2 · answered by campbelp2002 7 · 1⤊ 0⤋
It will need to be at least half the diameter of the mirror plus the height of the focuser away from the secondary, at least 8 inches away. A good eyepiece to start with is one which gives you a field of view of about one degree, roughly a 25mm focal length. An 8mm can be added later to give you detailed views of the Moon and planets.
2007-05-14 09:15:56 · answer #3 · answered by GeoffG 7 · 0⤊ 0⤋
By my calculations, the center of the secondary mirror of that size should be no closer than about 40" from the primary mirror in order to prevent vignetting in the largest field of view of the scope. In actuality, it is probably somewhat further away than that. The approximate distance of the field stop of the eypiece from the center of the secondary is equal to the focal length of the telescope minus the distance of the center of the secondary to the center of the primary.
2007-05-14 20:46:26 · answer #4 · answered by Arkalius 5 · 0⤊ 0⤋
Here's a simple computer program for Newtonian telescope design: http://www.dalekeller.net/atm/newtonians/newtsoft/newtsoft.htm
A pair of eyepieces, at around 10mm and 30mm, would be a good starting point for your telescope. A 25mm eyepiece and a 2x barlow is another option.
2007-05-14 12:04:11 · answer #5 · answered by injanier 7 · 0⤊ 0⤋