DSC problem and solution, your opinions please!Posted By Ed Moran |
Hi All,
My DSC's were not working well with my 12.5" Discovery PDHQ, with the first few goto's falling within a 1.0 fov, but subsequent objects farther and farther out. I discovered (hey, that's almost a pun!) that the hole in the bottom of the rocker box was about 3/16ths of an inch offset to one side, but ok front to back. I plugged the hole and re-drilled it on center and my last time out all objects fell within a 1.0 degree fov all night long. So the problem appears to be resolved. What I would like is your august and learned opinions on my reasoning as to why the 3/16ths offset was a problem. Here goes:
At the eyepiece, with the scope pointed at the horizon, one inch of movement in azimuth = 1.5 degree of movement on the sky (or about the apparent diameter of M42).
This is based on the fact that my eyepiece is about 3 feet from the point in the center of the OTA where the altitude and azimuth axes intersect.
At that radius, a 360 degree circle described by the eyepiece is about 226 inches in circumference. So 360 degrees / 226 inches = 1.5 inch per degree. Therefore a 3/16ths mechanical offset = .25 degree of sky offset.
This value gets worse with the scope pointed up at 45 degrees and higher, since the diameter of the circle (described by the eyepiece when the scope is rotated 360 degrees in azimuth) gets smaller.
Cont. next post.
My DSC's were not working well with my 12.5" Discovery PDHQ, with the first few goto's falling within a 1.0 fov, but subsequent objects farther and farther out. I discovered (hey, that's almost a pun!) that the hole in the bottom of the rocker box was about 3/16ths of an inch offset to one side, but ok front to back. I plugged the hole and re-drilled it on center and my last time out all objects fell within a 1.0 degree fov all night long. So the problem appears to be resolved. What I would like is your august and learned opinions on my reasoning as to why the 3/16ths offset was a problem. Here goes:
At the eyepiece, with the scope pointed at the horizon, one inch of movement in azimuth = 1.5 degree of movement on the sky (or about the apparent diameter of M42).
This is based on the fact that my eyepiece is about 3 feet from the point in the center of the OTA where the altitude and azimuth axes intersect.
At that radius, a 360 degree circle described by the eyepiece is about 226 inches in circumference. So 360 degrees / 226 inches = 1.5 inch per degree. Therefore a 3/16ths mechanical offset = .25 degree of sky offset.
This value gets worse with the scope pointed up at 45 degrees and higher, since the diameter of the circle (described by the eyepiece when the scope is rotated 360 degrees in azimuth) gets smaller.
Cont. next post.
