SharpCap Forums

For years I have been using a method of centering on the CNP by framing very close to it (within .5 degrees) and taking a 6 minute high gain exposure that reveals the circular star trails. That is just enough exposure to see 'arcs' which point out where the CNP is located. The CNP is located in a small pentagon shape made up of very faint stars. Then, using an erasable marker on a bright star, move that star with 7 second exposures to a place and distance that will put my camera looking dead center into what I call the dog house (pentagon)..

This works pretty good but I wanted to check this alignment out by rotating the German equatorial mount 90 degrees. If it is good, an d nothing shifted around during the RA rotation, the location of the CNP should stay in the same AREA as it was before the rotation was made. But I've repeated this MANY times and I have seen it move out to roughly the same place,, about a .7 degree change. I think the problem is caused by the RA axis is not parralel with the telescope tube. Also The mount may not be set up level enough. Can you think of other factors The mount is reasonably rigid.

The next time I go out I will use the SharpCap method of polar alinement. But a question or three first.

Do I need to not have a right angle between the camera and focuser?

Could it be that the SC method could overcome what mechanical problems I suspect that I have?

If not,, do you have any suggestions as to what I could try? Carl Wagle

Hi,

SharpCap polar alignment will not be affected by the telescope tube not being aligned with the RA axis, or by a slightly-off right-angle at the focuser. The main mechanical problem that can sometimes cause SharpCap's PA routine to give incorrect results is if any of the alignments *CHANGE* as the mount is rotated. Obviously as you rotate the mount the direction of the gravitational force on the tube, camera etc changes relative to the support points and if things are not fully tightened up then there can be movement. Even a dangling USB cable can be enough to pull on the camera and potentially cause it to move slightly in the focuser.

There's more discussion of the problem of flexing and how to spot it about half way down this page : https://www.sharpcap.co.uk/sharpcap/fea ... leshooting

cheers,

Robin

Thanks Robin. I feel 99% certain there is this misalignment you and I have mentioned, "SharpCap polar alignment will not be affected by the telescope tube not being aligned with the RA axis,". I've been absorbed by this possibility for at least 2 months. My reason for being so interested in it is I figure that without guiding and using an inexpesive Celestron CG-4 mount I need BETTER Tracking so that the SC selected stars that it stacks with will stay in the Frame longer so I have a longer time with my target before a loss of these stars leads to progressive failures to stack.
I was able to stay on M-101 for about 1.5 hours last May 14th. Got a great pic. by my standards. Hoping to find a way to track and stack for double that time by using the SC PA. Shimming the dove tail, as well as beneath the feet of the tripod has gotten me no where!
Now,, the future (in the dark) looks brighter! Carl