Quote:
Originally Posted by bojan
Yes and yes 
It is possible (but not easy) to see the designed offset on attached images.
However, on design drawing, the offset from optical axis of the secondary mirror centre is evident |
I see the offset clearly in the photo.
Check my first attachment.
Refer to the left-hand diagram. It represents a reflector with its secondary mirror mounted with the proper offset away from the focuser. This is the typical diagram most have in mind when they think of Newtonians.
Refer to the middle diagram. It represents a reflector with its secondary mirror mounted without the proper offset away from the focuser. Many would claim this is a problem because it will miss part of the light cone. I presume this is the issue you had in mind for a secondary mirror mounted without an offset, correct? This is a common misconception. There is really no optical issues because after the proper collimation steps are completed the primary mirror will end up tilted forward towards the focuser automatically -- as shown in the right hand diagram. Now the central star in the FOV is no longer coincident with the OTA axis which has no impact on the optical alignment.
The second attachment illustrates better how both secondary mirror mounts are equivalent from an optical perspective.
One thing to watch out for is to ensure the now tilted light path does not get eclipsed by the edge of the front opening of the scope. Unless the OTA opening is within few millimetters from the primary mirror size, this is not a concern.
I have my secondary mirror mounted without an away-from-focuser offset and I do not have any optical issues with this setup.
Jason