I achieve pretty good collimation with my 2" combo tool indoors, but observing in the field at higher magnification I have not been happy with the star images. They are nice in the lower half of the field, and not so nice in the upper field. Even high magnification planetary observing showed marked image degradation in one part of the FOV, but it improved as the image drifted across the FOV.
It took me a while to realize it was not a result of my collimation, rather it appears to be a problem with the registration of the focal extender and eyepiece in the 1.25" adapter. Experimenting one evening, I realized I could improve (or degrade) the star image by experimenting with the adapter and focal extender thumbscrew tension and orientation. I finally found a combination that is approximately repeatable.
I believe I understand the difference between eyepiece registration, tilt of the eyepiece optical axis, and the idea the eyepiece and focuser axes should be parallel, at least, rather than centered. The idea a small amount of registration error in the eyepiece can result in quite a bit of axial tilt over the focal length. Even with the focuser axis firmly on the primary center.
I am thinking about getting a Parallizer, and any experience with ES eyepieces and especially the tapered barrel of ES focal extender is appreciated. It looks like it will work. But, for now, taking some cues from other threads on CN, I managed to use what I have to keep the tilt to a minimum with much better star and planetary images across the FOV.
First, the 1.25" eyepiece adapter fits into the 2" focuser with three thumbscrews. I removed the compression ring a long time ago because it caused the adapter to unseat against the focuser. But, now, instead of three thumb screws, I chose to use only the two that are pointed toward the ground and removed the one on top. I understand this forces the adapter snug against the inside of the focuser to help keep it parallel with the focuser.
Second, I make sure adapter is seated in the focuser with the thumb screw on top to counteract gravity pulling on the focal extender, then snug the two thumb screws to hold it. The focal extender is then held seated in the adapter and the thumbscrew (compression ring) snugged enough so it does not move, even with the tapered barrel. The thumb screw pushes town on the focal extender barrel as the compression ring tightens.
Next, there is a compression ring in the focal extender to hold the eyepiece, but it does not seem to cause any adverse tilt of the eyepiece even with a tapered barrel. The thumb screw and compression ring are just touching the eyepiece barrel. Too tight does not work well.
Lastly, I observe the star field at high magnification and adjust the tension of each thumb screw until the star images look good everywhere. The 2 to 1.25" adapter is in the same configuration as I collimated the scope, and it appears to be working just fine. With that, planetary images appear to be in better focus from edge to edge.
Any thoughts or experience is appreciated. Also, any nudge toward getting a Parallizer is all I need to order one, provided the ES focal extender will seat nicely so the Parallizer works correctly. But, I seem to have worked out the bugs to a large degree and even learned to check my focuser and primary alignment at night using my combo tool. I've only seen the primary collimation change once, but I think I fixed that, too.
Thanks in advance.
Edited by Asbytec, 18 October 2020 - 02:26 AM.