I believe, as in post 7, it is more of an alignment issue than age related.
Binoviewer experts say the major difference between a budget binoviewer and a top end model is not as much optical as it is mechanical. The budget models have eyepiece holders and grippers that do not lend themselves to easy object merger at all times.
And, as with a true binocular, mis alignment or mis collimation affects small or point objects much more than larger extended objects.
Here is what has helped me with the Arcturus and similar type binoviewers...
If possible, use eyepieces with no undercuts. The undercuts add to the difficulty of getting the eyepieces aligned and objects merged. Even if you add some layers of tape to the eyepiece barrel, it helps.
The thing that worked the best for me is to put the eyepieces in the eyepiece tubes, again preferably without undercuts, and slowly tighten the collets until they just touch the eyepiece barrels, and no more. Really, just touch the barrel.
This will center the eyepieces and align them. It is the lateral pressure from tightening the collets that is the issue and throws the EP alignment off. This did wonders for me using the Arcturus.
Also so I wouldn’t use huge, heavy eyepieces. And you don’t want to position the scope so that the binoviewer is angled greatly in reference to the horizon. A line drawn from the center of one EP to the center of the other should be horizontal. This is easy to do and maintain with an alt-az mount, but requires re-adjustment with an equatorial as you move from object to object.
Be careful at certain positions the eyepieces don’t fall out. Unfortunately the loose eyepiece method works best, at least for me, to get easily merged images... even of single point stars. Give it a try.
Added: To see the effect of mis-aligned eyepieces and how having them tight affects alignment and merger, you might also give this a try:
With the eyepieces in their holders go a little past just touching to very slightly tightened. Look at a planet or bright star. Grab the top of the right eyepiece only and slightly twist it left or right. You will see the two non-merged images getting further apart or closer - even close enough to merge.
But, the loose just touching method is still better yet and should work. The eyepieces are essentially sitting loose in the holders but the collets adjusted so they don’t move around. Gravity is actually allowing the EPs to sit on the ring stop down the tube and thus be centered and on axis.
The binoviewers are factory collimated and the prisms glued into place. They likely have good collimation. Believe me, most problems are with the insufficient mechanics of the eyepiece holders!
Edited by Joe1950, 03 September 2019 - 02:27 AM.