Merlin66
26-02-2017, 10:19 AM
I have bought and used many refractors over the years and still use a Genesis, ED80 and a TS102.
Recently I was asked to look at an older ED80 which seemed to give "odd" star images.
The out of focus disk instead of having the usual three dark "fingers" intruding from the edge (due to the excessive size of the spacers used on some air spaced objectives) this had four bright "ears" symmetrically spaced around the disk!
These in turn caused the star image distortions.....
The focuser was removed to check for any obstructions/ edges on the inside and the baffles. Nothing obvious.
Removing the dew cap exposed the problem....
The objective elements each had four small (really small!) collimating adjustment screws bearing on the outer edge of the lenses.
These were as tight as hell! I'm sure they were pinching the optics terribly..
Backing off all the screws and leaving the objective for a few days seems to have fixed the problem - I still have to check and re-collimate.
Moral of the story: If you don't know what you're doing - Don't!!!!
Recently I was asked to look at an older ED80 which seemed to give "odd" star images.
The out of focus disk instead of having the usual three dark "fingers" intruding from the edge (due to the excessive size of the spacers used on some air spaced objectives) this had four bright "ears" symmetrically spaced around the disk!
These in turn caused the star image distortions.....
The focuser was removed to check for any obstructions/ edges on the inside and the baffles. Nothing obvious.
Removing the dew cap exposed the problem....
The objective elements each had four small (really small!) collimating adjustment screws bearing on the outer edge of the lenses.
These were as tight as hell! I'm sure they were pinching the optics terribly..
Backing off all the screws and leaving the objective for a few days seems to have fixed the problem - I still have to check and re-collimate.
Moral of the story: If you don't know what you're doing - Don't!!!!