Also without any lens, replacing these for 3 set of tube lens to increase o reach 200 mm.
Eeek.
It's an "infinite" lens, so isn't designed to be used that way. It's designed to be used with a "tube" lens in a microscope. You DO get a deterioration.
Your adapter is very close to the camera lens you're showing above which you're using to do the same function as a microscope Tube lens. That's usually OK, but does mean that any reflections in there can have several bounces between the glass and surround beforte winding up at your sensor. (But if you increase the distance, you'll
eventually get vignetting.)
The inside of the adapter should be dull black, and any bright rings on the back of the objective, covered. I used a dull material something like the "Protostar" you'll see quoted on the forum, to cover the adapter, plus about 4mm extra, which is enough to cover shiny objective back-ends.
Look into the back of the camera lens, with the objective pointed towards a bright light. You may see light coming from other than directly from the objective. On one 200mm camera "tube" lens. I see a bright ring which is masked by closing the lens aperture half a stop.
Put a tube of black paper around your objective, taped to itself so you can slide it, like a lens hood. You don't want any light coming from your light source directly into the lens. That gets tricky because it'll be in the way of lighting the subject as well.
The "E" and "BE" series of objectives are the cheap ones, it has to be said. It seems reasonable to assume that the manufacturer would put more effort into lens coatings, and potential shiny internal structures, on the more expensive ones with the same specifications.
* Some of these objectives are remarkably low cost these days. If you look back at prices of a few years ago, when Nikon were charging $3 for a 50 sheet pack of lens tissue, their Mplan 10x was $692.
One wonders where the savings were made.
(One of us is gonna have to change his name!)