In answer to post #11.
I own 2 Scoponets. They’re 20X. The two plano-convex lenses are uncoated and require the user’s eye positioned quite close to the eyepiece. Realistically, this is optically no better than the Paterson Micro Focuser. I find the view of the Paterson brigher and easier to use. The view has less contrast than that of the Paterson. Nonetheless, the Scoponet was the only focuser I owned for the first 15 years of my darkroom work.
One thing to keep in mind: All focusers work best when you close the aperture on the enlarging lens about 1 stop from wide open. That refines the view considerably, making it much easier to focus the enlarger accurately. If you already own the Paterson Micro Focus Finder, the Scoponet offers no practical advantage.
You might find the following Scoponet Notes useful:
Scoponet (France)
Thomas Instruments Scoponet 20X, uses two 2-element uncoated plano-convex lenses. The base to the center of the mirror is 105mm. The eyepiece tube is 45°from vertical. The mirror’s normal axis is 22.5° from vertical.
The first version was built on a cast aluminum alloy body. It is packaged in a tall yellow box with black horizontal bands at the top and bottom. The top of the box is marked, “Verifcateur de Mise au Point, SCOPONET por Agrandisseurs, Imp. Cart. CELLE & Gullin, St. Chamond.
The foil label on the base of the Scoponet reads,”Scoponet, Ets M. Torret, FRANCE.” The index reticule is on a thin, transparent plastic disc.
Disassembly: The barrel must be unscrewed from its receiver at the top of the instrument. The two lenses and their spacer are retained by a threaded brass retainer ring at the bottom of the barrel. The bottom of the retainer is flat and can only be turned by friction, since there are no drive slots. It bears against the bottom lens, so obviously, it can’t be tightened by much. Otherwise, the clamping force might damage the glass.
The retainer can be turned with the friction of one’s thumb. A better choice is the smallest tapered rubber ring in the Japan Hobby Tools rubber lens-opener set. The small end is the ideal size to drive the retainer while clearing the ID of the barrel.
It would be a good idea to set a white towel over the opening of a plastic dishpan and work there so that the parts don’t fall to the floor and get lost or damaged. Once the retainer is removed, you could simply turn the barrel upside down. The lenses and spacer tube will fall out onto the towel.
Lens Orientation: The design uses two plano-convex lenses. They are positioned “belly-to-belly” like a pair of condenser lenses. The only eyepiece design I can find in various references with this configuration is labeled a Ramsden eyepiece. The image is mediocre and somewhat low in contrast. But it gets the job done. I can see the grain well enough to determine when the enlarger is precisely focused.
The two lenes are separated with a thin blackened brass tube spacer of OD = 0.4524” (11.49 mm), ID = 0.393” (9.96 mm), length = 0.221” (5.61 mm). If you place the lenses on their flat sides on a sheet of white paper on a tabletop under good light, you can see that one lens is slightly thicker than the other. The thinner lens is mounted closest to the user’s eye. The marginally thicker lens is mounted at the bottom of the barrel, with the two lenses separated by the length of the spacer.
Both lenses and their spacer tube can only be inserted or removed from the bottom end of the threaded barrel. Disassembly and assembly are most easily done with the Japan Hobby Tools Lens- Sucker tool using the smallest diameter (about 5 mm diameter) suction cup in the kit. That makes positioning the lens easy without touching it with thumb and fingers.
I tried orienting both lenses with their flat sides facing upwards as in a Huygens eyepiece. It worked, but the image quality was degraded compared to that of the original orientation.
While it is possible to reposition the target reticule within the barrel of the chassis, it is a bad idea, as it was properly positioned by the maker at assembly.
The second version uses a tough, grey plastic body, with a thin sheet metal index reticle that makes indexing the eyepiece to your eyesight somewhat difficult due to the thickness of the reticle. That makes the edges of the reticle indistinct and produces a “rainbow of color” at the outer edges (due to diffraction, I suppose).