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Do these lens edges look black to you? Uuh, yeah, sure! But now? Oooh! That was the blackening applied to my new Astro-Professional doublet. Bear in mind that the light exiting at the front first had to pierce the layer of blackening on the other side, but it remained pretty intense, right? Good commendable will on the scope maker's part, and job done, but a second layer of felt marker paint was in order. Yes, paint, felt markers actually apply a kind of paint mixed with a solvent that evaporates very quick. Thus it's quite natural that a second layer is needed for opacity. Stray light will take any path that's open, and bounce off the rough side of glass that has the ideal texture to spread it in every direction, so I also treat bevels. Look at the previous pics, they were not covered at all. The real black distinguishes itself strongly from the mere factory gray. If you knew the lens' specs, and the angle of vision, you could reconstruct an image of that room with a specialized software, but that's another story. While I had the lenses out of the cell, I made permanent rotation marks. A ghost of the factory inverted "V" is visible, I made scratches with a needle the first time I opened the cell, but during the first reassembly I suspect the lenses have rotated because a miniscule amount of paint at the wrong place made the rings sticky. Turning them made the lenses turn, I suppose, based on some loss of snap at the eyepiece, while the star test seemed similar. For future maintenance I dug two notches with the edge of a diamond-coated knife sharpener. Thanks to diamond hardness the job was done in seconds. But what happened to those unblack edges, you ask? That compact led flashlight is viciously powerful but not enough for two layers of black paint at entry and two at the exit. An optician wrote that paint (or ink?) hardens and shrinks enough to compress a lens out of ideal shape, that could be detectable in sensitive tests. Maybe, because the tolerances are only several dozens or hundreds of molecules; 500 nanometers in wavelength of light divided by a good lamba/20 wavefront would amount to only 25 nanometers, we're talking layers of molecules, here. But I still don't figure if the claim is far-fetched or not. The two rear rings have been painted with ordinary blackboard paint. It can chip, I know, however unlike lacquer it dries fast enough to not interrupt the work session, and it's so easy to reapply. The black lens edges coupled to the matte rings produce this effect: the lenses seem to vanish. Direct light from two lamps, a white ring under the cell reflects light at the same angles as intrusive light during real-world observation, but only an extremely faint ghosting occurs. Do you see it? Why two locking rings, by the way? Because a single one could make the lens it touches turn, and ruin the critical rotation alignment. The second buffer ring prevents that. A little not-yet-dry paint that bleeded between them may have caused the problem for a while. Of course, at shallow angles the lenses reflect some light, but the rings behind them remain discreet. It took a white ceiling and a white column (plus a Strat) to make these reflections. Some blackboard paint bled inside the cell scribing, which is not bright ink but an actual etching done into the aluminum with an interesting pointy tool, that's why it's shiny gray. Instead of spending time trying to scrape it, I filled all the letters and numbers; it created a nice, unique variant. Turns out, I always wanted a cell with dark engraving, and it's not lazyness talking. The bevel and the inside of the outer cell is matted-painted, too. If you own an Hyperion eyepiece, the hard, dull black finish in the barrel is the ideal finish but I don't konw how to do it, unaware if it's a paint (doubt it) or some chemical process. I often stargaze from my city, lamps everywhere, so I don't want any shiny areas. Everything but the optical surfaces should be dull black. This will also be useful if I do astrophoto one day - uh, one night - because cameras are so sensitive, and exposures so long, any stray light could damage contrast. But, Ben, but Ben! What are those white dots on the outside of the cell? I never liked the velours that barely puts the brakes on the dewshield's motion, and lets it wobble. The solution is those simple foamy rubber adhesive pads. Trial and error determined the right number was eight. A ring of pads at the very rear of the cell, and another at the very front suppress wobble completely, and they keep the dewshield in place even with a 700 gram tilt-lock (my invention so I get to name it) counterweight attached to it, with the scope pointing vertically. A strip of tape takes marks at the screws' location. I remove the strip, measure the separation of the marks while it's on a flat surface, put it back on the cell, and voilà! Perfect centerline for the rubber pads. Removing lenses means recentering them but their screws are not standard, so I recut a damaged mini screwdriver... ...and quickly glued pieces of any tubing I had to repair the handle and make it more ergonomic. The two notches in different shapes at the screwsdriver's collar help me keep track of turns and half-turns. This slot shape is not standard, a non-matching driver would damage the plastic: The tolerance between cell and lenses was nicely tight, but thanks to the extra thickness of paint, they almost self-align. After inserting them, and driving the screws at the same depth, I did an artificial star-test, found only one screw needed 1/8th turn to get near-perfect centering. The lenses require a gentle push on the side with a toothpick in order to be seated in the cell. They just slide against the cell walls without rubbing, and exit the same without catching. If they were too close to the walls, centering screws would be disabled, and thermal pinching could occur. It seems to have turned out pretty okay. The semi-apo quality shows in the very pale lime, almost white disk, and the purple ring. Intrafocal thru Explore 4.7mm eyepiece (120x). The Explore 4.7 increases chromatism in this refractor and in my achro, but the Myriad 9 reduces it, however it does not magnify enough for star-testing. That rounds up my first line of defense against stray light. How does it perform? Well, with the dewshield retracted, and two lamps shining into the cell from less than two meters: The glass edge and its retaining rings don't shine, and they cast a nice black shadow. The two baffles down the tube are not enough, though, I need to add a couple more, that will be for a later date.
Don't blame me for the silly pun, Tele Vue actually used it in their ads back in the days when they were written on paper. Now that you are enlightened by this piece of trivia in the history of advertising, here's the topic. My urban observing spots are surrounded by public lamps so I need complete blackening in my finders as well as my scopes, or arcs of light and various shapeless flares will show when I don't aim high. Little stars in a 30mm scope can't compete, star-hopping is made difficult. This is how I do the blackening. I start with the amici prism. Cleaning it with alcohol proved necessary, some grease was on the exposed faces. Next I paint the rough surfaces with a sharpie. And the rough edges, too. When all non-polished places are black, funny, it's actually possible to make the prism look all black from a certain angle. Then its housing was not cleanly put out of its mold. I don't like finding uneven stuff, so I rectified it even it if was not important for the finder's function. 40-grit did the job in a couple minutes. The plate side is rough from the 40-grit paper but is now planed, the plate will screw onto it without leaving gaps. From its usable angles the prism now looks like that: a clear window with black sides that will absorb stray light. Larger amici prisms for full-size scopes might require the same treatment; practicing on cheaper stuff makes it less intimidating. The housing is garnished with blackboard paint. See how the inside and the barrel are darker than the surface with the screw holes. This paint is water-based, doesn't smell, dries in minutes, and can be removed from places it covers by accident, just scrape it and rub with a wet towel, not a trace will remain. But it sticks hard enough to not chip over time. Have you seen you school's blackboard chip? The sharpie also cures the objective lenses' rough edges disease. Another funny effect, when the side is barely half-blackened, the untreated edge already looks gray, as if black could reflect on other things; this is promising for the final effect! The promise is kept! In main scopes or finders, this black ring will kill off nearly all the light that touches it, I can guarantee it from experience! The dewshield (made in the proper length by Sky-Watcher, by the way, congrats!) is also painted. See how the bare anodized aluminum ring at the rear is shiny. I don't paint that area or the doublet won't enter. Its own layer of sharpie paint plus the blackboard paint would be too much. Where are all those white dust specks coming from? The retaining ring is a treacherous spot in telescopes because the total area is large even if the thing is narrow, can't leave it shiny, especially at those grazing angles! See the difference with the threaded outside of it. Not an essential job in a finder but done it a minute, so why not? The eyepiece lenses were white on the side, too, Before the sharpie touch, the objective was that white and bright, but you'd be surprised how quickly the non-yet-painted part turns dark gray when you start painting the rest. The inside of these retaining rings will receive the blackboard touch. Now that's how things should look! Both the lenses and their bevels are coated in black. The bevels seem a bit shiny from this angle but their absorption of bad light is vastly better. The eyepiece is a simple Plössl, only two cemented doublets with rounder bellies facing each other, mounting them right is foolproof, unlike other optical designs. You can improve the contrast in unexpensive and simple eyepieces with a good blackening. Costs nothing, proportionate to the thing's price. The eyepiece is fully-multi-coated, by the way, more congrats to Sky-Watcher for taking accessories seriously. Another improvement: the tiny original screws are replaced by homemade larger screws. Those white plugs are used in the assembly of furniture, but only one tool store had them, and only once. I bought the two packs they had, can't find them anymore, anonymous packaging. They include a piece of threaded 6mm rod of the right length, just had to plane the tip. I superglue a stainless washer at the top, and fill the space with O-rings. Only those at the outside need to be glued, the others are pinched between them. Just seeing the screws makes the advantages obvious, compare with the two original plastic screws. Hard to grab with gloves, or even without gloves for that matter. Now the flocking. The foam side of adhesive velcro is ideal for small areas. I don't glue it to the tube because that would make replacement messy. Instead, I glue it on a strip of paper. Then I fold it into a loop, and tape it. It's not round now but it will when it's forced inside the tube. That might be a useful trick when flocking larger tubes; glueing directly onto the tube allows no mistake, and can force you to leave a poorly applied flocking if it sticks too hard. Can't remove that thing but I need to adjust it! GRRRRR!! The finder is so short, only two rings did the job. Do not put that too close to the objective or it will enter the light cone. So, a few millimeters are not flocked but that's okay because the tube was already painted flat black, and all the rest of the finder is treated. Sky-Watcher put a sensible baffle in the back. There, the light cone is not eaten up by the foam, we have a clear view of the optics' edges from objective to eyepiece. The criteria are the same for bigger refractors. Before any flocking and blackening was done, the inside of the eyepiece was that shiny, the reflection on the side is very bright! Pic taken through the completely assembled finder. It was very tough getting a pic at the same angle, the flat camera objective is hard to position as accurately as the eye with its round cornea, but it's clear the lateral reflections are much dimmer. Again, picture taken through the complete finder even if it might look like the eyepiece was removed from the tube. Before the black-ops job. After the ninjas came. Sorry if the shot is blurry but the brightness comparison still stands. The area around the pupil is darker, and even the inside of the eyecup is darker since I applied a little blackboard paint there, too. It's shiny on the top picture but matte here. And if the difference does not impress you, see how the tests shots were made: with this setup, flashlight at an angle, and only one inch from the dewshield. Note how a few extra O-rings between the objective cell and the finder bracket keep it from playing. Another set of O-rings between the prism housing and the bracket complete the task. Finders moving fore and aft, and allowed to rotate lose alignment. Thanks to the firm push of these rubber rings, the tube is held tight but free to be adjusted. I had to buy a few O-rings for something non-astro, but of course you have to take the whole box. Not liking to leave tools unused, I looked for ways to make these rings profitable. One of the useful tasks was as loosened screw safety. This finder won't fall off to the ground. She's not missing anymore.