Ben the Ignorant

Sky-Watcher sells all types of refractors, achromats, semi-apos, apos, doublets and triplets, but Sky-Watcher sells no prism diagonals, only mirrors, so...

Saturn V exhaust?

They had a rubber buffer ring between the metal retaining ring and the lens. Tightening the metal ring made the rubber turn, and the rubber made the lens turn, ruining rotation. The solution was to replace the rubber ring with one that doesn't grip.

Warranties don't cover misuse, and that's how it should be. Vortex binoculars are an exception, they repair the thing no matter what the cause, but their price has to be raised to include that insurance.

It was a rhetorical question. Collimating a scope is like setting up a guitar, if the warranty says a setup voids the warranty, the maker should - either change the terms of the warranty - or sell guitars with a perfect and permanent setup Amazingly, I once heard a customer complain that his just-bought expensive guitar had fret buzz. The clerk answered the guitar would go to the luthier's shop, at extra charge, of course. The buyer answered back "Doesn't it come from a luthier's hands already?" I set up my guitars and my telescopes myself. Whew! What a relief!

Do you lose warranty when you collimate a newtonian or a Schmidt-Cass? How does collimation endanger the scope?

That's why people have to learn to center their doublet themselves. Set all the screws at the same depth on one lens. Orient the scope so two screws from the other lens are at the bottom and loosen the other screw(s). Use those two screws like a spring-loaded finder's screws, the weight of the lens will act as the spring force. Tighten top screw(s) gently. That's it.

Hexagonal because the three sets of screws push too hard. I've seen the same effect in an achro that I optimized. To suppress play in the cell I put 6 shims that were too tight at the first trial. The hexagon showed more in the extra image than in the intra for some reason. Thinning the shims solved the problem. Try loosening the screws on one lens only first. If nothing improves, try the other. While you're at it you might solve the decentering problem with an improv artificial star. It's best to have someone at the eyepiece and someone at the screwdriver, will make the process vastly faster. Set one lens at a fixed position by driving all its screws at the same depth. Then only one lens has to be adjusted relative to the fixed one.

Why is there felt tape between the cell and dewshield if the dewshield does not slide?

Yes, and not just for the looks. I've read countless reviews where they say they love the typical chinese green coating on Sky-Watcher lenses, but green is the color the eye sees best, whether in the dark or not. I've even seen yellow-green coatings on some binocular prisms, these are the least likable. Amber is more or less acceptable depending if it's brownish or orangish. Red is not common but very good, reflections are very faint. Deep blue, indigo and purple are excellent. I've almost never seen a parasitic reflection in my Baader Phantom-coated eyepieces, and they have no green coating. Unless it is the very dark forest green type, green is liable to cause dancing fairies in the eyepiece when viewing Venus or Jupiter. I don't believe reflections from the objective can be seen as dots in the eyepiece, but scattered light can. So, one more good mark for the new big 150.

Even a short 102 refractor if it's an apo. Like f/7. Doesn't relate to price but to physics. The Mak's advantage is only shortness and weight. Some light is absorbed by the mirrors, some is scattered, some is disturbed by the obstacle in the light path. Tolerances need to be very tight in a Mak, some are very sharp, especially the russian ones (Intes), but an apo that's a bit smaller will be about as bright with better contrast.

I don't feel I wasted money on astro gear, ever. But I do think light pollution is wasting a lot of my efforts, when it was so easy to start designing intelligent lighting eighty or ninety years before now.

The field width does not depend on f/ratio, it depends on focal length. Faster f/ratios make for a wider field for a given aperture, but change the scope's diameter and the focal length changes, too. A 100mm diameter f/7 scope has a 700mm focal length but a 300mm diameter f/5 scope has a 1.500mm focal length, about twice the length, so about twice less field width, despite the faster f/ratio. Then again a larger focuser allows eyepieces with larger front lenses that will accept a broader image. Focal length and focuser size determine the field, you need to compare these when you shop around.

Put a cap on the scope with an off-center hole, so the light enters the scope through a smaller aperture without hitting the secondary mirror or its spider. It's called an off-axis mask, and tames turbulence very well. Less powerful than the full-aperture scope but much steadier views. It's so cheaply made every large reflector should be sold with one. This is the one I made for my 300mm dob, the reduced aperture is 115mm, the space between the large mirror's edge and the small mirror's edge:

No, I was thinking of the 120ED you mentioned in your first post. The best planetary views I've ever had were through a friend's 130mm Vixen doublet. Calmest, sharpest views ever, no large reflector could compete, except the club's 400mm but it's a monster, not comparable, and steady images through the 400 are rare. We stop it down to 150mm for quieter views, an aperture close to the superb Vixen apo's aperture. On the other hand, a ten-inch mirror deep-sky scope can be stopped down to an obstruction-free 100mm planetary scope, that would make a fine two-in-one instrument.

Hi, Daniel. Since you seem to insist on planets, the apo refractor gives the steadier views that are required when you examine planets. It's always done at high magnifications because planets and Moon detail have small angular size. That makes steadiness important, and the apo refractor is the most contrasty and least disturbed by turbulence among all scope designs.

You can keep your favorite eyepieces if you add a counterweight at the front. This kind slides over the tube, and is very simple and unexpensive to build: A 90mm ring is a match for an 80mm scope tube, and a 100mm ring is the match for the dewshield. I assume it will also be the right size for those ED scopes that have an oversize main tube. The counterweight locks itself when it tilts because of its unbalanced weight. To move it, just untilt it, no need to loosen the screw.

Hi, James, and happy new year! I wonder why you exclude all other types and brands of eyepieces. For the price of the least expensive Tele Vue Plössls you could have one of these: https://www.astroshop.de/astro-professional-uwa-ultra-weitwinkel-okular-82d-16mm-1-25-/p,54981 https://www.teleskop-express.de/shop/product_info.php/info/p8989_TS-Optics-Optics-1-25--Ultra-Weitwinkel-Okular-UWAN-4mm--82--Gesichtsfeld.html https://www.teleskop-express.de/shop/product_info.php/info/p8988_TS-Optics-Optics-1-25--Ultra-Weitwinkel-Okular-UWAN-7mm--82--Gesichtsfeld.html And while they're not Tele Vue's, they are clones of the Nagler 82° eyepieces, which are a Tele Vue design. An 82° eyepiece shows you 2.7 times as much sky area as a 50° eyepiece. I own five 82° clones, all very sharp and contrasty. When I and a friend compared my 150€ Meade/Maxvision 24/82 to a 600€ Tele Vue 26/82 the only plus the Tele Vue had was some barely noticeable extra transparency, seen only after much going back and forth from one eyepiece to the other. And we had to poll our findings together for a long time before confirming the TV is indeed a tiny bit more transparent. But all other qualities were the same, same edge sharpness, same curvature of field, same contrast. The difference didn't matter, really, because a barely detectable effect in a shootout does not change anything in everyday use. You seem to think all other brands are inferior, but no, they're just less innovative. Tele Vue creates, and others follow. Like when Sky-Watcher issued the 100° and 110° Myriads after Tele Vue's Ethos. I have three of them, could never afford Ethos. I took them to the observatory, a friend who owns an Ethos (didn't have it with him this night) said quality of view was essentially the same. So, think carefully before you commit money. All other big optics makers provide very sharp and contrasty optics. 2.7 times as much sky, remember.

Actually your question makes sense but only visually. Look at something with one naked eye and the other eye in a reflex camera's viewfinder. If the focal length is 70mm both images have the same apparent size. I checked by setting the zoom at 35mm, the camera view became exactly twice smaller than the naked eye view. Thus a 700mm focal length scope magnifies 10x relative to the naked eye, but after a picture is taken it can be displayed in any apparent size from cell phone screen to giant living-room TV. Traditionally camera objectives have focal lengths that revolve around 70mm for that reason: the perspective at 70mm is the same as with the eye alone.

A bigger scope is like a better computer screen: smaller and brighter pixels, you see more even if the image has the same size. And when the core image can stand enlargement, you can do it without losing sharpness.

Hey, wxsatuser, I realize my previous post might sound scathing because it's brief, but I really appreciate the enlighting calculations you made, and the rare info you put out. Few people dig a subject that deep.

Thanks for the calculations but I was talking about apparent speed.

Yep, regular satellites fly 300km, 400 km and higher, but some of the spy sats are on very low orbits, barely above the 100km mark, which makes their apparent speed three or four times higher. They are so low they need little engines to reboot their altitude regularly because of atmospheric drag, but from lower orbit you spy better, of course.

Explore Scientific makes some basic 70° eyepieces that cost barely more than Plössl's. Remember you need field to frame open clusters and large nebulas.

Those made by Vixen must be good, because I've never found a poor review or lab test of their scopes, ever. And all the Vixen stuff I've personally observed with has been superlative, especially in polishing finesse, and centering. But this older Bresser refractor was made in China, and not well made: http://www.davidesigillo.eu/test_bresser.html