Ben the Ignorant

This is still the case. If it was my 130/900 would show spherical aberration but it shows none. Designations don't change what optics do so there has to be a mistake in the apparently outdated letter designation. Wouldn't be the first time, at some point an FPL-51 scope was labelled as FPL-53 by mistake and TS apologized and corrected the error.

Sky-Watcher surely doesn't make different newtonians for British or German outlets.

The Ronchi test is simply watching an artificial or natural star through the telescope, with the Ronchi grating placed in the focuser as an ordinary eyepiece. What this guy shows is a convoluted method that few people could use because it involves removing the mirror from the telescope, and not testing the secondary, which could make or break the wavefront. He then uses the Ronchi grating as a Foucault apparatus would be used, and claims the light source can be a slit when it HAS TO BE a dot, like a star. This is a Ronchi tester: Simply put it in the focuser and observe the lines. No one removes their mirrors from the scope to make a Ronchi test. That would be terribly inconvenient.

All the Sky-Watcher 130 in TS' page are parabolic, regardless of designation: https://www.teleskop-express.de/shop/index.php/cat/c59_Newton-Reflektoren.html/page/2 They specifically say these are not spherical because sphericals are and outdated idea that disappointed stargazers.

This is not an f/10 mirror but an f/7, it's not a small aperture, small would be 114m or 76mm, and small diameters don't allow spherical aberration in newtonians like they don't allow it in refractors and catadioptrics. Aberration is aberration, nothing hides it when it's there. If hiding it instead of correcting was possible the manufacturers and our wallets would have an easier job. If a Ronchi test is not sensitive enough, why are optics labs using it? https://astro-foren.de/index.php?thread/14862-zambuto-enjoy-your-mirror/ Which they do in addition to the Foucault test, which tells the same result. The "good" sphere "nulling out" means nothing, when a spherical shape is there instead of a parabolic one, the spherical aberration shows, the image is junk. If it didn't all our gear and the lab equipment could go the trash can. And the Hubble space telescope wouldn't have needed a billion-dollar repair.

According to the FLO blog page, 130M means M for motorized, 130 without additional letter is the f/5, but the 130P with a P should mean parabolic. There seems to be some confusion here. It was always my understanding that the P in 130P meant "parabolic", and the 130/900 I bought IS parabolic. Here is a reminder of what a spherical mirror's Ronchi pattern looks like: The lines of a spherical newtonian are not parallel, they form either a crescent or a barrel. And so they are thicker in some places and thinner in some places. This is my 130/900 Ronchi (10 lines/mm) pattern, sorry but complete cloud cover so I used a very remote road lamp as an artificial star, and ground turbulence was horrible. The unevenness is the lines is not due to zones or whatnot, just turbulence. What matters in this discussion about spherical aberration is the lines are parallel, no crescent, no barrel. They have the same width throughout despite the troubled atmosphere. My Sky-Watcher had the thicker spider vanes that I amputated and replaced, but it is a parabolic, the Ronchi test shows it. I tried to photograph the defocus test but air conditions are too bad. Visually the defocus test is excellent, intrafocal and extrafocal figures are the same. It looks like the descriptions of these telescopes need to be checked.

The 82's focuser drawtube seems to be quite large relative to the main tube, probably to illuminate large sensors, which suggests the thing can be fitted with reducers/correctors. Very large focuser lock and dual finder/guidescope holder suggests imaging, too. If Sky-Watcher bothers with a new scope they probably have improved the doublet objective, with aspherical surfaces maybe and/or a better glass formula? The very long dewshield is a good thing, condensation and stray light are such stupid things to have to deal with. I'm happy with my take-anywhere 80mm semi-apo and my stay-at-home 80mm triplet, so no personal interest in these, but the 62mm is smallish for my taste anyway. I was never satisfied with the brightness and resolution of scopes smaller than 70mm.

Beware that very old 130/900's might be spherical, but those of recent years are parabolic. The parabola is just a requirement of the newtonian, like having salt in the kitchen, if it's not there the whole kitchen is unusable.

Small or large, the spherical aberration will be the same for a given f/number. A spherical 130mm f/5 has the same aberration as a spherical 300 f/5, but fortunately Sky-Watcher seems to have stopped making spherical newtonians. The info about them has become too easy to find with the Internet, so the old claim that spherical mirrors of a certain f/ratio or a certain diameter are acceptable doesn't catch on anymore.

Sorry to contradict but I own a 130/900 and it is parabolic. https://www.teleskop-express.de/shop/product_info.php/language/en/info/p4778_Skywatcher-Explorer-130---130-900-mm-Newton---optischer-Tubus.html I would never have bought one otherwise, and upon receiving it I did a star test which was one of the very best I've ever seen in any scope of any type. I still remember the orange star's diffraction patterns that were a mirror image of each other on either side of focus.

It's not a matter of taste, film solar filters that give an orange image are made of an inferior material (mylar) that makes the image less sharp and contrasty. Only Baader's AstroSolar film retains most of the telesope's sharpness and contrast. Some makers used to offer (maybe they still do) high-grade glass solar filters flat and polished to the same degree as fine telescope objectives but they cost 6 to 8 times as much as a standard-grade glass filter. I used to own a standard-grade Thousand Oaks glass filter with nickel-chrome plating, it did produce a nice "easy on the eye" orange Sun but some sharpness and contrast were lost. Buying the higher-grade glass filter was out of the question but switching to AstroSolar solved both the price and quality problem. I made three Baader filters for my scopes, the largest being 300mm across, and several more for club members; all make a bright white Sun with very strong contrast and resolution that remains there at high powers. By the way, 5-inch is the threshold at which planetary, solar and lunar observation becomes really rewarding, I found.

Not always. Some modding can save money: And the AZ-4 head has more potential than its price suggests but it also takes some modifying. This is what I call a Z-arm, it carries a standard counterweight at the front and to the left of the head to balance the scope whose weight is at the rear and to the right. It's bolted to the baseplate but it could also be clamped between the baseplase and the arm without drilling any extra holes. This allows to drive the azimut axle with barely any friction so the motion is more fluid and accurate. Made with stuff from any tool store, L-brackets bolted together to make a Z-arm. And speaking of balance, the elevation axle needs quite a bit of friction if the tube is not balanced but a system like this... ...allows much less friction, so the cheap AZ-4 performs like a higher-grade mount. The tube tilt-lock counterweight, as I called it, simply slides along the tube and locks itself in place because there is play between the tube and counterweight, whose weight is all on one side. So it tilts and that forces the counterweight to stick to the tube. Doesn't scratch the tube and doesn't move one millimeter after one hour when the tube points vertically, I tested that. As you see, spending a lot is not mandatory.

Look at that, slashed prices on minimal-power, maximal-field eyepieces that give the right exit pupil for scopes around f/7 or f/9! https://www.bresser.de/Sale/EXPLORE-SCIENTIFIC-Maxvision-68-Okular-40mm.html https://www.bresser.de/Sale/EXPLORE-SCIENTIFIC-68-Ar-Okular-34mm-2.html

True. My sixteen-years-old 16x70 Fujinon is like new; I cleaned the objectives today (wondering how they got these stains by the way, do gremlins go out at night and mess with my equipment when I'm not looking?) and they got like new, shiny like jewels. The warranty will last another nine years, so total peace of mind. Not everything has that 25-years warranty, but as johninderby says, it's worth buying solid equipment without necessarily going for the top-class and top-price gear. It's more stable and trouble-free, and the resale value is good while still moderate enough that the new buyer makes a bargain.

Look up spot diagrams like this one (from an 80mm f/6.25 triplet) for various telescopes. They show the shape and size of star images across the field; the standard black circle is 10 microns across but sometimes it's another size so beware of that when you compare diagrams. The first line shows the spot size and shape at the center of the field for each color from violet to deep red. The second line does the same 0.25° from the center, and the last one is 0.5° away from center. The AIRY DIAMS : 6.7-10.86 REFERENCE : MIDDLE line probably means Airy disks vary from 6.7µ to 10.86µ across in green light (at the middle of the diagram and of the spectrum), as green light is the standard reference. You should also view spot diagrams for eyepieces and reflector telescopes to grasp the whole concept.

https://www.cloudynights.com/topic/661652-new-ts-102-f7-apo-refractor/ No false color at 178x, recent optical formulas perform better.

Which of the two TS f/7 apos are you talking about? They have a 599€ FPL-51 doublet and a 999€ FPL-53 doublet. https://www.teleskop-express.de/shop/product_info.php/language/en/info/p4964_TS-Optics-ED-APO-102-mm-f-7-Refraktor-mit-2-5--R-P-Okularauszug.html https://www.teleskop-express.de/shop/product_info.php/language/en/info/p9868_TS-Optics-PhotoLine-102mm-f-7-FPL53---Lanthan-Apo-mit-2-5--Auszug.html

Not sure about the 100mm apo vs 127mm mak thing but the large achro with a steep f/5 would be bettered by many well-corrected scopes of a sligthly smaller diameter. I would sell the achro to a beginner. Don't forget the 115mm apo diameter, on paper it's in-between the 100mm apo and the 127mm mak but it outperforms both without weighing much more than the 100mm.

According to Best Binoculars Reviews the current winner among those costing not much more than 400€ is the Hawke Frontier ED X 8x42. https://www.bestbinocularsreviews.com/Hawke-Frontier-8x42-ED-X-Binoculars-Review-232.htm And FLO has a new Celestron Granite 8x42 that's offered at 285€ instead of 450€ but for some reason it's been sitting there for three or four weeks and no one has jumped at the opportunity yet. https://www.firstlightoptics.com/offers/offer_celestron-granite-42mm-binoculars_123497.html

First question, yes. Second question, it's a form of mould (mold in US English), and it grows on optics because they have mineral coatings, a mix of various dust compounds, and condensed water at some moments. Mould survives on extremely small amounts of food and water so, unlucky us, it likes optics. Third question, prevention is keeping optics dry and clean, with an eye on condensation, do not let uncovered cold optics in a warmer room where air humidity can condense.

A slightly defocused star at high power tells the truth about collimation. A motionless light source is more convenient so use Polaris or a a pinhole in aluminum foil. When the defocus rings are concentric there is no doubt.

Start slow. But with 350£ you can have a scope much bigger than 90mm; look at the Bresser dobsonians.

It depends A LOT more on your sky's quality than on your binoculars, but any 10x50 that's not defective will show you most of what a 10x50 can show. What is the magnitude of the faintest stars you can see with the eyes only from your village? (I'm assuming it's a village and I'm too lazy to check) In a very dark sky a just acceptable 10x50 will show far more than what an excellent - I know because I own the APM 10x50 apo - one shows in a non-dark sky like what I contend with in my city. It will be easier to escape to darker settings after I get my next car in a few weeks but for now I limit my driving to the bare essential. Say you see stars of the 5th or 5.5th magnitude at the zenith, that's quite good for a suburban setting, the 10x50 will multiply the number of stars and make the viewing rewarding. However if it's no better than 3rd or 3.5rd mag the multiplication won't feel that impressive. Of course a larger binoc like a Celestron Pro 15x70 (140€ from First Light Optics) will improve the view without having to drive to darker places. But sky quality is the main ingredient, even with telescopes. Hello and welcome, by the way. Your hope of being "wowed" is shared by everyone, regardless of gear and experience. 😀

Ever since I tried several basic Skymasters I felt a 70 should be waterproof and have stable prism housings. Spending less than 100€ on a twin 70mm telescope doesn't seem very realistic if one hopes to use it for a long time without problems. On one humid night some guy's cheapo 80mm binoc fogged up inside and it felt like being stranded with no rescue in sight. My Fuji 16x70 was there and saved the day. Sincerely, the view through a basic Skymaster and my Fuji FMT-SX is shockingly similar (because the Fuji is not an apo) but the Fuji is like new after sixteen years while a sixteen-years-old Skymaster would surely be out of alignment after such a long time. A friend bought two of the earlier versions and both got cracks in the adhesive that holds the prisms so they became skewed. Attempts at repairs failed because the thing is not designed to be repaired but replaced because of its expendable nature. So, spending a little more for stable prism clamps and fogproofing seems vey reasonable. In truth I want an APM 16x70 apo since I got my APM 10x50 apo six weeks ago but I am getting another car this month so spending 600€ on a binoc is not for now. For those who want a non-apo 70 the extra expense will be justified and very moderate with the Pro. I own a seven-years-old waterproof 10x50 and a six-years-old waterproof 8x40 an they never leaked of fogged up.

Where many soles rub on granite stairs the stairs are worn out yet rubber is softer than granite. Anything can scratch anything if it rubs hard or often enough, and aluminum in astro gear is never bare, it's always anodized, meaning it's coated with the aluminum's own oxide, which is the hardest material next to diamond.