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Cold War Spoils: Amateur Builds Telescope With 70-Inch Lens

timothy posted about 5 months ago | from the just-winging-it dept.

Hardware Hacking 101

First time accepted submitter 192_kbps writes "Mike Clements, a long-haul trucker from West Jordan, Utah, built the largest amateur telescope ever with a whopping 70 inch primary mirror he purchased at auction. The entire telescope is 35 feet tall, 900 pounds, and he hopes to tour it in parks. As a hand-turned Dobsonian the telescope lacks the photographic capacity and tracking required for professional astronomy but the views must be breathtaking." (Are there other compelling candidates out there for "largest amateur telescope ever"? The 71" scope listed by nitesky.org appears to be dormant.)

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101 comments

Did he buy the mirror, or make it? (2)

DaTrueDave (992134) | about 5 months ago | (#45337779)

This is unclear to me:

"One of the riskiest parts of the project was turning the huge 70-inch piece of glass into a mirror by applying the silvering himself."

vs.

"Clements bought the 900-pound mirror — which was originally destined to go into space as part of a spy satellite until the edge of it was chipped during its manufacture — after it was auctioned off."

Re:Did he buy the mirror, or make it? (4, Informative)

Anonymous Coward | about 5 months ago | (#45337873)

He put a reflective metal coating on a purchased piece of glass with the proper final curvature.

Re:Did he buy the mirror, or make it? (4, Interesting)

pla (258480) | about 5 months ago | (#45337925)

I took that to mean they just cancelled the satellite project after casting and polishing the mirror but before silvering it.

Alternatively, the intended use may have involved some classified exotic coating that serves some special purpose and they needed to strip the coating before selling the mirror at auction.

Re:Did he buy the mirror, or make it? (4, Informative)

Frobnicator (565869) | about 5 months ago | (#45338137)

I read it the same way.

They probably cut the mirror and polished the glass, and then the edge chipped.

A chip in the glass could be a fatal injury for a spy satellite as the article suggests was the intended use. Such telescopes use active optics to improve image quality; they apply pressure over the glass to bend it slightly. A chip could have micro-cracks and other damage that would easily spread across the surface. Without the actuators deforming the glass the image won't be as clear, but it would be good enough for a hobby telescope.

Once the glass chipped they likely just stopped the process, so the new owner would need to add the mirror surface on his own.

Re:Did he buy the mirror, or make it? (1)

Anonymous Coward | about 5 months ago | (#45338633)

They talk about it over on cloudynights,
The crack goes about a foot into the glass. The spray on coating leaves much to be desired, it needs to be re-coated every so often and it has a fairly low reflection index for whats commonly used in telescope mirrors. But with that said its still a hell of a project and I'd love to use it!

Re:Did he buy the mirror, or make it? (3, Interesting)

wagnerrp (1305589) | about 5 months ago | (#45340015)

A chip in the glass could be a fatal injury for a spy satellite as the article suggests was the intended use. Such telescopes use active optics to improve image quality;

Why? It's in microgravity and temperature controlled. There's not going to be any sort of variation during operation to make active optics worthwhile. It's certainly not going to be adaptive optics, because you're moving across the atmosphere too rapidly to have any hope of keeping up with localized distortions. The only reason I could see it being useful is it would allow for more lax manufacturing tolerances, since you could fine tune it once you hit orbit.

Re:Did he buy the mirror, or make it? (2)

HuguesT (84078) | about 5 months ago | (#45341311)

State of the art spy satellite require active optics because they look at things through the atmosphere. Not upward like a ground-based astronomy telescope, but downwards.

Re: Did he buy the mirror, or make it? (1)

wagnerrp (1305589) | about 5 months ago | (#45341653)

The atmosphere has nothing to do with anything. Active optics exist to maintain the shape of a mirror to compensate for changing external stresses. Unless you're inside the atmosphere, the atmosphere cannot produce external stress on the mirror. Of course, if you are inside the atmosphere, you have bigger issues than worrying about good quality images.

Re: Did he buy the mirror, or make it? (0)

Anonymous Coward | about 5 months ago | (#45351741)

Active optics can also remove atmospheric distortion.

Re: Did he buy the mirror, or make it? (2)

wagnerrp (1305589) | about 5 months ago | (#45353729)

No. That's called adaptive optics, and it only works for ground based telescopes. There's no way in hell you're going to be able to adjust the mirror for atmospheric distortions when you're flying past it at 8km/s.

Re:Did he buy the mirror, or make it? (3, Informative)

Deadstick (535032) | about 5 months ago | (#45341313)

Why? It's in microgravity and temperature controlled.

When you're in orbit, "temperature controlled" is a slippery concept. You've got direct sunlight on one side, dark space on the other side, temperatures to the fourth power fighting it out, and no air to redistribute heat -- and an hour later, the sides will have switched.

Re:Did he buy the mirror, or make it? (1)

LifesABeach (234436) | about 5 months ago | (#45340281)

So what kind of detail can one see on the moon; maybe the Hollywood sets of the moon landings?

Re:Did he buy the mirror, or make it? (2)

umafuckit (2980809) | about 5 months ago | (#45340657)

A chip in the glass could be a fatal injury for a spy satellite as the article suggests was the intended use. Such telescopes use active optics to improve image quality; they apply pressure over the glass to bend it slightly. A chip could have micro-cracks and other damage that would easily spread across the surface. Without the actuators deforming the glass the image won't be as clear, but it would be good enough for a hobby telescope.

Once the glass chipped they likely just stopped the process, so the new owner would need to add the mirror surface on his own.

Not so. Firstly, adaptive optics is still fairly rare and likely this mirror was never intended for use in such a telescope. Secondly, the mirror deformations on a telescope with adaptive optics are not done at the primary mirror (the large chipped one) but at the secondary or even tertiary mirror. It's much easier to do this on a small, thin, mirror than large, thick one. Finally, a little chip is no big deal. You just coat the mirror as normal then paint over the chipped area. You'll never see the difference. There are observatory mirrors out there into which someone unloaded a hand gun. They work just fine.

Re:Did he buy the mirror, or make it? (1)

danceswithtrees (968154) | about 5 months ago | (#45340797)

I don't know this for a fact but I am dubious that adaptive optics can or are used for telescopes looking down at earth. From my lay understand of adaptive optics, a "guide star" or artificial star (artificial spot in the sky lit up with a frickin laser!) is used to correct for the atmospheric disturbances. I am having a hard time thinking of what could be used as a point source when looking at the ground from space. Maybe a point light source near the area of interest?

Re:Did he buy the mirror, or make it? (1)

Anonymous Coward | about 5 months ago | (#45342727)

I'm a scientist working in adaptive optics. Reading this whole thread, in which essentially every statement made is untrue or imprecise, gives me some idea of what it must be like to be a climate scientist listening to constant babble from people trying to talk about a technical area outside their area of expertise. (No insult intended toward any commenters in this thread, I'm just sharing my epiphany.)

Re:Did he buy the mirror, or make it? (1)

drinkypoo (153816) | about 5 months ago | (#45343771)

I am having a hard time thinking of what could be used as a point source when looking at the ground from space. Maybe a point light source near the area of interest?

So just to be clear, you're having such a hard time figuring it out, that you just figured it out?

Re:Did he buy the mirror, or make it? (0)

Anonymous Coward | about 5 months ago | (#45354875)

Do things that you want to spy on have a convenient point source near them?

Idiot.

Re:Did he buy the mirror, or make it? (1)

drinkypoo (153816) | about 5 months ago | (#45354925)

Do things that you want to spy on have a convenient point source near them?

If they don't, you drop one. It's not as hard as you imagine when you have an effectively unlimited supply of taxpayer money.

Re:Did he buy the mirror, or make it? (1)

cellocgw (617879) | about 5 months ago | (#45346759)

No, the main reason that AO is not used for atmospheric correction in satellite systems is the so-called "shower curtain" effect. The atmospheric aberration effect is strong for ground telescopes because the atmosphere is near the 'scope, and thus is in the region where the light's phase is important. Looking down from a satellite (analogous to looking from the far side of the room at a person just behind a shower curtain), the atmosphere is where the light's angle is important, not phase.

Re:Did he buy the mirror, or make it? (0)

Anonymous Coward | about 5 months ago | (#45338003)

Why does the headline call a mirror a "lens"?

Re:Did he buy the mirror, or make it? (0)

mrchaotica (681592) | about 5 months ago | (#45338353)

Because it has a non-uniform thickness and therefore bends the light in addition to reflecting it.

Re:Did he buy the mirror, or make it? (0)

Anonymous Coward | about 5 months ago | (#45338413)

I know why mirrors are used in telescopes. I want to know why someone used the word "lens" for something that isn't a lens.

Re:Did he buy the mirror, or make it? (0)

khellendros1984 (792761) | about 5 months ago | (#45338681)

Because a mirror used in such a way is effectively a lens, even if it isn't one technically. Is the headline correct? No, but it's correct enough that you've got to be in a pedantic mood to bother complaining about it.

Re:Did he buy the mirror, or make it? (1)

hawguy (1600213) | about 5 months ago | (#45338759)

Because a mirror used in such a way is effectively a lens, even if it isn't one technically. Is the headline correct? No, but it's correct enough that you've got to be in a pedantic mood to bother complaining about it.

It's hardly pedantic to point out that a mirror is not a lens. Would you complain to your contractor if he accidentally installed a bathroom lens instead of a bathroom mirror? Or just let it slide since they are pretty much the same thing and only a pedant would complain?

Re:Did he buy the mirror, or make it? (1)

khellendros1984 (792761) | about 5 months ago | (#45338985)

The mirror in question is performing the same function as a lens would (changing the path of light in a way that's useful in an observational tool).

Would you complain to your contractor if he accidentally installed a bathroom lens instead of a bathroom mirror?

Depends on if it performs the function of letting me see a low-distortion image of myself or not.

Of course mirrors and lenses are different; the reason I posted is that I'm annoyed how many people thought they were being clever by pointing it out.

Re: Did he buy the mirror, or make it? (2)

Erik WP (3406995) | about 5 months ago | (#45339617)

No, you try to outpedant them by pretending that it doesn't matter.

Re: Did he buy the mirror, or make it? (1)

khellendros1984 (792761) | about 5 months ago | (#45340291)

Just the way that everyone else seems to be pretending that mistakes in a Slashdot article title matter, especially when the linked story contains even more errors.

Re:Did he buy the mirror, or make it? (3, Informative)

necro81 (917438) | about 5 months ago | (#45338495)

Reflecting telescopes use front-side mirrors. The glass is just there to provide the shape; it is not part of the optical path.

Re:Did he buy the mirror, or make it? (2)

Jeremy Erwin (2054) | about 5 months ago | (#45338693)

because a 70 inch reflector is interesting, but a 70 inch refractor is extraordinary. By not making the type of telescope clear in the headline, the submitter is practicing good click bait techniques. Not nearly as enticing as "Charlize Theron NSFW", but...

Re:Did he buy the mirror, or make it? (5, Funny)

mcmonkey (96054) | about 5 months ago | (#45338835)

"Charlize Theron NSFW"

I keep clicking on those words, but nothing happens :(

Re:Did he buy the mirror, or make it? (2)

grep -v '.*' * (780312) | about 5 months ago | (#45340063)

"Charlize Theron NSFW"

I keep clicking on those words, but nothing happens :(

.... that you KNOW about :)

Re:Did he buy the mirror, or make it? (0)

Anonymous Coward | about 5 months ago | (#45342369)

Anyone knowledgeable about astronomy, and I'm just an amateur, would know that a 70 inch refractor is interesting because there aren't any. There was one at the 49.21" at The Great Paris Exposition of 1900. The largest one so far is the 40" Yerkes. The limiting factor is the weight of the glass itself, which causes it to sag, bend, and deform. The issue of using modern lighter weight glasses has been looked into. I forget if lighter weight equals greater susceptability to sage and bending.

The other limiting fact is cost and risk. For the money to build a large refractor, with the risk it may not be as good as you want it, you can build a larger catadioptric that you can be pretty sure can be done and it will work just fine.

Re:Did he buy the mirror, or make it? (2)

Hadlock (143607) | about 5 months ago | (#45338365)

If you stick a 900 lb piece of glass on top of a rumbling shaking rocket and expose it to 5Gs of acceleration, rapid heating and cooling cycles etc, you probably don't want a chip in the glass where forces can propagate a crack. It's easier to make a new one rather than wait for it to fail in space.
 
For something that will only see occasional use with slow temperature changes it's ideal for a "low cost" telescope. It will still fail eventually, but it won't shatter in orbit while imaging a North Korean missile base (or whatever).

Re:Did he buy the mirror, or make it? (1)

kimvette (919543) | about 5 months ago | (#45339883)

> it will still fail eventually

Not necessarily, if he took the time to de-stress the chip. It will still be a weak point but will not necessarily propagate.

HST comparison, really? (2)

Arkh89 (2870391) | about 5 months ago | (#45337969)

According to TFA : enabling users to see constellations previously visible only through the $2.5 billion Hubble Space Telescope
Hahaha, but no...

Re:HST comparison, really? (3, Interesting)

Virtucon (127420) | about 5 months ago | (#45338109)

Riiight.. I mean the guy lives in Utah so there are dark skies close enough to him but I'm plagued with air pollution and light pollution in my area and have to go at least 3 hours away to get a decent night of observation. Even then you still have upper atmospheric interference at times whereas the HST doesn't have any of that. The other problem I'd see with a Dobsonian of this size is maneuvering it and hauling it without damaging it. Props too him though for building it though, I wonder how many times he had to go to Home Depot to finish it?

Re:HST comparison, really? (0)

Anonymous Coward | about 5 months ago | (#45338315)

I think the problem here might be the word 'constellation'.

Re:HST comparison, really? (2)

bruce_the_loon (856617) | about 5 months ago | (#45339263)

I think the problem here might be the word 'constellation'.

And that they're claiming it outperforms any of the other terrestrial telescopes from 70.1 inches up to the 409 inch Gran Telescopio Canarias, and presumably any bigger ones still being built.

Re:HST comparison, really? (2)

gandhi_2 (1108023) | about 5 months ago | (#45339769)

Actually, west jordan is in the massive sprawl complex that stretches from North Ogden to Nephi. He would probably have at least a couple hours drive to get up past Park City, Heber, Payson, or out towards the west desert, Tooele, or even Dugway He will have some driving if he wants darkness. Utah'ns in general take a "consumptive model" view of nature, and aren't big into reducing pollution, let alone LIGHT pollution.

Re:HST comparison, really? (1)

RespekMyAthorati (798091) | about 5 months ago | (#45341533)

Also, I think any of the scopes on Mauna Kea or the Andes would blow this thing out of the water.
Cool project, though.

Like HST (but not in a good way) (1)

Narrowband (2602733) | about 5 months ago | (#45342487)

It's an impressive amateur engineering feat, but its performance as a telescope might not be anything to write home about. It probably shares one quality with the hubble that you wouldn't want: a problem with gravity.

Remember how when it first went up, the hubble had problems focusing clearly? The designers forgot that its mirrors would be deformed/reshaped by the lack of gravity. Essentially, the hubble's primary mirror was optically designed to work as a telescope mirror on earth, not in space. It wasn't until the later mission to fix it with some corrective optics that it really achieved its best capabilities.

Now, since the surplus 70" mirror this guy used was designed to work on a satellite, it would very likely have the same problem but in reverse. If the mirror was designed to be shaped properly in a microgravity environment, it would also be deformed when on earth (as it is when used in the amateur telescope.) That might make the images from it quite a bit worse than one might hope for from a 70" instrument.

Re:Like HST (but not in a good way) (3, Informative)

the_other_chewey (1119125) | about 5 months ago | (#45342833)

Remember how when it first went up, the hubble had problems focusing clearly? The designers forgot that its mirrors would be deformed/reshaped by the lack of gravity. Essentially, the hubble's primary mirror was optically designed to work as a telescope mirror on earth, not in space.

Uh, no. That would've been an amateur mistake to make and didn't happen.
Instead, the amateur mistake made was not to properly verify that the grinding
machine was actually grinding correctly. They even ignored measurments by
another instrument showing a faulty shape, assuming the instrument to be faulty instead.
And skipped the final post-assembly check to save time and money.

The mirror simply was ground extremely precisely into a wrong shape, and nobody noticed.

But as always in cases like this, the whole story is more complex and consists of a lot of
things not going as planned. It's a good and instructive read. [tamu.edu]

Re:Like HST (but not in a good way) (1)

hubie (108345) | about 5 months ago | (#45347849)

The beauty, of course, is because it was so precisely ground into a wonderfully specific shape (it gave perfect spherical aberration), it was easy to make corrective lenses.

Daily Mail is like National Inquirer (3, Informative)

Joining Yet Again (2992179) | about 5 months ago | (#45337973)

Just a heads up for you non-Brits. There will be truth in this article... somewhere.

Re:Daily Mail is like National Inquirer (3, Insightful)

HornWumpus (783565) | about 5 months ago | (#45338085)

FYI over the last 10 years or so the 'National Inquirer' has done more genuine 'investigative reporting' then the New York Times.

They have the nerve to report stories that 'the powers that be' have put an embargo on.

Re:Daily Mail is like National Inquirer (3, Insightful)

GodfatherofSoul (174979) | about 5 months ago | (#45339419)

Let's not get hyperbolic. As many problems as I have with the NYT, a couple of sex scandals involving politicians doesn't measure up to what the NYT does every day. Now, take a look at what the Enquirer reports on every day.

Re:Daily Mail is like National Inquirer (0, Troll)

HornWumpus (783565) | about 5 months ago | (#45339825)

doesn't measure up to what the NYT does every day.

Being the PR wing of the DNC is not a good thing.

Name one example of real investigative journalism from the NYTimes in the last 10 years?

Hyperbolic (0)

Anonymous Coward | about 5 months ago | (#45342397)

Actually, Ritchey-Chretien telescopes use a hyperbolic primary mirror....good enough for the Hubble Space Telescope

Re:Daily Mail is like National Inquirer (2)

Jeng (926980) | about 5 months ago | (#45339485)

Yes, the National Inquirer may do more investigative reporting, but if no one believes it because 90% of what they report is false then who gives a fuck?

Re:Daily Mail is like National Inquirer (0)

Anonymous Coward | about 5 months ago | (#45338179)

Here's a more reputable source: http://www.ksl.com/?sid=27301024

Largest Amateur telescope. (4, Informative)

Anonymous Coward | about 5 months ago | (#45337997)

Technically Lord Rosse (https://en.wikipedia.org/wiki/William_Parsons,_3rd_Earl_of_Rosse) was an amateur, and his telescope was 72 inches.

Re:Largest Amateur telescope. (1)

Servaas (1050156) | about 5 months ago | (#45338067)

I think once you carry the Lord title you can never again be revered to as an amateur in anything.

Re:Largest Amateur telescope. (2)

SuricouRaven (1897204) | about 5 months ago | (#45338981)

It's not as impressive as it sounds. The title is heretitary, so it basically means 'My ancestors were filthy stinking rich, and I probably am too.'

When we want to grant someone a title of respect, they get the 'Sir' before their name, not Lord. You have to earn that one personally, not just get born into it.

Re: Largest Amateur telescope. (0)

Anonymous Coward | about 5 months ago | (#45339655)

Right, like Sir Fred Goodwin

Re:Largest Amateur telescope. (1)

gandhi_2 (1108023) | about 5 months ago | (#45339843)

This guy earned "Long Haul Trucker" and is building a telescope with money he works for.

I find that much more respectable than the right honorable lord sir fuckface pursuing hobbies with leisure time and leisure money.

Re:Largest Amateur telescope. (1)

forkazoo (138186) | about 5 months ago | (#45340669)

To the contrary, you can never be referred to as a professional. Having to work a job is for the little non Lord people.

What is it with us guys! (0)

Anonymous Coward | about 5 months ago | (#45338107)

We always got to say ours are bigger!

Re:Largest Amateur telescope. (2)

careysub (976506) | about 5 months ago | (#45339629)

Lord Rosse's telescope used a cast speculum metal mirror [wikipedia.org], basically pewter, which had a reflectivity of 66%. Glass silvering technology had not been developed to a level adequate for astronomical mirrors. As a result the light gathering power of the 72" Leviathan of Parsontown was equivalent to a 58" mirror of 100% reflectivity. Clement's mirror is coated with silver, and with even a mediocre silvering job a reflectivity at least 90% should be obtained. This makes his mirror equivalent to a 66" mirror of 100% reflectivity, so it is a more "powerful" mirror.

Re:Largest Amateur telescope. (1)

martinux (1742570) | about 5 months ago | (#45370749)

William Parsons (Lord Rosse) cast and figured his mirrors with 1845 technology that he helped improve through his own efforts. It doesn't matter what the sensitivity or apparent size is in relation to a mirror created with 20th century technology developed by Lockheed with unknown millions in government funding. The Leviathan has a larger diameter mirror which is the criteria many news sources are using to claim that Mr. Clements's telescope is the largest ever built.

I'm saddened to see that this has turned into some kind of competition.

A guy in Utah built a 70 inch telescope using a prefabricated mirror smaller in diameter than one that was created over 200 years earlier, the fact that it's not a world record does not undermine his achievement. Reporting it as being the largest amateur telescope ever constructed is inaccurate at best no matter how one reasons it out.

Clements deserves serious kudos for his efforts but comparing them to those of Parsons is unreasonable. Parsons achievements far exceed those of Clements.

Trust me (1)

OhSoLaMeow (2536022) | about 5 months ago | (#45338053)

You really don't need a mirror this large to spy on your neighbor.

Or so I've heard.

Re:Trust me (2)

olsmeister (1488789) | about 5 months ago | (#45338173)

No, but oriented in the proper way, you can start fires at random locations all over their property, causing them to believe that they have poltergeists.

Isn't there even one picture through it? (3, Insightful)

Dr. Manhattan (29720) | about 5 months ago | (#45338083)

How hard is it to rig up a camera adapter? That'd help demonstrate exactly how powerful it is...

Re:Isn't there even one picture through it? (1)

DaTrueDave (992134) | about 5 months ago | (#45338125)

I was wondering the same thing. Thought it might be a stability issue since the rig has no gears and it's moved by hand?

Re:Isn't there even one picture through it? (2)

BullInChina (3376331) | about 5 months ago | (#45338267)

Even with tracking capability, which isn't that hard for a dobsonion, alta-azimuth mounts like this suffer from field rotation effects and exposures longer than about 30 seconds are not ideal. But you can take many 30 second exposures and stack them to give you something resembling a much longer exposure. The stacking de-rotates the images and aligns them.

Re:Isn't there even one picture through it? (2)

jeffb (2.718) (1189693) | about 5 months ago | (#45338619)

Or you can build a rotating camera mount, or insert a rotating element in the optical path. Either way, you're supporting and moving a relatively small weight, so it's a much easier task than building the main drive.

Re:Isn't there even one picture through it? (1)

BullInChina (3376331) | about 5 months ago | (#45338879)

Yep field de-rotators are an option. Sometimes the right option, but they are an added drive system and can be pesky. I would say in this case a much better option than trying to build an equatorial mount for an instrument this large.

Re:Isn't there even one picture through it? (4, Interesting)

careysub (976506) | about 5 months ago | (#45339667)

Taking short exposures and processing them on a computer is the "poor man's adaptive optics". A very powerful technique (if the object is bright enough) is too take a large number (thousands) of short exposures, then sort through them for a "lucky" image - one in which the atmosphere is momentarily stable. Multiple lucky images can be stacked together to get longer exposures. This really is a very powerful technique, not requiring extremely expensive high precision tracking hardware.

Re:Isn't there even one picture through it? (1)

necro81 (917438) | about 5 months ago | (#45338523)

Well, you see, the reporters from the Daily Mail came and did the interview and photographs during the daytime. They may have glossed over that part that astronomical telescopes are typically used at night.

Not a Lens (0)

Anonymous Coward | about 5 months ago | (#45338091)

It's a mirror, not a lens.

Re:Not a Lens (0)

Anonymous Coward | about 5 months ago | (#45338153)

What is the definition of a lens? And what does a curved mirror do?

Re:Not a Lens (-1)

Anonymous Coward | about 5 months ago | (#45338311)

a: Refracts Light
b: Reflects Light

So basically the same thing.

Re:Not a Lens (2)

BullInChina (3376331) | about 5 months ago | (#45338459)

No not really the same thing at all. Both strategies will form an image but the physics are different. The mirror reflects the light via a paraboloid and thus forms the image without any chromatic abberation. For the lens to form an image the light must pass through the glass and because the speed of light in the glass depends on the wavelenght, the refractive index is slightly different for every wavelenght and the therefore the lens will show significant chromatic abberation. This is assuming that it is a single lens. Multiple element lens are possible to design with different refractive indicies that will minimize this effect but they are much more complex and expensive. Oh by the way the largest refractor ever built is the Yerkes telescope which is only 40" in diameter. Anything larger would distort under it's own weight.

Re:Not a Lens (0)

Anonymous Coward | about 5 months ago | (#45338361)

I know that I should be over this by now, but I had to: http://lmgtfy.com/?q=define%3Alens

70 inch Mirror or Lens? (-1)

Anonymous Coward | about 5 months ago | (#45338135)

Fucking hell. This is slashdot - a place frequented by nerds and you guys can't post a headline that doesn't confuse a reflector with a refractor and a mirror for a lens?!?!?!?

Bad Headline: Mirror Not a Lens (5, Informative)

crunchygranola (1954152) | about 5 months ago | (#45338143)

Here is the scoop on the 70" telescope. Mike Clements purchased a polished but uncoated mirror that is 70" across that was intended for a spy satellite project that was cancelled. A huge uncoated mirror is not a telescope anymore than (car analogy - wait for it...) a V8 engine is a racecar. Building a good performing telescope (collimation tolerances are measured in thousandths of an inch) is a significant task, a huge telescope like this is a major engineering feat. What's more this is a transportable telescope. It is possibly the biggest transportable telescope in the world. This telescope is more powerful than any telescope that existed before 1917 (when the 100" Hooker telescope saw first light).

Successfully silvering the mirror using updated 19th Cedntury mirror coating technology was nifty too.

Re:Bad Headline: Mirror Not a Lens (1)

The Grim Reefer (1162755) | about 5 months ago | (#45338635)

Here is the scoop on the 70" telescope. Mike Clements purchased a polished but uncoated mirror that is 70" across that was intended for a spy satellite project that was cancelled. A huge uncoated mirror is not a telescope anymore than (car analogy - wait for it...) a V8 engine is a racecar. Building a good performing telescope (collimation tolerances are measured in thousandths of an inch) is a significant task, a huge telescope like this is a major engineering feat. What's more this is a transportable telescope. It is possibly the biggest transportable telescope in the world. This telescope is more powerful than any telescope that existed before 1917 (when the 100" Hooker telescope saw first light).

Successfully silvering the mirror using updated 19th Cedntury mirror coating technology was nifty too.

From another site: Clements began began building a steel structure to house the mirror in 2012. He did it without formal training in telescope construction or welding and without any blueprints. "He's got nothing on paper," said Clements' friend, Steve Dodds. "He did make a model out of popsicle sticks." Clements finished the telescope and in late September, he said he put a reflective coating on the mirror with a weed sprayer. [ksl.com]

Re:Bad Headline: Mirror Not a Lens (0)

Anonymous Coward | about 5 months ago | (#45341291)

Here is the scoop on the 70" telescope. Mike Clements purchased a polished but uncoated mirror that is 70" across that was intended for a spy satellite project that was cancelled. A huge uncoated mirror is not a telescope anymore than (car analogy - wait for it...) a V8 engine is a racecar. Building a good performing telescope (collimation tolerances are measured in thousandths of an inch) is a significant task, a huge telescope like this is a major engineering feat. What's more this is a transportable telescope. It is possibly the biggest transportable telescope in the world. This telescope is more powerful than any telescope that existed before 1917 (when the 100" Hooker telescope saw first light).

Successfully silvering the mirror using updated 19th Cedntury mirror coating technology was nifty too.

+1 sounds like someone actually knows what they are talking about!

Re:Bad Headline: Mirror Not a Lens (0)

Anonymous Coward | about 5 months ago | (#45342735)

How will this not crack during continual transport? If I had the biggest Amateur telescope ever, I would never transport it anywhere, but make an internet feed instead and keep it in the best possible seeing location.
I'm an amateur telescope maker AND a professional welder, Clements has no training in either, and if this works, this guy is seriously some kind of Savant.
My hat is off to you, sir. Good luck, have fun, and I hope you inspire a whole generation of new scientists! I wish you the best.

Re:Bad Headline: Mirror Not a Lens (1)

drinkypoo (153816) | about 5 months ago | (#45343759)

You don't need to be a savant to overbuild a metal structure. Good for him that he apparently did so, though, and didn't underbuild it.

We used to build stuff ONLY by copying others, or by building stuff and then rebuilding it if it broke. We only iterate faster now, with fewer failures.

22" Mirror (1)

S810 (168676) | about 5 months ago | (#45338211)

I have a Dobsonian 22" Mirror that I built from scratch about 10 years ago.

A telescope is only as good as it's lenses. Normal lenses I call Coyote Lenses because they are so crappy that they are only good for throwing at coyotes during star parties.

70" primary mirror (-1)

Anonymous Coward | about 5 months ago | (#45338219)

The title should read 'mirror', not lens....two very different things...

Hats off to this man! And for once, the Eds.. (5, Insightful)

Bearhouse (1034238) | about 5 months ago | (#45338679)

Truely "news for Nerds". Brings back fond memories of building 'scope and staring at the skies with my father.
This man has drive, dedication and the ability to both conceptualise and physically realise his dreams.

Instead of bullshit "surveys" with no-longer-funny "CoboyNeal" options, here's a serious suggestion - how about we instigate the /. annual "Nerd" awards?

Fuck it, this is going way offtopic, but I don't care...categories anyone?

Re:Hats off to this man! And for once, the Eds.. (1)

Inda (580031) | about 5 months ago | (#45343619)

Yep, more of these please.

I know nothing of Astrology* and telescopes, but these stories spark imagination.

*I know what word I typed.

Just Yesterday I saw this telescope tracker (0)

Anonymous Coward | about 5 months ago | (#45338757)

Just yesterday I saw this telescope tracker [hackaday.com]. You need your own motors/gears (actually you need to build the whole thing yourself). Its low cost, and all the plans and software is there. Looking at stars is nice, looking at stars from a warm room by way of a high-res computer monitor is even nicer. You could even look at stars by way of a web interface. Now *that* is remote content.

70- inch mirror, not "70 inch lens"! (2)

192_kbps (601500) | about 5 months ago | (#45339163)

Right after submitting this I noticed my goof in the title. As a refracting telescope the primary optical device is a mirror, not a lens. Slapping myself in the face.

Its soo good (1)

citizenr (871508) | about 5 months ago | (#45339559)

he didnt bother to post any pictures captured with it. Only pictures of an ugly metal contraption.

Re:Its soo good (1)

Noofus (114264) | about 5 months ago | (#45344797)

Dobsonian-style telescopes are generally not capable of proper astrophotography. Withouth significant work to put this thing on a barn-door-style tracking motor drive, as well as a setup that rotates the camera in the "eyepiece" holder to account for field rotation, this wont work well to capture images.

A Lens Is A Lens... (0)

Anonymous Coward | about 5 months ago | (#45339779)

Whether reflective, refractive, or with a bunch of electromagnets, a lens is designated not by what it is made of, or how it does what it does, but by the fact that it just does.
A lens by definition changes the physical size of a virtual image. This does not always mean that the virtual image gets smaller, or that the effect is in two, or even three dimensions. The physics world is full of FDDF/DFFD lenses, usually with some very good vacuum near the center.

Now about that coating... vacuum deposition is not out of the question as long as not to much area is "silvered" at a time. My own experience is with Gold, but the tech is easy enough: a reasonably stout container, a reasonably good vacuum pump, a sealant, (In the Biz, this was commonly called "Monkey Shit".), a thin wire of suitable material, some cabling, and a bunch of car batteries.
A slightly larger and more fun version of the old-fashioned Flash Bulb.

Frankly, Dobsonian mounts are a pain; I never saw the point of them myself. But with a couple of beefy servos, some drive electronics, an Arduino-level computer, and the mount could be made to track reasonably well for short period of times.

My big lens story (3, Interesting)

mknewman (557587) | about 5 months ago | (#45339919)

Years and years ago, around 1976, I had a tube type TV that went fritz so I took it to an Austin, Tx TV repair shop. The guy took it in the back to work on and while he was doing it I looked around his shop and there were quite a few very nice amateur astronomy photos, Jupiter, Saturn, the Moon and such. I was taking some astronomy classes at UT. When he came out we got talking and he told me he was into astronomy. Now, this shop was a WRECK, much like most TV repair shops I have ever seen. pretty much a dump. He asked me to come in the back to 'See something'. The guy was about 6'6" tall and BIG, and rough looking, and I am NOT, so I declined, but he insisted so I finally went through a maze of old junk, narrow dark halls, and finally got to the back of the store. I was kinda scared. He pointed to something on the ground. It was a round plug of glass on a large wooden palate. My jaw dropped, I asked him if it was what I thought and he confirmed it was a slug for a 6 ft telescope. I believe he said he got it at auction when a Swiss observatory had two made and the first worked out, so he got it cheap. It was unfinished, just a blob of glass, but at the time I'd only seen telescopes in the 36" range and this was huge! He was grinning ear to ear, and I was astounded. I believe his name was Chuck Knesek but I may be wrong or only close. It's been 35+ years. I never saw him again. If anyone knows what happened to him or his slug I'd love to know.
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