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Folded Newtonian Telescope

timothy posted more than 10 years ago | from the carry-on-luggage dept.

Space 164

johanneswilm writes "Michael Fallwell has figured out a way to overcome many of the problems of traditional telescope construction - making it way more compact and economical. And the whole thing is completely portable and achieves accuracy down to one or two millionths of an inch across an 18 inch surface!"

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CmdrTaco arrested for spitting on schoolgirl (-1, Offtopic)

Anonymous Coward | more than 10 years ago | (#8167618)

OSAKA -- CmdrTaco, a man who spat on a high school student, was arrested after being caught-red-handed at a station in Settsu, Osaka Prefecture, police said Tuesday.

CmdrTaco, 31, was arrested for spitting on the back of the 17-year-old student at JR Senrioka Station in Settsu at about 7:25 a.m. on Tuesday.

Investigators said the student was using JR to get to Kyoto Station while she was on her way to school. She had noticed what appeared to be spit on her uniform about 10 times in the past, and had discussed the problem with the Kyoto Prefectural Police railway police unit.

A member of the unit accompanied the student as she was on her way to school on Tuesday, and caught CmdrTaco spitting at her.

Police said they suspected CmdrTaco was involved in other similar crimes and they were continuing to question him. (Japan, Dec. 2, 2003)

M 4 D p R 0 p Z 7 0 G N A A
-HilaryDuff

FP (-1, Offtopic)

Anonymous Coward | more than 10 years ago | (#8167619)

sorry, had to try... move on.

Thats amazing. (-1, Offtopic)

Anonymous Coward | more than 10 years ago | (#8167620)

But this first post beats the pants off that. and american idol sux

I think I speak for all of us when I say.. (0, Redundant)

michaelhood (667393) | more than 10 years ago | (#8167621)

Neat.

Woohoo! (3, Funny)

graveyardduckx (735761) | more than 10 years ago | (#8167624)

So now instead of using my telescope to look at my neighbor's 20 year old daughter, I can look at THEIR neighbor's cuter 20 year old daughter! Yay! +5 Hormonal

Re:Woohoo! (4, Funny)

timsmells (727918) | more than 10 years ago | (#8167672)

You're going to spy on your own 20 year old daughter? Pervert!

Re:Woohoo! (0, Funny)

Anonymous Coward | more than 10 years ago | (#8167707)

Nice catch!

Re:Woohoo! (1)

irc.goatse.cx troll (593289) | more than 10 years ago | (#8167771)

Dude, have you seen his daughter? I'd install x10 cams in her room any day!

Re:Woohoo! (1, Funny)

SethJohnson (112166) | more than 10 years ago | (#8167837)



Mods missed logic of this post.

Flaw in the design. (-1, Troll)

Samuel Duncan (737527) | more than 10 years ago | (#8167628)

Due to the folded design the quantum fields of the photons interfere and the optical resolution will be reduced. You get basically a standing photonic waves between the mirrors. Due to non-elatic reflection (the mirrors eat up some energy) the visual output is reduced. Furthermore with his design you'll get problems watching object which omit mainly red light - the mirror absorption is highest there.

Re:Flaw in the design. (0, Offtopic)

paganizer (566360) | more than 10 years ago | (#8167638)

If I could understand that, I'd probably disagree.

You neglected to factor in the tesseract lens, BTW.

EFF-FUCKING-PEE YOU KIKES! (-1, Troll)

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Re:GNAA==TEH SUX0R!!! JOIN BPAA!!! (-1, Offtopic)

ReVeR5408 (723233) | more than 10 years ago | (#8167635)

Where can i sign up:)

different? (4, Interesting)

grosa (648390) | more than 10 years ago | (#8167634)

a question to those who've built their own newtonians:

how is this fundamentally different?
(to me, the picture looks basically like a standard newtonian)

Secondary mirror angle (5, Informative)

mangu (126918) | more than 10 years ago | (#8167699)

how is this fundamentally different?


Usually, the secondary mirror is elliptical and at a 45 degrees angle. In this case, it's a circular mirror at a 15 degrees angle. This puts the eyepiece closer to the main mirror, making it easier to mount a long focal distance telescope. Notice the eyepiece position spec. A circular secondary mirror is easier to make than the usual elliptical that's required if you mount it at 45 degrees. A larger secondary mirror has a lot of advantages (listed in the article) at the cost of more obstruction.

Re:different? (5, Interesting)

donheff (110809) | more than 10 years ago | (#8167741)

I built a six inch DOB with my daughter see photo at bottom of page [heffernans.org] but we were not confident going for a 12 to 18 incher because of the size, weight, and overall difficulty. This design looks different than any I saw when my daughter and I researched DOBs. The larger, circular secondary picks up a lot more light from the primary and the extreme angle reflects the light back down the structure to a lower eyepiece increasing the length of the light path without increasing the length of the scope. This is the "folding" that allows the scope to be much shorter and lighter than is the case with a standard model. I don't know anything about the silvering approach he mentions, but it sounds interesting. Grinding and silvering the primary is a big deal with mirrors 12 inches and up. 18 inches (his scope) is quite difficult.

Re:different? (2, Funny)

lars_stefan_axelsson (236283) | more than 10 years ago | (#8168005)

I built a six inch DOB with my daughter see photo at bottom of page

I gotta say though; she doesn't look too happy in the picture. Maybe you should have gone for the 18 inch DOB after all? ;-)

Seriously though, nice pictures.

Faster link (2, Informative)

Megane (129182) | more than 10 years ago | (#8168135)

Those of you who just want to see the pic of the telescope itself, go here:

http://www.heffernans.org/gifs/scope6.jpg [heffernans.org]

It's a bit slow to load the whole page, and the picture is the last one on the page. I'm sure his bandwidth will thank you.

Re:different? (0)

Orion442 (739483) | more than 10 years ago | (#8167780)

There's a fat guy standing next to it instead of a hot chick in a bikini.

Re:different? (3, Interesting)

OneOver137 (674481) | more than 10 years ago | (#8168336)

This design has been around for quite some time and telescope makers have been folding light paths of reflectors since their inception. Check out these designs [seds.org] , which not only fold the light path but make it ubobstructed as well. HIs telescope, while nice for viewing deep sky objects, will likely produce low-contrast planetary images due to the large central obstruction. This project is really about optimizing a design around his viewing habits rather than anything revolutionary.

what would waterhouse say?! (3, Funny)

schmack (32384) | more than 10 years ago | (#8167636)

A job well done -- always nice to see someone revist and improve on past research rather than blindly following the current trends.

The only problem with my knowledge of Newton these days is that 70% of it involves Waterhouse and other Neal Stephenson creations.

I mean I could regale you with tales of Newton deforming his eye with a knitting needle but it could be complete fiction...

Re:what would waterhouse say?! (4, Informative)

Anonymous Coward | more than 10 years ago | (#8167778)

No, that story isn't fiction at all. Read a biography of Newton. James Gleick's is short and readable and has a good bibliography.

Total is over $10,000.00 (4, Interesting)

Anonymous Coward | more than 10 years ago | (#8167637)

Only for the extreme hobbyist and universities.
Probably hell of a lot cheaper than University telescopes!

Re:Total is over $10,000.00 (4, Insightful)

kfg (145172) | more than 10 years ago | (#8167783)

True, but much of the point of the article is that it is within the reach of the extreme hobbiest to build a scope of this size.

And I know any number of hobbiests who spent far more on bicycle racing, or a kart, or golf, or their stamp collection, or modifying their car, etc. Fairly lower middle class income types among them.

Not to mention what the computer geeks/gamers I know have spent. The flight sim folks can get downright silly at times. God bless 'em; and I'd love a full motion cockpit myself.

Call it passionate hobbiest rather than extreme, and I'd say anybody setting out to grind their own mirrors rather than drive to the mall and pick up a Meade is, by definition, passionate about telescopes.

KFG

Re:Total is over $10,000.00 (-1)

Anonymous Coward | more than 10 years ago | (#8168282)

You know, it's spelled 'hobbyist". HOBBYIST. At least you didn't write 'defanition'.

Re:Total is over $10,000.00 (1)

Fr33z0r (621949) | more than 10 years ago | (#8167973)

Which for the rest of the world, by today's exchange rates, is around the same cost as a loaf of bread.

Re:Total is over $10,000.00 (-1)

Anonymous Coward | more than 10 years ago | (#8168084)

You're way off, man. 10 grand is about 100 Euro. So we're talking dinner and a movie... :)

Wow (-1, Offtopic)

Unleashd (664454) | more than 10 years ago | (#8167641)

Ok I'm well known as a geek but that article flew right over my head. I guess now I know how people feel now when I start talking about tweaking bios settings.

Prices (4, Informative)

imbaczek (690596) | more than 10 years ago | (#8167642)

Bino Viewer $250
Focusers
1.25" $49
2" $69
4" $140

Equatorial Table $275
Mirror Grinder
10" $250
20" $475
40" $1800

80mm Binocular Holder $250
16" DOB $1800
18" DOB $2200
16" Mirror $900
2" Adapter $30
Led Colimator $30
Silvering Kit $50
Encoder $30
Guide Scope $40
Interferometer 10" $160
10" Folded Schmidt Camera $4500

I wouldn't call $13298 Very Low Cost...

(Assuming all of this stuff is needed of course.)

Re:Prices (0)

Anonymous Coward | more than 10 years ago | (#8167651)

Not sure that the $4500 Folded Schmidt Camera is really needed. Neither Interferometer.
Using your own camera (I mean eye) is enough.
Wait for the next year to buy electronic eyes.

Re:Prices (5, Funny)

brad-d (30038) | more than 10 years ago | (#8167659)

Bino Viewer $250
Focusers
1.25" $49
2" $69
4" $140

I wouldn't call $13298 Very Low Cost...
... and so on

You must be new around here. The correct take off of a Ma$tercard add is:

18" DOB $2200
Mirror Grinder 40" $1800
10" Folded Schmidt Camera $4500

Finding out you spent ALL your money on glass and plastic and are getting kicked out of your apartment. Priceless.

For some things in life there is Slashdot, for everything else there is Google.

Re:Prices (0, Flamebait)

SkoZombie (562582) | more than 10 years ago | (#8167757)

and you must old around here ... The rest of the world abbreviates "advertisement" as "ad" ;)

Well, I for one,... (0)

Anonymous Coward | more than 10 years ago | (#8167801)

welcome our new Damon Stern's Monster Observitory building Overlords.

Re:Prices (0)

Anonymous Coward | more than 10 years ago | (#8167911)

/Quote

For some things in life there is Slashdot, for everything else there is Google. /Quote

My new email sig....let those PHB's sort that out!!!!

Re:Prices (2, Funny)

asifyoucare (302582) | more than 10 years ago | (#8167660)

Bino Viewer $250
Focusers
1.25" $49
2" $69
4" $140
etc.


Quality nude pics of the neighbor's wife : Priceless

Re:Prices (1)

Mr_Dyqik (156524) | more than 10 years ago | (#8167664)

Compared to the 4 million GBP bid we're about to put in for a telescope, it's quite cheap. Mind you, I don't know what an 16" optical telescope should cost.

AND the MOST BIZARRE thing about those PRICES (4, Informative)

deathcow (455995) | more than 10 years ago | (#8167800)

This looks like low quality or poorly made stuff. Basically, in Astronomy, you get what you pay for. Quality is going to be LOW at these prices.

$250 for a binoviewer will get you crap! The good ones are about $900 - $1500 for a Denkmeier [denkmeier.com] or for a Baader Planetarium [astro-physics.com] model.

Focusers for $49... to $140 for a 4" model? puh-lease! Superb Feathertouch focusers [buytelescopes.com] are going to run you $300 at least for a 2" model. Clement Focusers [clementfocuser.com] are going to be around $400. AP [astro-physics.com] focusers are going to be $400 - $700.

And the biggest problem of all. 16" mirror for $900?? 18" DOB for $2200?? Go fish! Some crackpipe dreams here. Superbly figured mirrors, which focus light superbly well, in well built dob structures, are going to run you into bucks. A quality 18" dobsonian telescope like a Starmaster [starmastertelescopes.com] is going to run you $6,400 without any options, a far cry above $2200.

I'll put my refractor up against this guys mirrors any day! ;)

Re:Prices (4, Informative)

cbmeeks (708172) | more than 10 years ago | (#8168140)

>I wouldn't call $13298 Very Low Cost...

You don't add all of that together. If you did, you would have about 3 full telescopes and another 16" mirror for a 4th. Plus, you would have mirror making equipment. It is quite possible to build that 18" scope you see for probably $1100 to $1500. With about 90% of the cost always being the mirror (pre-made).

cb

In comparison to...? (3, Interesting)

Jugalator (259273) | more than 10 years ago | (#8167644)

"And the whole thing is completely portable and achieves accuracy down to one or two millionth of an inch across an 18 inch surface!"

Wow, that sounds really cool and accurate. But current telescopes are obviously also very very accurate too. So this doesn't really say much. I wonder how good this one is compared to current ones, made for the same purpose. Is there a noticeable loss of quality?

Re:In comparison to...? (1)

elvum (9344) | more than 10 years ago | (#8167711)

READ THE ARTICLE!

Re:In comparison to...? (1)

timerider (14785) | more than 10 years ago | (#8167750)

what article? the few lines there that basically say "hey i'm so cool i built a telesope that is just a little bit different", then list a few items, the most of which dont have anything to do with the 'folded newtonian' or whatever he calls it?

Re:In comparison to...? (1)

elvum (9344) | more than 10 years ago | (#8168042)

How about the section where the author compares his design qualitatively to conventional Newtonian and Cassegrain designs?

Re:In comparison to...? (0)

timerider (14785) | more than 10 years ago | (#8168085)

All I can see there is a list of Statements without proof.

Sorry, but I have seen better quality comparisons on the meade and celestron websites.

Re:In comparison to...? (4, Interesting)

Lips (26363) | more than 10 years ago | (#8167756)

Hand made scopes tend to have better figures than commercial scopes. Like any product, commercial scopes are made to a certain quality. By making your own scope, you can make it to your own standard of quality. My home made 8" newtonian is optically far superior than the average commercial scope, and thats why I made it.

Incredible breakthrough (0)

Anonymous Coward | more than 10 years ago | (#8167646)

For years scientists have been trying to figure out how to make telescopes way better and this magnificent bastard has pulled it off. Well done sir.

His construction doesn't look very stable. (1)

pointzero (707900) | more than 10 years ago | (#8167650)

Great idea and all, but his construction looks a little "mickey mouse". I hope that his telescope doesn't Fall apart to well. I think i'll stick to my nice shiny telescope in a big white tuben.

It's a normal construction method (5, Interesting)

fmaxwell (249001) | more than 10 years ago | (#8167720)

He's using a truss tube design similar to that used by many makers of large commercial Dobsonian telescopes. In addition to being very lightweight, it's easily broken-down for transport. The triangulation makes it extremely strong and rigid.

It may look spindly, but it's a good design.

Great chick magnet at parties (2, Funny)

fruey (563914) | more than 10 years ago | (#8167654)

Talking about his
# 30% reduction in tube length
# 50% reduction in eye piece height
# 4x more back focus

Compared to, of course, smaller secondaries...

It's a semi interesting page but frankly doesn't do it for me. Great for telescope geeks no doubt. But the key question he surely missed... if you point it at some interesting bedroom or bathroom windows... is it able to see better through slightly opaque curtains?

Re:Great chick magnet at parties (1)

hodet (620484) | more than 10 years ago | (#8167776)

...if you point it at some interesting bedroom or bathroom windows... is it able to see better through slightly opaque curtains?

Doubtfully, but if you are going to spy on people don't you think something less conspicuous then an 18" f/8 might be in order?

Re:Great chick magnet at parties (0)

Alan Partridge (516639) | more than 10 years ago | (#8168304)

than

New? (0)

FreeMath (230584) | more than 10 years ago | (#8167655)

This really isn't much more than a truss tube dobsonain. Nicely done, but not that different.

I wonder... (1)

Trillan (597339) | more than 10 years ago | (#8167658)

Does this qualify as an invention? Is it patentable?

If so, I hope a big corporation doesn't manage to scoop it behind his back. Any time you radically reduce the cost of something there's a big risk of that.

Re:I wonder... (1, Offtopic)

orthogonal (588627) | more than 10 years ago | (#8167727)

Does this qualify as an invention? Is it patentable?

If so, I hope a big corporation doesn't manage to scoop it behind his back. Any time you radically reduce the cost of something there's a big risk of that.


We look through the telescope and we wonder...
why Darl McBride is staring back.

Isn't it great the way modern patent and copyright law frees us all to concentrate on creativity and innovation, rather than legal minutia and protecting our work from overbroad and stealth patents?

No Patents here... Move along (1)

twoslice (457793) | more than 10 years ago | (#8168248)

Does this qualify as an invention? Is it patentable?

Prior Art - I know Captain Ahab had a folding telescope when he was looking for Moby Dick. Unfortunately he was looking straight down when from the depths of hell he stabbed at it...

Michael Fallwell? (-1, Troll)

illuminata (668963) | more than 10 years ago | (#8167666)

Hallelujah. I bet he plans on using this technology that he's developed to spy on homosexuals. He probably just doesn't want any faggy innuendos in the media or God letting terrorist attacks slip through the cracks because of it. Now, he has them by the balls (in a non-gay way), they can't get around this 'scope, baby!

The design looks a bit silly to me. I think he's probably watching a bit too much Puppetry of the Penis. But, he'd never admit to watching that kind of queer shit, even if he was!

Re:Michael Fallwell? (-1, Flamebait)

illuminata (668963) | more than 10 years ago | (#8167724)

I knew it, I just knew it. I thought to myself, "illuminata, don't click the submit button. Don't do it! There's dumbasses running rampant and they have mod points. They'll mod you as a troll!" Well, thank you for proving my initial thought correct.

Now, I have to spell it out for some dipshit moderator who just didn't get it, even though it might spoil the parent's joke. You see, this invetor's name is Michael Fallwell. There is a crazy minister called Jerry Falwell. Jerry hates gay people. He led a campaign against Teletubbie Tinky Winky because he thought it was gay. He blamed gays for the 9/11 attacks, claiming that God was angry with gay people. Search up on him, you'll find out much more.

You know, up until now, I never did know that they made computers with internet access available to people in special ed. Even if I did know beforehand, I would have never fathomed that Slashdot wouldn't be filtered out. Regardless, even being a genuine retard leaves no excuse for modding that post as a troll. If you have the mental capacity to moderate posts on Slashdot, you should also be capable of finding out what a post is talking about before moderating.

Re:Michael Fallwell? (1)

Cragen (697038) | more than 10 years ago | (#8167813)

We /.'ers ain't got time to think! We gotta post fast to get them mod points or the chance is just gone. BTW, I am not the one who modded you down, but your post just wasn't funny. Well, to me, for what that's worth. If you gotta explain your joke, it ain't funny. Actually, I read your explanation (parent) first, changed my settings, and then read your initial post. It still didn't help. Unfunny. Probably too, too subtle, as in "i had no clue you were referring to JF, vice MF". Further consulting parsing of humor on /. can be contracted at run_your_joke_by_me@joke_analyzers.com^H^H^Hnet.

cragen

Re:Michael Fallwell? (-1)

Anonymous Coward | more than 10 years ago | (#8167834)

Having read the explaination, this still doesnt qualify as funny. Try again. Good job Mod's.

Re:Michael Fallwell? (-1)

Anonymous Coward | more than 10 years ago | (#8168040)

Maybe you wouldn't have gotten a troll if you headed your post "Jerry Fallwel" and ended it with...

Huh? Whaddayamean, MICHAEL Fallwel?

And even then it isn't really funny

Still too big... (0)

Anonymous Coward | more than 10 years ago | (#8167668)

I cant haul that down to the beach in the summer, someone would surely be suspicious. :-/

Stars are for looking at, not touching.

Portable is in the eye of the beholder (4, Funny)

Rosco P. Coltrane (209368) | more than 10 years ago | (#8167676)

18" f: 8 Folded Newtonian
Weight 70lb

Eyepiece Ht. at Zenith 5'4"
33% Obstruction
3 Min: Setup - Ultra Portable

I assume the guy doesn't live in an appartment. My 12' Schmidt Cassegrain telescope however, while less interesting that this project, can be moved with a bicycle trailer to go stargazing on the high hill near my place, and doubles as a handy tool to watch my neighbours' boobs in the appt complex down the street.

Re:Portable is in the eye of the beholder (0)

Anonymous Coward | more than 10 years ago | (#8167713)

I think you mean 12", not 12'. Unless you've got a *really* big bicycle trailer.

Dont you wish... (1)

twoslice (457793) | more than 10 years ago | (#8168191)

watch my neighbours' boobs in the appt complex down the street.

You neighbour had installed "full length windows"?

``Ultra Portable'' (3, Funny)

R.Caley (126968) | more than 10 years ago | (#8167679)

Talk about culture clash. Imagine putting in an order ofr an `ultra portable' laptop and getting back something that size.

Not much information (5, Interesting)

Xolotl (675282) | more than 10 years ago | (#8167690)

There's actually very little concrete information in the article, just some very general and often confusing statements, like:

The figure itself is stabilized by a trick developed years ago for stabilizing glass lasers eliminitaing any need for Pyrex at least for mirrors of this size.

The reason for using Pyrex is thermal stability (ordinary glass expands, changing the carefully-worked shape in the process). What's this trick then? How does it work? Being able to use plate glass effectively would make amateur telescope making much easier, yet I've never heard of this method. Some references would be nice.

Would you trust a computer review which said something like "this machine is cooled using a trick developed years ago for cooling nuclear reactors, eleminating the need for fans for a processor of this speed" without some kind of additional information? That's what this article sounds like to me.

These kind of statements and the lack of, say, an optical diagram, make it very hard to judge the article. Theres a photo of a guy with a telescope, so I guess he built it, but I'd prefer to see some more concrete information and proper test results (diffraction rings, spot diagrams, whatever).

The price list is strange - an encoder? There's no drive on that thing. A $4500 Schmidt camera? that has nothing to do with this telescope (its a kind of telescope in itself, used for very wide fields). 40" mirror grinder? 16" mirror? The article talks about an 18" mirror telscope. The only thing I can think of is that this an attempt at a price comparison with other technology.

In short, interesting, but strange.

Re:Not much information (5, Informative)

Lips (26363) | more than 10 years ago | (#8167731)

You don't need a drive to use of an encoder. There are hand controllers which take input from encoders, but provide instructions, left/right/up/down x units, so that a human user can point the thing in the right direction. Something like this: http://www.wildcard-innovations.com.au/

Last year I finished my first, an 8" f6.6 and the figuring was rather hard. I think my next attempt should be better, but something like this at f8 is much easier to figure!

I'll show the article to my ATM mentor and see what he thinks about it. Especially some of those contentious sentences.

Re:Not much information (3, Insightful)

Xolotl (675282) | more than 10 years ago | (#8167774)

You don't need a drive to use of an encoder. There are hand controllers which take input from encoders, but provide instructions, left/right/up/down x units, so that a human user can point the thing in the right direction.

Quite true. A particularly nice example exists on the old 74" telescope at the David Dunlap Observatory [utoronto.ca] . The encoders feed into a computer which displays not the absolute position but the difference between the current position and where you want to point to. All you have to do is move the telescope until the display shows zero. (The 1920's design of the telescope makes it impractical to fully automate, large movements are done by hand, once the telescope has been roughly pointed the automatic guiding system takes over. The offset encoder system is very accurate though.)

My original point was that the price list seems to have little relation to the telescope itself. Neither the photos nor the list of dissasembled parts shows an encoder, hand controller or the like. I'd be interested to read your ATM mentors comments, perhaps you could post them up here as reply when you have them.

I feel sorry for the guy (-1, Offtopic)

Anonymous Coward | more than 10 years ago | (#8167691)

He just got a link from slashdot and his email address is plainly harvestable at the bottom of the page. How long before his yahoo account is saturated with spam?

I remember a saying.... (3, Funny)

tanveer1979 (530624) | more than 10 years ago | (#8167706)

The world will beat a path to the door of the man who builds a better mousetrap

Now it should read: Slashdot will burn a hole in the server of the man who builds a better telescope

Re:I remember a saying.... (1)

KjetilK (186133) | more than 10 years ago | (#8167767)

AFAIK, the box it's running on is a four-CPU solaris box with a 1Gbits/s pipe. My old homepage is on the same server. But then, it could be interesting to see if it can withstand /.ing when everybody loads the pics.

I found a folding website! (-1, Troll)

Anonymous Coward | more than 10 years ago | (#8167743)

I found a folding website@! Here [sco.com]

My favorite Homebrew 'Scopes (5, Informative)

SoupIsGood Food (1179) | more than 10 years ago | (#8167748)

Flatness measurements, often represented as fractions of the height of a lightwave, smaller fractions are better) for hand-figured mirrors from amateur telescope makers are about as reliable as performance gains claimed by enthusiastic overclockers. Large doses of salt required unless verified by a reputable third party.

As homebrew telescopes go, this one isn't terribly refined. It uses a unique optical arrangement, but not all that unique. Check out this folded refractor [aol.com] , or this set of 22-inch newtonian binoculars [foothill.net] for some real jaw-droppers. (Also check out that last guy's all-metal 14-1/2" Alt-Az telescope... truly a beautiful instrument, even if it's a conventional design.)

There are a ton of exotic telescope designs out there being crafted by enthusiastic hobbyists, many of them on-par with deleriously expensive research-grade instruments. Most of them aren't made out of cheap plywood and bed rails. (I plan on building a 12" off-axis newtonian this summer.)

SoupIsGood Food

Re:My favorite Homebrew 'Scopes (0)

Lips (26363) | more than 10 years ago | (#8167814)

d00d, 1 b3l13v3 th0s3 L337 4TM HaXoRs wh0 m4k3 th31r 1/20th w4v3 m1rr0rs

Re:My favorite Homebrew 'Scopes (1)

The real PoD (734939) | more than 10 years ago | (#8167886)

Erm. Unique but not all that unique?

the truth about all this (-1, Offtopic)

Anonymous Coward | more than 10 years ago | (#8167753)

This line opens with some mis-informed bullshit about a company that produces a proprietry operating system. This line refers to a bug uncovered when a dickhead used the OS. This line neglects to mention that the all open source alternatives either a) dont support the feature(s) or b) didnt support it until either SGI or IBM handed over the code. This lines makes a really annoying and tired connection with the Santa Cruz Org or Microsoft that is only understood by Stallman fanboys. This line is funny because the text is bold and italic. Now laugh you stupid little cunt.

Huge central obstruction (5, Informative)

MonkeyDluffy (577002) | more than 10 years ago | (#8167759)

The secondary mirror is a huge 33% (by diameter) - usually, for a telescope like this you would try for around 20% or so. The larger the central obstruction, the lower the contrast. The upside is that it is a F8 (focal length/diameter ratio) scope, so that it is easier to collumnate (keep the mirrors in proper alignment) and will have less coma (stars near the outer edge are more eliptical, instead of circular points).

I would imagine that it must have been a bitch to figure (shape) the mirror - it's not a simple parabola, and would require much more effort than a conventional mirror the same diameter. Kudos to Mike Fallwell for doing something different!

-MDL

Ob spelling rant (0)

Anonymous Coward | more than 10 years ago | (#8167807)

The correct spelling is Cassegrain (after the French sculptor Sieur Guillaume Cassegrain), not Cassagrain. There are two major subtypes: Maksutov-Cassegrain or Schmidt-Cassegrain). Reference [howstuffworks.com] .

Ob Cassegrain Rant (3, Informative)

Anonymous Coward | more than 10 years ago | (#8167932)

Your reference is a bit simplistic since it focussus
on consumer products. Maks and
Schmidts are not subtypes, they are are Cadioptics based on the Cassegrain design which have
a corrector plate at the front. A cassegrain
(note no prefix) has no corrector plate. Spoken
as one who has worked with several cassegrain telescopes.

Re:Ob Cassegrain Rant (0)

Anonymous Coward | more than 10 years ago | (#8168102)

My days as an amateur astronomer are long gone, and I stand corrected. This page [scopecity.com] is a little better if anyone's interested.

Oh, and while I still have the <pedant> tag open, it's catadioptrics, not Cadioptics ;-)

16" f5 (4, Informative)

nacturation (646836) | more than 10 years ago | (#8167811)

Check out this telescope [sympatico.ca] . It weighs a total of 52 pounds (40 was the target) instead of the article's 70 pounder, and has an f5 aperature instead of f8 so it lets in more light. Very similar construction, but this one was made 6 years ago.

Re:16" f5 (4, Informative)

nacturation (646836) | more than 10 years ago | (#8167846)

Oh, and not to totally karma whore, but from his main page there's a link to his ultra-portable 10" f5 [sympatico.ca] . Click and drool.

No disrespect to the builder (1)

bhima (46039) | more than 10 years ago | (#8167812)

But the Hubble Space Telescope and Chandra more or less eliminated my interest in building or buying a telescope of my own. No cold nights. No light pollution. No Setup problems, No searching the night sky for hours to discover I'm an incompetent fool and looking in the wrong place! The faulty optics were repaired. Those big images look great on my 23 inch cinema display. I really hope the JWT is not watered down to the point where it is not that useful. And I'm really enjoying the images from Mars....

Now I want to know when I can go to Mars with my hydrazine powered Maxi-Mog!

Folded Newtonians are nothing new. (5, Interesting)

fmaxwell (249001) | more than 10 years ago | (#8167851)

The folded Newtonian [oldham-optical.co.uk] is nothing new, though the design described here is a bit odd, to say the least. Here's an example of a similarly designed scope with much better construction [irony.com] .

There are more ways to fold telescope optical paths than most people imagine as shown here [k12.wv.us] .

That said, the referenced article is filled with inaccuracies and I almost wonder if it's intended as some kind of practical joke. For example, it describes the "tracking accuracy" of Schmidt Cassegrains, Newtonians, and Folded Newtonians as "poor", "poor", and "very high" respectively. That's bunk. The tracking accuracy is determined by the mounting and drive. In the case of his scope, it's on an altazimuth (Dobsonian, to be specific) mount with no apparent drive at all, so it doesn't track anything! The author mispells Cassegrain repeatedly throughout the article, which I would hardly expect from someone knowledgeable about telescope optics. He describes the mount of a conventional Newtonian primary mirror as "fussy" while describing the mount of the primary in the folded Newtonian as "robust." There is no difference. The folding of the light path at the other end of the tube has nothing to do with how the primary is mounted. He describes the "weight" of Cassegrains and Newtonians as "heavy" and classifies the Folded Newtonian as "Very Light", yet there is no evidence that his folded Newtonian is any lighter than a conventional Newtonian -- and it's probably heavier due to the larger secondary, larger secondary mount, and the baffled tube that holds the focuser. He says that the "Field Width" of Schmidt Cassegrains, Newtonians, and his Folded Newtonian are "Narrow", "Wide", and "Very Wide" respectively. That's simply wrong and illogical -- as anyone with a reasonable knowledge of telescope optics can tell you. The tilt of the secondary mirror has no effect on real or apparent field width. In fact, because he is advocating a longer focal ratio (f8), he will have a narrower real field of view than a typical Dobsonian Newtonian (typically f4-f6) with the same eyepiece.

He makes absurd claims like "So the only real advantage of a small diagonal in a large telescope is a tiny improvement in contrast/resolution that can easily be recaptured with image processing." Anyone who knows anything about telescope construction can tell you that the secondary obstruction causes light loss and that's a serious concern. Also, image processing implies astrophotography. Astrophotography implies long exposure times and that necessitates an equatorially mounted telescope -- which his is not.

I don't find the article to be at all credible.

I don't know telescopes, but I do know crackpots (3, Insightful)

Anonymous Coward | more than 10 years ago | (#8168364)

Let me check the trace from my crackpot-o-meter:
+2: frequent spelling mistakes
+4: train of thought derailments
+5: extraneous figures
+7: grandious claims not backed up by facts
+6: derision towards common theories/devices
-5: cool picture of finished product
crack-point total: 19
crackpot category: eccentric

Re-running the scan after callibrating for your input, we get:
+2: frequent spelling mistakes
+4: train of thought derailments
+5: extraneous figures
+7: grandious claims not backed up by facts
+6: derision towards common theories/devices
-5: cool picture of finished product
+10: ignorance of standard knowledge in the field
+5: misspelling common technical terms
+15: claiming common techniques as unique innovations
crack-point total: 39
crackpot category: wingnut

Thanks for helping tune my crackpot-o-meter for astronomy.

Not much to see here... (5, Informative)

jalbro (82805) | more than 10 years ago | (#8167871)

IAAATM (I am an amature telescope maker, working on my third design)

There isn't much to see here. This is an old concept, one with advantages and disadvantages.

The main issue is that a folded design allows for a lower eyepiece height when you have a long focal length.

A long focal length mirror is faster to make (less grinding) and easier to figure (making a high quality mirror is easier when it is shallower).

The problem with a long focal length is you end up needing a ladder. You also lose the ability to get the brightest images (exit pupils of 7mm) when you go over an f/6.

The folding also introduces loss of contrast... from both the big secondary and the MAJOR baffling problem. You run the risk of extra star light entering the eyepiece and washing out the image when the eyepiece is pointed up.

So this design is nothing more than what this designer wanted for trade offs. There is no major design advances that lets an ATM do something they couldn't do before.

For more designs, check out:
http://members.efn.org/~mbartels/tm/ul-dobs. html
(scroll to the bottom)

and specifically another folded design...
http://www.irony.com/Ed/astro/18inch/

-Jeff

Re:Not much to see here... (2, Informative)

jalbro (82805) | more than 10 years ago | (#8167882)


I forgot to mention... a longer focal length also gets you lower coma, which is an off axis abberation. It makes stars on the edge of the field look like seagulls.

-Jeff

emplies (1, Informative)

Anonymous Coward | more than 10 years ago | (#8167874)

The article "emplies" something; could an English native tell me if that is slang, or... what?

Re:emplies (0, Informative)

Anonymous Coward | more than 10 years ago | (#8168262)

The article "emplies" something; could an English native tell me if that is slang, or... what?


It's not slang, it's "...what". He should have spelled it as "implies".

His neighbours must live pretty far away.... (3, Funny)

CProgrammer98 (240351) | more than 10 years ago | (#8167948)

if he needs a 'scope THIS big to see them nekked

Does anyone have a picture of the optical diagram? (3, Insightful)

p_trekkie (597206) | more than 10 years ago | (#8167990)

In other words, one of those pictures that show where the light rays go? Those generally tend to do a better job of explaining the setup than a picture of the scope and a long description.

New chatup line (1, Funny)

maroberts (15852) | more than 10 years ago | (#8168126)

The scene: First meeting on an OSDN personals date...

Her: "Is that a Folded Newtonian Telescope in your pocket, or are you just pleased to see me?"

Non-story (4, Informative)

Pedrito (94783) | more than 10 years ago | (#8168148)

Sorry, but as others have pointed out, this is a non-story. It's a variation of a Dobsonian design. A real story is the story of John Dobson (short bio here [nasa.gov] ), a monk from San Francisco who designed and built the original Dobsonian telescopes and got people interested in astronomy by taking his telescopes to the streets. Being a monk, he lived in poverty and built his telescope as cheaply as possible. Because he had to continue living in poverty, he was unable to sell them and become rich, so now the bigger telescope makers are making money off of his design.

You wanna run a story about amateur telescopes, that's a good one. Or I could point you to the story of the three guys who ground their own 30" mirror and built a telescope from that. There's a lot of cool stuff being done by amateurs. Sorry, but this isn't that cool compared to most of it.

It would probably be useful (1)

porkchop_d_clown (39923) | more than 10 years ago | (#8168302)

to point out that Dobson is a Buddist monk, not the Catholic sort.

Not that this has any impact on his telescopes or importance (I've built one of his scopes myself) but for years I had a rather incorrect mental image of what he looked like. :-P

TLAs? (2, Interesting)

Megane (129182) | more than 10 years ago | (#8168204)

For those of us who haven't been watching the stars all night and just woke up, could we have a few jargon definitions here? ATM got explained, but what's a DOB?

Re:TLAs? (4, Informative)

lal (29527) | more than 10 years ago | (#8168355)

Dob is short for "Dobsonian" - it is the type of mount used in this scope. It was invented by a Buddhist monk name John Dobson.

Junkyard wars? (1)

MongooseCN (139203) | more than 10 years ago | (#8168261)

Did anyone else see the photo and think Junkyard Wars: Race to Space?

Slashdot: Taking the NEW out of NEWS (1, Interesting)

Anonymous Coward | more than 10 years ago | (#8168283)

This has been done to death. I can probably locate a 50+ year old article by an amateur astronomer that did this at one point. What's so great about a "folded" (no, it isn't really) 18" f/8 newt? Great, less coma! Long fl so I can get up close and personal with Jupiter or Mars or Saturn... Oh, but there's a 33% obstruction. There goes contrast. And you don't need all that much light gathering for the planets, they're pretty bright already. You need good contrast to see detail.

Hmm, so it's good for wide field views then! Oh, but its long fl makes it less attractive for that, unless I use very low power, very expensive 2" eyepieces. And the obstruction sorta leaves visual viewing less than impressive. I don't want to spend $20,000 on a 2 ton steel and concrete mount to do good astrophotography with this, either.

Tell ya what, I'll put my home-made f/3 primary, f/18 Gregorian system, 19% central obstruction 12.5" telescope on a G-11 up against his 18" on planetary or galaxy viewing any day. And my 12" f/5 is nothing to sneeze at either on the DSOs.

Can anyone explain to me? (1)

wizarddc (105860) | more than 10 years ago | (#8168373)

I'm a telescopic layman, and I admit I only know peripherally about telescope design, but doesn't having an open telescope like this allow light to bleed onto the mirror? Doesn't he need to cover it up with a tube from the lens to the mirror, or at least wrap a tarp around this? How can this thing work if the street light down the road is blurring my view of Jupiter?
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