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Folded Newtonian Telescope
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!"
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.)
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.
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.
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, or this set of 22-inch newtonian binoculars 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
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
Happy meals fund terrorism
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.
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 or for a Baader Planetarium model.
Focusers for $49... to $140 for a 4" model? puh-lease! Superb Feathertouch focusers are going to run you $300 at least for a 2" model. Clement Focusers are going to be around $400. AP 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 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!
Check out this telescope. 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.
Want to improve your Karma? Instead of "Post Anonymously", try the "Post Humously" option.
IAAATM (I am an amature telescope maker, working on my third design)
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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
(scroll to the bottom)
and specifically another folded design...
http://www.irony.com/Ed/astro/18inch/
-Jeff
The article "emplies" something; could an English native tell me if that is slang, or... what?
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.
http://www.heffernans.org/gifs/scope6.jpg
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.
#naabhaprzrag, #sverubfr-000, #agi-fcbafberq, negvpyr[pynff*=' negvpyr-ary-'] { qvfcynl: abar !vzcbegnag; }
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), 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.
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.
Yeah, a Newtonian already has a folded path. I was wondering what was going on. This is a slightly different use of the word "folded", I think. The text is not precisely clear and the photo, while rather neat, didn't help as much as I expected.
Instead of going straight out the side of the tube (normal to the tube's surface, that is), the path from the secondary mirror goes back in the general direction of the primary, but canted a bit so that you don't need a hole in the primary. The idea is to bring the path out somewhere near your natural eye height, so you don't have to stand on a ladder to view through such a monster as you would with the 90-degree bend.
Way to not read the article.
The thing colapses and would easily fit in the back of a honda. With a bit of care you could probably get it into your bicycle trailer.
-Peter
Here's a design for a Newtonian reflector that uses the building as the tube. It works well conceptually. The eyepiece(s) are in the middle of the tube itself, but because the mirror is 18feet in diameter, and it focuses to infinity, there is not that much image degradation. The site is www.digitaldarc.net goto 'projects' - 'observatory' Mike