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Carbon Fiber

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#1 Guest_**DONOTDELETE**_*

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Posted 07 April 2004 - 02:31 PM

"thebach" in his reply about liking the Celestron NS11, because it doesn’t have an aluminum tube, got me to thinking about carbon fiber and, specifically, it's longevity. So I'll put the question to you all, how long does carbon fiber last? Can it get brittle like old plastic? Does it age well? Can sunlight damage it? I’d think that the aluminum would potentially last longer. What are your thoughts?

Bart

#2 Rusty

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Posted 07 April 2004 - 09:37 PM

The carbon-fiber tube is actually what's called "CRP" or "CFRP" - Carbon-fiber Reinforced Plastic, meaning that it's resin reinforced with carbon fiber filaments.

Some years ago, when FRP (Fiberglas Reinforced Plastic) was new, the Coast Guard, one of its first users, did studies on its boats. What they found was that their fiberglass boats got stronger over the years.

That said, I wouldn't count on a service life much over 500 years for CRP...even though it has some advantages over aluminum....

:rollgrin:

#3 Guest_**DONOTDELETE**_*

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Posted 08 April 2004 - 01:13 AM

CFRP is used as a structural material in many areas, many of them outdoors (e.g. bicycle frames, F1 racing car structures). Considering how little stress there is on telescope tubes, I wouldn't worry about it.

CFRP is truly space-age material, used extensively on satellite structures including some newer space telescopes. Aluminum is so 20-th century. :lol:

#4 matt

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Posted 08 April 2004 - 02:32 AM

We also have racing boat shells made out of it. My personnal boat is carbon / kevlar / nomex. It's about 2mm of honeycomb sandwiched in two sheets of CFRP.

Boat builders (or Shipwrights, like Cirdan) collectively refer to them as 'plastic' boats as opposed to wood or aluminium ones.

#5 wilash

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Posted 08 April 2004 - 04:32 AM

Actually, I wish the telescope manufacturers would get into this millenium and use more modern materials like carbon fiber and magnessium alloys. I'm really getting tired of all this dead weight I carry around.

#6 Guest_**DONOTDELETE**_*

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Posted 08 April 2004 - 10:03 AM

A lot of power tool manufacturers are using magnesium and other lighter materials to make their tools easier to use. I'm sure it's a cost issue for telescope manufacturers.

-Dave

#7 Guest_**DONOTDELETE**_*

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Posted 08 April 2004 - 10:22 AM

I've been doing some research, and carbon fiber is better than aluminum, lighter, stronger, conducts heat and cold better, lasts forever, doesn't dent, seems like it's a good thing to have a scope tube made out of it, it seems Celestron is always a little ahead of Meade, most people think their SCT's are designed a little beeter than Meades

#8 Guest_**DONOTDELETE**_*

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Posted 08 April 2004 - 12:12 PM

I've been doing some research, and carbon fiber is better than aluminum, lighter, stronger, conducts heat and cold better, lasts forever, doesn't dent...

Don't forget the small thermal expansion coefficient. A very desirable quality for optical instrument structures.

I too would like to see more exotic materials used - and more importantly, new designs which are only possible with those new materials. The bicycle industry started using carbon tubes a couple of decades, but the first carbon bikes had the same old design - just like the current Celestron SCTs. Soon they started making innovative designs which were impossible or impractical with other materials, like the monocoque racer, the Trek Y-foil and the Velokraft NoCom. I expect the same will eventually happen to the telescope industry.

#9 matt

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Posted 08 April 2004 - 02:04 PM

The problem with working carbon is that working it is a specific knowledge and requires special installations such as molds and ovens, so it's a big investment in infrastructure and manpower for whoever starts using it.
I guess the risk of carbon for the bike industry is that it's extremely rigid, so it does not bend or dent, it just SNAPS! I've seen carbon oars snap on a "crab" or when hitting a buoy, I'd hate that to happen on a carbon bke frame I'm riding!

#10 jrcrilly

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Posted 08 April 2004 - 04:00 PM

it seems Celestron is always a little ahead of Meade, most people think their SCT's are designed a little beeter than Meades


They did have a head start! :roflmao:I have found the two brands to be equally good optically, though.

#11 erik

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Posted 09 April 2004 - 12:05 AM

hey, don't forget, meade has......SONOTUBE!! talk about technologically advanced material(just don't EVER get it wet) :)

#12 Guest_**DONOTDELETE**_*

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Posted 09 April 2004 - 12:15 AM

The problem with working carbon is that working it is a specific knowledge and requires special installations such as molds and ovens, so it's a big investment in infrastructure and manpower for whoever starts using it.
I guess the risk of carbon for the bike industry is that it's extremely rigid, so it does not bend or dent, it just SNAPS! I've seen carbon oars snap on a "crab" or when hitting a buoy, I'd hate that to happen on a carbon bke frame I'm riding!


OT, but there was that exact problem in one of the first CF Mountain Bikes. Cannondale, made a dual suspension bike, and the rear suspension consisted of a pivoting carbon fiber swing arm. The problem was that they designed the crank arms (piece that goes down to the pedals) to only clear this arm by a fraction of an inch. A strong rider can actualy flex the hub a bit, and strong bikers were having their rear end shatter, because they flexed the hub, and the crank arm struck the CF swing arm, breaking it.. not a good situation!!

#13 Guest_**DONOTDELETE**_*

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Posted 09 April 2004 - 12:47 AM

I guess the risk of carbon for the bike industry is that it's extremely rigid, so it does not bend or dent, it just SNAPS!!

Actually, CFRP can be made quite flexible. We recently had a thread about the Johnsonian GOTO telescope which uses CFRP strips as flexible, collapsible support. CFRP is a very complex material, like wood - strength and rigidity depends not only on type of epoxy and curing method, but also on the pattern of grains. Difficult to work with, but also a lot of potential to fine-tune the material for each application.

#14 Rhadamantys

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Posted 09 April 2004 - 04:33 AM

I have used a Para-Cassegrain from Clavé (something very special) with a CFRP OTA two years ago. It seemed that CFRP OTA have better thermal behaviour than aluminium, at least for open tube (not a truss tube or pseudo-truss). This 160mm (6.3") scope wasn't especially lightweight (5kg), but Clavé has since refined the whole thing (optically & Mechanically) and I placed an order for the newer version (166mm/6.5" f/5.8 Para-Cassegrain): this time, the complete OTA weights 3.2kg and the only mechanical parts not made of CFRP are the focuser and the spider. Even the diagonal makes heavy use of CFRP. The mirror is meniscus shaped to save weight.

One of my friend placed an order for a Clavé 18.1" f/4.6 Para-Cassegrain (truss tube): OTA weight, with the optics, is 22 kg (Glass/composite primary mirror).

#15 Guest_**DONOTDELETE**_*

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Posted 09 April 2004 - 05:04 AM

Rhadamantys, that sounds very interesting. Where on the web can I find out more about these telescopes? And what's the price range? More or less than the Questar? :p

#16 matt

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Posted 09 April 2004 - 05:22 AM

Rhad, I saw the ad for the 460mm Clavius... Do you know what the price is? I'm about to sell my car :lol:

Ken, you can find details on the astronommix.com/clavius website. Unfortunately it's all in French.

#17 Rhadamantys

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Posted 09 April 2004 - 05:42 AM

For the 6.5" f/5.8 (Central Obstruction=24% diameter), there is no official price yet. I know however that it will be roughly € 2,500, give or take. The 10" f/5 OTA (same central obstruction) should be priced roughly € 6,000. The price of the 18.1" f/4.6 is unknown to me. However, I can give you my friend's private e-mail. You can also contact Mr Paul-Louis Vinel who runs Clavé (astronom@noos.fr).

There is one interesting website made by an amateur who use one of the first 6.3" f/6.7, made two years ago. Unfortunatly, it's in french, but he understands english. Here is his web site: www.astrosurf.com/laurent and the e-mail adress is on his page. I fully share his opinion about this unusual telescope. Another colleague signed an excellent image of Saturn with this scope last year (It is the opinion of several french astro imagers that it is the best saturn shot ever made with such a small scope). I think it is slightly overprocessed and slightly overexposed. (if you think you see Encke on this picture, you are not exactly mistaken: it is the diffraction effect that Encke's division creates on 150mm-200mm telescopes enhanced by the digital processing, not Encke's gap itself)

Posted Image

Hope this helps.

#18 Guest_**DONOTDELETE**_*

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Posted 09 April 2004 - 06:11 AM

Thanks for the information. That's an amazing image. :bigshock:

2500 Euro for a 6.5" seems pretty reasonable. But no, I don't need to find out the price for the 18.1".... :crazy:

#19 wilash

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Posted 09 April 2004 - 08:40 AM

That is amazing. It optical path looks like a telescope at the front end and then uses a system that looks like it is from a microscope to transmit the image to the eyepiece.

#20 Rhadamantys

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Posted 09 April 2004 - 09:29 AM

In fact, the trick has been in use for a long time. Foucault himself used it on his very first glass mirror Newtonians (in 1860), to reduce central obstruction. But he had to refigure the primary mirror to compensate for the induced spherical Aberration of the relay lens. More recently (1977), Dilworth made a 16cm f/7 and a 40cm f/7 all spherical relay cassegrain with 26-28% central obstruction (can't remember exactly). On axis and for the green wavelength everything is fine on the Dilworth. But for the full visible spectrum, the picture is no longer rosy and off axis aberrations are enormous.

Mr Paramythioti pushed the end of the enveloppe with his all spherical design. Unlike the Dilworth it has no perceptible chromatism, no perceptible spherochromatism, no coma, low field curvature, etc. I had a long chat with the conceptor: he is very much aware that his all spherical design can further be improved (many tried) but that many of those "improved" designs would be incredibly trickier, if not impossible to produce.

#21 matt

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Posted 09 April 2004 - 02:09 PM

Thanks Rhadamantys. I was asking the price out of curiosity; with the 6" in the 2,500 euro range and the 10" at 6,000, I guess I have to sell my wife's car too to get the 18"!

Interesting that a diffraction/processing effect should cause the illusion of the Encke Gap. I guess it's the same processing which creates that bright 'ring' next to the Cassini Division?

#22 Rhadamantys

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Posted 09 April 2004 - 02:56 PM

Yes. Definitly.

If you have time on your hands (and perhaps aspirin), I suggest you check this discussion of the image above, among others (Too bad some ill-intentioned posters polluted this thread). You may find it most enlightening.

http://www.astrosurf...L/006865-2.html

The posts of Laurent, David Vernet, Thierry Legault and Ulysses on this page are most interesting.

#23 Gary BEAL

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Posted 09 April 2004 - 06:20 PM

While I agree the unusual designs in this thread are spectacular don't forget the Maksutov Newton, and especially in the carbon fibre tube. And at a m ore user friendly price
Gary

#24 Guest_**DONOTDELETE**_*

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Posted 10 April 2004 - 12:52 AM

You mean someone makes a CFRP-tube Maksutov Newton? Who?

However the Clave para-cassegrain seems to be much better than a Mak-Newt in terms of cooldown time and weight. At least that's what I infer from reading the descriptions.

#25 Gary BEAL

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Posted 10 April 2004 - 02:27 AM

I believed that ITE had a C/F tube available for them, and I was always going to have a C/F tube made locally, but have decided to sell the optics. Given it's 20 kilo weight at present, the C/F option looked good, but I just ran out of interest. Not rocket science, just a bit of looking about for the right tradesman, and money.
I downsized Mak/Newt wise with a 7".
Gary


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