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London_David

Carbon Fibre or Metal / UNC / ONTC

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Posted (edited)

I’m upgrading and I’ve decided on one of these two scopes:

10” f4 1000mm TS Photon metal

https://www.teleskop-express.de/shop/product_info.php/info/p10225_TS-PHOTON-10--F4-Advanced-Newtonian-Telescope-with-Metal-Tube.html

10” f4 1000mm TS UNC carbon fibre

https://www.teleskop-express.de/shop/product_info.php/info/p5034_TS-Optics-10--f-4-UNC-Newtonian-Telescope-with-Quartz-main-Mirror-and-Carbon-Tube.html

Has anyone any experience with carbon fibre and metal tubes on a Newtonian? Or quartz v regular glass? Or any experience with the TS scopes?

I will be mainly using this for eaa with a asi294pro and an asi290. 

Cost isn’t a particular issue, except I’d rather not waste money if there’s not much difference.

I had read that metal cools quicker but is less stable, cf is slower to cool and more suceptable to dew, but more stable once it’s at the right temperature. I had also read that nine times out of ten you won’t tell the difference in performance, only on nights of great seeing. So I think the only difference is down to 2kg lighter and the properties of cf v metal...

Or if anyone has used the ONTC version and can say why the extra cost is worth it?

Any other experiences to note? 

Edited by London_David

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Used the steel Quattro scopes and found the focus very stable, I would happily get another steel one.

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I only use telescopes for visual observing, so this is for what it's worth. I have a 8" F/6 UNC (carbon) from TS and I like it very much. Very well put together, holds collimation well and is easy to tweak when needed. On my request, they swapped the focuser for a Baader Diamond SteelTrack and the scope has turned out to be all I want in a Newt.

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I have only ever used steel scopes. Mostly visual.

However, looking at how the OTA might change size with temperature. Steel has an expansion coefficient of about 13 parts per million, per degree centigrade.

This means a 1000mm optical path length (a long newt or frac) will drift by 0.013mm for a 10C temperature change.
This temperature change is a chilly evening right through a cold night.

I have seen data indicating carbon fibre is about 3x better.

Is this worth worrying about?

If your motor driven focusser has good enough resolution on the drive, you could compensate for this by measuring temperature through the night.

Just my two pennorth..

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I don't think you would notice much difference for EAA use.    ?

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Carbon will cool down far quicker than steel and won't expand as much.

Why is is than most if not all of the high end OTA's are either truss designed or carbon or both, but very rarely steel if ever.

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On 02/04/2019 at 14:38, Jkulin said:

Carbon will cool down far quicker than steel and won't expand as much.

Why is is than most if not all of the high end OTA's are either truss designed or carbon or both, but very rarely steel if ever.

Actually carbon will cool slower. It will expand and contract less though.

 

On 30/03/2019 at 02:46, London_David said:

I’m upgrading and I’ve decided on one of these two scopes:

10” f4 1000mm TS Photon metal

https://www.teleskop-express.de/shop/product_info.php/info/p10225_TS-PHOTON-10--F4-Advanced-Newtonian-Telescope-with-Metal-Tube.html

10” f4 1000mm TS UNC carbon fibre

https://www.teleskop-express.de/shop/product_info.php/info/p5034_TS-Optics-10--f-4-UNC-Newtonian-Telescope-with-Quartz-main-Mirror-and-Carbon-Tube.html

Has anyone any experience with carbon fibre and metal tubes on a Newtonian? Or quartz v regular glass? Or any experience with the TS scopes?

I will be mainly using this for eaa with a asi294pro and an asi290. 

Cost isn’t a particular issue, except I’d rather not waste money if there’s not much difference.

I had read that metal cools quicker but is less stable, cf is slower to cool and more suceptable to dew, but more stable once it’s at the right temperature. I had also read that nine times out of ten you won’t tell the difference in performance, only on nights of great seeing. So I think the only difference is down to 2kg lighter and the properties of cf v metal...

Or if anyone has used the ONTC version and can say why the extra cost is worth it?

Any other experiences to note? 

Have you experience of a F5 Newtonian? I do and its enough for me to know I never want to own a F4 Newtonian lol.

If you go for it then I recommend the ES coma corrector.

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Thanks all. I currently have a 6" f4 which I've liked a lot. But you know... aperture...

I have a sesto senso and actually, @iPeaceI was thinking of doing exactly as you have and switching the UNC focuser for a Baader Steeltrack. Did they charge you extra for it in addition? Or just the price difference of the Baader?

My gut is certainly that the extra €700 for the ONTC is probably not needed for what I'm using it for. The main thing I like on the ONTC is being able to move the mirror to change back focus. I want to pair whatever I get with the Ackerman corrector/reducer that they have to take it to f2.9. However, if I'm thinking if I get the focuser set for the 90mm backfocus offered, I can use an extension tube if I want to use the scope without the Ackerman corrector. I spoke to TS and they said they would build the scope so the draw tube is always out of the tube when in focus.

I suspect too that I wouldn't notice a huge amount of difference for EAA use, but I'm tending towards the UNC for a couple of reasons.

I'm not scared of collimation, but I am scared of collimation stability and focuser stability on the scope. I suspect from above that the UNC will be good enough - especially with the Steeltrack. Plus this is for EAA with small chip cameras doing short exposures so I feel I should go carbon fiber because of weight (I have to lift it on and off each night) and physical rigidity over the steel. It's expensive, I think it'll be a small difference but a nice luxury to enjoy.

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51 minutes ago, London_David said:

I was thinking of doing exactly as you have and switching the UNC focuser for a Baader Steeltrack. Did they charge you extra for it in addition? Or just the price difference of the Baader?

Just the price difference; I asked not to include the standard finder scope and they discounted that as well. If you get in touch with them and explain exactly what you (don't) want, they can get it done.

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On 02/04/2019 at 11:59, Carbon Brush said:

This means a 1000mm optical path length (a long newt or frac) will drift by 0.013mm for a 10C temperature change.
This temperature change is a chilly evening right through a cold night.

Hi @Carbon Brush,

I think you have the decimal point in the wrong place.

Linear expansion coefficient is 13 ppm per degree C.

10  degrees change gives 130 ppm expansion

1000 mm focal length is 1 million microns

So, 10 degrees expansion is 130 microns = 130/1000 = 0.13 mm.

Just for interest, using my 530 mm focal length Tak, I need to refocus every 0.5 degrees change to keep the focus in the critical zone. So, most of the focus change with temperature is something other than the thermal expansion of the metal.

HTH

Regards, Hugh

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UNC carbon tubes have problems of flexion and dilation.
Ontc tubes are Carbon fiber foam sandwich, much more stable.

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@cabfl did you have one? Anything else you liked/disliked? My camera load should be light with under 1kg on a baader steeltrack. Plus this is mainly for eaa on galaxies so I’m going to be using a small chips or ROI. 

Edge coma I’m not too worried about, focus stability I’m not too worried about since I have a motor focus and exposures are going to be 0.1s - 30s, mainly under 10.

As I understand it, collimation stability is more key for me.

Do you think that will still have issues for flexion and expansion?

I saw someone on CN with tilt problems but that in the end seemed to be his camera to focuser. 

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Hi, I'm from the Canary Islands (Spain).
Here in the observatory of my group, at 1850m altitude, the temperature at night drops to 10ºC in summer and -4ºC in winter.

A partner, has a UNC 10 "f / 4.
The tube gives you problems of stability. Flexions and dilation / contraction.

I want to buy another 10 ", but ONTC, because sandwith carbon is more robust.

If it's for visual, it does not matter. But for astrophoto it is important.

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If you can bring youself to re-check the collimation once after a couple of hours cooling down during the night- then you'll save yourself 600 Euro's............

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Posted (edited)

@laser_jock99 I think that sums it up! I think for eaa it may be a luxury I don’t need. 

Thanks all!

I still like the ability to move the mirror on the ONTC. But again... maybe that’s a luxury not worth it, since for 600 euro I could buy a new ota for visual as well. 

Edited by London_David
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