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Old 08-04-2016, 08:04 PM
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Prototype 17" f/8 scope from Astro-Physics

I wonder if I can sell the kids?

http://www.astral-imaging.com/AP-NEAIC2016.html
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Old 08-04-2016, 08:39 PM
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Doing window shopping Rick?

But more seriously, looks like a truly awesome telescope. And less seriously, I would get one for sure but it is probably not the best match for my tiny ICX814
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Old 08-04-2016, 08:48 PM
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Originally Posted by Slawomir View Post
Doing window shopping Rick?
Who me?

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Originally Posted by Slawomir View Post
I would get one for sure but it is probably not the best match for my tiny ICX814
I'm sure it would be fine binned as a guide camera, Suavi
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Old 08-04-2016, 09:11 PM
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Gorgeous. It looks a lot smaller than 17" because of the light Meccano-style frame. If I did not know I would have guessed 8 or 10" at the most (from the first two photos; the third one gives a better sense of scale). And just how thin is that mirror!!
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Old 08-04-2016, 09:14 PM
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billdan (Bill)
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I like how it says in the description it is a portable telescope suitable for field trips and can be setup easily by one person. I don't know if I could lift 30Kg up onto a mount that easily.

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Bill
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Old 08-04-2016, 09:27 PM
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I like how it says in the description it is a portable telescope suitable for field trips and can be setup easily by one person. I don't know if I could lift 30Kg up onto a mount that easily.
If you read a bit further, it looks like it disassembles into two parts at 10Kg and 20Kg.

I can get my 30 odd Kg Ceravolo on to the mount but it does require a few deep breaths in preparation
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Old 11-04-2016, 08:21 AM
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I look at this with some amusement given the statements made here several months back regarding the use of a Serrurier Truss on RC's. In particular how they would not hold the mirrors correctly etc. Hmm looks like AP think otherwise too; just like GSO.

I'll never be able to afford this scope but I like the idea that AP is making larger scopes like this. I wonder how much they are expecting to charge for their level of perfection?
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Old 11-04-2016, 08:52 AM
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Paul,
They don't say they are actually using a Serrurier truss design - just a carbon fibre truss.
The Serrurier truss is a very complex (not really, for a structural engineer) combination of tube strengths, sections and end joint conditions. When designed properly it will definitely hold the alignment between the secondary and primary mirror.
(I was lucky enough to spend some time with Grubb Parson's during my final university year and saw their telescope design and manufacturing processes.)
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Old 11-04-2016, 09:15 AM
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There are two opposing truss sections in the images, unlike any of the other simple truss designs I've seen from OS, GSO, etc. so it is possible that this has got the correct amount of flexure engineered into it. However, every true serrurier truss I've seen has much thinner tubes on the back end.
Cheers,
Andrew.
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Old 11-04-2016, 09:29 AM
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https://en.wikipedia.org/wiki/Serrurier_truss

Anthony Cook also posted a good message on another forum:

Your definition for a "Serrurier Truss" actually describes only half of the double parallelogram square tube invented by Mark U. Serrurier of Caltech in Pasadena in 1935 as a way of controlling flexure in the tube of the 200-inch (5m) telescope that he helped to design. The idea was that a square section at the tube at its center of gravity (where the declination axis is attached) would also be where the bases of 8 triangular trusses (one on each side of the box) would be attached. The apex of each triangle would be attached to the end rings of the tube, one end carrying the mirror and cell and the other the prime focus cage and secondary mirrors. Bending by gravity is resisted by its force in the plane of one pair of triangles, while the adjacent sides act something like a hinge, allowing any motion of the end rings to be of equal magnitude and in parallel, thus keeping the optical elements collimated in spite of flexure. In equatorial telescopes, these properties are shared by all parts of the tube as the telescope points at various parts of the sky.
Telescopes with the center of gravity close to the mirror have to compensate for the unequal lengths of the triangles by adjusting the tension of the trusses or the thickness of the tubes (or I beans) so that the shift (translation) of the tube rings perpendicular to the optical axis is equal.
Nearly every large telescope (with the exception of the Keck telescopes and the Hobby-Eberly telescope) have used this system since Palomar was finished in 1948 (including the BTA).
The triangular truss square tube used on most truss-Dobsonian telescopes do not have the property of parallel translation of the primary mirror (which does not translate) and the top tube ring (which does).
While the triangular truss is relatively strong, it does not have the important property of parallel translation, and it is not a Serrurier truss.
By the way, some telescopes (like the Kitt Peak 4m, the Very Large Telescope, Subaru, etc. may look at first like the "half Serrurier truss", in fact the mirror cells are attached to the end of small triangular trusses, or sometimes just straight beams to preserve the parallel translation of the ends of the tube. Sometimes these smaller trusses are enclosed in the structure containing both the declination axis and mirror cell, so they cannot be seen.
Perhaps the type us ATM's use should be called ‘Pseudo Serrurier’, ‘Semi Serrurier’ or ‘Half Serrurier’ or ’triangular’ Trusses.
Anthony Cook
Griffith Observatory
Astronomical Observer.
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Old 11-04-2016, 09:34 AM
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See also:
https://www.youtube.com/watch?v=97OMAmOgyvU
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Old 11-04-2016, 01:20 PM
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Ken and Andrew, perhaps you are misreading my comments here or I was not clear, but I think the truss is a great design. My GSO 12 has this very truss design (though not held together by a square connection in the middle) and it holds the imaging package very well. I have attached an image to illustrate the point. The shroud has no physical connection to the truss or acts as a restraint in anyway. It floats in a channel front and rear. To my eye it looks almost identical to the AP version and I am pleased to see that design is being used by a company such as AP.


Quote:
Originally Posted by alocky View Post
There are two opposing truss sections in the images, unlike any of the other simple truss designs I've seen from OS, GSO, etc. so it is possible that this has got the correct amount of flexure engineered into it. However, every true serrurier truss I've seen has much thinner tubes on the back end.
Cheers,
Andrew.
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Old 11-04-2016, 02:51 PM
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Ken and Andrew, perhaps you are misreading my comments here or I was not clear, but I think the truss is a great design. My GSO 12 has this very truss design (though not held together by a square connection in the middle) and it holds the imaging package very well. I have attached an image to illustrate the point. The shroud has no physical connection to the truss or acts as a restraint in anyway. It floats in a channel front and rear. To my eye it looks almost identical to the AP version and I am pleased to see that design is being used by a company such as AP.
Sorry Paul - I wasn't critiquing the design. As Ken has pointed out its a question of nomenclature - amateur designs don't need to consider the differential flexure problem because it can be effectively eliminated completely on 'small' telescopes like this. When you have a primary weighing a few tons, and a secondary cantilevered several metres away you have to accept that there is a lot of flexure, and that's where the Serrurier bit comes in to keep it all parallel.
However, I recall a bit of freeware years ago that would allow you to design a true Serrurier type truss for a scope. however it turns out Bunnings doesn't carry aluminium tube in diameters of sufficient variety for it to be practically useful.
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Andrew.
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Old 11-04-2016, 05:36 PM
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however it turns out Bunnings doesn't carry aluminium tube in diameters of sufficient variety for it to be practically useful.
Forget Bunnings. Try an ATC outlet for aluminium. They sell dirrect to public and have pretty much anything you could want. https://www.aluminiumtc.com.au/
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Old 11-04-2016, 07:30 PM
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Quote:
Originally Posted by Paul Haese View Post
Ken and Andrew, perhaps you are misreading my comments here or I was not clear, but I think the truss is a great design. My GSO 12 has this very truss design (though not held together by a square connection in the middle) and it holds the imaging package very well. I have attached an image to illustrate the point. The shroud has no physical connection to the truss or acts as a restraint in anyway. It floats in a channel front and rear. To my eye it looks almost identical to the AP version and I am pleased to see that design is being used by a company such as AP.
That's a VERY nice setup you have in your obs Paul! Quite a lot of mass hanging off the focuser too...
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Old 12-04-2016, 06:54 PM
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Wow a 17 inch AP Cassegrain. Notice the lots of holes in the main baffle. To combat tube currents. Roland is very good at engineering solutions to tube currents. I notice that in my RHA305. The outer tube is oversized to 14 inches so there is 1 inch all the way round for tube currents to fall away from the imaging circle. Also his scope will have way better baffling, another thing I find AP is superb at. Again I find my RHA 305 the best scope I have ever used for cutting through light pollution. Amazing really.

This scope would be phenomenal. Thin mirror - quick cooldown times and would match the ambient well in rapidly dropping temperatures.

Portable. I didn't see that coming. A 17 inch scope that is portable. That would make it totally unique right there.

Roland has expanded his skill set to expert mirror maker.

I imagine if this had a price it would be around US$30K at a guess.

Greg.
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Old 13-04-2016, 02:48 AM
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Roland mentioned this scope when I spoke with him last Oct at AIC. He was ready to sell me one right away.

BTW, he isn't making the mirrors. I believe Mike Lockwood makes them. He might possibly rely on other mirror makers with Roland acting as the quality gate.

AP will make the mechanics of course but Roland just doesnt have the time to make any more optics.
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Old 13-04-2016, 11:29 AM
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Did he mention a price?

Greg.
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Old 13-04-2016, 02:23 PM
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Quote:
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I look at this with some amusement given the statements made here several months back regarding the use of a Serrurier Truss on RC's.
I think this was eloquently addressed above by Anthony Cook...

There is nothing wrong with a truss...but a Serrurier Truss it is not.

Looks like it has all the hallmarks of AP....I wonder if I would have bought one if they had been available when I decided on the RC16 ....

While the light weight is *very seductive* there is no mention of a dedicated compressor ( I do see it has a field flattener). With a fixed secondary the back focus may also be a little tight.

I am certain however, that like all things AP, it would be a superb instrument.
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Old 13-04-2016, 05:13 PM
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If you zoom in on the photo that has the AP description it mentions a wide field telecompressor accessory.

The scope though is not listed on the AP website and their seems to be little discussion about it on the Yahoo Group which is surprising.

It does look like an interesting scope and maybe something the team could make without requiring Roland's personal ability to figure optics. He may be setting things up for his eventual retirement.

Greg.
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