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20" f/3 New Moon Telescopes Hybrid

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#26 a__l

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Posted 05 December 2018 - 09:47 PM

Clarifying The first plane (the Z axis - which you turned) must be turned 180 degrees along with the other (the Y axis is also turned 180 degrees). But along the Z axis, all the bends (focuser board) will remain the same as the  initially did made.
This is the correct position in my opinion.


Edited by a__l, 05 December 2018 - 09:57 PM.

 

#27 tommm

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Posted 05 December 2018 - 10:08 PM

Am I the only one that thinks Ryan owes you a proper length set of poles? And maybe there's a conversation to be had about the orientation of the rollers on the whiffletrees.

Yes, the rollers on the mirror cell edge supports should be oriented so they roll up/down along the edge of the mirror, not around it.  Like these:
http://www.jpastrocraft.com/cells.htm

 

Also see Lockwood article:

http://www.loptics.c...rorsupport.html


Edited by tommm, 05 December 2018 - 10:10 PM.

 

#28 Kunama

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Posted 05 December 2018 - 10:08 PM

Clarifying The first plane (the Z axis - which you turned) must be turned 180 degrees along with the other (the Y axis is also turned 180 degrees). But along the Z axis, all the bends (focuser board) will remain the same as the  initially did made.
This is the correct position in my opinion.

It cannot be turned that way Andrey, the top folded portion and bottom folded portion are different as the bottom lip attaches to the truss pole connection while the top attaches to the ring.

 

I think the OP may have found a way that suits him.

 

The 'proper' course of action would have been as Dick indicated, to replace the unwanted short poles with the correct length. The easiest 'workaround' would be to clamp the focuser board in a soft-jaw vice to prevent marring the finish and then adjust that angle to 90º......

 

I'll leave it to the OP to sort it and wait for his actual observing reports once all the things line up.  I have an 18" F3/5 dob and love that I can sit to view at all elevations....


Edited by Kunama, 05 December 2018 - 10:12 PM.

 

#29 a__l

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Posted 05 December 2018 - 10:42 PM

It cannot be turned that way Andrey, the top folded portion and bottom folded portion are different as the bottom lip attaches to the truss pole connection while the top attaches to the ring.

 

 

There is symmetry along the Y axis. As seen in the photo there is no prohibition on turning 180 degrees.

The only possible limitation is if the upward movement of the secondary holder abuts the spider. This is not visible in the photo.


 

#30 a__l

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Posted 05 December 2018 - 10:54 PM

The 'proper' course of action would have been as Dick indicated, to replace the unwanted short poles with the correct length. The easiest 'workaround' would be to clamp the focuser board in a soft-jaw vice to prevent marring the finish and then adjust that angle to 90º......

 

I think that it is not necessary to adjust the angle of 90 degrees.
If the manufacturer has conceived such a correct position (along the Z axis), then everything should be fine.


 

#31 Kunama

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Posted 05 December 2018 - 10:59 PM

There is symmetry along the Y axis. As seen in the photo there is no prohibition on turning 180 degrees.

The only possible limitation is if the upward movement of the secondary holder abuts the spider. This is not visible in the photo.

Your method does not work as the top lip has two holes for attaching to the ring, the bottom lip has only one attachment point for attaching to the truss pole bracket.......


Edited by Kunama, 05 December 2018 - 11:00 PM.

 

#32 a__l

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Posted 05 December 2018 - 11:05 PM

Your method does not work as the top lip has two holes for attaching to the ring, the bottom lip has only one attachment point for attaching to the truss pole bracket.......

There are three holes on both lips.

 

I liked this idea for using bino. Perhaps I will use it in the future on my one telescope.


Edited by a__l, 06 December 2018 - 01:14 AM.

 

#33 KJL

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Posted 05 December 2018 - 11:37 PM

There are three holes on both lips.

Crikey, what are you on about, mate? The end of the focuser board with the three holes is designed to attach to the UTA ring, while the other side is designed to attach to the truss tubes. Isn't it blatantly obvious that the two ends are different?

 

And besides, how would flipping it end-to-end resolve the need for more out-focus? scratchhead2.gif

 

46169964331_17ab25440a_c.jpg


 

#34 a__l

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Posted 06 December 2018 - 01:08 AM

Crikey, what are you on about, mate? The end of the focuser board with the three holes is designed to attach to the UTA ring, while the other side is designed to attach to the truss tubes. Isn't it blatantly obvious that the two ends are different?

 

And besides, how would flipping it end-to-end resolve the need for more out-focus? scratchhead2.gif

 

attachicon.gif 46169964331_17ab25440a_c.jpg

Is it really? Crikey? 

 

In any case, it is easier than changing all 8 tubes. And better than adding 1" spacer (probable add vignetting)

I would do just that. Three holes (or as needed).


Edited by a__l, 06 December 2018 - 01:41 AM.

 

#35 KJL

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Posted 06 December 2018 - 02:41 AM

Is it really? Crikey?

I was just watching an Australian get some chiropractic help on YouTube, and "crikey" came up. I'm largely Californian valley girl in my accent, TBH.

 

In any case, it is easier than changing all 8 tubes. And better than adding 1" spacer (probable add vignetting)

I would do just that. Three holes (or as needed).

The other end is flat. You not only need three holes — you'd need a square end to put the holes in ...

 

... Which is exactly what Mike is going to get when Ryan sends him a (presumably properly square) replacement focuser board.

I'm only continuing this hilarious exchange because it's 2:30 am where I am and my typing limiter came off like four hours ago. I'll stop now. 

Back on topic. Again, beautiful scope, and it's looking like all the troubles will be solved by the replacement focuser board and offset spider. (I'm in favor of the shorter poles for greater flexibility not only for binoviewers but NV eyepieces too).

 

Good luck!


Edited by KJL, 06 December 2018 - 02:41 AM.

 

#36 a__l

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Posted 06 December 2018 - 05:46 AM

 

The other end is flat. You not only need three holes — you'd need a square end to put the holes in ...

 

I do not understand  above relations to chiropractic .
There was a question, there was an answer.

 

There would be a sufficient of photos, there was no discussion. 

 

There was an assumption about the unification. Since there was a seller recommendation  (turn 180 degrees). This is normal logic.

If unification is not thought out, the seller has a problem. Probably not the first. But it is taboo.


Edited by a__l, 06 December 2018 - 08:00 AM.

 

#37 Mike Wiles

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Posted 06 December 2018 - 03:19 PM

The Next Chapter

I spent nine glorious days in the desert.  Through the miracle of solar power on the truck camper, and excellent 4G access so far away from civilization I was able to work during the day, and observe at night.  A guy could get accustomed to this.  I can't stay up too late because of work obligations, but some serious observing is getting done.  Cruising the periphery of the California Nebula with an H-Beta filter kept me busy for awhile.  Other highlights included checking out the tidal bridge from M110 to M31, and the Horsehead was downright easy with the combination of big optics and extremely dark skies.

 

New Moon contacted me again about the focuser board asking me to take measurements of the various holes on the board, because the focuser board that shipped with this telescope is a one of a kind piece.  New Moon ships a standard focuser board for their f/3.3 to f/5 scopes, but mine is an f/3.  I'm not sure how that's any different as it's the same focuser and same upper truss ring - so I expect the focuser board shouldn't be any different.  Then I think to myself...if this focuser board is a one of a kind, wouldn't you check to see that it was made correctly before putting it on a telescope? That clearly didn't happen but, whatever. 

 

In an effort to achieve the highest level of accuracy, I shipped the focuser board back to New Moon Telescopes upon my return home.  When the new focuser board arrives, the angle is now more or less square.  There's nothing wrong with it, but it's notable that it's not the same as the previous focuser board.  The center of the focuser axis is 100mm from the top of the truss ring, instead of 103mm like the previous board.  And the hole in the board for the optical path isn't centered with the holes for the Feathertouch mounting bolts.  None of this affects the function of course, but its an indicator to me the quality control on such a large purchase as this isn't what I had expected it would be.  

 

46205997431_65deb426c0.jpg

 

I mounted the focuser board, and went through the procedure to identify the 180º point on the virtual tube, and a point 100mm from the top of the truss ring.  This was to identify the proper axis for the focuser.  Putting a laser into the focuser showed that it was a little bit off....as was expected.  

 

46206355051_f3a15354d9.jpg

 

Some adjustment of the mounting plate solved the problem.  The side of the focuser closest to the primary mirror was now raised up about 1mm in order to square the focuser.  

 

46206355061_cc799bc00b.jpg

 

44389198730_e2c03bef10.jpg

 

In our discussion about collimation shift, Ryan said that the spider vanes weren't tight enough.  When he tested the scope he said that he observed less than 1/32" movement from zenith to horizon.  So, my 1/4" of observed movement from zenith to horizon was an 800% increase.  I find it hard to believe that the spider became that loose during transport considering how tightly it was all wrapped in protective bubble wrap.  Whatever the case, he said the vanes needed to be very, very tight. 

 

I had concerns about the offset secondary holder, as it was just going to shift the mirror 0.4" while the spider remained in its current place.  I question the sanity of moving that much mass off-axis when collimation shift is already a problem.  In preparation for the offset secondary holder, I ensured that the spider itself was exactly centered in the truss ring and tightened the vanes very tight as had been instructured.  And then I put the laser back in the focuser.  

 

32334274968_052d261da5.jpg

 

The focuser axis has shifted a full inch (25 mm).  I'm not an optical genius nor am I a mechanical engineer but I'm pretty sure this is not a good sign. I’m also concerned that tightening the spider causes any change in the alignment of the focuser.  It seems to me that the two should be unrelated, and it indicates that something in the structure is flexing. Installing the secondary is pointless if the focuser isn’t square to the axis.  So at this point, I have a half assembled telescope with no clear path forward.  I contacted Ryan with my experiences and waited for some guidance.  It came quickly - he's quite responsive, and always has been.  

 

In his response he tells me that I don't need to tighten them that much, to back them off some.  That tightening them too much will flex the ring.  That's probably okay, as the flex is the new shape - but they don't need to be that tight. He also says that the top bolt in the spider vane will need to be a little tighter as the mounting post flexes slightly - but I've probably noticed that.  I am very concerned that things are flexing.  I spent a good amount of time doing deep sky astrophotography at longer than normal focal lengths, and was reasonably good at it.  It taught me an important lesson - flexure is bad.  Always.  

 

The offset secondary holder has arrived.  The holes drilled in the secondary holder for the mounting screws don't line up with the shroud currently encasing my secondary mirror.  Ryan has another shroud and holder made and they'll be shipped to me as soon as they're done.

46205998711_e5a3c15b1d.jpg

 

My confidence is low that moving the weight of the secondary mirror this far away from the spider's center is going to benefit my issue with collimation drift.  I loosened the vanes on the spider and ensured the focuser was hitting the proper point on the opposite side of the tube.  I then ensured the spider was still centered in the tube and tightened the spider vanes right up to the point that tightening any further pulls the laser off-axis.  Once I reach this point, it's surprising how far and quick the laser moves offline with just a slight turn of the screwdriver.  I put the original non-offset secondary holder in and collimated the telescope with it pointed at about 60º altitude.  Then I checked again for collimation drift.  The results this time were better....but still nowhere near acceptable.  

 

Here's the tublug at zenith

31267771517_916d48ea95.jpg

 

Here's the tublug at about 45º

31267771277_965e2a1a7b.jpg

 

And finally, the tublug at about 20º altitude

31267771887_a7cf841a2c.jpg

 

I'm pretty frustrated at this point.  I contacted Ryan again with these results.  I told him that I expect better than this - that my 15" Obsession has none of these issues and it was 1/4 of the cost.  I've spent more time working on this New Moon Telescope in six weeks than I've spent working on that Obsession in 17 years.  I don’t know how we resolve this, because to my eye it doesn’t look possible. If I tighten the spider to prevent the drift, the upper truss ring will warp and pull the focuser out of axial alignment. If I leave it alone, the weight of the secondary shifts collimation as the telescope is moved lower in altitude.

 

Ryan told me that the best way to collimate will be to put the secondary mirror in the telescope first, and then to align the focuser to the secondary.  This is completely opposite to everything I've ever understood about Newtonian telescopes.  I suggested that this was untrue - that the focuser should be aligned, and then the secondary placed to intersect that path in the proper place.  I also said - "I hope we agree that if tightening the spider vanes more than they are causes the focuser to tilt, that's a bad thing.   I think we both agree that tightening the spider vanes beyond a certain point does warp the upper truss ring and we want to avoid that regardless of how the rest of the telescope is aligned.  A warped truss ring is bad." 

 

If I have a telescope here where the spider vanes can't be tightened enough to prevent collimation drift *and* keep the focuser on axis without warping the upper truss ring, then I have a telescope that doesn't work.  Astrosystems says that the spider vanes should have 70-100 pounds of tension.  There's no way this ring holds its shape with that kind of tension placed on it.  

 

In his response, Ryan told me that "The ring can flex some."  I now fully realize that my idea of a proper telescope structure and New Moon's idea of a proper telescope structure have some fundamental differences.   I pretty strongly said that "No, the ring can not have some flex."  It doesn't flex in my 15" and I expect the same from this telescope. 

 

The primary/secondary/focuser need to be at 90º angles to each other with a secondary mirror that doesn't move 1/8" (3.2 mm) as the telescope moves through altitude.  Ryan's response is to say that I'm correct that the light path needs to be at a 90º angle, but wrong in that I can't accomplish that with a slight flex of the upper truss ring.  

 

I give up.  The third secondary holder has arrived.  It's slightly too small for my non-standard 4.8" secondary.  So it has to go back.  I'm shipping back all three secondary holders, as the first one fits - its just not offset.  So the state of affairs at the moment is that this premium-level dobsonian is not usable - there's no working holder for the secondary mirror.

 

Mike


Edited by Mike Wiles, 06 December 2018 - 03:24 PM.

 

#38 IVM

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Posted 06 December 2018 - 03:21 PM

Mike, thanks for the detailed review and account. I trust you will make it all work well, although I agree that the whole idea of making such a boutique purchase was that the buyer supposedly didn't have to. What I would check at this point is that the secondary size is OK for its distance to the primary.

 

P.S. The above was actually written before Mike's last post appeared. I still more thank Mike for his continued and detailed account.


Edited by IVM, 06 December 2018 - 05:59 PM.

 

#39 Kunama

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Posted 06 December 2018 - 04:11 PM

A single ring secondary will flex when you tension the spider.  To reduce the amount warp in the single ring you need to apply the tension gradually and evenly in both axis.

once you have the spider tensioned hand tight you need to apply a very small amount to each end of one axis, then the other axis and repeat this until tight.  I assume your previous Obsession had a full UTA...

 

Only once you have the spider fully tensioned should you begin the alignment of your focuser board as the two are related.....


Edited by Kunama, 06 December 2018 - 04:13 PM.

 

#40 Allan Wade

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Posted 06 December 2018 - 05:13 PM

Mike, I can feel your frustration. It would appear there’s a design issue with the mounting system for the spider that obviously is going to twist the support ring as tension is applied to the spider vanes, and that twisting is going to pull the focuser board out of alignment.

 

If you replaced the ‘L’ brackets that the spider vanes are bolted to with a bracket like this  ]  then you could bolt a second support ring on top of that bracket, and that would increase the brackets rigidity tremendously. Then you would be able to torque the spider vane tension up significantly without the support brackets flexing and twisting that lower support ring.

 

That would be only a small job with Ryan’s help to machine you the extra parts, but I’m sure would go a long way to solving your main problem.


 

#41 stubeeef

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Posted 06 December 2018 - 05:38 PM

 

Previously there had been a delay, as the secondary holder and spider that shipped were the wrong parts, and it threatened to push the timeline out several more months.  I got pretty grouchy about it.  This had the unintentional effect of causing him to feel pressure to deliver the scope as soon as possible.  Ryan's response indicated that he didn't do as much testing as he does with a normal build as a result.  

 

Not making any excuses but this seems more the macro issue, delays in delivery of these beasty scopes with low tolerance fast optics seem the norm. Precision is a timely thing in one-off craftsmanship. I've told optics and scope makers in the past- "no hurry" and this thread seems the proof of that. In the end it will get done right I'm sure, but haste makes waste.

Sorry about the issues and after all the other great NMT threads I'm hopeful this is a specific to you issue (doesn't help you any). Sounds like a killer scope from your observations and more bullet proof it will last a lifetime.


Edited by stubeeef, 06 December 2018 - 05:39 PM.

 

#42 Kunama

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Posted 06 December 2018 - 06:05 PM

As a general hint to people following this thread and contemplating a single ring UTA......... adding even a 12mm x 3mm aluminium flatbar by bolting it around the outer edge of the single ring thus forming a 'T' section adds a great deal of stability to prevent the kind of 'Pringles' effect that is likely happening to the OP's UTA ring.

 

thanx.gif very much to the OP for posting this thread and patiently wading through all these suggestions, though ultimately the matter is his to solve with NMT, it has given many ATMs a lot to think about. waytogo.gif

 

 

(here's another one:  Adding a 'counterweight' to the protruding end of the secondary holder shaft will aid in preventing gravity induced shift of collimation with these sizeable secondary mirrors...)


Edited by Kunama, 06 December 2018 - 06:08 PM.

 

#43 Allan Wade

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Posted 06 December 2018 - 06:08 PM

Not making any excuses but this seems more the macro issue, delays in delivery of these beasty scopes with low tolerance fast optics seem the norm. Precision is a timely thing in one-off craftsmanship. I've told optics and scope makers in the past- "no hurry" and this thread seems the proof of that. In the end it will get done right I'm sure, but haste makes waste.

Sorry about the issues and after all the other great NMT threads I'm hopeful this is a specific to you issue (doesn't help you any). Sounds like a killer scope from your observations and more bullet proof it will last a lifetime.

I waited three years for my 32”. When the build started, I told Peter Read, I’ve waited this long so take your time now and make this thing perfect.

 

Thinking about it, I’m sure this problem would be fairly isolated to Mike’s experience. I’m sure the secondary system works well in smaller scopes with smaller secondary mirrors. But a 4.8” mirror is a large, heavy piece of glass, and perhaps the secondary system has outlived its design for bigger scopes in its current style.


 

#44 bratislav

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Posted 06 December 2018 - 06:09 PM

A single ring secondary will flex when you tension the spider.  

No it won't. If designed correctly. 

 

And a correct way is to reinforce the ring and keep secondary attachment points very close to ring's plane (not 3 or 4 inches above as shown in OP's pics). You can put as much tension as you want (this wire spider can hold 5kg!) and there's no measurable flex.

 

IMG_4092_web.jpg

 

This also means offsetting the secondary mount points, which actually is a huge plus at it makes secondary incredibly resilient to any rotation, twist or sag. Note that secondary's center of gravity is in line with spider vanes, not 4 or 5 inches above.

 

IMG_4095_web.jpg

 

It also allows that focuser lays as close as possible in line with the ring plane as well.

 

IMG_4090_web.jpg

 

The only price to pay is that your structure looks odd. But despite strange look everything is still perfectly square, and you have "normal" diffraction pattern.

 

IMG_4089_web.jpg   

 

It really baffles me that today's Dob makers still live in 19th century as far as telescope structure is concerned. 


Edited by bratislav, 06 December 2018 - 06:14 PM.

 

#45 Kunama

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Posted 06 December 2018 - 06:13 PM

No it won't. If designed correctly. 

 

And a correct way is to reinforce the ring and keep secondary attachment points very close to ring's plane (not 3 or 4 inches above as shown in OP's pics). You can put as much tension as you want (this wire spider can hold 5kg!) and there's no measurable flex.

 

attachicon.gif IMG_4092_web.jpg

 

This also means offsetting the secondary mount points, which actually is a huge plus at it makes secondary incredibly resilient to any rotation, twist or sag.

 

attachicon.gif IMG_4095_web.jpg

 

It also allows that focuser lays as close as possible in line with the ring plane as well.

 

attachicon.gif IMG_4090_web.jpg

 

The only price to pay is that your structure looks odd. But despite strange look everything is still perfectly square, and you have "normal" diffraction pattern.

 

attachicon.gif IMG_4089_web.jpg  

 

It really baffles me that today's Dob makers still live in 19th century as far as telescope structure is concerned. 

Hello Bratislav, it is your UTA I was thinking of when I mentioned that adding the rim to the ring will stabilise it well, and I agree that that keeping the 'pull' close to the plane of the support ring is the right way to do it.


 

#46 The Ardent

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Posted 06 December 2018 - 06:20 PM

How does one obtain a copy of these plans? Looks like a great design.

Hello Bratislav, it is your UTA I was thinking of when I mentioned that adding the rim to the ring will stabilise it well, and I agree that that keeping the 'pull' close to the plane of the support ring is the right way to do it.


 

#47 bratislav

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Posted 06 December 2018 - 06:21 PM

Hi Matt, I'm afraid that no rim will help with the existing design. Forces are just too much offset, you'd need titanium parts to reduce flex! It is just not designed well.


 

#48 phonehome

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Posted 06 December 2018 - 07:11 PM

Hi Matt,

 

Even with bratislav's stronger & elegant single ring design it still won't be enough for your much larger and heavier secondary, it's offset weight and super-fast optic.  

 

Your shorter truss tube set, where it is attached to the focuser board is well below the ring and it compromises the rigidity of that entire connection.  The upper truss tube connectors are not designed to resist flexing in-to-out very well so any flexing  there is also transferred directly into the focuser board compounding the shift.  IMO it would be better if all 4 truss tube pairs were carried though to a dual-ring cage.  If offset secondary spider vanes (whatever flavor) were located closer to or inline with the truss tube connection points even better. 

 

In addition to an offset spider design and an ultra-rigid focuser board, I used four pieces on my f2.75 UTA: dual rings in a reinforced cage + another ring w/turned band [as a mounting ring] that provided additional reinforcement to the cage.  The tension on these spider vanes is calculated to be about 350+ lbs. per axis!  

 

The "rule of thumb" that was applied for my ultra-fast optics was simple, but it worked: the structure had to exhibit about 1/10th the flexure of a traditional f4.5 to f5 dob.

 

Ed


Edited by phonehome, 06 December 2018 - 07:12 PM.

 

#49 bratislav

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Posted 06 December 2018 - 07:30 PM

 

 

Even with bratislav's stronger & elegant single ring design it still won't be enough for your much larger and heavier secondary, it's offset weight and super-fast optic.  

 

 

Surely it wouldn't, with the ancient secondary hub/holder idea used by NewMoon where secondary's axis/center of gravity and secondary's mount point (where vanes cross) are 6 inches away. 

But if you mount the secondary properly (COG and vanes intersect, and vanes don't "meet" in center), I assure single ring is more than strong enough for even largest of secondaries. They won't rotate, flex nor lose collimation, becasue offset structures are MUCH stronger than even beefiest and hardest tensioned "central" hub designs. These structures have been advocated by late Texereau for at least 70 years, so again I'm completely baffled by a lack of their acceptance.

 

IMG_4096_web.jpg

 

I use similar design in my 12" f/4 photographic Newtonian (but use 0.1mm thick steel vanes instead of wire). My CCD has 3.8 micron pixels and I don't see any shift in collimation after 90 degree swings. 


Edited by bratislav, 06 December 2018 - 07:33 PM.

 

#50 stubeeef

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Posted 06 December 2018 - 08:10 PM

No it won't. If designed correctly. 

 

Where do you buy those parts?


 


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