105 replies to this topic

[Allan Wade]

Steve, could you describe the set up of the boundary layer fans. Where are they fitted and which way do they blow. Plus where are they positioned in relation to the face of the mirror.

 

I'm looking at options for an upcoming build and there's varying information about the fans blowing on the edge of the mirror if positioned low vs positioning them slightly above the face of the mirror so as not to overly cool the mirror edge and change its figure in that spot.

[FrankG]

How the vibration of the eyepiece after stopping the motors? maybe wind? Usually large metal structures vibrate. Is any demper used?
A good demper is wood.

Vibration not an issue (of course, wind is for any dob). Owned two wooden dobs before a StarStructure.

 

* I neglected to point out in initial comment above that wind is an issue with any dob if you are doing EAA, not visual. Unless looking at moon or planets I almost always use a camera on the dob.

Edited by FrankG, 30 October 2018 - 01:59 PM.

[Mike Lockwood]

Vibration not an issue (of course, wind is for any dob). Owned two wooden dobs before a StarStructure.

One thing that made a distinct impression on me some time ago was using a StarStructure at WSP in the face of a stiff sea breeze.

 

It didn't move.  It didn't vibrate.  It just tracked the target at high power and we kept observing.  Really impressive.  I know that there are some damping materials in the structure.  Whatever Mike Z. is doing, it works.

 

I'm looking at options for an upcoming build and there's varying information about the fans blowing on the edge of the mirror if positioned low vs positioning them slightly above the face of the mirror so as not to overly cool the mirror edge and change its figure in that spot.

If the mirror is quartz, it doesn't matter as much.  In general recommend blowing *at* the mirror's surface from various directions more than blowing across it.  My recommendations are based on real experiments that I have done with different fan arrangements.  I actually shot schlierin videos using real, warm mirrors in mocked up mirror boxes.  I did a talk about it, but I haven't had time to write up the article about it yet.

[havasman]

The innovations in place to produce that Starstructure Horizon and take advantage of their chosen material really impress me a lot. That's going out of the box effectively. I'm interested to hear your 1st light and expect tales of real satisfaction and no small measure of wonder. Congratulations on your new scope!

[Allan Wade]

If the mirror is quartz, it doesn't matter as much.  In general recommend blowing *at* the mirror's surface from various directions more than blowing across it.  My recommendations are based on real experiments that I have done with different fan arrangements.  I actually shot schlierin videos using real, warm mirrors in mocked up mirror boxes.  I did a talk about it, but I haven't had time to write up the article about it yet.

Your Okie-Tex talk was a good one, showing the videos with various fan systems. It gave me some good ideas for my baby SDM.

[Beesknees]

For what it's worth I don't have any fans installed in my 20" f3.3 Starstructure with the Lockwood quartz mirror, and in the past year I have never had any issues with cooling. The mirror is thin - 1.35" - and the metal structure of the Starstructure dissipates heat very quickly.

 

John 

[FrankG]

One thing that made a distinct impression on me some time ago was using a StarStructure at WSP in the face of a stiff sea breeze.

 

It didn't move.  It didn't vibrate.  It just tracked the target at high power and we kept observing.  Really impressive.  I know that there are some damping materials in the structure.  Whatever Mike Z. is doing, it works.

 

If the mirror is quartz, it doesn't matter as much.  In general recommend blowing *at* the mirror's surface from various directions more than blowing across it.  My recommendations are based on real experiments that I have done with different fan arrangements.  I actually shot schlierin videos using real, warm mirrors in mocked up mirror boxes.  I did a talk about it, but I haven't had time to write up the article about it yet.

Mike, sorry, my bad. I should have made clear the wind is an issue for any dob, including my 15" StarStructure, if you are doing EAA, not visual. I almost always observe with a camera these days unless moon or planets.

Frank

[Don H]

Is anyone else having a problem opening the StarStructure website? I have not been able to view it for a few weeks now.

 

Thanks,

Don

 

https://starstructure.com/index.html

[Mike Wiles]

Is anyone else having a problem opening the StarStructure website? I have not been able to view it for a few weeks now.

 

Thanks,

Don

 

https://starstructure.com/index.html

It's been recently redesigned.  The index.html page no longer exists....try https://starstructure.com/

[Don H]

Thanks Mike!

[starzonesteve]

Steve, could you describe the set up of the boundary layer fans. Where are they fitted and which way do they blow. Plus where are they positioned in relation to the face of the mirror.

 

I'm looking at options for an upcoming build and there's varying information about the fans blowing on the edge of the mirror if positioned low vs positioning them slightly above the face of the mirror so as not to overly cool the mirror edge and change its figure in that spot.

The photo below illustrates the relative placement of one of the four boundary layer fans, which are each placed at a corner of the mirror cell, in relation to the surface of the mirror. The photo is taken from the approximate height of the surface of the mirror, maybe a centimeter or two above it. The central portion of one of the whiffletree supports is pictured with a mirror clip just above it, so the surface of the mirror would be at the bottom of the clip. You can see that a small portion of the fans output, maybe 10% or so, might hit the side of the mirror and the rest would blow across it. The four fans are placed symmetrically facing in toward the center of the mirror. The current set up does not allow for any rotation of the fans side by side, along the plane of the mirror surface, or up and down from the mirror surface.

 

I suppose if thermals proved to be an observable issue it would be possible to modify the tilt of the fans without too much difficulty.

 

[starzonesteve]

One thing that made a distinct impression on me some time ago was using a StarStructure at WSP in the face of a stiff sea breeze.

 

It didn't move.  It didn't vibrate.  It just tracked the target at high power and we kept observing.  Really impressive.  I know that there are some damping materials in the structure.  Whatever Mike Z. is doing, it works.

On the new StarStructure web site there are some nice photos that illustrate some of the construction materials that go into the scopes. For instance, although the majority of the telescope is aluminum the drive board is plywood and the base of the rocker box is made from fiberglass reinforced plastic. I'm sure that a well thought out application of these materials in various combinations helps allow for rigidity without sacrificing damping.

Edited by starzonesteve, 31 October 2018 - 06:43 AM.

[starzonesteve]

For what it's worth I don't have any fans installed in my 20" f3.3 Starstructure with the Lockwood quartz mirror, and in the past year I have never had any issues with cooling. The mirror is thin - 1.35" - and the metal structure of the Starstructure dissipates heat very quickly.

 

John 

Mike Z discussed with me the issue of the need for fans on this scope. I decided to go for them just in case. Ultimately I will be happy if I never find the need to turn them on at all.

 

By the way, if I'm not mistaken my Lockwood quartz  20"F/3.3 mirror is also 1.35" thick. I'm going to guess that we got the two mirror blanks this size that Mike L had on hand. It seems our two scopes are truly fraternal twins. Maybe we will get a chance to get them together for a family reunion some time.

[TOMDEY]

Regarding turn-around time from contracting/deposit to delivery:

 

If you want a biggish, functional Dob fast and cheap... well we all know where you can order that, Now, and expect it to arrive Soon! And that's exactly what you will get: Big, functional and cheap... and worth it!

 

If you want a big, superior, custom Dob... well we all know the handful of reputable, established, specialty shops that can work with you. The mirrors will be commissioned and the structure agreed as to features and provisions. Ample communications thru the entire process, from build to installation, to 1st light. That will take a while, cost more... and worth it!

 

Either approach can be the Right One... for You!

 

At work (aerospace optics) we had a (soto voce) Motto that went: "Faster/Better/Cheaper - Pick and Two."

 

Indeed, it seemed to be as inexorable as a mathematical invariance theorem... Never Violated. Customers' Wish-Lists would demand all three... but they and we knew the reality only allowed two. Anytime you pushed on one, the others would rear up.

 

CONCLUSION: A soft agreement/target for 1-year delivery on a custom scope... quite reasonable. If you know the shop is hustling, stand back and let them work.

 

PS: I'll throw this one in, customers might want to consider. If I'm working with the best vendors, I ask them to use their judgment re' details, so they don't get slowed down by customer horning-in, second-guessing every nit of execution. I also offer, preemptively, to accept extension and cover added expense if technical issues arise... especially if I'm wanting something developmental or beyond... which for me is... Always!  Tom

 

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[Bob S.]

Regarding turn-around time from contracting/deposit to delivery:

 

If you want a biggish, functional Dob fast and cheap... well we all know where you can order that, Now, and expect it to arrive Soon! And that's exactly what you will get: Big, functional and cheap... and worth it!

 Tom

Tom, Concerning your above post, I did not replay all that you said but completely agree with the Venn diagrams and the premises they are based on that you put up to display the realities of what it takes to get a great scope from an experienced telescope maker.

 

However, there have been several 25" scopes that I know of, one I personally had an opportunity to work on directly from the manufacturer for a college and another that an acquaintance had obtained that met the "Big, functional and cheap..." scope definition but I would question your premise that they were "worth it". If a large, relatively expensive scope is purchased even though it is "cheap" compared to other more custom scopes, I have personally and anecdotally found that those lesser scopes do not necessarily become satisfying instruments because of the lack of precision that they bring to the viewing experience and the myriad of little and some larger glitches that they sometimes can present.

 

In this thread, someone had asked the new owner Steve, if the scope was sufficiently damped? I recently had an opportunity to visit Zammit's new shop and saw Steve's and two other StarStructures in the close to final stages of completion. Zammit, the designer and owner of SST, has such a long history of making superb telescopes that he has figured out many years ago how to overcome many of the gremlins, including damping issues that can plague some scopes. Mike demonstrated the smooth movements of one of the scopes which happened to be a 24" f/3.5 and without the optics, the scope was amazingly balanced and as rigid and free of vibrations as one could imagine. The reason for this are that Zammit over the many years he has been building telescopes has refined his designs such that some parts that come in contact with each other are purposely isolated to prevent the types of harmonic vibrations that can be transmitted from ground board/rocker box up to the upper tube assemblies (UTA) and quickly back down the stack that is a Newtonian. This attention to detail and refinement of structure are many of the unsung aspects of a scope like an SST that Zammit builds into them and does not do a lot of public talking about.  

 

I was frankly rather envious for the three lucky people, including Steve, that were going to be receiving such well thought out telescopes that have been developed via the Horizon II designs. Bob Schilling

Edited by Bob S., 31 October 2018 - 05:03 AM.

[TOMDEY]

Tom, Concerning your above post ...

However ... those lesser scopes do not necessarily become satisfying instruments because ...

I was frankly rather envious for the three lucky people...

Bob Schilling

Hi, Bob; thanx for the response! Those scopes sound Great!

I read thru yours a few times and not quite following what you are sharing.

Are you saying that there are historic exceptions to the generalized Faster/Better/Cheaper?

Where, in the exceptional case, the three set "and" operators ARE all simultaneously actualized?

You seem to say the rule applies, at the top, and then that it might not, toward the bottom.

In practice, there is one situation where the rule would seem to not apply:

That is when the vendor (often concealed), internally decides to "eat the overage" on cost.

That was how P&E bid Hubble; they low-balled the cost, to get the contract.

My recollection is that they bid (an unrealistic) $60M, whereas EK bid (a realistic) $80M.

I could be wrong on the exact #s, but the ratio was something like that.

The rest is history. Indeed, ALL THREE requirements were massively violated!

Eric covers that in his book.

Tom

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[Bob S.]

Tom, In the early part of my response, I was agreeing with you that a particular manufacture I am aware of that makes large wooden Newtonian telescopes in large quantities that can provide big, fast and "relatively" cheap scopes were not "worth it" in at least TWO instances I am aware of if my message was clear? Both 25" scopes from the manufacturer did not work as advertised out of the box and one may never have been fully functional as created. This was an argument against considering relatively off the shelf instruments if one wants the level of precision that you so articulately identified in more custom scopes with the attendant wait times.

 

The OTHER three scopes in question (SST's) are absolute masterpieces of the Newtonian makers art in StarStructures. I am being purposely vague per the TOS to not identify by name the TWO instances of 25" scopes that performed with significant flaws from a readily available source with short to non-existant wait times. Whew, it is sometimes challenging to stay between the TOS guard rails. I wish I could just blurt out the name of the offending telescope maker but again, my one experience is actual and the other is hearsay 

 

Is this muddled attempt any clearer about the recommendation to be patient and get the best Newtonian scope builders that you can find like StarStructure and a few others with wait times that are generally in the 1-1.5 year time-frame with custom optics?

Edited by Bob S., 31 October 2018 - 08:21 AM.

[Steve Harris]

It looks like the truss poles are all equal length now if my eyes aren't fooling me.  I remember one or more ATMers had pointed out that differing pole lengths could lead to collimation changes as the poles changed temperature, though I'm not sure it was ever established that it would be significant in real world conditions.

Edited by Steve Harris, 31 October 2018 - 12:42 PM.

[starzonesteve]

It looks like the truss poles are all equal length now if my eyes aren't fooling me.  I remember one or more ATMers had pointed out that differing pole lengths could lead to collimation changes as the poles changed temperature, though I'm not sure it was ever established that it would be significant in real world conditions.

Your observation is correct. The new Horizon that Starstructure makes has all equal truss tubes. I believe the original iteration of the Horizon design did have uneven truss tube lengths. I don't know why Mike Z made the changes, whether it had to do with collimation issues or the shape/characteristics of the mirror box. What I can say is that the current iteration feels wonderfully smooth and solid in its movements. Although I haven't yet tested how well it holds collimation I expect to be doing so in the relatively near future.

[Allan Wade]

The photo below illustrates the relative placement of one of the four boundary layer fans, which are each placed at a corner of the mirror cell, in relation to the surface of the mirror. The photo is taken from the approximate height of the surface of the mirror, maybe a centimeter or two above it. The central portion of one of the whiffletree supports is pictured with a mirror clip just above it, so the surface of the mirror would be at the bottom of the clip. You can see that a small portion of the fans output, maybe 10% or so, might hit the side of the mirror and the rest would blow across it. The four fans are placed symmetrically facing in toward the center of the mirror. The current set up does not allow for any rotation of the fans side by side, along the plane of the mirror surface, or up and down from the mirror surface.

 

I suppose if thermals proved to be an observable issue it would be possible to modify the tilt of the fans without too much difficulty.

 

thumbnail_IMG_1678.jpg

Hey thanks Steve for the information on the fans. It looks like you've got a good configuration on your dob, I've seen that work well on other dobs. 

[stubeeef]

you know I'm dying here Steve, sounds great, now throw out some meaty pics for meat lovers!! (is that 3 sets of truss poles and not 4?)

(sooooo jealous.....)

Edited by stubeeef, 10 November 2018 - 05:17 PM.

[starzonesteve]

you know I'm dying here Steve, sounds great, now throw out some meaty pics for meat lovers!! (is that 3 sets of truss poles and not 4?)

(sooooo jealous.....)

You’re dying? How do you think I feel?! Tonight is another clear moonless night with good transparency and fair seeing in my neck of the woods and instead of getting ready for first light I’m getting ready for work.

 

On on the bright side I am having a concrete pad poured next week and BYO is scheduled to come down and do my ROR Dobservatory within the next month. First light will come eventually - and with it a slew of ‘meaty’ pics.

 

I didn’t notice it until you called my attention to it but that photo I took is a cool optical illusion. The one truss completely blocks out the one behind it creating the appearance of only three trusses when in fact there are four.

[stubeeef]

Great job perfectly masking the 4th truss!

I think a "sick night" is in order tonight there Steve....or you can just leave that out back and me and possums might just take of it for ya!

[starzonesteve]

Great job perfectly masking the 4th truss!

I think a "sick night" is in order tonight there Steve....or you can just leave that out back and me and possums might just take of it for ya!

Once I get up and running you and the possums are both welcome to come on down to the party. In the meantime, first light is for me! Stay tuned...

[stubeeef]

Don't think of this as me trying to push ya, think of it as me shoving really hard!

Edited by stubeeef, 10 November 2018 - 07:43 PM.