Mylar vacuum mirror

[robz]

Hi everyone, I have actually spoken to Peter Waddell back in 1989 on his development of the attached ''strechable membrane mirror'' pics.

Has anyone considered trying this?............I know I have considered it many times(but never had the guts to try it) and also have quite a few secrets on how to make it work. This has been collected from various sources over all these years.

It has been used in a smaller form as a telescope mirror and was once presented at the U.K Astronomical society with an apparently enthusistic response.

I know it sounds like vaporware,and was originally designed for 3D imaging, but it really does exist and produces extremely high quality images........good enough for astronomical purposes from my information at hand..................no proof of such however........so who knows?

May be worth discussing as an alternate method to those giant and incredibly expensive glass mirrors?

Comments welcome

[Peter Ward]

I've read the occasional piece on these over the years. The main problem is vacuum deformation of a mylar sheet (greatest stretch on the edges) ends up giving nearly the opposite form of a hyperbolic mirror (ie stronger curve in the centre).

[robz]

Hi Peter, I have some more pics that indicate the actual curve generated.
Standby..........................:)

[robz]

Having trouble. File size too big. I'll work it out when I can.:rolleyes:

[robz]

For some reason, I can't download the image of the plotted curve.

Howvever, it DEFINATELY follows a PARABOLA with only a slight deviation........a deeper curve which ends up meeting the ideal parabola in the centre.

So, is this a hyperbola?

Can this be used for astronomy?

[scopemankit]

How much does temp variation of the partial vacuum change the curve?

[Peter Ward]

No ...just me using RC's for too long :) ....I should have typed Parabola.....but I still understand the same problem applies....vacuum deformed Mylar is too steep at the edges and not enough in the centre

A hair's width will do it...just talk to the Hubble team :)

It would also be interesting to see how the system handles wind gusts ;)

[Merlin66]

I went to uni in Scotland with Peter, and have copies of all his reseach notes on the mylar mirrors.
In the early 90's I made two 16" frames and a vacuum system to trial the concept. The issues were lack of surface accuracy; the edge wrinkles distorted things well into the centre. I tried pre-streatching before pulling the vacuum; modifying the edge radii and clamp rings etc etc. I could not get any worthwhile imaging results. The ronchi testing showed the surface was all over the place.
I then tried with a 2mm thick sheet of plate glass and managed from memory, to pull it to f9; it sat on an O ring edge seal... looked very promising.
I'm overseas at the moment so don't have access to my notes etc.
It's certainly a VERY interesting concept, but one which doesn't seem to work with optical accuracy.
(BTW I also tried some samples with slumped 3mm glass disks.... you can get the radius but they still need polishing...not an easy feat with such a thin mirror)

Ken

[robz]

Thanks Ken and all.

This has answered my questions that have been bugging me for so many years.

It's obvious now that trying to make something like this work is nera on impossible for the average diy telescope enthusiast.

On an interestng note however, I am talking with a team here in Australia that have manged to created small telescope mirrors using a gel/resin........weird stuff :

http://www.cfree.com.au/lightweight-mirrors

wadayarekon?????:eyepop:

[AndrewJ]

Gday Robert

You should grab a copy of "Unusual Telescopes" by Peter Manly.
It actually has a bit on Waddels mylar mirrors,
as well as heaps more, like obsidian mirrors, mercury mirrors, "plastic" lenses.
Full of all the weird and wonderfull optics and mounts people have come up with.

Andrew

[bojan]

I always thought this was my secret idea from back in early '60-ies :P

Mylar was not know to me then.. but, as Ken suggested, my conclusion after some experimentation with various materials and methods was that it would be impossible to obtain the quality, not to mention the coping with variability of the optical surface shape due to temperature and air pressure changes (I imagine even air circulation may be detrimental to the resolution of such a mirror).

While playing with this, one friend of mine suggested electrical field as a mean to obtain curvature (high voltage, in other words - couple of kV.
BTW, electrostatic loudspeakers use the same principles for sound generation).

However, I also remember one S&T article on ATM - there was a description of pre-distortion of flat glass plate by means of attached low pressure chamber, used in process of figuring of Schmidt correction plate.

[robz]

G'day guys...............thanks for your confirmation and personal experiences.

I'm allways thinking outside the circle, but there's a limit to what can be done of course.

Any thoughts on the link I provided?

I know absolutely nothing about this link/product, but in an email conversation, I was told that their PRIMARY INTEREST was in astronomy applications as a telescope mirror.

Rob.

[robz]

No takers??????????:P

O.K...................looks like I'll start saving up for my 12 inch Meade LX90:D

[bojan]

Wise decision ;)

[robz]

Thanks bojan..................I think so.................damned mylar!:mad2:

[bobson]

Mate, I understand you. I was very tempted to send my wife's big glass lid of the cooking pot to be aluminised :)

cheers

bob

[robz]

YOU TOO????............and I thought it was only me!;)

[robz]

Ken, just a curiosity that you may be able to answer?

Looking at Peter Waddell's giant 1.2 meter mirror, would I be correct in assuming that even though he succeeded to make a large mirror using vacuum deformed mylar for ''3D IMAGING'', it was however no good as a telescope mirror?..........or, was your attempt unsuccessful due to precise machining required etc?

Cheers,
Rob.

[bojan]

IMHO, this mirror could not support itself.. I bet even the weight of mylar is deforming it enough to render it useless.. we are talking here about 1/10 of visible light wavelength.. 0.04um.
But then again, I might be wrong..

[robz]

bojan, I see where you're coming from and understand the accuracy required.
What gets me is the documentation I have read and what was said to me by Peter Waddell all the way back in the late 80's.

Up until joining this forum (fabulous by the way.great blokes!:D),I was lead to believe that the mirror is allways used in a vertical position, so how can the figure be of any use?

Secondly,the U.K Astronomical society used a mylar prototype mirror made by Waddell(who presented it one night) and were impressed sufficiently by the images it produced...apprently.

The spiel on the mirror technology ''applications'' lists ''high quality telescope optics'' at a fraction of the weight and cost amongst other uses:confused2:
There was also an interrview with Waddell where he stated that ''indivudual hairs'' on a person's face could easily be resolved?:screwy:

Now, I don't know where the B.S. starts or ends and where the truth lies here:rolleyes:

I do know that if it takes ultra high precision machining and polishing of the edges that come in contact with the mylar, and that the method of clamping and selecting the ''appropriate mylar''(another Waddell statement) are all critical to the thing working, I'll forget about it instantly:hi:

By the way, got some more info from the ''cfree lightweight mirrors'' mob(link I provided earlier on).
They have made a 20inch mirror but it suffers from abberation caused by inperfections on the mold and dust particles in the air.They stated that a ''clean room'' is very important in making good mirrors.
They are at the early stages of research and development.

I would suggest that we keep an eye on these guys as they have a revolutionary(we'll see?) system in process here and they have asked me to keep in touch with them..............something about September this year was mentioned, so I guess that this is when they will begin the serious part of the development?

Cheers,
Rob.

[robz]

UPDATE:

With the help of a forum member and some P.M's, patent copies and further research in to the understanding of the mechanics and physics involved to make this work, I would say that progress is slowly being made.

I have U.S patent number 4,822,155 which is the original patent by Peter Waddell who is the inventor in the photos I posted earlier.
This patent is very useful as it explains how the whole concept comes together to a workable optic.

Of some significance this week, after talking to Australia's DUPONT films supplier is that Mylar ain't Mylar in many cases:eyepop:
I was informed that many inferior metallised films called ''MYLAR'' are nothing like the actual product at all and actually breach copyright by doing so!!!!!!!!:whistle:

I have no doubt that any crazed experimentors like myself have in the past, given up or just plainly failed due to the lack of realisation that the film needs to be what it's supposed to be and that the mylar frame holds a few key/special requirements to stretch that film evenly and correctly.........or else!:rolleyes:

Obtaining an optically flat surface before applying a vacuum is critical also otherwise it just won't work............period.

So, things are coming to the surface as I dig deeper..............just hope I don't hit sewerage on the way:lol:

Anyhow, research and work on this will continue.
Any input is welcome:thanx:

[Wavytone]

Hmmm... Spotted this thread a bit late.

Peter Waddell isn't the first to try it, either.

In the late 1970's the chief engineer at the AAO, Ed Simmonds, had the same idea and made an almost identical set of rings to deform circular glass disks cut from old glass plates from the UK Schmidt telescope. Why ? Because the Schmidt plates were optically flat to quarter wave, on both sides and plane parallel, as well as being very thin so they could be bent to fit the curved focal plane of the telescope.

Ed found that using an 18" aluminised glass disk, the central 6" or so might be useful at about f/20 but the rest of the plate produced so much spherical aberration as to be useless for imaging anything. It was only fit for use as a solar cooker.

I was a physics student at ANU at the time and solved the maths to work out the curve achieved... it's no good for telescopes... The thought of aluminised mylar occurred to us too but the surface quality was simply dreadful compared to the thin Schmidt plates.

There is also a much older reference to the same idea somewhere in one of the ATM books from the 1950's.

Why Waddell wanted to waste money on a patent lord knows, the idea is useless...

[robz]

I see:sadeyes:

Spherical abberation is a result of inadequate edge clamping..........that's a known fact, no matter what the material.

If the Mylar is no good as an accurate surface for a mirror, why have there been small working telescopes made and pictures of such published?............I have seen them on the web site of the stretchable membrane mirror under Strathclyde University and Ethereal Technology.

I for some reason at the moment, can't post the evidence of the PDF I have on my work computer, but will get our I.S dept. to assist me next week.

That site also has a graph of the actual curve. It differs from a parabola, but I'm not convinced that it''s totally opposite or wrong to what is required by a telescope??

[robz]

Just adding to my last post, lf you read the patent I have listed, it doesn't take much to realise that blaming the Mylar surface is an easy way out to establish a reason for failure.

The patent, when carefully studied, clearly indicates the immense importance and methodology applied to clamping the film and the processes that follow.

That ''perimeter'' which comes in to contact with the stretched Mylar is where many companies that have spent large sums of money in R&D on this idea, have NOT taken in to consideration.
This, in conjuction with the very thorough adjustment points to flatten the film before a vacuum is applied is what makes this design work.

Stretching Mylar over drums, bicycle wheel rims and other stupidity will indeed produce only a ''shaving mirror'', if that.

I have been told in person by someone involved in this project all those years back, that the above mentioned ''tricks'' is what sent many researchers and developers in to bankruptcy.
I was also told that holding a vacuum is not diifficult at all with ''just a thin smear of silicone grease'' and that ''a simple regulator had easily been deployed at very little expense to hold the vacuum constant''.

We can sit here and **** can this as much as we like, but read the following link, about half way down in particular, where a paragraph starts with ''In 1985'' :P :P;)

http://spie.org/x26677.xml?ArticleID=x26677

[bojan]

Well..
In the meantime, we have GSO, and their good and affordable mirrors..

I fully understand the inventors' "buzz" from adrenaline when something seems to be working.. but.. we have to be practical as well.
And, I have seen a lot of B.S., many times produced with perfect, genuine honesty..

I was also playing with the mylar idea in '64 and onwards.. and today I still have and happily use my Coulter Optical 10" mirror, purchased in '82, for 105 US$.
Se here you go..

[robz]

Bojan/ALL, who are ''GSO'' ?..............can you provide some details?


I'm not trying to convince everyone on this forum that Mylar mirrors can be made to work as good a chunk of expensive ground and polished glass.

What I AM trying to indicate is that it's very easy to make a solar collector or shaving mirror...............as have many,........ who have then come to the conclusion and spread the word that the principle doesn't work and never will...............as is obviously the case from some of the reactions I have received..........and expected.

If you DO take the time to look at the patent, which I don't think anyone has bothered, you will realise the complexity that goes in to the holding/streching mechanism that I know for certain NO ONE in the years past has followed.............not even close.The number of bolts and screw adjustments in that area alone shows a serious effort at fine tuning the film in to a flat opticallly perfect film surface.If you don't have that, you have nothing and can stop right there.
Of course, many did not, and concluded that this just doesn't work.

Short cutting this intricacy mentioned, will indeed produce a total joke image quality wise. A distorted and edge wrinkled pile of garbage is the usual prize for an incorrect attempt at this........guarenteed.

On the subject of Mylar, the patent states 125 micron film thickness which is 4.92mil or nearly 5 one thousandths of an inch.
That is ''if'' you have ''real'' Mylar that is:rolleyes::rolleyes:

On a closing thought, I'm sure many of you have seen mylar used over the fronts of SCT's for solar viewing?
I know I have(10inch) and observed a sun spot at high magnification. I then turned off the drive and watched the image move accross the field of view.......not once, but many times.
I NEVER saw any thing to indicate that the mylar was anything like cheap window film. The image was distortion and ''wavy'' free.

If Mylar is good enough for this purpose, why should it's surface accuracy be lousy for a mirror?

[bojan]

Well
you just answered your question with the question itself:
Reflecting light from surface is not the same thing as passing the light through the same surface (doubled, if you like).
Mylar foil acts as a plan-parallel plate, so it is suitable for window, even if it is not perfectly flat and stretched. But to use it as mirror is something entirely different.

And, the very complicated method of adjusting the mylar film is just too complicated to be practical.. simple junk of polished glass does the better job, in a cheaper and more stable way, it is not temperature and air pressure dependent.
So why bother at all with all this?

GSO is Guan Sheng Optical company, a Taiwanese manufacturer of cheap (but good) and conventional glass mirrors.

[robz]

Hey Bojan!...............you're a tough nut to crack :lol: :P LOL !!!
Yes, all that complexity is really a deal breaker when you consider what has to be manufactured and accomplished before you even stand a chance of making a ''BIG'' mirror.

By the way, what nationality is ''Bojan''?

Thanks for the company details.............I'll check them out!:thumbsup:
Rob.

[bojan]

It is a Slovenian name.. occasionally used throughout Former Yugoslavia and Croatia where I was born long time ago ;)

[robz]

That's interesting.....................I was born of Polish parents here in Australia.
They settled in Western Australia after WW2. They had a hard time all those years ago...............especially with a one and only son who would not stop looking through telescopes each night:lol:

My first scope was a ''slider''....you know...........the sailor's spy scope..........now that was fun!;)..............not!

[Wavytone]

It isn't - as anyone who has used a scope with a GLASS solar filter will know - Mylar scatters a ****load of light, the surface is quite rough at the microscopic scale compared to properly glass. And a mylar mirror scatters just as badly, having tried it.

But lets not go there because the surface shape is quite simply wrong, anyway; useless for a decent aperture where it might have been worthwhile. On small apertures under 20" it's easier to us a glass mirror.

[robz]

Wavy, you have every right to stick to your guns............I'm not going to debate what you believe in or your ''maths'' all those years ago.

I'll just refer to all here, on what I have found during my ''digs'' through the documentation on hand. What anyone thinks doesn't really matter as the ''anomalies'' in everyone's theories still stand:

1. a telescope mirror WAS made in 1985 by Braithwaite. It was tested and a telescope built with a sliding secondary mirror/focusser. Had the curve been all ''wrong'', the mirror would not have made it past that stage.........let alone a fully built reflector.Black and white photo of telescope mirror and reflector exists.
2. the much hated(?) Peter Waddell, built a small scale 8 inch ,perspex bodied, mirror (as per the patent number I posted)designed as a space telescope primary optic and NASA was very interested in it after testing and looking in to the design parameters.Colour photos of this mirror exist.He then went on and built a 12 inch, 24 inch and finally a 1.2 metre that can resolve the thin light hairs on a person's face (and I'm not talking about a beard)in 3D imaging applications.
3.The ''curve'' as published, compares favourably to a parabola, with a small deviation............how that affects the image, ''telescope'' wise I don't know?(still can't post the *******!!!!)
4. To enable a Mylar mirror useable, it seems that considerable effort needs to go in to the mounting frame and consequent adjustments.Together with this is the curious fact that THICK Mylar is specified in the Patent?..........why not the thin stuff:question:
5. there is no point in listening to anyone's own personal experiences with Mylar if those attempts involved stretching film over dish pans,tupperware, potties or skinless drums etc. We know that this doesn't work.

I would not have started this post if I wanted a mirror 20'' or less.....I'd just go out and buy one.

I'm talking about a considerably larger one that can operate at f 2.0 or even less.

Now, about that ''curve'' that's ''wrong''..............anyone care to enlighten me on how it's ''wrong''??............I'd be very interested, even if this subject is laid to rest as a result:D

[robz]

Yeah,.............................. ......:question:................... ...hmmmmmmmmmm???.................. ................:confused2:........ ................................... .:P................................ .....:help:........................ ............I'm gonna get me sum glad wrap, sum silver spray paint and a cookin pan and pulll me a mirra!!!!:screwy:

[robz]

The curve:

[robz]

Still no comments?!

C'mon guys,..................surely this curve tells all?..................or has it proved everyone wrong????:question:

[samia]

Hi evry one,
I do collaborate with peter, using his mirrors for a different application.

I asked him if he would like to be contacted?
He agreed

He is a retired academic but still interested in helping people to use his mirrors!
peter.waddell2@btinternet.com
good luck! (peter.waddell2@btinternet.com)
Samia
(peter.waddell2@btinternet.com)

[Merlin66]

Robz,
Drop the "theoretical parabola" to match the sag at 150mm and the curves match very well; there will be some error at the centre (covered by the secondary) and the extreme edge ( mask it off)
Question: do you have similar curves for say a f4 or f5 mirror - this ratio would be of more interest to the average amateur astronomer....

[ZeroID]

Re your 'Curve'. Mylar is relatively nonstretchy material, very little give. Yo could never pull a curve anywhere near that deep from a theoretically flat stretched sheet of the stuff.

[robz]

Thanks guys,.......I really thought I was alone on this one:thanx:???

It's good to hear Peter is still around and willing to help:thumbsup:

In regards to the curve, I would not pull it down to such an extremely short focal ratio...............would be more sensible.

Well my freinds, I may have a crack at this by roughly following the patent design to some extent but not entirely of course.

I have access to true MYLAR and some people/work colleagues who can help me build something that at least would give me have a chance at succeeding:)

[bojan]

I wish you all the luck with this project... However I wouldn't be surprised at all if you don't succeed.

[robz]

Thanks Bojan, and I respect your comments.

I have emailed Peter Waddell and have asked a few critical, straight to the point questions regarding the curve and whether it's suitable for a telescope mirror.

Also questioned was the surface quality/accuracy of the Mylar, and whether the mirror housing construction can be simplified without massive industrial machining costs.

I stated that if this was at all possible, a large mirror was in consideration, not a small one, otherwise purchasing the real thing would be a better alternative.

I hope he replies..........with good news, not bad.
I'm not expecting to hear anything positive some how.Either way, I'll report my findings to the forum just the same

Rob.

[robz]

O.K,...over the weekend, Peter Waddell has replied....3 times, has asked for my address and will send documents, measurements and data.

In short, without directly quoting him :
1. The curve shown previously is for special 3D/STEREOSCOPIC IMAGING purposes and would not be relevant for telescope usage.
The same problems that exist with a hyper fast glass mirror, also apply to the Mylar mirror in regards to image distortion etc.
2. He has stated that with the project's success and recent developments and applications, ''you will be amazed at the results that can be achieved''
3.In regards to the thickness of the mylar..............he mentions using 100 micron(10 mil ) !!!:eyepop: thick film......................not 4 or 5 mil which is commonly available from your local agricultural/horticulture shop.
Thus my suspicion on why ''thicker Mylar'' has been the only option, and him mentioning in an article that the choice/type of Mylar is important.We may also be dealing with a particular ''grade'' of Mylar here............who knows?

4. for a telescope, at a reasonable focal ratio, he stated that the results would be ''fantastic!''

So, ..............he has stated that he will gradually assist with information and advised that I ''standby'' for further news.

I don't know what y'all think about this so far?................it's easy to slag off this method when we're all used to ground and polished glass for our optics.
To me, I sense that something of great significance has been missed(ATM wise) in this invention all these years ago:question:
I mean, who would have even considered that 100 micron thick Mylar is even remotely acceptable to stretch in to an accurate curve????:confused2:............... .surely the thinner the better I would have thought?

More importantly.........and this is significant whether you like it or not, he NEVER said........Rob, forget it...............this is not a workable system for astronomical purposes I'm afraid................so,.......... .:question:..................he probably knows that it DOES work.
The question is,as he did not answer my relevant and specific questions on the details of the mirror mounting system, is whether it can be done on a largish scale without spending thousands on advanced machining technology etc.:shrug:????
I think that the details coming in the mail and forthcoming information/conversations may answer this?

[bojan]

Thick mylar means, he had a problem with sagging due to the weight of the mylar itself... plus rippling due to air turbulence near mirror.. plus who know what.

Why not go straight for a thin glass plate?

I advise you to forget about it...
If this approach is/was of any worth (with currently available materials), it would have been in use already, IMHO.

[robz]

Bojan, fantastic attitude mate!.............................. I wish that all developers and researchers had that method of thinking............we'd still be rubbing two sticks together to make fire in 2010.:P..........at least that's a ''proven method'' that works and fires are lit that way everywhere:D

[bojan]

Entirely up to you mate..
Your time, your money.
I've been there, done that ...

[robz]

I'm not spending a cent until I infuse as much information on this as possible. Even then I may not proceed.............it all depends on the logistics if there are any worth considerng.
S***.............let's give Wadell half a chance for heaven's sake.............this is ridiculous!:rolleyes:
Unlike a lot of people, ''been there done that'' doesn't cut it with me.
I'm willing to investigate the failures with intense interest.......not just give up and spread the bad news.

There's a new thread on another forum on a ''giant binocular telescope'' using ADAPTIVE OPTICS.

Now this is right up our slagging territory fellow ATM's...............a thin glass disk that has heaps of magnets glued to the underneath. These magnets are actuated by an electrical field to pull the mirror in to shape.

Sounds crazy?...................yeah, the developers were told that right from the start from what I recall, yet here they have the working product ready to go;)

[Miaplacidus]

(Getting a tad *****y, here, children...)

If it could work, then this would seem like a nice project to launch into space, where some of the objections alluded to in this thread might be overcome, and some truly gargantuan mirror might be assembled.

Then GSO can get to work on the clone version....

[Peter Ward]

I knew I had read something on this in Sky & Tel. With a little digging I found this

http://home.freeuk.com/m.gavin/flux.htm

The author quaintly puts the airy disk size or "circle of confusion" at around 5mm....this is several orders of magnitude worse than a diffraction limited
glass mirror ;)

[bojan]

Also, the owner of the telescope with mylar mirror must be VERY quiet when using it - electrostatic microphones are designed around a mylar membrane, which moves as acoustic waves are hitting a membrane surface. Electrical signal is picked up as variation of capacitance between membrane and back plate.
Another example is something from James Bond movies, but also from real world: laser microphone.. Laser beam reflected from glass window is modulated by the sounds produced inside the room.
Nobody wants telescope mirror shape to be sensitive to sounds, and this is exactly what is happening with thin membranes....

[robz]

Yes, I have seen this article, more than once.The article is ancient, stupidly implemented and does not relate to a telescope mirror in the trues sense, yet it's posted here for me to be ''informed'' that the Mylar mirror idea is a waste of time!:screwy:

What the hell does one expect when they ''crudely'' stretch film on bike rims without any consideration towards evenness or optical flatness as a first and most important pre-requisite and then expect perfect optical performance while the frame bends under vacuum forces.............c'mon everyone..............get a grip on this.

I've said it before.............LOOK AT THE PATENT..............is it a couple of bike rims with metalised glad wrap?????

It's a complex system designed to control every square mm of that Mylar and it's subsequent tensioning and contact with the purposely designed wide rim when a vacuum is applied.
Is everyone ignoring the details or just not bothering?

If we're going to talk about audio and microphones, I'm an expert on that with direct experience as a recording engineer .
Microphones do have ''thin'' membranes............the Wadell mirror is 100microns.............one hundred + times thicker than an electret microphone:rolleyes:.............le t's leave that one for ''James''.

If we consider vibrations in a telescope, I have seen some of the very best wobble like jelly in a slight breeze or nearby foot steps at moderate to high power(Perth Observatory)

I'm not defending the Wadell mirror or his methods and am no way affiliated with him apart from email contact and some documentation that I am waiting upon.
I would have thought that this thread would be of benefit to my fellow ATM's, even if it was just considered as a possibility until further documentation came to light.
The result has been the opposite with critics who insist that it's impossible when they know the product is in existance and in use.

Irrespective if the application is relevant for telescopes or not, my expectation was to at least generate some interest and ''positive'' input towards the subject and not just ''been there done that''......... when you know quite well that you did not even get close to what's required as a start to possible success.

With all due respect to those who read the thread with some interest but did not contribute post wise, I personally will stop posting on this subject from here on.

Happy observing:hi:

[bojan]

Rob,
I am sorry if I offended you in any way.

I was just trying to point to some problems I encountered when playing with this idea back in late '60-ties.

This was not a criticism for the sake of criticism, in my opinion it was a contribution to a discussion.. . You cant' have only positive response on the subject when there are people out there with negative experience.

Anyway, if you succeed, please let us know. I will be happy to try all this again, knowing someone has really done it.

[robz]

No offense taken Bojan or anyone :thumbsup:

If there is anything worthy to report on in the future, I will do so.

Cheers,
Rob.

[robz]

O.K,..................FINALLY!..... ..............got an email back from Peter Waddell..............quite lengthy as my wife has just informed me.

When I get home from work, I'll check it out and report on what it entails.

In the mean time I got a couple of responses from another astronomy forum yesterday.
Interestingly,one person had tried two 24inch ply wood rings and mylar over some sort of steel container and initial tests were positive, but the project was never carried on with due to family moving and commitments.

Anyhow, standby all:)

[robz]

The email from Peter Waddell has advised that documentaion on the mirror's performance at conventions and seminars and proof that superb results have been obtained in fine resolution imaging are on their way to me.

Peter has asked me to email him immediately after I receive the documents and he will begin to provide instructions on how to build the mirror and where to buy the materials.

This may be a first for ATM as this information has been kept under close wraps for many years now.
On top of that, the critical methodology required in it's construction will be of great value as this is what makes or breaks a successful working product.


Rob.

[robz]

I have received the documentation as promised.

Some of it(and there is a hell of a lot) I have already come accross on the net, most I have not seen. Generally it relates to 3D imaging applications.:question:

My email to Peter tonight will confirm that I have received and read the documentation.

I will pose the question if this system will work for telescope applications and ask for his assistance in the manufacturing of such a device without resorting to expensive materials and machining(if at all possible).:question:

[robz]

Got a reply back from Peter Waddell.

As suspected, he has mentioned the need to have a large and accurate ''ring'' made for stretching the mylar over it's curve. He suggests that this may be built in sections to form an entire circle:shrug:

As well, he is talking about finding out about 150 micron thick mylar sheet (as opposed to 100 micron) for me as a start to the project.

I already know that there is at least $200-300 minimum length costs here alone:rolleyes:

Interestingly, he stated that a ''solid'' version of the membrane mirror was even developed, but it's use for 3D imaging was overshadowed by the release of commercial 3D flat T.V. screens and the project was discarded as a result.

I don't really know what to make of all this. If I knew for certain that it would work I'd go for it...............but I can see a gamble here at great cost possibly:confused2:

[Merlin66]

Look upon it as an investment or the cost of entry to this exciting technology....
Once you've cracked it the cost won't mean anything compared with the partical experience and knowledge you will have gained!!
( I "invested" about $13K in a venture to design and manufacture a cost effective intermediate spectroscope...don't know if I'll ever recoup my costs, but the amateur community will/ are getting the longer term benefits!)

Ken

[jossupp]

I play whit millar Mirror and glass plate also

BUT

it is not for Imaging purpose or astronomical purpose

only for collecting lot of light from dark moon in the moon impack group

we just need lot of light to detect the impack of meteor on the dark side or part of the moon
because that we do not need perfect image jus collect lot of light

ALSO

>I work in spectroscopy
AND there also just need lot of light
we are limit to about mag 12 for the moment but whit a 30 inch chaneway Mirror we have maybe all the light we need and go to mag 14

also probalby working in off axix we do not care about astigmatisme

just a big collector of light

the work of all the mylar grop a re good but it look like they do not know the vacuum produce a chaneway curve not a parabola

maybe like the pheric Mirror whit pulling give a parabola

maybe a chaneway just by pushing give a better parabola
that is my next reshearch

jack 47'n 71'W

[jossupp]

the catenaway and parabola have this math formula

generates a parabola
y=a x2 +bx+c
catenaway
y = a + bx + cx^2. parabole
y = a/2 * (e^(x/a) + e^(-x/a) chainette catenaway



jack 47'n 71'W

[jossupp]

if you plot the 2 formula that give you this
http://www.knewance.com/comparisons/parabola-v-catenary.html

or this
http://www.clausentech.com/lchs/dclausen/algebra2/CompExercises/Graphing_Parabolas_with_Excel_v2.pd f

but if you put the start of the plotting at the same place you can see the catenary can be push ((( like a flex can be pull http://media.skyandtelescope.com/documents/Adler-MirrorFlex.pdf )))

the catenary probalby can be push also

my test just beging

jack 47'N 71'W

[Shiraz]

this might be worth a read (note Roger Angel is one contributor!).

Their method yields a spherical shape. also note the authors' contention that this type of technology is not suited to terrestrial mirrors (due to gravity and sound).

http://fp.optics.arizona.edu/loft/Publications/Papers/Burge/Stamper%20Proc%20SPIE%204451.pdf

[Wavytone]

Robert, do not waste your time and money. You really need to gain a clear understanding of the tolerances for the surface to be used for forming an image, vs the uncontrollable surface errors that will arise in what you propose.

FWIW I was able to solve the differential equations to calculate the surface profiles analytically and showed that what you will get is not satisfactory - not even close to parabolic, optically.

I will also add this idea has certainly been tried even earlier. One effort I am aware of is that of Ed Simmonds circa 1986, then president of CAS, and at the time I recall Ed saying he was aware of earlier attempts.

Initially Ed had the AAO workshop knock up some massive adjustable aluminium rings to flex 1mm glass disks cut from rejected 18" Schmidt plates into shape, the clear aperture was about 350mm. Ed also tried mylar, with a vacuum behind. The point of using the Schmidt plates was that they were accurately flat and plane parallel to better than a wavelength (though this is still well short of 1/4 wave).

I had the opportunity to test both the glass and the mylar versions. Both were dismal failures, they were only suitable for making solar barbecues - "light buckets" is an understatement.

The 1mm glass sheets typically lasted a few days before shattering as a result of the strain applied - fairly hazardous.

I'll also add that the size of the rings and the vacuum chamber, plus the equipment needed to make it all work is prohibitive, to the point you will rapidly realise it is a LOT simpler to go buy a thin glass mirror.

[jossupp]

((((Robert, do not waste your time and money. You really need to gain a clear understanding of the tolerances for the surface to be used for forming an image, vs the uncontrollable surface errors that will arise in what you propose.))))

yes ok for astro picture but for spectro no need of perfect picture just collec lot of light maybe better goald


((((FWIW I was able to solve the differential equations to calculate the surface profiles analytically and showed that what you will get is not satisfactory - not even close to parabolic, optically. ))))

the catenary is not parabola the formula is simple like the pheric just push ontil pull maybe




(((The 1mm glass sheets typically lasted a few days before shattering as a result of the strain applied - fairly hazardous.)))

I plan to used 1\4 plated glass or simply Mirror in the back do not care bout double reflexion for spectro easy to remove

(((I'll also add that the size of the rings and the vacuum chamber, plus the equipment needed to make it all work is prohibitive, to the point you will rapidly realise it is a LOT simpler to go buy a thin glass mirror. )))

at 30 inch just a byke rimm and little vacuum very sheap setup

for moon impack perfect

realy not for astro picture special purpose only


jack 47'N 71'W