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Old 11-12-2014, 10:47 PM
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Honeycomb mirrors

I wouldn't mind building a 10" f3.8 Newt. but something special -
with perhaps a honeycomb mirror.


Have a look at this web page:

http://www.mdpub.com/scopeworks/hexagons/index.html

I admire Michael Davis for having a go.
The honeycomb design reduces weight & makes it easier to stop boundary
layer temperature differences from distorting the image.

Anthony Wesley goes to great trouble to get the temperatures the same:
http://www.acquerra.com.au/astro/cooling/ballarat/
I also remember that Anthony tried a honeycomb mirror but ran into problems with it's construction.

Newport says they make them:
http://www.newportglass.com/afuscelr.htm

but there aren't any in a 10" size that I would like.

Questions:
what do you all think of honeycomb mirrors?

Who makes them for sale?

I wonder if anyone can make one out of zero expansion glass?


cheers
Allan
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Old 12-12-2014, 01:41 PM
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What about hubble optics in Hong Kong? They seem to be producing some great optics of fused mirrors at the moment?
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Old 12-12-2014, 02:21 PM
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Quote:
Originally Posted by John K View Post
What about hubble optics in Hong Kong? They seem to be producing some great optics of fused mirrors at the moment?

Thanks John,
It seems like it's all there:

http://www.hubbleoptics.com/mirrors.html

And it says:

Quote:
The main problem is not the aberrations due to deformation, but the
layer of warm air in front of the primary mirror. This layer of warm air is
the main cause of the image distortion called "mirror seeing", which is
caused by the non-uniform index of diffraction in the cooler air over the
warm mirror surface. No mirror, regardless of the type of glass used,
will perform adequately until the mirror is close to the temperature of
the ambient air. This occurs when the temperature difference between
glass and air is less than one degree centigrade (°C), and best
performance is achieved when this difference is less than 0.2 °C.



They also have protected silver coatings - interesting.
I am not sure if they have 10" size.
They don't state the weight.
I'll write to them.


cheers
Allan
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Old 26-12-2014, 01:30 PM
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Thanks John,
I am just organising a 10" f/4 sandwich mirror from Hubble Optics.
This will eventually go into my 10" f/4 Newt. that I just ordered.

cheers
Allan
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Old 27-12-2014, 10:25 AM
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From my experience of working with fused blanks and testing those made by others they don't take as good a figure as monolithic - My experience is they just don't behave as well as monolithic during cooling and under pressure of manufacture nor mounting induced stresses in the telescope. By that I mean in a 3 dimensional sense .
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Old 27-12-2014, 10:53 AM
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Quote:
Originally Posted by Satchmo View Post
From my experience of working with fused blanks and testing those made by others they don't take as good a figure as monolithic - My experience is they just don't behave as well as monolithic during cooling and under pressure of manufacture nor mounting induced stresses in the telescope. By that I mean in a 3 dimensional sense .
Yes but if you look at Hubble Optics
http://www.hubbleoptics.com/mirrors.html
They say
Quote:
40" sandwich mirror delivered to NASA in 2014
If they can make a 40" mirror for Nasa then they must be able to make a 10" mirror for me.

Apparently sandwich mirrors can suffer from "print through".

I intend to find out for myself.
It could be that a new wave of telescopes will start off with sandwich mirrors.
I am trying to break new ground.

I will be able to compare the performance of a standard mirror & a Hubble Optics sandwich mirror & report back to everyone.
I won't get the sandwich mirror for between 4 to 6 months.

cheers
Allan
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Old 27-12-2014, 11:11 AM
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Allan - fused glass blanks have been around for 50 years , it just now that the chinese are making then out of plate glass and offering to amateur astronomers. What I have learn from 40 years around optics is that most that you read is self serving spin - lets see how NASA's foray into dirt cheap plate glass 40" mirrors pans out in time . Even with the buttons in between that is a relaively thin blank - the chances of it being 'diffraction limited' at that thickness and from a fused blank are zero I am afraid but that is aside . I was just passing on some actual experience in the field.

Do let everyone know how your mirrors compare - it certainly might not make any difference in the prime focus imaging world - I am an old school visual guy.
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Old 27-12-2014, 11:28 AM
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Quote:
Originally Posted by Satchmo View Post
Allan - fused glass blanks have been around for 50 years , it just now that the chinese are making then out of plate glass and offering to amateur astronomers. What I have learn from 40 years around optics is that most that you read is self serving spin - lets see how NASA's foray into dirt cheap plate glass 40" mirrors pans out in time . Even with the buttons in between that is a relaively thin blank - the chances of it being 'diffraction limited' at that thickness and from a fused blank are zero I am afraid but that is aside . I was just passing on some actual experience in the field.

Do let everyone know how your mirrors compare - it certainly might not make any difference in the prime focus imaging world - I am an old school visual guy.

We'll see for ourselves.
They say Strehl ratio of >= 0.975 & also Pyrex not plate glass.

I am willing to take the risk to try & push the envelope.
The giant lumps of glass in peoples mirrors now just couldn't possibly reach
thermal equilibrium as fast as the temperature drops.

Just look at the trouble Anthony Wesley goes to to get the temperatures the same:
http://www.acquerra.com.au/astro/cooling/ballarat/

cheers
Allan
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Old 27-12-2014, 11:40 AM
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Quote:
Originally Posted by alpal View Post
Just look at the trouble Anthony Wesley goes to to get the temperatures the same:
http://www.acquerra.com.au/astro/cooling/ballarat/
He's imaging at much smaller image scale than us DSO guys and doing lucky imaging. By comparison, DSO imaging is a lot less demanding wrt resolution and typically limited by the seeing rather than the optics.

Cheers,
Rick.
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Old 27-12-2014, 03:25 PM
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Quote:
Originally Posted by RickS View Post
He's imaging at much smaller image scale than us DSO guys and doing lucky imaging. By comparison, DSO imaging is a lot less demanding wrt resolution and typically limited by the seeing rather than the optics.

Cheers,
Rick.

Hi Rick,
That's true - he's doing lucky imaging at high frame rates.
I am still hoping to pick up that little extra clarity by not
having a boundary layer of air affecting my image.

cheers
Allan
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Old 27-12-2014, 03:53 PM
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Quote:
Originally Posted by alpal View Post
Hi Rick,
That's true - he's doing lucky imaging at high frame rates.
I am still hoping to pick up that little extra clarity by not
having a boundary layer of air affecting my image.

cheers
Allan
Fair enough, Allan. I agree that would help.

Cheers,
Rick.
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Old 28-12-2014, 07:13 AM
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Quote:
Originally Posted by Satchmo View Post
From my experience of working with fused blanks and testing those made by others they don't take as good a figure as monolithic - My experience is they just don't behave as well as monolithic during cooling and under pressure of manufacture nor mounting induced stresses in the telescope. By that I mean in a 3 dimensional sense .
Hi Mark,

I am surprised by this comment, as I thought that you figured Anthony Wesley's fused 16" blank which seems to be producing some really fine images.

I had the pleasure of looking through a 16" mirror made by Hubble Optics a few weeks ago and must admit that the views were excellent and it looked like a very fine mirror - all depends I guess on the optician.

My dream telescope is a 20" Newtonian with a fused/composite mirror for rapid cool down assisted by a peltier cold plate to be used for planetary and deep sky imaging.

These one piece cellular blanks look interesting:

http://www.dreamcellularllc.com/40cm.htm
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Old 28-12-2014, 08:00 PM
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Quote:
Originally Posted by John K View Post
Hi Mark,

I am surprised by this comment, as I thought that you figured Anthony Wesley's fused 16" blank which seems to be producing some really fine images.

I had the pleasure of looking through a 16" mirror made by Hubble Optics a few weeks ago and must admit that the views were excellent and it looked like a very fine mirror - all depends I guess on the optician.

My dream telescope is a 20" Newtonian with a fused/composite mirror for rapid cool down assisted by a peltier cold plate to be used for planetary and deep sky imaging.

These one piece cellular blanks look interesting:

http://www.dreamcellularllc.com/40cm.htm


Good post John,
About 5 years ago when I bought my 8” f/6 Newt. - carbon fibre tubes were almost unheard of -
now everyone wants them & they are almost standard for anyone doing proper imaging.
Now sandwich mirrors are not in any telescope that I can buy but perhaps in a few years
they will become standard features as no other mirror can meet their air boundary layer thermal capability.

Progress is tried - & if the results are good - it catches on.


cheers
Allan
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Old 18-03-2015, 09:40 PM
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Yes - further research based on the post below:

The only other company I can find doing cellular mirrors is Dream:



http://www.dreamscopes.com/pages/07/cellular24-01.htm


Their Dream Astrograph - 16" f3.75 costs US $33,000 so I
would imagine that these space age mirrors are not cheap if bought separately.
see here:
http://www.dreamscopes.com/pages/pro...t-astro-16.htm


Notice something?
Dreamscopes doesn't show how the mirrors are mounted - they somehow make use of the holes underneath
& special carbon fiber custom mirror holders.
Maybe Mark - below can help with a photo?




I make a prediction -
cellular mirrors will be all the go within 5 years.
Other companies will have to make them to keep up.
That means we'll all have to sell our scopes & buy ones with cellular mirrors to have the bragging rights.




cheers
Allan
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Old 19-03-2015, 07:33 PM
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There is another company making cellular mirrors:

http://www.telescopeshercules.com/#!...r-mirrors/cgl5

and another here:

http://www.opticwavelabs.com/products.php
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Old 20-03-2015, 07:52 AM
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Those Hercules scopes look fabulous. I tried to send them a message but their messaging system on their website is bugged.

Do you know of any images on the net taken with one of these?

Greg.
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Old 20-03-2015, 07:51 PM
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Originally Posted by gregbradley View Post
Those Hercules scopes look fabulous. I tried to send them a message but their messaging system on their website is bugged.

Do you know of any images on the net taken with one of these?

Greg.

No - sorry Greg,
I made an extensive search with Google & can find nothing.
It seems that the Company that does the polishing - Optiques Fullum -
would do proper Zygo Interferometer tests? - but there is nothing I can find yet.

Dream - does have a Zygo Interferometer on site to test all their mirrors.
After many emails:
It would seem that many of us would have to increase our buying power
by pooling our money together to get a discount on a number of mirrors -
mirrors in bulk.
I am thinking about that to try & get the astronomical price of cellular mirrors down.
I want a 10" f4 because that's the only size that will fit on a low end mount like most of us have - an EQ6 -
( which I have - although it's modified
https://www.flickr.com/photos/247194...in/photostream )
& that the telescope will fit in the back seat of any car to take to a dark site.
I don't want to spend big dollars on a solid heavy mirror &
then within 5 years want to replace it because everyone else has better cellular mirrors
offering greater lightness & much faster cool down times -
to help keep the boundary layer of air steady above the mirror.
That boundary layer problem may not affect deep sky imaging
as much as lucky planetary imaging but I want to find out.
I want to try & be at the cutting edge & not just buy something that's expensive & ready to go
but that everyone else has too.
I would only be repeating their experiment.

Those interested can PM me.

cheers
Allan

Last edited by alpal; 21-03-2015 at 12:58 PM.
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