1.5m (60") f/3.75 ZERODUR Research Grade Observatory Telescope Mirror

StarDust

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Oct 15, 2021, 12:45:12 AM10/15/21

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https://www.ebay.com/itm/143164027946?chn=ps&_trkparms=ispr%3D1&amdata=enc%3A1NCBGwyJKQNaWqqO76WCCRA24&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=143164027946&targetid=1262931797002&device=c&mktype=pla&googleloc=9032048&poi=&campaignid=12873834688&mkgroupid=116682566330&rlsatarget=pla-1262931797002&abcId=9300536&merchantid=8174544

eBay item number:143164027946

Only !😮
Price:
US $98,000.00

Quadibloc

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Oct 15, 2021, 1:40:28 AM10/15/21

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On Thursday, October 14, 2021 at 10:45:12 PM UTC-6, StarDust wrote:

> Only !😮
> Price:
> US $98,000.00

Actually, the price is quite reasonable. While my reaction may be unwarranted and unreasonable,
for an item of this scarcity, I have to ask: does the seller actually have one, and if so, is it
of legitimate provenance?

I mean, a sixty-inch reflecting telescope. There aren't many of those in the whole world; while
that's less than 200 inches, and it's less than 100 inches, one is still talking about one of the
world's major observatories here, not anything "amateur" in size or performance.

John Savard

StarDust

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Oct 15, 2021, 1:51:17 AM10/15/21

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I personally, would not buy it for telescope, unless I know it's optical quality!
It can be very expensive to re-polish this huge mirror, I think!
To cut pieces out is a different story!

Quadibloc

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Oct 15, 2021, 1:53:40 AM10/15/21

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Having now examined the listing:
Apparently it is military surplus.
The mirror is f/3.75.
Also, the seller is unsure of whether the figure is parabolic or hyperbolic, and of the
grade of Zerodur used for the mirror.

While the Mount Wilson 60-inch is f/16 in Cassegrain configuration, I couldn't find
out what the focal ratio of just the mirror was.

John Savard

StarDust

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Oct 15, 2021, 5:05:56 AM10/15/21

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Well, here's 6" Zerodur mirror, optical flat!
$1359
eBay item number:265265609010

Optical flats, even glass, can be very expensive, 'case used for checking other optics.

fred k. engels®

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Oct 15, 2021, 12:57:38 PM10/15/21

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Prime Minister Justin Blackface tweeted his condolences that those Chicoms
have just launched ANOTHER massive spy satellite into
orbit!!!!!!!!!!!!!!!!!!!

https://www.youtube.com/watch?v=sRa74rUnUSs

RichA

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Oct 15, 2021, 5:51:37 PM10/15/21

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Truly awesome. You could build one of the largest amateur scopes in existence and trailer it to sites. Or permanently mount it. $98,000 is a lot but some (idiots) pay that for a car that'll be worth 1/2 that in 2-3 years.

palsing

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Oct 16, 2021, 12:17:22 AM10/16/21

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And this for a mirror that is not even known to be parabolic!

StarDust

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Oct 16, 2021, 12:42:37 AM10/16/21

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Just flip a coin and you'll know it, either parabolic or hyperbolic!
LOL!

Chris L Peterson

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Oct 16, 2021, 9:39:27 AM10/16/21

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On Fri, 15 Oct 2021 21:17:21 -0700 (PDT), palsing <pnal...@gmail.com>
wrote:

>On Thursday, October 14, 2021 at 9:45:12 PM UTC-7, StarDust wrote:
>> https://www.ebay.com/itm/143164027946?chn=ps&_trkparms=ispr%3D1&amdata=enc%3A1NCBGwyJKQNaWqqO76WCCRA24&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=143164027946&targetid=1262931797002&device=c&mktype=pla&googleloc=9032048&poi=&campaignid=12873834688&mkgroupid=116682566330&rlsatarget=pla-1262931797002&abcId=9300536&merchantid=8174544
>>
>> eBay item number:143164027946
>>

>> Only !?

>> Price:
>> US $98,000.00
>
>And this for a mirror that is not even known to be parabolic!

It doesn't necessarily need to be parabolic... but it does need to be
accurately figured to some known curve. That's kind of an important
detail to be missing!

StarDust

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Oct 16, 2021, 6:10:01 PM10/16/21

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Re figuring / repolishing this 2 m mirror can be very expensive and time-consuming, I think.

fred k. engels®

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Oct 16, 2021, 8:27:16 PM10/16/21

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ALL ASTROPHOTOGRAPHERS - PLEASE READ - IMPORTANT ANNOUNCEMENT!!!

The world's Leading astrophotographer Arnold Ziffel at the Hooterville
Observatory has found the perfect place for you to pursue that useless
pretty picture horseshit® nobody cares about!!!!!!

https://i.insider.com/561ff695dd0895f70a8b460c?width=700&format=jpeg&auto=webp

What are you waiting for? Act NOW before its too late!!!!!!!!!! And your
equipment is junk!!!!!!!!!!

Quadibloc

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Oct 16, 2021, 10:31:13 PM10/16/21

to

On Thursday, October 14, 2021 at 11:53:40 PM UTC-6, Quadibloc wrote:

> While the Mount Wilson 60-inch is f/16 in Cassegrain configuration, I couldn't find
> out what the focal ratio of just the mirror was.

I have now found out the focal ratios of that telescope in its four possible
configurations:

f/5 in the Newtonian configuration;
f/16 in the basic Cassegrain configuration used for spectroscopy;
f/20 in the modified Cassegrain configuration used for photography;
f/30 in the Coude configuration.

John Savard

StarDust

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Oct 16, 2021, 11:09:01 PM10/16/21

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Can't wait to act!
https://www.youtube.com/watch?v=tkD85aC8GRo

Martin Brown

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Oct 17, 2021, 3:36:15 PM10/17/21

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At that size and focal length it will be either figured for a parabola
or more likely a hyperbola. However, the matched secondary may prove
rather an expensive additional component to have to make or have made.

Within reach of a very advanced amateur but only just.

One of the scopes I grew up with had the capability of using a Naysmyth
focus where the optical axis came out of the main bearing. Unfortunately
the optical components for doing that had been lost along the way.

https://en.wikipedia.org/wiki/James_Nasmyth

It was a scale model prototype of the big scope at Pretoria by Grubb
Parsons and at one time was collocated with Jodrell Bank. Donated to
Bernard Lovell by the chief engineer of Alvin cars Captain Smith-Clarke
(iron lung designer). He fixed quite a few astronomers engineering
problems although his contributions are largely undocumented today. His
other scope(s) are still at Loughborough university (I think).

https://news.coventrysociety.org.uk/2020/11/30/captain-smith-clarke/

https://www.gracesguide.co.uk/George_Thomas_Smith-Clarke
(skip to the obituary for the astronomy stuff - his hobby)

I knew someone who built a 6" Maksutov from scratch back in the 1970's.
Admittedly he did have a bit of help from Pilkington's glass research
team who were somewhat bemused by his perseverance with the project.

--
Regards,
Martin Brown