Are they serious - monster dobs?

[dcalleja]

Thanks for the info and pics Gary - One can dream

[icytailmark (Mark)]

if i win the 30 million dollar lotto i would buy a 50" Dob and my own observatory

[icytailmark (Mark)]

would u be able to see blackholes and quasars with a telescope this big?

[mozzie (Peter)]

you would have to stand on the roof of your house to see out the focuser or grab a rope and hang out a tree

[seeker372011 (Narayan)]

who wants to be a a (very tall) millionaire?

[AG Hybrid (Adrian)]

Don't point a Monster Dob at the sun! Just pointing this at the sun can instantly damage eyepieces and cause irreversible eye damage and burns. Use extreme caution leaving it uncovered during daylight. Concentrated sunlight from this much aperture can damage the telescope or set its surroundings on fire!

Oh yeah now were talking. Fire zeee laserrr!

[multiweb (Marc)]

Originally Posted by gary

Large aperture Dob and here -
http://www.wildcard-innovations.com....es/lowrie1.jpg

I reckon I'd forget to step down the ladder and would walk sideways after a few minutes going "wow" at the eyepiece...
This is high-risk observation.... anything above 20 degrees.

[pgc hunter]

Originally Posted by Spanrz

<sarcasm>
Hehe, you are allowed to go to 3.5 mt's wide with out these...
So buy what you can...
</sarcasm>



These large dobs would be a waste for Melbourne location, well I mean *cough* by the time you drive out on a clear night (or day) to a dark spot, setup for the few hours, it's clouded over.
I mean, it's that man Murphy, he lives a lot in Melbourne...

But boy, lovely to have , I know where my lotto winnings will go to.

that 50" is tall enough to punch thru the Melbourne Cloud, so no worries there!

Originally Posted by mozzie

you would have to stand on the roof of your house to see out the focuser or grab a rope and hang out a tree

A house? Try a 3 story McMansion and a stepladder

[Satchmo]

Originally Posted by Rodstar

I assume the prices are largely for the mirror?

Rod

These large mirror blanks are made with low cost technology so the normal commercial mirror blank prices wouldn't apply . The plate glass blanks have very thin face sheets with an array of rectangular stalks in between that give the blanks their 'thickness'. I haven't seen this kind of design ( where the internal ribs are just stalks ) . I guess it remains to be seen how they perform both practically and in the market place. It will be interesting to see some sort of credible independent optical testing of the large mirrors. Testing such a mirror would be a major feat in itself.

Have a look at this link and down the bottom for photos of the blanks, and the pricing structure.

http://www.normandfullumtelescope.com/mirror_en.html


Mark

[Satchmo]

Mirror blank picture from Fullham website...

[erick (Eric)]

That is fascinating mirror technology. I take it the "thickness" is to hold the front surface rigid? Why couldn't the thickness be provided by something else rather then pillars of glass onto another glass plate - a lump of plastic, wood?? I guess the front surface should only be rigidly connected to something with the same coefficient of expansion?

[mithrandir (Andrew)]

Tradeoff? The cost and weight of a solid blank would be prohibitive. It could be drilled to reduce the weight, but that would just increase the cost.

The glass pillars and the back must have the same thermal properties as the mirror, which other materials wouldn't.

I would have thought that having some radially aligned strips with intermediate pillars would be more vibrationally stable, but I'm not a materials physicist.

[Satchmo]

Originally Posted by mithrandir

I would have thought that having some radially aligned strips with intermediate pillars would be more vibrationally stable, but I'm not a materials physicist.

These plate glass blanks are made by an amateur astronomer in his basement in Quebec. Its open slather really if you want to tinker with blank design and can build a kiln to fuse glass: you are not anwerable to NASA

Mark

[bratislav (Bratislav)]

I expected they'd moved into faster f/ratios (f/3 and like) for those monsters. I hate those tall scopes. Not that I'm afraid of height, but they are so hard to move from top of the ladder, especially closer to zenith. I'd much rather stick with 30" f/3 than go 40" if it had to be f/4.
50" f/4 - forget it. That is going to be unusable.

Just saw Orion site - 50" is planned to be f/3.75. Still almost 5m tall. Still unusable in my book (perhaps unless actively driven. Even then, not many people will climb 4+ m ladder for a peek)

[erick (Eric)]

Originally Posted by bratislav

(perhaps unless actively driven.)

ServoCAT and Argo Navis standard equipment, I think. So yes, actively driven. Push the goto button and it sweeps you off the ladder as it slews! Perhaps have ladder on wheels and wrap your arms around the UTA before you push the button!

[gary]

Originally Posted by bratislav

Not that I'm afraid of height, but they are so hard to move from top of the ladder, especially closer to zenith.

Hi Bratislav,

Certainly tall scopes aren't everyones cup of tea! However keep in mind that you
don't need to manually push the scope as they have full servo motor controlled slew
and track capability. With the wireless handpad, one can also make small corrections
whilst at the eyepiece.

I remember joking to Larry Mitchell whilst coming down the ladder of his
36" f/5 that probably one of the reasons galaxies looked so spectacular
through it was because by the time you went up the ladder you were almost
half way there.

Many American observers use ladders with half-steps, that is twice as many steps
as normal. For some reason one doesn't encounter many ladders with half steps
at star parties here in Australia. Some of the best observing ladders I have
encountered are those designed for the use in orchards in the US that have additional
hand rails at the top that then allow the user to take a more secure, relaxed and
comfortable stance when one reaches the top.

Some fixed observatory users employ scissor lifts.

Jimi Lowrey's OMI designed telescope is a 48" f/4.
http://www.lowreyobservatory.com/
Every report I have heard from anyone lucky enough to look through this
instrument seems to confirm the views makes the climb very worthwhile.
This particular scope also has a ServoCAT slew and track system so that the
operator is not having to manually wrestle with the scope, which otherwise
could prove a handful, particularly at the zenith.

I was lucky to spend some time on Steve Kennedy's 32" f/3.66 in California.
As an optician, Steve's specialty was in producing these large aperture,
short focal length scopes. When Al Nagler popped the prototype 13mm Ethos
into it, he confirmed it definitely needed a Paracorr. Nevertheless, this scope
provided fabulous views.
See http://www.wildcard-innovations.com....s/kennedy1.jpg

At the IceInSpace AstroCamp, Mark Suching commented to me about some
of the technical challenges in producing such large aperture short focal length mirrors
and over time we will undoutedly see more of these types of mirrors come to
market as the science and art in producing them evolves.

Best regards

Gary

[Rodstar (Rod)]

Originally Posted by Satchmo

Rod

These large mirror blanks are made with low cost technology so the normal commercial mirror blank prices wouldn't apply . The plate glass blanks have very thin face sheets with an array of rectangular stalks in between that give the blanks their 'thickness'. I haven't seen this kind of design ( where the internal ribs are just stalks ) . I guess it remains to be seen how they perform both practically and in the market place. It will be interesting to see some sort of credible independent optical testing of the large mirrors. Testing such a mirror would be a major feat in itself.

Have a look at this link and down the bottom for photos of the blanks, and the pricing structure.

http://www.normandfullumtelescope.com/mirror_en.html


Mark

Thanks for that info Mark. Very interesting. Some of those beautiful hand crafted scopes look incredible (if somewhat impractical for transportation etc).

Just out of interest, what is the biggest mirror you have figured, and what is the biggest you would be prepared to try??!! (one can always dream of that future project....an f/3 40" mirror would suit me!!!)

[Louwai (Bryan)]

Originally Posted by erick

Push the goto button and it sweeps you off the ladder as it slews! Perhaps have ladder on wheels and wrap your arms around the UTA before you push the button!

Brilliant idea Eric. I'll talk to Peter about some such thing for my 20".

[bratislav (Bratislav)]

Originally Posted by gary

Jimi Lowrey's OMI designed telescope is a 48" f/4.
http://www.lowreyobservatory.com/
Every report I have heard from anyone lucky enough to look through this
instrument seems to confirm the views makes the climb very worthwhile.

Hi Gary,

make no mistake, I would definitely be there, in the line for a climb ! But best scope is scope that gets used most often, and at last ASVs Starbeque I strongly felt it was not worth climbing the ladder of society's 25" Obsession where a nearby Phil's and Stephen's 20" f/3.7 (with one of Marks excellent mirrors) offered almost the same views with both feet firmly on the ground. Spending time going up and down the ladder to re-aim the scope is now becoming bothersome to me.
I know how hard it would be to make a 30" f/3, but such scope (with folding flat, hence ground level or single step observing) would offer the views to perhaps 100 times more people than 50" f/4, driven or not. Even if I would queue to have a peek in one of those skyscraping monsters, I would NOT long owning one of those.

Bratislav

[Paddy (Patrick)]

I like the way they tout these huge scopes as the cure for aperture fever. It seems to me more like they are its ultimate expression!