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Midkiff 50" Normand Fullum Newtonian

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#1 25585

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Posted 17 November 2019 - 02:18 PM

https://youtu.be/yAfUBiWOjNc

 

https://www.optiques...acinia-2-2-2-3/

 

Nice to see a couple of astronomisses too.

 

 


Edited by 25585, 17 November 2019 - 02:32 PM.

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#2 Richard O'Neill

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Posted 17 November 2019 - 04:52 PM

ATM has certainly come a long way in the last  50-60 years.


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#3 25585

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Posted 17 November 2019 - 07:52 PM

Collimation seemed easy for a F3.5. I wonder how large large the secondary is in its axes. 



#4 turtle86

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Posted 17 November 2019 - 08:32 PM

Here’s how it would handle 2” Tele Vue eyepieces:

 

FD4564AB-C10F-4B5A-AC4F-56C5F65C23E0.png



#5 Cotts

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Posted 18 November 2019 - 10:43 PM

ATM has certainly come a long way in the last  50-60 years.

Normand Fullum is no amateur....

 

Dave


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#6 Cotts

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Posted 18 November 2019 - 10:46 PM

And an optics question.  With a tilted secondary and the eyepiece position as seen in the video is some special grinding of the Primary or secondary needed to prevent astigmatism?  

 

Dave



#7 Bob S.

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Posted 19 November 2019 - 06:26 AM

Wow! Fullum's Techno-Fusion mirrors and unique structures appear to be an incredible game changer in the uber-large Newtonian world. Some of the participants in the video were talking about primary mirror equilibration times in less than a half an hour on days where the scope is not in blistering hot weather.

 

As many of us who have used and owned large-mirrored Newtonian telescopes are aware, the equilibration issues of the primary and secondary mirrors are a fundamental key in these large scopes performing optimally. In many instances, large monolithic mirrors are never in an environment that allows for equilibration with ambient air temperatures. The Techno-Fusion's ability to track temperature deltas throughout the night appears to be a huge advantage over our monolithic large slabs of glass.

 

It will be interesting to get feedback from the owner as to how the figures of the two mirrors perform during the nights in VA.


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#8 macdonjh

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Posted 19 November 2019 - 09:02 AM

Did you see how thick those spider vanes are?  I wouldn't want a scope with that much diffraction.  I wonder which star party they'll travel to first?



#9 turtle86

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Posted 19 November 2019 - 10:16 AM

Did you see how thick those spider vanes are?  I wouldn't want a scope with that much diffraction.  I wonder which star party they'll travel to first?



I would think that the vanes need to be robust due the size of the secondary to maintain collimation.

If I ever move out west, this is the scope I'd want at my observatory.
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#10 Cotts

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Posted 19 November 2019 - 11:31 AM

Did you see how thick those spider vanes are?  I wouldn't want a scope with that much diffraction.  I wonder which star party they'll travel to first?

funnypost.gif

 

Dave



#11 tommm

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Posted 19 November 2019 - 01:03 PM

And an optics question.  With a tilted secondary and the eyepiece position as seen in the video is some special grinding of the Primary or secondary needed to prevent astigmatism?  

 

Dave

No.



#12 tommm

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Posted 19 November 2019 - 01:15 PM

Normand Fullum is no amateur....

 

Dave

Yes indeed! But it seems ATM has become somewhat blurred these days. It used to mean the person built the entire scope, purchasing only a few parts like focuser and secondary, and some made those too - in the Porter or Texereau spirit. Dave Brock's 10" scope he reported on recently is in that vein.  But these days many people buy the primary mirror too, or pay to have some of the construction done by others, and some have a scope made for them, so ATM seems to be more general now, more like AA, amateur astronomy. 


Edited by tommm, 19 November 2019 - 10:57 PM.


#13 MitchAlsup

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Posted 19 November 2019 - 08:22 PM

Yes indeed! But it seems ATM has become somewhat blurred these days. It used to mean the person built the entire scope, purchasing only a few parts like focuser and secondary, 

and aluminum plate, and aluminum tube, and threaded rod, and screws, and bolts, and nuts, and paint, and plywood, and teflon, and laminates, and cloth (to make shrouds,...), maybe some decals,.....


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#14 Keith Rivich

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Posted 19 November 2019 - 11:55 PM

Wow! Fullum's Techno-Fusion mirrors and unique structures appear to be an incredible game changer in the uber-large Newtonian world. Some of the participants in the video were talking about primary mirror equilibration times in less than a half an hour on days where the scope is not in blistering hot weather.

 

As many of us who have used and owned large-mirrored Newtonian telescopes are aware, the equilibration issues of the primary and secondary mirrors are a fundamental key in these large scopes performing optimally.In many instances, large monolithic mirrors are never in an environment that allows for equilibration with ambient air temperatures. The Techno-Fusion's ability to track temperature deltas throughout the night appears to be a huge advantage over our monolithic large slabs of glass. 

 

It will be interesting to get feedback from the owner as to how the figures of the two mirrors perform during the nights in VA.

That is simply not true. My 25" 80# mirror has never, ever suffered a thermal issue that hurts viewing. The worst case scenario is TSP during late spring. Daytime temps hitting 100f. 30 minutes before nightfall a fan blowing onto the mirror cures any heat related problems. Images are just as good at sunset as they are in the early morning. In fact I would bet my scope cools down faster then an 8" Cassegrain under the same conditions.



#15 Bob S.

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Posted 20 November 2019 - 05:40 AM

That is simply not true. My 25" 80# mirror has never, ever suffered a thermal issue that hurts viewing. The worst case scenario is TSP during late spring. Daytime temps hitting 100f. 30 minutes before nightfall a fan blowing onto the mirror cures any heat related problems. Images are just as good at sunset as they are in the early morning. In fact I would bet my scope cools down faster then an 8" Cassegrain under the same conditions.

Keith, Saying something is simply "not true" is a rather strong statement and unfortunately does not square with empirical testing myself and others have done using infrared heat guns and thermal camera experiments with large monolithic mirrors. My interest in thermal issues with retained energy started with 8" blanks and has gone up to two 32", two 28" and one 24" mirrors that I have owned over the years.

 

To suggest that an 80# mirror has "never, ever suffered a thermal issue that hurts viewing" is amazingly disparate with what I and others with larger (>24") have experienced over the past couple of decades? I guess, if your images are as satisfactory at sunset as they are in the early morning, that it is a good thing and you remain pleased with your monolithic mirror's performance which is a good thing?

 

From a physics standpoint, I am not sure how you have been able to successfully not have to contend with boundary layer issues, changes in figure, etc. related to the stored energy in a large piece of glass but apparently these are not issues for you which is a good thing.


Edited by Bob S., 20 November 2019 - 05:42 AM.


#16 Keith Rivich

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Posted 20 November 2019 - 09:55 AM

What I meant by the "not true" is the implication of your (and others) statement that large monolithic mirrors do not perform well as the night progresses. When this comment started showing up regularly on these threads the group I observe with tested visually whether our mirror temps affect image quality as the night progresses. Our scopes range from 18" up to 36". Many of us have 25+ years of observing and can tell the difference between soft images and tack sharp images. When the seeing is good its good for all, when the seeing is bad its bad for all. 

 

While your testing may indicate there should be a problem we just do not see it under actual observing conditions. 


Edited by Keith Rivich, 20 November 2019 - 11:00 AM.

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#17 stargazer193857

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Posted 21 November 2019 - 12:31 PM

And an optics question. With a tilted secondary and the eyepiece position as seen in the video is some special grinding of the Primary or secondary needed to prevent astigmatism?

Dave


Not for a flat secondary. Just special cutting of the edges and holder.
That low rider means lower eyepiece, larger secondary, and higher baffle if one is needed.

#18 stargazer193857

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Posted 21 November 2019 - 01:30 PM

This 50" scope shows that 50" is now a realistic amateur scope size. I wonder how much the aluminizing costs.

#19 MitchAlsup

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Posted 21 November 2019 - 03:59 PM

 I wonder how much the aluminizing costs.

Not much after you buy the vacuum chamber, roughing pump, and Ion pump.


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#20 davidpitre

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Posted 26 November 2019 - 07:17 PM

What I meant by the "not true" is the implication of your (and others) statement that large monolithic mirrors do not perform well as the night progresses. When this comment started showing up regularly on these threads the group I observe with tested visually whether our mirror temps affect image quality as the night progresses. Our scopes range from 18" up to 36". Many of us have 25+ years of observing and can tell the difference between soft images and tack sharp images. When the seeing is good its good for all, when the seeing is bad its bad for all. 

 

While your testing may indicate there should be a problem we just do not see it under actual observing conditions. 

Perhaps I'm misinterpreting what you are saying. Are you saying that massive mirrors cool as fast as smaller mirrors , and or that the images that they produce don't suffer when the mirror's temps substantially lag ambient temps. Regardless of the material from which the mirror is made i.e. plate glass, pyrex, quartz...?



#21 tommm

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Posted 27 November 2019 - 01:46 PM

Perhaps I'm misinterpreting what you are saying. Are you saying that massive mirrors cool as fast as smaller mirrors , and or that the images that they produce don't suffer when the mirror's temps substantially lag ambient temps. Regardless of the material from which the mirror is made i.e. plate glass, pyrex, quartz...?

There is not enough info in Keith or Bob's posts.  Heat flow through the mirror occurs mainly parallel to the mirror axis - out through the faces, so depends mainly on mirror thickness.
Bob has decades of experience, much of which was likely with thicker mirrors.  Keith's group may be using newer, thinner mirrors.    Also depends on material as you stated, and on the
rate of ambient temperature change which was not specified.  Could be that Keith has a newer 1 1/4" thick quartz mirror and Bob used older 2" thick borosilicate glass mirrors.



#22 reddog1972

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Posted 27 November 2019 - 01:49 PM

My understanding is that this will eventually wind up in a dome at cherry springs state park if what I heard was true.

#23 Keith Rivich

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Posted 27 November 2019 - 07:10 PM

Perhaps I'm misinterpreting what you are saying. Are you saying that massive mirrors cool as fast as smaller mirrors , and or that the images that they produce don't suffer when the mirror's temps substantially lag ambient temps. Regardless of the material from which the mirror is made i.e. plate glass, pyrex, quartz...?

I'll take the bait...

I understand the physics. I also have 30 years with a massive telescope and do not see the "cooling down" problem as being a problem. Nor do the people I observe with.

 

I regularly use our observatories 36" RC, closed tube with a 600# mirror. On a summer day the inside of the dome can easily reach 120 degrees. I get there around 2 hours before dark and stick a fan in the tube pointed at the mirror. Once the mirror has cooled off its perfectly fine the rest of the night. 

 

What I am saying is when we read "Large mirrors never cool down to ambient", or some such wording, what is implied is the image quality degrades as the night progresses. If I were new to the hobby I would run away from a full thickness mirror as the telescope must be near useless as the night cools down. We do not find that to be true.


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#24 Keith Rivich

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Posted 27 November 2019 - 07:13 PM

There is not enough info in Keith or Bob's posts.  Heat flow through the mirror occurs mainly parallel to the mirror axis - out through the faces, so depends mainly on mirror thickness.
Bob has decades of experience, much of which was likely with thicker mirrors.  Keith's group may be using newer, thinner mirrors.    Also depends on material as you stated, and on the
rate of ambient temperature change which was not specified.  Could be that Keith has a newer 1 1/4" thick quartz mirror and Bob used older 2" thick borosilicate glass mirrors.

Nope. 

Galaxy mirror, full thickness. 30 years old. Not sure what kind of glass.



#25 Keith Rivich

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Posted 27 November 2019 - 07:16 PM

This 50" scope shows that 50" is now a realistic amateur scope size. I wonder how much the aluminizing costs.

Not much if you DIY...

 

https://angelgilding...mirror-kit.html




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