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The Definitive Newtonian Reflector

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#26 ZeroID

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Posted 17 May 2015 - 09:40 PM

HI Ed, Interesting reading. I am in the process of building a 8" F8 Newtonian scope as an astrograph. As you say the F8 is kinder for focussing tolerances and also reduces coma compared to the modern F5-F4 versions.  In my case I can't afford an 8" APO whereas a 8" mirror made by Garry Nankivell of New Zealand, Mt John Observatory fame which appeared for sale locally lets me build something quite different. A 2x Barlow as you say makes this F16.

I have hopefully reduced star spikes by suspending the secondary on a spider of steel.23 mm  top "E" guitar strings fittingly controlled by 8 Guitar machine heads.

The scope is a Serruier Truss style design, open, very light but very stiff. It will be on my EQ6 Pro SynScan in a tin shed Observatory in the back yard.

I'm not far from completion now, a few weeks maybe. But having survived a few criticisms about my decisions to build in this form it was nice to see a few of my thoughts on how I wanted it justified in your article.

Thanks and take care

Brent


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#27 dcornelis

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Posted 18 May 2015 - 06:34 AM

I polished an 8 inch F8.3 25 years ago, I need to find me a tube to put it in. I now have the mount too to make it shine ...


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#28 DragosN

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Posted 18 May 2015 - 01:11 PM

Very beautiful and well build telescope. Congratulations Ed.

 

I want to support the importance of some of the solutions used by Ed in his DNR.

 

1. Stray light. For someone this could be a secondary problem, or not at all, but I think is a problem. For example, in photography, for every lens there is a hood, similar to Ed dewcap. And every experienced photographer agrees that the contrast is enhanced with the use of those hoods. More than this, many (all) manufacturers use blackened edges for lenses inside eyepieces and other accessories, for the same reason. And I still wonder why they are neglecting to blacken the edges of mirrors, and especially that of the secondary mirror. We must remember that light is not traveling in a Newtonian only in parallel line with the optic axis.

 

2. Ed dewcap is a solution that I have used intensively. And I have discovered that it has a second benefit, other than keeping the stray light away. Years ago, I have used a 8'' Newtonian in a summer resort, night after night, for many hours, in a place where big crowds was passing by, walking by the seaside. And there was a lot of dust and also sand in the air. The beach was only 10 feet away.  Without dewcap, the dust from the atmosphere goes down the telescope tube straight to the fans, and the primary mirror, and I must clean the telescope every two or three days. With it, must of the dust stops on the inside walls of the dewcap (I call it parasolar). I don't know why, but this is the fact. And the time between cleaning goes to more than two weeks. The only difference is that my dewcap is much larger, about 2'' by the diameter that the telescope tube, also 14'' long ( coudn't make it longer because of transport reasons), and is detachable. Also, is almost closed at the telescope end, with very little gap between the telescope tube and the dewcap.

 

The dark bucket is an very good idea. And I will certainly keep in my mind for the next Newtonian I will build. What I don't like is that I have to modify a project which is almost finished. 


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#29 ed_turco

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Posted 18 May 2015 - 03:26 PM

Jeff,

 

I'd pick out the best telescope making book you can find; the processes are the same to make a mirror or a window for that matter.   But you have to keep in mind that you are going for a piece of optical glass that is flat on both sides and with a uniform thickness.  There is a lot of discussion in Telescope Making about just how flat (or not) a window has to be.

 

I kinda like Ellison in ATM-I (old style) and his writing about making lenses too.  When you get into it, the objections to using a micrometer on a lens don't hold true when making a window.

 

And you really have to get the Texereau book; he has a lot to say about material that applies to windows.  He may sound like a crank at times, but this is the man they hired to refigure the 82" at the McDonald observatory and his results on this project were absolutely amazing.  The story was in S&T in the mid 60s, with before and after photographs!

 

Gee, I wish I could do that . . .

 

 

ed



#30 exAppl088

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Posted 20 May 2015 - 02:59 AM

Excellent article Ed,

 

I really like the dark bucket element.  I have an Orion 190mm Mak-Newt and 

due to the corrector at the front, didn't want the fan to blow inward at the 

base, injecting dust, etc into the closed OTA, but that means the 2+" focuser 

opening is the main intake during cool down.  It has 120mm fan with

a rear fan housing, but i am now thinking a dark bucket addition would really

speed up cool down, maybe as a 4" ABS pipe with a 4" test plug to seal it

(a std plumbing tool ).

 

regards, John


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#31 Galicapernistein

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Posted 20 May 2015 - 08:35 AM

 

Very beautiful and well build telescope. Congratulations Ed.
 
I want to support the importance of some of the solutions used by Ed in his DNR.
 
1. Stray light. For someone this could be a secondary problem, or not at all, but I think is a problem. For example, in photography, for every lens there is a hood, similar to Ed dewcap. And every experienced photographer agrees that the contrast is enhanced with the use of those hoods. More than this, many (all) manufacturers use blackened edges for lenses inside eyepieces and other accessories, for the same reason. And I still wonder why they are neglecting to blacken the edges of mirrors, and especially that of the secondary mirror. We must remember that light is not traveling in a Newtonian only in parallel line with the optic axis.


That's an excellent point about blackening the edges of secondary mirrors. My scope was showing an offset, hazy blob in unfocused images of Jupiter that I never had before. I tracked it down to a tiny chip at the edge of my secondary that was creating a star-like bright spot right in front of the eyepiece. It's the kind of thing that can seriously degrade the image.
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#32 terraclarke

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Posted 20 May 2015 - 11:59 AM

Thank you Ed for an article that was as entertaining to read as it was informative. There is much to be absorbed here, not only for the ATM but also for the "tuner" who might wish to incorporate some of your thoughts and methods in improving their existing Newtonian. You call your innovative design, the Definitive Newtonian Reflector and I cannot think of a better name. It seems that you have considered every design flaw, every optical caveat that has existed in any evolving Newtonian reflector since Sir Isaac produced his first, and incorporated a fix of one type or another to address each of them to produce a truly defraction limited, no limits, reflecting telescope that will compete with any apo refractor of equal aperture, nose to nose and and perhaps even beat many of them. Your telescope is truly "definitive" and will certainly raise the bar to a new standard for many amateur telescope makers.
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#33 ed_turco

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Posted 20 May 2015 - 05:25 PM

Terra,

 

Thank you very much for those comments.

 

 

ed    :flowerred:


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#34 ed_turco

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Posted 20 May 2015 - 05:48 PM

Excellent article Ed,

 

I really like the dark bucket element.  I have an Orion 190mm Mak-Newt and 

due to the corrector at the front, didn't want the fan to blow inward at the 

base, injecting dust, etc into the closed OTA, but that means the 2+" focuser 

opening is the main intake during cool down.  It has 120mm fan with

a rear fan housing, but i am now thinking a dark bucket addition would really

speed up cool down, maybe as a 4" ABS pipe with a 4" test plug to seal it

(a std plumbing tool ).

 

regards, John

Thanks for your very constructive ideas.  I never considered using ABS but it certainly will work.   I have to say that a coffee can is cheaper (for the can itself) once we've enjoyed the coffee first.   So many cans, so few telescopes to put them on.  :lol: The nice thing about cans is that you have a choice in diameters to choose from.  My telescope's Dark Bucket uses a can 4" in diameter; the more aperture you have, the bigger the can.   The can is the easy part.  Getting a hole saw to drill your tube is easy on EBay or Amazon but the investment is not small change; it will set you back $50 or $75.  Drilling that hole in your tube will be an adventure.  You will need to possess a drill press or have access to a neighbor who has one and knows how to use it, and I'm not speaking about some of the dinky one's I've seen.  Better yet, seek out an instructor of a community college that teaches such things.  I've had work done for me as a student project, and when the project worked well,  the instructor wanted me to grade the student.  After all, I was the one who was going to use the item. (I always handed out A's.).
 

 

ed


Edited by ed_turco, 20 May 2015 - 05:51 PM.


#35 Ed D

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Posted 22 May 2015 - 08:12 PM

Ed, thank you for the great and very informative article.  I like your unique approaches to maximizing performance, such as the Dark Bucket.

 

Ed D


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#36 DragosN

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Posted 27 May 2015 - 11:00 PM

If there was a need to stress more the importance of reducing the stray light in telescopes, a recent article in ''Astronomy now'', about a new ''telescope'' called Dragonfly, used by the University of Toronto shed a clear light on this problem.

 

 http://astronomynow....laxy-structure/


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#37 Jeff Morgan

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Posted 28 May 2015 - 10:59 PM

If there was a need to stress more the importance of reducing the stray light in telescopes, a recent article in ''Astronomy now'', about a new ''telescope'' called Dragonfly, used by the University of Toronto shed a clear light on this problem.

 

 http://astronomynow....laxy-structure/

 

Interesting article, those coatings sound great. Perhaps Canon will start building telescopes  ;)

 

I wish they would have gone into more detail on the role of multiple "telescopes" in the role of reducing stray light. Unfortunately, since the Dobsonian Revolution began, the mindset seems to be that more aperture will out-horsepower any flaw in a telescope, scattered light or otherwise.


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#38 DragosN

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Posted 29 May 2015 - 03:18 PM

Similar coatings are also used by Pentax, and Nikon. Pentax is still making eyepieces, and Nikon too, but I don't know if they use this new coatings for it. Pentax, by afraid, is no longer making telescopes. But maybe, this will change in the future.


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#39 GShaffer

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Posted 29 May 2015 - 10:33 PM

Sure would like to see an image looking into the "dark bucket", though I am sure that may not be possible given it is just a "black hole" devoid of and sucking up all light lol
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#40 ed_turco

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Posted 02 June 2015 - 10:29 AM

Sure would like to see an image looking into the "dark bucket", though I am sure that may not be possible given it is just a "black hole" devoid of and sucking up all light lol

You've struck a point that was a problem for me in taking photos for my article.  I wanted to show my Dark Bucket with its cover off to show the felt ring I had to prevent light from seeping through when the cover was put back on.  The contrast was so low that as much as I tried, that annulus of 1/4" felt set inside the rim could not be shown in any image I took or how much I processed it.

 

I guess this means I did a good job, but I lost some verifiable bragging rights.  I think an image from the front of the tube down at the mirror cell, (I'm speaking of the mirror not being ready for mounting.) would have the same problem photographically.  In fact, without the mirror being there, under bright illumination, I've had some slight problems  (putting my face down the dewcap a bit) seeing the mirror cell at the bottom of the tube.  The remark I quoted in my article contains more than a little element of truth.

 

With this same problem, I couldn't show anyone the baffling I had in front of the mirror to deflect the flow of air from the fan in back of the mirror cell.  (For you ATM folks, that baffle was larger than the mirror's diameter, not smaller -- tee-hee !)  As for the hole I have in the mirror cell to let that fan work, I have this baffled too, so that light cannot been as I look down the tube, as I described earlier..

 

 

All in all, I guessed enough was enough when I designed my telescope this way.  It made things inside impossible to photograph,  but hooray for the images in the scope !!!!

 

 

 

ed


Edited by ed_turco, 02 June 2015 - 10:30 AM.

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#41 ed_turco

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Posted 04 June 2015 - 09:41 PM

HI Ed, Interesting reading. I am in the process of building a 8" F8 Newtonian scope as an astrograph. As you say the F8 is kinder for focussing tolerances and also reduces coma compared to the modern F5-F4 versions.  In my case I can't afford an 8" APO whereas a 8" mirror made by Garry Nankivell of New Zealand, Mt John Observatory fame which appeared for sale locally lets me build something quite different. A 2x Barlow as you say makes this F16.

I have hopefully reduced star spikes by suspending the secondary on a spider of steel.23 mm  top "E" guitar strings fittingly controlled by 8 Guitar machine heads.

The scope is a Serruier Truss style design, open, very light but very stiff. It will be on my EQ6 Pro SynScan in a tin shed Observatory in the back yard.

I'm not far from completion now, a few weeks maybe. But having survived a few criticisms about my decisions to build in this form it was nice to see a few of my thoughts on how I wanted it justified in your article.

Thanks and take care

Brent

I faced some of the same criticisms here  when I designed the features in my Definitive Newt.  The most frequent criticism was "Aren't you doing a lot of overkill for insignificant issues?"   It has been reassuring that you went through a similar experience.

 

Thank YOU!

 

 

ed


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#42 Jon Isaacs

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Posted 18 June 2015 - 03:08 AM

:goodjob:

 

Ed:

 

Well written.

 

Clean and concise, with many interesting and unforeseen details, right to the point.. 

 

In fact, I am describing your article but I bet it would also describe the views through your Definitive Newtonian Reflector.. 

 

:bow:

 

Jon


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#43 jrslivon

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Posted 14 November 2015 - 05:22 PM

Ed, 

 

Thank you for the very informative article.

 

I'd like a 6" aperture scope and your ideas are just what I needed to get me going. Thanks.

 

jrslivon



#44 Paul Rini

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Posted 12 January 2016 - 08:31 PM

Hi Ed; Beautiful written and full of great useful information. I knew even before reading some of your notes that the secondary had to be small. Personally I use small aperture items (except for the primary mirror) and some people don't' think the light gets through but then look at the sizes of the celestial objects. With a 40" focal length telescope then Jupiter's diameter is only 0.10" in diameter on the film plane or at the final image of the telescope before the eyepieces can magnify it. A barlow lens is always good for further reduction of secondary obstruction but there is some slight light lost but is it gained by an even smaller secondary since the barlow lens at 2X reduces the final image by 1/2. Also, the longer the focal length the blacker the sky background and better imagery. Keep up the excellent work and clear skies, Paul Rini


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#45 catboat

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Posted 12 March 2016 - 05:27 AM

Ed, the Turco Dark Bucket has been incorporated into a production scope!

 

See this link to Kasai Trading’s Nero 200N.   Molded tube with TDB.

 

They should have called it the Turco 200N.  

 

Way to go!   :waytogo:  :waytogo:

 

http://www.kasai-tra...p/nero200e.html


Edited by catboat, 12 March 2016 - 06:05 AM.

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#46 trueblueTEX

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Posted 21 April 2016 - 01:15 PM

Hi Ed, et al.

 

Please forgive my silly question, but what size is the secondary that was used in this telescope?  I could only ascertain that it is smaller than 1 inch.  

 

This leads to one other question regarding the Barlow Lens.  If the secondary is less than 1 inch, what size is the Barlow Lens? Is this a .956 inch Barlow?  Are the optics removed from the barrel and re-assembled in a smaller tube?

 

I have a couple of 6 inch Pyrex blanks (and can get a 6.7 inch BK-7 3/8 inch window) and this might be the best thing to do with them. :-)

 

Thanks!!!


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#47 radiomaan

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Posted 02 October 2016 - 06:13 PM

Hi Ed, et al.

 

Please forgive my silly question, but what size is the secondary that was used in this telescope?  I could only ascertain that it is smaller than 1 inch.  

 

This leads to one other question regarding the Barlow Lens.  If the secondary is less than 1 inch, what size is the Barlow Lens? Is this a .956 inch Barlow?  Are the optics removed from the barrel and re-assembled in a smaller tube?

 

I have a couple of 6 inch Pyrex blanks (and can get a 6.7 inch BK-7 3/8 inch window) and this might be the best thing to do with them. :-)

 

Thanks!!!

It's not a silly question at all. I was wondering the same thing.



#48 ed_turco

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Posted 12 January 2017 - 12:24 PM

It is coming up on two years from the time I published this article.  And since that time, not one apo owner, who thought I was so wrong on this topic took the time to write a similar article proving my stupidity on such matters.

 

My point is that anybody who pays $500 or more for a 2.4" apo really needs to believe that I am totally wrong about his telescope being so overpriced for a difference in performance that a huge percentages of folks cannot see.

 

I guess it is a sign of the times.

 

 

ed


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#49 pastorgalactico

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Posted 21 January 2017 - 05:02 PM

Hello;

I am in full construction of a newton of 16 "F4.5 and I am still doubting which secondary mirror to put it.
I know that the minimum size would be 73mm aprosimadamente, but I do not know what intermediate size to put it in order not to lose much light and that the contrast in planetary does not suffer for putting a secondary to him too great.
I'm thinking of putting an 80mm mirror on it.
You can help me in the best choice for me.
I like to observe planetary, but also I do not want to lose anything of deep sky.
I leave you a link where you can see my work so far;

 

http://www.astronomo...p?topic=18684.0

 

Regards;



#50 wcw

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Posted 21 January 2017 - 07:23 PM

pastorgalactico, as you say, selecting the size secondary is a matter of balancing trade-offs.

These web sites are useful for calculating size of secondary:

https://stellafane.o...b/newt-web.html

and

http://www.bbastrode...om/diagonal.htm

To use this one, do not enter anything for secondary size. Fill in all the other blanks and then click "Update chart".

 

Hope this helps.

-Bill




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