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MKV
Carpal Tunnel
*****

Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: Daniel Mounsey]
      #5583570 - 12/22/12 03:45 AM

Quote:

An optimized Newt with overwhelm any refractor. 12.5" to 14.5" is the sweet spot.



You make a good point. It's almost too obvious. I would say the same holds for the various unobstructed reflectors as well, unless they come in larger apertures than the usual 4.25 to 8 inches.

Kfrederick has a 17" unobstructed scope. It would be interesting to have it compared simultaneously with another 17 inch of good quality (simple - pick a star or a planet, point both scopes to the same target, two digital cameras of the same make, and two laptops next to each other, freeze the images, save them, stitch them together in Paint, and compare. I am sure there is some freebie grayscale analysis software around).

As for DSO, a 4.25" simply cannot resolve or even see the detail a 12.5" can, even with a 25% central obstruction. A distant star cluster may look like a fuzz ball in a 4.25' or a 6", but in a 12.5" it will be ablaze with fully resolved stars, and will show incomparably more of them!

Mladen


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MKV
Carpal Tunnel
*****

Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: tim53]
      #5583575 - 12/22/12 03:58 AM

Quote:

I think the biggest problem with fiberglass is its flexibility.

People like Jeff Beish and Don Parker have bee outspoken proponents of aluminum tubes, unpainted on the outside, and of course at least painted black on the inside (paint is an insulator).

I make my tubes out of wood because I like it.



Tim, paint is an insulator but it's thin, and thin insulation is not very effective. Paper is insulation, but you wouldn't paper your house with a couple of layers! If aluminum is the choice, then cork is probably the best material. I would imagine 1/4 inch thick or even 1/8 would go a long way. It's also important that your tube doesn't end a short distance from where your focuser is. Old fashioned Newotnians had at least the mirror diameter's worth of the tube extension past the eyepiece, so that the heat from your hands and breath doesn't get in the light path.

I really like Texereau's solution - four 2x2 and thin 1/4 inch plywood skin, reinforced where it ought to be with as many layers as needed. Square tubes have many advantages, when it comes to mounting the tube as well as accessories, for example. One thing they don't have is the snob-appeal.

It's everybody's world, to each his own.

Mladen


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kfrederick
Carpal Tunnel
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Reged: 02/01/08

Re: Optimized Newts vs APOs new [Re: MKV]
      #5583749 - 12/22/12 09:14 AM

Miaden One thought /would be to put a fake spider and secondary on the 17 WBChief to see the effect.I think it could be mounted on the primary .

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MKV
Carpal Tunnel
*****

Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: kfrederick]
      #5583966 - 12/22/12 11:51 AM

Quote:

Miaden One thought /would be to put a fake spider and secondary on the 17 WBChief to see the effect.I think it could be mounted on the primary .



The important thing is to observe both unobstructed and obstructed images simultaneously. If you look through one scope, then walk away to another and check, this is wrong on so many levels! When you're dealing with "hairline" difference, the samples have to be examined together at the same time.

Again, when there's doubt I defer to the professional community, and I don't see that community using unobstructed reflectors.

Mladen


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Norm Meyer
sage
*****

Reged: 02/08/09

Loc: Warren, ME 04864
Re: Optimized Newts vs APOs new [Re: Daniel Mounsey]
      #5584142 - 12/22/12 01:54 PM

I have both aluminum and paper (sonotube) I haven't noticed
that much difference. Here in Maine the atmosphere is the
biggest culprit. It is not usually steady enough to detect
any turbulence from the tube. I used my 10" Newt for quite awhile and was disappointed with it's performance until one
night I saw detail on Jupiter I had never seen before it was
amazing. My conclusion was it wasn't my optics it was the
atmospheric conditions. My first commercial scope was a
criterion RV6. I bought it in 1965 and I was expecting a white tube and was a little disappointed when I discovered
they had up graded to a grey phenolic with a krinkle finish.
I quickly got over the
disappointment. Then I lent the scope to a HS student and
his brother knocked the tube over and it broke a large piece
out of it. He tried replacing the tube with one like the
original but Criterion didn't make those anymore. Anyway
I ended up with one of the white ones after all. I always
have trouble deciding what kind of tube to make when building a new scope. Has anyone ever tried one of those bollard covers? they are plastic and come in 7" size which
is good for a 6"mirror. I think they are around $37.95
for a 60" one. No need to paint the outside as they already
have the color molded in.

Norm


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MKV
Carpal Tunnel
*****

Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: Norm Meyer]
      #5584205 - 12/22/12 02:36 PM

Quote:

I have both aluminum and paper (sonotube) I haven't noticed that much difference. Here in Maine the atmosphere is the biggest culprit.



That goes without saying. Texereau states the same thing. Large telescopes actually never experience a steady diffraction image unless they have adaptive optics. For smaller ones, that are closer to air-thermal cell size, the tube currents are much more prejudicial. No matter what size, it still makes sense to use material that is not a heat conductor.

Mladen


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paul01
newbie


Reged: 12/21/12

Re: Optimized Newts vs APOs new [Re: Pinbout]
      #5584691 - 12/22/12 08:56 PM

Hello there,
I am new to CN but have been scanning the site for some time and like the format so here I am. I have a question for anyone out there who knows the build design for an Orion 110ED premium refractor. I just got one and discovered the focuser assembly that connects at the main tube is spinning quite freely. Not the focuser itself but the whole assembly. Does this assembly twist on similar to the dew sheild cove on the objective lens? I don't want to do any damage trying to tighten unless this is what I should do. Thanks for any information I can get..
Paul


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kfrederick
Carpal Tunnel
*****

Reged: 02/01/08

Re: Optimized Newts vs APOs new [Re: paul01]
      #5585244 - 12/23/12 09:06 AM

Paul Welcome .You might wont to ask on the refractor forum. If you do not get a reply here

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Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
Re: Optimized Newts vs APOs new [Re: paul01]
      #5585270 - 12/23/12 09:30 AM

check this review Orion 110 ED

its a rotating focuser.

from the review

Quote:

The focuserís rotating feature works well. I have had two other scopes with inexpensive rotating focusers. On both of those the rotating hubs really needed to be locked down because they had play in them. This focuser fits the adapter very well and I can rotate it with the camera in place without worrying about keeping things squared. In fact recently I finished an imaging run and discovered Iíd forgotten to lock the focuser hub. When I checked the data there was no evidence in the images. I canít compare it to a Feathertouch but the focuser on the 110 ED has been a pleasant surprise




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ccaissie
professor emeritus


Reged: 09/13/10

Loc: Whitefield, Maine
Re: Optimized Newts vs APOs new [Re: Mark Harry]
      #5585611 - 12/23/12 01:19 PM

Quote:

I've used AL tubes for years, and -NEVER- had an issue with 6" aperture, period.
M.




If the tube fits too closely, it might cause problems. I use an 8" tube on my 6" reflector designs. Perfect.


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ccaissie
professor emeritus


Reged: 09/13/10

Loc: Whitefield, Maine
Re: Optimized Newts vs APOs new [Re: ccaissie]
      #5585624 - 12/23/12 01:29 PM

Just like with guitars...anyone serious about it will have several different types...Archtop, flat top, electric, classical, 12 string and a few other items like mandolins, fiddles and pennywhistles.

Parallel to Newts, Maks, refractors, binoculars, schmidt cameras, antique scopes and toilet-paper-tube/spectacle-lens refractors to amaze and educate the kids.

As the saying goes..It's all good.


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cheapersleeper
Post Laureate
*****

Reged: 01/22/10

Loc: Sachse TX
Re: Optimized Newts vs APOs new [Re: ccaissie]
      #5585751 - 12/23/12 02:48 PM

Quote:

Just like with guitars...anyone serious about it will have several different types...Archtop, flat top, electric, classical, 12 string and a few other items like mandolins, fiddles and pennywhistles.

Parallel to Newts, Maks, refractors, binoculars, schmidt cameras, antique scopes and toilet-paper-tube/spectacle-lens refractors to amaze and educate the kids.

As the saying goes..It's all good.




Nonsense. Four electrics, one steel string acoustic and there you go. People have preferences...

Regards,
Brad


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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: Optimized Newts vs APOs new [Re: cheapersleeper]
      #5586215 - 12/23/12 08:17 PM

A week ago I had been contemplating putting my 6" refractor up to your challenge then last night I took a minute looking at Jupiter through a very good 10"f/8 newt. sigh. I suppose there is room for all kinds of decent scopes in this world.

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MKV
Carpal Tunnel
*****

Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: Sean Cunneen]
      #5586375 - 12/23/12 10:23 PM

Quote:

A week ago I had been contemplating putting my 6" refractor up to your challenge then last night I took a minute looking at Jupiter through a very good 10"f/8 newt. sigh.



That's right. Here is a good article to read to understand why good bigger scopes outperform smaller "perfect" scopes every time.

Mladen


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Dave O
sage
*****

Reged: 12/21/11

Loc: Sri Lanka
Re: Optimized Newts vs APOs new [Re: MKV]
      #5586405 - 12/23/12 10:39 PM

I believe that the 'challenge' was for equal aperture? Not very fair tossing up a 6" APO against a 10" ...

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MKV
Carpal Tunnel
*****

Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: Dave O]
      #5586481 - 12/24/12 12:02 AM

Quote:

I believe that the 'challenge' was for equal aperture? Not very fair tossing up a 6" APO against a 10" ...



Even then, with equal apertures, at 20% obstruction or below, the difference is tenuous (look at Figure 2b), especially if an optical window is used to support the secondary.

Some people are purists and enjoy expensive, apochromatic unobstructed telescopes and they don't need any other reason for it. It's all good.

Neverthless, people should be informed what the science says.

Mladen


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cheapersleeper
Post Laureate
*****

Reged: 01/22/10

Loc: Sachse TX
Re: Optimized Newts vs APOs new [Re: Dave O]
      #5586573 - 12/24/12 01:27 AM

Quote:

I believe that the 'challenge' was for equal aperture? Not very fair tossing up a 6" APO against a 10" ...




It's not fair to the Newt given the cost of the APO...


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MKV
Carpal Tunnel
*****

Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: MKV]
      #5586578 - 12/24/12 01:41 AM Attachment (36 downloads)

Using Aberrator(R), I constructed this collection of Jupiter shots starting from 0% obstruction (APO) all the way to 45% (for Newotnians). I intentionally chose a picture that resembles the kind of image reaching the eye rather than the Photoshop(R) art that is commonly used. I think this is a much more realistic portrayal of what an observer can expect to see.

The only thing I did not include are the atmospheric effects at this magnification which would make these images all but stable.

Clearly, the images in the top row are sharper - relatively speaking. You can see minor details that progressively disappear as the central obstruction (CO) continues to increase. But you will also notice that these changes are rather subtle and can be observed if one looks at them simultaneously, and, of course, without any atmosphere involved, rather than running from one scope to another trying to remember the image form the previous one in all its detail.

Now here is the revelation: even with this setup, neatly lined up, you still have to have to look darn close to see the difference.

To make a point, I marked one of those tiny details you can see if you squint, along the equatorial belt, where the clouds make a small dip below the band. This detail is clearly visible in scopes from 0% to 15% obstruction.

It begins to fade progressively at 20% to 30% CO, and is practically invisible with obstructions from 35% to 45%.

Is this really something you'd notice going from one telescope to another, all things considered? Maybe, if you specifically looked for such tiny detail, but it would not be something that would hit you in the face, where you'd say "Wow!".

You be the judge - an APO costing thousands of dollars versus a good quality equivalent aperture and f/ratio Newtonian with an optical window for secondary support or a 3-vane spider, either one is okay, and the cost difference up to 100:1. The quality of image difference - not even close.

Regards,
Mladen

Edited by MKV (12/24/12 01:56 AM)


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MKV
Carpal Tunnel
*****

Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: cheapersleeper]
      #5586583 - 12/24/12 01:45 AM

Quote:

Quote:

I believe that the 'challenge' was for equal aperture? Not very fair tossing up a 6" APO against a 10" ...




It's not fair to the Newt given the cost of the APO...



Good point. For the price of an APO you can afford a Newotnina so big you can use that APO as its finder scope.

Mladen


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Dave O
sage
*****

Reged: 12/21/11

Loc: Sri Lanka
Re: Optimized Newts vs APOs [Re: MKV]
      #5586609 - 12/24/12 02:45 AM

Quote:

Quote:

Quote:

I believe that the 'challenge' was for equal aperture? Not very fair tossing up a 6" APO against a 10" ...




It's not fair to the Newt given the cost of the APO...



Good point. For the price of an APO you can afford a Newotnina so big you can use that APO as its finder scope.

Mladen




Again (for those who failed to read the opening post), the challenge was between equal apertures, not equal cost ...


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