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dpwoos
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Reged: 10/18/06

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Re: Optimized Newts vs APOs new [Re: Dave O]
      #5587081 - 12/24/12 11:45 AM

I agree. I am a very scientific/quantitative oriented person, some would say to a fault. However, I do think there is a lot of poorly understood stuff going on between the time the light enters the pupil and the mouth utters "wow", and so I take Aberrator images and other optical modeling results with a grain of salt - they are not modeling the entire system. I am a HUGE reflector fan, but I have to say that putting a high-end APO at one end has resulted in proportionally more "wow" utterances at the other than with reflectors. And, SCTs have rarely produced a "wow". Very unscientific, and totally anecdotal, and I am sure totally unconvincing to those with strongly held opinions, but I have enjoyed the "wow"s nevertheless and intend to continue doing so. BTW, all of my own "wow" producing scopes are homemade reflectors and little refractors.

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NHRob
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Re: Optimized Newts vs APOs new [Re: MKV]
      #5587156 - 12/24/12 12:31 PM

Questar obviously is a better master of optics than most.



It all depends on what your definition of "resolves" is.


Quote:

Quote:

[My 3 1/2" Questar provides better images visually than these digitized images do ... just saying.



Maybe your atmosphere is better then ours. It's irrelevant what image you use, the central obstruction effect would be the same had I used sharper images. You still have a gradual loss of detail and contrast. I just think using those stacked Photoshop images is not what one sees, and therefore cannot judge.

BTWm, Questar still makes fantastic claims that defy everything we know about optics. In this Questar brochure, which I remember back from the late 70's, the company claims a 3.5 inch clearly resolves license plate number (1/4 inch wide) at a distance of 3.5 km (2.2 miles) over water (!). That's a resolution of less than half an arc second, and theory (Dawes limit = 4.6/D in inches) says 3.5 inch aperture (assuming wavelength of 0.55 um) can resolve no more than 1.3 arc seconds under ideal conditions.

Mladen




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kfrederick
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Reged: 02/01/08

Re: Optimized Newts vs APOs new [Re: dpwoos]
      #5587158 - 12/24/12 12:33 PM

You would think glass improvements would have refractors better by now .

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mikey cee
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Re: Optimized Newts vs APOs new [Re: kfrederick]
      #5587273 - 12/24/12 01:46 PM

I don't get it. For some reason strange or otherwise I just don't feel the need to "qualify" my scope's performance against other types. I know what type of views I can expect nearly 100% of the time seeing permitting and that's more than OK by me! Knock yourselves out reinforcing each other. Mike

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Mark Harry
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Re: Optimized Newts vs APOs new [Re: MKV]
      #5587323 - 12/24/12 02:30 PM

That's about 3-6x more power with a 6" F/10 than is necessary for an average individual with 20/20 vision. I rest my case.
*****
There are quite a few accomplished and knowledgeable individuals who have persued unobstructed reflector telescopes for a good reason throughout the last century. And at least 2 Yahoo forums dedicated to them that I'm aware of at present. Must be a reason for all that kind of attention to the subject. There are, however some hurdles as to constructing and making them. They aren't as simple as a long Newt. But doable with someone who has made a good scope before.
Merry Xmas to all,
M.


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pstarr
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Reged: 09/17/04

Loc: NE Ohio
Re: Optimized Newts vs APOs new [Re: NHRob]
      #5587342 - 12/24/12 02:42 PM

Quote:

Questar obviously is a better master of optics than most.



It all depends on what your definition of "resolves" is.


Quote:

Quote:

[My 3 1/2" Questar provides better images visually than these digitized images do ... just saying.



Maybe your atmosphere is better then ours. It's irrelevant what image you use, the central obstruction effect would be the same had I used sharper images. You still have a gradual loss of detail and contrast. I just think using those stacked Photoshop images is not what one sees, and therefore cannot judge.

BTWm, Questar still makes fantastic claims that defy everything we know about optics. In this Questar brochure, which I remember back from the late 70's, the company claims a 3.5 inch clearly resolves license plate number (1/4 inch wide) at a distance of 3.5 km (2.2 miles) over water (!). That's a resolution of less than half an arc second, and theory (Dawes limit = 4.6/D in inches) says 3.5 inch aperture (assuming wavelength of 0.55 um) can resolve no more than 1.3 arc seconds under ideal conditions.

Mladen







Don't know what vintage the Questar was but at one point, Cave Optical was making mirrors for Questar. I wouldn't think they did any better on those mirrors than the ones they put in their own scopes. Some Cave mirrors were very good and others, not so much. Making a 3.5" optical surface to a decent standard shouldn't be that difficult.


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ed_turco
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Re: Optimized Newts vs APOs new [Re: pstarr]
      #5587389 - 12/24/12 03:18 PM

I reiterate. With equal apertures, one of my optimized Newts will equal the performance of an APO, period. Honest, neutral observers will not be able to tell the difference. This challenge was never was taken up. Despite all the hoopla over the advantages of an APO and all the optical theory going against my Newt, no APO owner was willing to stake his APO's reputation and price on the line. I had everything to lose here...

The reader can draw his own conclusions.


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StarStuff1
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Re: Optimized Newts vs APOs new [Re: ed_turco]
      #5587431 - 12/24/12 03:47 PM

IMHO the only difference between an optimized 6-in newt and a 6-in APO, both f/10,under ideal similar seeing conditions and no cool down issues would be costs of the scope, mounting (costs, again) and the abilty of the refractor to reach a lower power and thus wider fov.

Again, as the owner of 22 scopes, 18 of them of them being refracters.


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Gary Fuchs
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Reged: 05/22/06

Loc: Easton, PA, USA
Re: Optimized Newts vs APOs new [Re: Mark Harry]
      #5587442 - 12/24/12 03:59 PM

Mark Harry wrote:

Quote:

There are quite a few accomplished and knowledgeable individuals who have persued unobstructed reflector telescopes for a good reason throughout the last century. And at least 2 Yahoo forums dedicated to them that I'm aware of at present. Must be a reason for all that kind of attention to the subject. There are, however some hurdles as to constructing and making them. They aren't as simple as a long Newt. But doable with someone who has made a good scope before.
Merry Xmas to all,
M.




Yes.

I was recently asked why make say a 4 1/4" Schief when for probably less investment in time and materials you could have a 6" f10 or f12 Newt, or perhaps an 8".

Initially it was because I had a chance to view through a couple of really good ones and it was an impressive view; and I wanted to challenge myself and have a fine scope that wasn't just like most others.

But after using it for a few years I realized I really enjoy lunar and planetary observing and the Schief's approximately 1/2 degree field can just fit the lunar disk in, as well as a fair number of extended targets.

Being an f27 means I can get about 110X with an ordinary 26mm eyepiece and a really nice 240X with a 12mm ortho and still have plenty of eyerelief--which I need with glasses. On a rare good night I like to think I can push it even further but that's probably just my imagination that the image hasn't degraded.

That and the low viewing position suits me. A 6" f27 Newt would be over 13' long and I'd be on a ladder--which I don't like. Never mind the structure, and mounting.

Construction is more demanding; but certainly do-able by anyone that has made a Newt or is seriously considering one.

Maybe the biggest prior obstacle has been that there were few resources for guidance--which isn't the case now--and the somewhat widespread notion that collimation is very hard--in fact it's fast, simple, and quite a bit easier than for a Newt.

To each their own for whatever reasons.

Having said that, I'm all for knowing the facts about performance and the strong suits and shortcomings of each design.

The Herrig looks pretty neat. I don't have room on my plate now to try one and am a little scared of the alignment requirements...but maybe that wouldn't be an issue if someone made one and worked out any kinks? Since Kevin seems to have conquered that concern with his CHief I nominate him to try a Herrig...

Merry Christmas to all!

Gary


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tim53
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Reged: 12/17/04

Loc: Highland Park, CA
Re: Optimized Newts vs APOs new [Re: mikey cee]
      #5587461 - 12/24/12 04:13 PM

Quote:

I don't get it. For some reason strange or otherwise I just don't feel the need to "qualify" my scope's performance against other types. I know what type of views I can expect nearly 100% of the time seeing permitting and that's more than OK by me! Knock yourselves out reinforcing each other. Mike






Being a telescope addict with multiple optical configurations represented, it's in my own best interest to stay "astronomically PC", but when it comes to planetary definition, long focus Newts are gods!

Tim


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dpwoos
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Reged: 10/18/06

Loc: United States
Re: Optimized Newts vs APOs new [Re: ed_turco]
      #5587462 - 12/24/12 04:14 PM

Quote:

I reiterate. With equal apertures, one of my optimized Newts will equal the performance of an APO, period. Honest, neutral observers will not be able to tell the difference. This challenge was never was taken up. Despite all the hoopla over the advantages of an APO and all the optical theory going against my Newt, no APO owner was willing to stake his APO's reputation and price on the line. I had everything to lose here...

The reader can draw his own conclusions.




Are you willing to acknowledge that, in the real world, (almost) all newtonian reflectors suffer from one or more defects (e.g. collimation, thermal, stray light) that can easily explain why many folks have experienced APO superiority? Personally, I am certainly willing to accept that it is possible to build an optimized newt that exhibits none of these defects and so can go toe-to-toe with any APO (or any other design). However, I don't think that I have ever looked through such a newt, including my own. Could I build one? I think that I could. Why haven't I built one? My newts work really, really well and it isn't worth it to me and it isn't why I build newts and I don't think it would be much fun. If somebody else wants to do it or has done it then great - bring it to Stellafane and let's all enjoy it!

I feel really, really good about my newts and the other great newts in our club, and I really, really enjoy observing with excellent APOs (none mine), and I can hold those two positions simultaneously no problem.


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MKV
Carpal Tunnel
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Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: Mark Harry]
      #5587481 - 12/24/12 04:30 PM

Quote:

That's about 3-6x more power with a 6" F/10 than is necessary for an average individual with 20/20 vision. I rest my case.



Maybe you should just rest. FYI, I always used that power because I like it that way.

Mladen


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ed_turco
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Reged: 08/29/09

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Re: Optimized Newts vs APOs new [Re: dpwoos]
      #5588360 - 12/25/12 11:32 AM

Quote:

... If somebody else wants to do it or has done it then great - bring it to Stellafane and let's all enjoy it! ....

You've never looked through one of mine. As for me, as I mentioned before, I am now a shut-in with no capabilitities to make any more telescopes. But the challenge was good when I made it.

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474747
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Reged: 04/19/08

Loc: Florida, USA
Re: Optimized Newts vs APOs new [Re: ed_turco]
      #5588919 - 12/25/12 09:21 PM

Ed,
What's your take on the value of windows on newts? Some say they cause more trouble than they're worth.
Thanks
Brian


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Asbytec
Guy in a furry hat
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Reged: 08/08/07

Loc: La Union, PI
Re: Optimized Newts vs APOs new [Re: Pinbout]
      #5588983 - 12/25/12 10:19 PM

Quote:

So observe. it's not realistic to try for perfection in every aspect of doing anything.



It might not be realistic to achieve perfection, but to try for it is "fun" and worth while, IMO. Optimizing is enjoyable knowing we're getting the most form our instruments and ourselves. The resulting views are that much better making observing much more enjoyable.

Quote:

ATM's love to maximize performance in their telescopes as much as observe through them. To optimize is as much or more fun than to observe, though the quality of the observing comes out so much better.



I'd agree, especially for those of us bitten with the love for our hobby where we begin picking the fly s*** from the pepper. Learning about and how to do that adds dimension to our hobby: observing.

Quote:

One of my precision optical windows negates the need for any spider diffraction whatsoever.



That's an interesting challenge. The parabola can work wonders on the wavefront. Maybe, to be fair to the APO, you might consider using a spherical "window" and induce some spherical aberration? Maybe toss in an appropriate diffraction grating to generate the tiniest bit of chromatic aberration (optimized for green), too? That may be unnecessarily difficult an inexpensive. Forget it. I dunno, with a super small CO and a very good figure, not sure I would take that challenge, either, especially with a very experienced observer at the eyepiece.


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azure1961p
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Reged: 01/17/09

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Re: Optimized Newts vs APOs new [Re: ed_turco]
      #5589046 - 12/25/12 11:21 PM

Why a shut-in Ed?

Pete


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ed_turco
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Reged: 08/29/09

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Re: Optimized Newts vs APOs new [Re: azure1961p]
      #5589771 - 12/26/12 01:39 PM

First of all, about windows -- They are worth every penny in cost and every hour of time put into them. If you think a window is some random piece of glass thrown in front of Newt, you are in for a disappointment. A true window is optically ground and polished out of optical glass to a high level of perfection, such that it makes no difference when it is placed in front of a Newt, except for a slight shift in focus. And you can throw that d**ned spider away. Why add spider diffraction to a potential perfect image and mess it up with lines of scattered light ?

On the shut-in thing. My Rheumatoid Arthritis got really bad really quick, and a lot of the time I am bedridden.


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MKV
Carpal Tunnel
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Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: 474747]
      #5590799 - 12/27/12 07:58 AM

First let me say that it is indeed surprising that ever since the "APO fever" bit the ATM community, some 30 years ago, no one has actually done what Ed Turco suggested: compare an APO and a Newtonian with an optical window of the same size and focal ration.

Second it is indeed surprising that no one tried to capitalize on the opportunity to offer such Newtonians commercially as cheaper alternatives to the APOs (perhaps because with APOs the profit margin is a lot higher!).

Optical windows are a lot more work than many realize, which is probably why people like to talk about them but not make them. A 3-vane spider causes minimal diffraction and is a lot cheaper and easier to obtain than an optical window, so naturally people go for what's easier and cheaper.

Making a quality optical window is certainly a major project but not for the industry. From an industrial point of view they are easier than mass-producing Schmidt correctors.

Assuming you decide to make one, say a 6-inches clear aperture, let's not forget that even a perfect 6-inch telescope is just a 6-inch telescope. It may outperform mediocre ones of slightly bigger aperture, but it will not outperform even a mediocre 10-inch. If you don't believe it, look at some globular cluster in a 6-inch and then in an 8 or a 10-inch. Try splitting a 0.5 arc-second double star with a 6-inch. And as for APOs, for the price of an 6-inch APO you can buy a reflector just about big enough to sit in it!

Mladen


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Darren Drake
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Re: Optimized Newts vs APOs new [Re: Dave O]
      #5590905 - 12/27/12 09:57 AM

Quote:

Quote:

Quote:

[My 3 1/2" Questar provides better images visually than these digitized images do ... just saying.



Maybe your atmosphere is better then ours. It's irrelevant what image you use, the central obstruction effect would be the same had I used sharper images. You still have a gradual loss of detail and contrast. I just think using those stacked Photoshop images is not what one sees, and therefore cannot judge.

BTWm, Questar still makes fantastic claims that defy everything we know about optics. In this Questar brochure, which I remember back from the late 70's, the company claims a 3.5 inch clearly resolves license plate number (1/4 inch wide) at a distance of 3.5 km (2.2 miles) over water (!). That's a resolution of less than half an arc second, and theory (Dawes limit = 4.6/D in inches) says 3.5 inch aperture (assuming wavelength of 0.55 um) can resolve no more than 1.3 arc seconds under ideal conditions.

Mladen




Have never looked at license plates. But, I know what I see at the eyepiece, when looking at Jupiter.




According to my calculations this is reasonable. It's possible a Q could resolve a license plate as far away as 2.75 miles. I based this on an article I wrote here on CN a while back.
http://www.cloudynights.com/item.php?item_id=1354


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magic612
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Reged: 09/30/08

Loc: S. of Chicago's light dome
Re: Optimized Newts vs APOs new [Re: MKV]
      #5590935 - 12/27/12 10:25 AM

Mladen, where I live, my 6" f/5 and f/10.9 reflectors generally will outperform my 10" Dob because the atmosphere overhead introduces enough turbulence that the 10" fares worse most nights. That's not to say it can't; I've had the 10" up to 480x on exceedingly stable nights, in which yes, my average 10" will outperform the optimized 6". It's that old saying in any telescope discussion:

"All things being equal."

As we know, they rarely are equal. An APO has no central obstruction. Then we get into optical windows, and CO, and how big is that CO, and what is thermal cool-down time, and... well, every other argument already discussed in this thread and many others.

I am building an optimized 6" reflector because of several reasons:

1) I can afford it.
2) I can do it with the tools I have.
3) I have room to store it.
4) I don't mind moving it in and out of my garage (weight / bulk).
5) That 1" thick, 6" mirror will cool WAY faster than the 2.5" thick, 10" mirror.

It's that simple. I'd love to have a larger, optimized 8" or 10" or 12" Newt. But I have a daughter going into college next year. I can afford to make the 6" OTA and mount. And neither will be so heavy or bulky that I will be hesitant to bring it out and set it up. Yes, larger aperture will let me see more. But it will cool quickly, offer excellent magnification with long focal length eyepieces which means others who view through it with glasses will have little difficulty seeing an image, and as I have discovered at star parties and outreach events, sometimes "size matters."

And there's the "wow" factor.

Sometimes simply the length of a telescope makes people think the image they are seeing is more impressive than it is, even if we more experienced observers know it is not. And when we talk cost with the person and they realize it is in the realm of affordability (or something they can make themselves), they just might get interested in the hobby too. And the way I see it, the more people we have looking up, the more likely we are to get people pointing their lights down.

To me, that's a win, no matter the aperture.


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