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StarStuff1
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Re: Optimized Newts vs APOs new [Re: Meep_Esq]
      #5579796 - 12/19/12 10:50 PM

A long f/r newt such as in my avatar can give a similar sized apo a good run for it's performance.

BUT, as Richard Berry said, inch per inch nothing beats an apo. OK, beat me up. (Saying this as an owner of 18 refractors and 4 newts)


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mikey cee
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Re: Optimized Newts vs APOs new [Re: Pinbout]
      #5579846 - 12/19/12 11:45 PM

Too bad we can't get a likewise consensus on expensive big bucks eyepieces vs plain label orthos and plossls! Mike

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MKV
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Re: Optimized Newts vs APOs new [Re: ed_turco]
      #5579932 - 12/20/12 12:52 AM Attachment (49 downloads)

Quote:

Pictures were shown of unobstructed images of a 6" f/10 APO and a 6" f/10 Newt with 16% obstruction. The difference was barely perceptible. In fact, Suiter and I agree that there is no difference at the eyepiece...Tell me the aperture of your APO and give me time to make an optimized Newt of the same size, with a precision optical window and a 12% obstruction. Special coatings all around.



That was a fair challenge and, clearly some 30 years overdue!

The picture below shows (in reverse color) PSFs for a 6-inch f/10 configuration with various amounts of central obstruction. The negative image helps visualize the amount of energy in the Airy disc better than against black background. Clearly, some difference exists between these shades of gray, but under real nighttime observing conditions, even under superior seeing, it would be more an act of willful imagination than actual perception to say that this difference would be noticed - even if the images could be observed simultaneously and right next to each other, and a very dark sky.

So, the experiment could never be fully objective, or effective, simply because no one can see these images at once, so close and perfectly still. Maybe one could take photographs of a star (say a Polaris) under high eyepiece projection, using the same eyepiece and exposure time, etc. and then compare the images side by side.

There is no doubt that a well made f/10 Newtonian, as Ed describes, with 12% CO will perform better than an APO simply because it has zero color! At some point a very bright image will reveal chromatic residual even in the best of APOs.

The real difference liles in the fatc that Ed's optic can probably be made with materials costing about $250. A 6-inch f/10 2-element APO objective today sells for more then 10 times that price.

Mladen


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tim53
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Re: Optimized Newts vs APOs new [Re: magic612]
      #5579947 - 12/20/12 01:06 AM

Quote:

Quote:

Long focus newtonians should be renamed "hyperapochromats".

Rant off.

-Tim.




I think I'll name my 6" f/10.9 reflector that, Tim!!




Yep! I call my 6" f/10.3 that!


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MKV
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Re: Optimized Newts vs APOs new [Re: MKV]
      #5580011 - 12/20/12 03:13 AM Attachment (40 downloads)

In 1981, Roland Chirsten came out with his "oiled" triplet apochromat which was a major sensation at Stellafane. This started the "APO fever".

The beauty of the Christen design was that the lens was not only apochromatic (i.e. corrected for four colors simutaneously), but the OG was also perfectly symmetrical. The two outer radii of curvature were equal but opposite, as were the two inner ones. This means they could be matched perfectly by Newotn's interference method, a very elegant solution indeed from the shop production point of view.

In April of 1982, Paul Weissman, an optical engineer at Ferrand Optical in Valhalla, NY, wrote to Sky & Telescope objecting to Christen's original design as under-corrected for color and offered his "correction" as an alternative.

Christen replied shortly thereafter, saying that he "inadvertently" used an old set of figures for the 1981 configuration and then submitted a new set which was better than the original as well as Weissman's but the OG lost its symmetrical elegance Christen made a big deal of in 1981, plus it now introduced a field-limiting coma.

Clearly, a 6-inch well made Newtonian - like the one Ed offered to build for his proposal, i.e. with a 12% central obstruction, and of equivalent focal length - would have easily beaten all three versions of the Christen's f/10.8 triplet.

I wrote a letter to Sky and Telescope, calling attention to this, but it was never published. Christen's APO soon began selling for $2200 or thereabouts, yet it's performance was inferior to that of an equivalent quality, diameter and focal ratio equivalent Newtonian that in 1982 could be built for around $100.

Mladen


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MKV
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Re: Optimized Newts vs APOs new [Re: MKV]
      #5580012 - 12/20/12 03:15 AM Attachment (36 downloads)

And these are gray-scale integrated PSF image simulations at 0.336 deg. off-axis, and normalized at 0.15.

Mladen


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Mirzam
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Re: Optimized Newts vs APOs new [Re: MKV]
      #5580090 - 12/20/12 05:19 AM

I have the optics ready for a 10" f/6.5 newt that will be designed for binoviewing and seated observing. It will be mounted on a driven dobsonian style structure.

So much for the supposed ergonomic advantages of an APO.

JimC


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Jon Isaacs
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Re: Optimized Newts vs APOs new [Re: Datapanic]
      #5580107 - 12/20/12 05:56 AM

Quote:

I found it! It's actually about an APO vs. Questar Funny and probably fitting for what this thread will turn out to.




It was cute... It is true that often discussions like this boil down to "my telescope is better than your telescope" rather than an objective discussion of the merits of each. There's a lot of emotional baggage...

Me, I got it too but at least I choose my apo refractor for bird watching and use a good sized Newtonian when I want the best views of the planets.

Jon


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Daniel Mounsey
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Re: Optimized Newts vs APOs new [Re: Datapanic]
      #5580244 - 12/20/12 08:53 AM

Quote:

I found it! It's actually about an APO vs. Questar Funny and probably fitting for what this thread will turn out to.




It's 5:30 in the morning and my wife wants to know why I'm laughing so hard. I have to admit, that was pretty funny. We all do get a bit obsessed sometimes.


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Jeff Morgan
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Re: Optimized Newts vs APOs new [Re: ed_turco]
      #5580303 - 12/20/12 09:44 AM

Quote:

Comments and pictures were shown on a thread concerning Herrig designs and I popped in and went off on a tangent.

Pictures were shown of unobstructed images of a 6" f/10 APO and a 6" f/10 Newt with 16% obstruction. The difference was barely perceptible. In fact, Suiter and I agree that there is no difference at the eyepiece; anyone who says differently is thinking more of what he paid for his telescope than what he is seeing through his telescope in comparison.

Tell you a story: I went on the Refractor Forum (EGads!) and made this offer. Tell me the aperture of your APO and give me time to make an optimized Newt of the same size, with a precision optical window and a 12% obstruction. Special coatings all around. Then, some neutral people would have to be picked to make an assessment as to what was what.

The issue was to be imagery only; not the appearance of either telescope. Perhaps the Stellafane optical judges would be a good choice.

In any case, no matter, win lose or draw, my telescope would be donated to charity.

You know what? No one took the challenge against my 1/20 wave optics. Not one. Not one dared.

I waited 6 months; the offer is withdrawn; why should I put up with all this "mighty APO" BS?




Great post Ed, unfortunately I caught it only about 5 minutes before I have to dash out the door this morning ... but I'll catch up to all the great responses later.

Unfortunately, you won't find too many Mercedes Benz-driving, bottled water-drinking, Nieman Marcus-shopping, Gucci-wearing, APO owning people on the ATM Forum

But seriously, the best advantages of the APO aren't necessarily optical, but mechanical. That being the objective is farther away from the ground where one normally finds a rather sharp temperature gradient and it's detrimental effect on seeing. Sadly, by nature the primary mirror sits right in that gradient.

I'd love to see you go ahead and build that closed-tube Newt and set-up next to the Astro-Physics tent at AstroFest or Stellafane. Perhaps you could invite some of the writers at Sky & Tel to stop by. Now that would create quite a stir!


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Jon Isaacs
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Re: Optimized Newts vs APOs new [Re: Jeff Morgan]
      #5580330 - 12/20/12 10:00 AM

Quote:


I'd love to see you go ahead and build that closed-tube Newt and set-up next to the Astro-Physics tent at AstroFest or Stellafane. Perhaps you could invite some of the writers at Sky & Tel to stop by. Now that would create quite a stir!




Or you could just read Roland's advice concerning the "Best Planetary Telescope" and build an 8 inch F/8 and be done with it...

What is the Best Planetary Telescope

But the most important question is.... "Is my telescope better than your telescope." Until we answer that, no progress is possible. In general, I think it is reasonable to say that the best planetary telescope is the one that lives where the seeing is the best.

Jon


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ed_turco
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Re: Optimized Newts vs APOs new [Re: Jon Isaacs]
      #5580423 - 12/20/12 10:51 AM Attachment (38 downloads)

I am now too crippled with rheumatoid arthritis to make another telescope or go to Stellafane. *BLEEP*! That is why Al Hall made his noble effort at the Friday Night Talks to present my Comascope. I don't think he showed it on its "ball mount".

Edited by ed_turco (12/20/12 10:53 AM)


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Jon Isaacs
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Re: Optimized Newts vs APOs new [Re: ed_turco]
      #5580466 - 12/20/12 11:18 AM

Quote:

I am now too crippled with rheumatoid arthritis to make another telescope or go to Stellafane.




Ed:

I am sorry to hear that. Your proposed design sounds like a winner and I am sure it would provide some wonderous planetary views. One of the reasons I have never been interested in a refractor much bigger than 4 inches is that I have a pretty nice RV-6 from the early 70's.

Jon


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magic612
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Re: Optimized Newts vs APOs new [Re: Jeff Morgan]
      #5580500 - 12/20/12 11:34 AM

Quote:

But seriously, the best advantages of the APO aren't necessarily optical, but mechanical. That being the objective is farther away from the ground where one normally finds a rather sharp temperature gradient and it's detrimental effect on seeing. Sadly, by nature the primary mirror sits right in that gradient.




This very issue is one I may address with my 6" f/10.9 Newt by considering a fan pulling air through the tube from the sky, downward at the mirror - so the air would be coming from about the same height that an APO lens would be sitting. Presently, even with the concrete-pier prototype tube it's in at the moment (unflocked, waxed/cardboard interior) with a 17% obstruction and self-built curved vane spider, the images at the eyepiece have so far been quite impressive, and to me, reminded me of view through a quality refractor, because the curved spider produced no straight diffraction spikes. Eventually this will go in a Hastings aluminum tube, with various added things to minimize thermal issues and stabilize the image (the aforementioned fan, etc.).

So far it's run me about $200 or $250 in parts and accessories. I expect to spend another $200 to $400 on it by the time it's done. I certainly can't argue the finer points of optical theory, so I won't try. But I think I'll be pretty darn close to the visual results of similarly sized apo for... what does a 6" APO run these days anyway? (I seriously don't even know.) And besides, I have a daughter going into college next year. So this is the only "apo" in my budget for a long, long time (the next daughter will follow her four years later).

And by the way, this is not an "apo bashing" post. I'm just of the opinion that a quality reflector can be optimized to produce nearly as good views as one for a lot less money. But if others prefer the apo for aesthetic or other mechanical / design reasons, there's nothing wrong with that either. The more the merrier.


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tim53
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Re: Optimized Newts vs APOs new [Re: magic612]
      #5580619 - 12/20/12 12:48 PM

A long focus 6" Newtonian with rotating rings is still small enough to be quite comfortable to use, and a lot easier to move around and set up than a 6" refractor.

Here's my hyperapochromat 6" f/10.3 "Kludge Classic" on a Tak EM-10 mount:



OTA detail. This doesn't even have a small secondary (yet). I think it's a 1 1/4". I have a 3/4", but it's in a 3" f/6 now. I should probably order a couple of 1" diagonals - one for the Kludge and one for my 8" f/9 (under construction).


And here's Mars with it:



-Tim.


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*skyguy*
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Re: Optimized Newts vs APOs new [Re: ed_turco]
      #5580659 - 12/20/12 01:08 PM Attachment (27 downloads)

Can an optimized Newtonian reflector compete successfully with an APO refractor of similar size? Absolutely ... YES!

I own an optimized reflector ... 6" f/10 (1/8th wave) primary mirror from Edmond Optics, 25mm. secondary mirror (1/20th wave - 16% obstruction), curved vane spider and low profile focuser. It shows very "clean" images with amazing contrast. Not only are planetary views spectacular, but deep-sky objects also benefit greatly from the high contrast. Unfortunately, this scope makes the views from my Criterion RV-6 6" reflector look rather shabby in comparision.


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bremms
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Re: Optimized Newts vs APOs new [Re: *skyguy*]
      #5580685 - 12/20/12 01:21 PM

Cost for cost.. NO CONTEST. 12.5" F8 newt vs a good 6" APO.
My 6" F8 newt is still my best planetary scope My C11 has more resolution but less conrast. 4" F15 Jaegers looks promising at 4" but still has some color. My old 10" F6 was better than a 6" AP nearby on Jupiter. At less than 1/5 the cost. From a cost standpoint not by a long shot. But I'd love a 6" + APO
Really you could build a killer 14-16" newt for the cost of a 6"AP.


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magic612
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Re: Optimized Newts vs APOs new [Re: *skyguy*]
      #5580686 - 12/20/12 01:22 PM

I'd just like to say it is great seeing all these long focal length 6" Newts!

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Pinbout
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Re: Optimized Newts vs APOs new [Re: mikey cee]
      #5580830 - 12/20/12 02:46 PM

Quote:

Too bad we can't get a likewise consensus on expensive big bucks eyepieces vs plain label orthos and plossls! Mike




I used my es14mm 82* against my tv15mm plossl on m15 with my 8inf6. no contest, night and day, I no longer have the es14mm.


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bremms
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Re: Optimized Newts vs APOs new [Re: Pinbout]
      #5580887 - 12/20/12 03:14 PM



Eyepieces!!! Me I like good simple EP's. TV plossls, UO orthos, Brandons, I have a no name 12.5mm vintage Ortho that is killer. Don't know why it's so good but it works great in all my scopes(I have no scopes under F6)


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