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Abhat
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Mark MacKenzie]
      #6487494 - 04/25/14 10:26 AM

The stop down does wonders on very bright objects. I used my ST-80 stopped down exclusively on Venus, Moon and Sun (with filter of course). Especially on moon stopped down St-80 not only sharpens the view but also eliminates need for moon filter and you can view the moon in natural white color. Th excessive boil and shake on Venus calms with the stop down and you can actually analyze the phase and % illumination nicely.

However on Jupiter and Saturn and other less bright objects I lose lot of detail when stopped down and I am better off with full 80mm even with the fringing.

Edited by Abhat (04/25/14 10:31 AM)


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GOLGO13
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Mark Costello]
      #6487511 - 04/25/14 10:36 AM

We certainly should not give the impression that achromats are bad. I had a C102 HD (4 inch F9.8 achromat) and it was an excellent scope and very reasonably priced. Chromatic abberation was a bit annoying and I used a minus violet filter here and there. But it provided great planetary images as well as good images on DSOs.

Nothing wrong with achromats for sure. Especially if cost is of concern. While many folks recommend reflectors because of the bang for the buck. I think a lot of people would also benefit from a 4-5 inch achromat as a first scope. There are benefits to them over reflectors (cool down, collimation usually not needed, etc). This is certainly not a one size fits all hobby.


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David PavlichAdministrator
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Mark Costello]
      #6487536 - 04/25/14 10:51 AM

Mark pretty much covers it. One of the best deals in our hobby is the venerable Celestron C6R. Terrific on the big open clusters and enough aperture to go smudge hunting. Yea, it has false color, but at f8, it's not as bad as the faster AR6 class, especially at the CR6 price point. There's a used one in our Classifieds for $350!

You have to keep in mind what you have and know its quirks. And it's always impressive at an outreach to have a C6R on an Atlas with that 8" extension.

David


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Tony Flanders
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Abhat]
      #6487549 - 04/25/14 11:00 AM

Quote:

The stop down does wonders on very bright objects. I used my ST-80 stopped down exclusively on Venus, Moon and Sun (with filter of course). Especially on moon stopped down St-80 not only sharpens the view but also eliminates need for moon filter and you can view the moon in natural white color.




Those are special cases, for the following reasons:

The Sun can rarely be viewed at high magnification because sunlit ground causes atmospheric instability. So there's relatively little to be lost by throwing away aperture.

There's such a vast amount of detail to be seen on the Moon that even if you do throw away aperture, it still leaves a huge amount of detail remaining. However, if seeing maximum detail on the Moon is your goal, you would do far better to use higher magnifications than to reduce the aperture. This would also eliminate any conceivable need for a Moon filter.

As for Venus, there's essentially zero detail to be seen except for its size and phase. (Unless you are very patient and skilled, observe it daylight, and have ultraviolet-sensitive eyes.) So again, throwing away aperture has little or no cost. Moreover, Venus is the single object in the sky where false color is most obtrusive.


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GOLGO13
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: David Pavlich]
      #6487550 - 04/25/14 11:01 AM

I saw that classified David and would love to get it. But my wife would absolutely kill me if I got that puppy! I've looked through one and it was excellent.

Here is a picture of my old C102:



Here is a picture of a C6R mounted on a 30 inch dob



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Jon Isaacs
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Vondragonnoggin]
      #6487565 - 04/25/14 11:10 AM

Quote:

I don't know why these conversations don't go hand in hand, but there is always someone asking about which filters to buy for astronomy use and usual answers consist of UHC, OIII, H-Beta, or the like and everyone gets happy about the thought of getting a little MORE detail out of nebula viewing.

Mention achromat and filtering it out like with Longpass, or semi-apo, or minus V and suddenly people are worried and discussing how much LESS detail is seen.

People are okey dokey with one application and always whining about the other and it makes little sense to me.




It is unfortunate that it does not make sense to you but there are good reasons for these differences. The fundamental difference here is that nebula filters are chosen for enhancing the contrast of a specific object whereas the minus violet filters and such are chosen to limit the chromatic aberration of the telescope. These are two different issues.

-Narrowband filters are very effective for increasing the contrast of a small class of objects which emit light in a very narrow band of the spectrum. The light that comes from many nebulae is the result of the atomic level activity that is most prevalent in the nebulae. The O-III filter is designed to pass the light the results from Doubly Ionized Oxygen.

If an object primarily emits light in the O-III band, then by only allowing the light in that band to pass and blocking all other wave lengths, then the contrast, the difference between the object and the background sky is greatly enhanced. This is not a small difference, it is sufficient to allow me to see considerable detail on the Veil Nebula from my San Diego backyard... A notch filter like this might have a band pass of 10-20 nanometers, with the visual spectrum being about 200 nanometers in width, by blocking the background sky, this can result in an increase in contrast by a factor of 10 or 20..

This is really no different than using your cell phone, listening to your radio, or watching broadcast TV. Each of those depends on very sophisticated narrow band filters to detect a very faint signal from the broad electromagnetic spectrum..

- Filtering the light from an achromat is quite a different problem. You are not trying to match the filter to an object, you are not trying to listen to a specific radio station. Rather, you are trying to make up for the aberrations, the noise added by the telescope optics themselves. Since much of the spectrum is defocused to some extent, trying to filter the worst part of the spectrum can be somewhat helpful but the issues still remain.

One might think a fast focal ratio achromat as a radio that greatly distorts both the bass and the treble but does a half decent job in the mid ranges even though it is not perfect. One can remove the bass and treble but the music, it just not sound the same, information is lost. You can recognize the music, you can enjoy the music, but it definitely not the same as listening to the full spectrum.

I hope this helps explain the differences, in one case a specific filter is being used that matches the emissions of a particular object and in the second case, rather broad band filters are being used to try to make up for significant aberrations in the optics. Very different.


Jon Isaacs


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Vondragonnoggin
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6487586 - 04/25/14 11:21 AM

To both Jon and Tony:

Filtering is the purposeful elimination or reduction in spectrum to bring out detail. Whether filtering to fine tune a frequency or eliminate unfocused light, the intended purpose is to lose information to see more detail.

Tony - you said what I said. I mentioned planetary filtering for detail even in reflectors. Check. I mentioned aperture and reflector cost. Check.

Again - filtering is the purposeful elimination or reduction in certain spectrum to enhance detail. Whether by eliminating bad information from aberrations or by fine tuning a frequency to bring more information that is swamped usually by your needless information (such as narrowband to eliminate unwanted spectrum) it is the same effect on different scales.

But whatever. Of course you two are always correct whether paraphrasing or concentrating on snippets of entire posts.

Same as it ever was here. This is why I stay out of beginners section usually.

Edited by Vondragonnoggin (04/25/14 11:22 AM)


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Jon Isaacs
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Mark Costello]
      #6487613 - 04/25/14 11:32 AM

Quote:


But it was the first object that gets closer to the discussion into the forum. The first object was Jupiter. I guess the "achro-is-dead-don't-waste-your-money-on-one-because-it's-good-only-for-stuff-like-M44" bunch would say that was a waste, but what the hey, the ES AR127 is my only scope. And it didn't look like a waste to me.






Mark:

Your points are good ones and are similar to my experiences with similar achromats. Fighting chromatic aberration with filters does little good, the views maybe more aesthetically pleasing but I seem to find that little if any is gained in what I see when viewing the planets and it's better to just accept the chromatic aberration as part of life and make the best of it.

Your post also points to the importance of the observer's skill. Over the years, I have come to realize that the most important factor is the observer and not the equipment. You make some remarkable observations with your equipment and such abilities can only come from spending time at the eyepiece and learning how to see everything there is to see.

You also point to the economics of the equation.. mirrors versus lenses. APO refractors are very expensive and of limited aperture. I am glad that I am able to afford some very fine equipment but it wasn't always that way... And even today.. or more appropriately, last night.. it looked promising for the seeing and with both Jupiter and Mars both well positioned, a good night for observing the planets.

After work I had enjoyed watching my granddaughter's Karate lessons and there wasn't time to setup and cooldown my number 1 Planetary scope so I had to choose between my 4 inch apo and my 10 inch Dob. The apo was purchased used for $2000, the 10 inch Dob was purchased used for $240..

It was a no brainer, I wanted the good planetary views, I went with the Dob..

Jon


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coopman
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6487669 - 04/25/14 12:02 PM

If you can afford to get an ED or triplet refractor, do it. The cost of buying it only hurts once, and you will benefit from the enjoyment every time you use it.

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GOLGO13
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6487681 - 04/25/14 12:11 PM

As Jon points out the used market can really help. Sometimes the costs can be half of a new scope (as in Jon's case). But even used many Apochromats are pretty expensive reletive to other designs.

It think Apos are a good choice for grab and go scopes from 60mm-100mm around F6-F8. Worth having one to compliment a larger scope.


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jgraham
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: David Pavlich]
      #6487722 - 04/25/14 12:29 PM

"...but at f8, it's not as bad as the faster AR6 class..."

Hmmm, the AR6 is also f/8. The ES6s are f/6.5s. I took a hard look at the ES152 before settling on a used AR6. I was concerned about the color in a faster achromat. It turned out okay for me.


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Cames
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6487803 - 04/25/14 01:01 PM

Quote:

I've read that acromats are prone to this violet color effect, something that apochromats apparently fix. What's the actual non-BS take on this? If one wants to avoid the violet blues, do they have to step up to a more expensive triplet? Or is it possible to get no-color views through the "right" achromat in the "right" configuration?




If you are up to reading one more article may I suggest one that puts some numbers to an answer to your question: Seeing spots: A Picturesque and Unmathematical Analysis of Achromatic Objecti...
In the article, respected optician and optical designer, Robert Royce, addresses both the degree of secondary spectrum in achromats and ways to minimize it. Also, he touches on the variability in the individual ability to perceive those extraneous colors. His discussion is also useful to help you understand spot diagrams as they relate to the analysis of secondary spectrum.

Perhaps use it as a counterpoint to see if what you are hearing and reading is based on fact or hyperbole.
-------
C


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Jon Isaacs
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Vondragonnoggin]
      #6487874 - 04/25/14 01:31 PM

Quote:

Again - filtering is the purposeful elimination or reduction in certain spectrum to enhance detail. Whether by eliminating bad information from aberrations or by fine tuning a frequency to bring more information that is swamped usually by your needless information (such as narrowband to eliminate unwanted spectrum) it is the same effect on different scales.




Well...

I am well aware of the purpose of filters. This is what your wrote:

Quote:

I don't know why these conversations don't go hand in hand, but there is always someone asking about which filters to buy for astronomy use and usual answers consist of UHC, OIII, H-Beta, or the like and everyone gets happy about the thought of getting a little MORE detail out of nebula viewing.

Mention achromat and filtering it out like with Longpass, or semi-apo, or minus V and suddenly people are worried and discussing how much LESS detail is seen.

People are okey dokey with one application and always whining about the other and it makes little sense to me.




You asked the question "why the conversation about filtering achromats and filtering deep sky objects do not go hand in hand."

I spent a considerable amount of time answering your question and explaining why they do not go hand in hand. Both involve the use of filters but the purpose is quite different.

One enhances object itself by only passing the very narrow band that the object itself emits whereas the other attempts to make up for optical deficiencies by discarding otherwise desirable information. I thought the radio analogy was particularly appropriate, with one, you are picking out a faint signal from the broad spectrum, the other, you are attempting to make up for deficiencies in the equipment.. a bad amplifier or fuzzed speaker.

I will also add that your implication that one only sees "a little MORE detail out of nebula viewing" is misleading and incorrect. The reality is that narrow band nebula filters greatly increase the contrast of many nebulae and in many cases allow them to be seen in detail when they would otherwise be invisible. Deep sky filters make huge differences for those objects which they enhance.

On the other hand, it is questionable whether the long pass, Semi-APO and minus violet filters actually enhance the detail seen. In my experience, the difference is primarily aesthetic and does not result in me seeing more details. As Mark does, I look past the purple haze, it is the remaining lack of sharp focus that seems to most affect the what I see.

If one wants to view the planets with an achromat, longer focal lengths, slower focal ratios are better. My goal here is to help folks just starting out understand their choices and what differences those choices make at the eyepiece and in the field. I do not generally recommend someone first starting out invest in an expensive apochromat. But at the same, since the original question was asked, sharing my experiences and understandings of the differences, there is a place for that.

I find the side by side comparison between my 4 inch F/5.4 apochromat and my 100mm F/6 Achromat quite enlightening. As much as I enjoy the achromat, as much as I love the thing, as much as I try different filters, different aperture masks and such, the difference between the two when viewing the planets is still very noticeable, nothing I have found does much in the way of closing the gap. Masking the 100mm achromat to an 80mm F/7.5 and then comparing it to my 80mm F/7 apochromat bears similar results..

Jon Isaacs


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Ed Holland
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6488001 - 04/25/14 02:23 PM

I have a Celestron C102, a Meade AR5, C8 and Orion Mak 127. No APO refractors for me, I cannot justify the cost, and prefer longer focal lengths. I would not give up the variety of my instruments, it's something that makes observing enjoyable. The Mak and C8 give me colour free views, and lots of detail, especially the C8.

However, if I want a quick setup, rapid thermal settling and pleasing views without concerns for collimation etc., the AR5 or 102 are in the front line. Yes there are purple fringes, possibly also some spherical aberration (both of which change with temperature). But to me, these are good scopes that get used. I find it hard to get annoyed, concerned or disappointed about an instrument that is still providing detail and interest at the EP, and is easy to use.

I have thought about adding a filter (lots of good info here on CN about choices), but am reluctant to spend money on an experiment of this nature.

Ed


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coopman
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Ed Holland]
      #6488049 - 04/25/14 02:43 PM

I have various types of scopes too. I'd rather be using a 4" or sim. sized refractor as soon as the tripod hits the ground than another type of scope that will have cool down issues that reduce my observing time. Back when I had my C8, my refractors got a lot of use when the C8 proved to be unusable.

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Jon Isaacs
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Ed Holland]
      #6488071 - 04/25/14 02:50 PM

Quote:

However, if I want a quick setup, rapid thermal settling and pleasing views without concerns for collimation etc., the AR5 or 102 are in the front line. Yes there are purple fringes, possibly also some spherical aberration (both of which change with temperature). But to me, these are good scopes that get used. I find it hard to get annoyed, concerned or disappointed about an instrument that is still providing detail and interest at the EP, and is easy to use.






One of my favorite John Wooden quotes:

"Don't let what you can't do interfere with what you can do.."

Enjoy your equipment for what it is and don't try to make it into something it is not...

Jon


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Vondragonnoggin
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6488091 - 04/25/14 02:59 PM

Quote:

Quote:

Again - filtering is the purposeful elimination or reduction in certain spectrum to enhance detail. Whether by eliminating bad information from aberrations or by fine tuning a frequency to bring more information that is swamped usually by your needless information (such as narrowband to eliminate unwanted spectrum) it is the same effect on different scales.




Well...

I am well aware of the purpose of filters. This is what your wrote:

Quote:

I don't know why these conversations don't go hand in hand, but there is always someone asking about which filters to buy for astronomy use and usual answers consist of UHC, OIII, H-Beta, or the like and everyone gets happy about the thought of getting a little MORE detail out of nebula viewing.

Mention achromat and filtering it out like with Longpass, or semi-apo, or minus V and suddenly people are worried and discussing how much LESS detail is seen.

People are okey dokey with one application and always whining about the other and it makes little sense to me.




You asked the question "why the conversation about filtering achromats and filtering deep sky objects do not go hand in hand."

I spent a considerable amount of time answering your question and explaining why they do not go hand in hand. Both involve the use of filters but the purpose is quite different.

One enhances object itself by only passing the very narrow band that the object itself emits whereas the other attempts to make up for optical deficiencies by discarding otherwise desirable information. I thought the radio analogy was particularly appropriate, with one, you are picking out a faint signal from the broad spectrum, the other, you are attempting to make up for deficiencies in the equipment.. a bad amplifier or fuzzed speaker.

I will also add that your implication that one only sees "a little MORE detail out of nebula viewing" is misleading and incorrect. The reality is that narrow band nebula filters greatly increase the contrast of many nebulae and in many cases allow them to be seen in detail when they would otherwise be invisible. Deep sky filters make huge differences for those objects which they enhance.

On the other hand, it is questionable whether the long pass, Semi-APO and minus violet filters actually enhance the detail seen. In my experience, the difference is primarily aesthetic and does not result in me seeing more details. As Mark does, I look past the purple haze, it is the remaining lack of sharp focus that seems to most affect the what I see.

If one wants to view the planets with an achromat, longer focal lengths, slower focal ratios are better. My goal here is to help folks just starting out understand their choices and what differences those choices make at the eyepiece and in the field. I do not generally recommend someone first starting out invest in an expensive apochromat. But at the same, since the original question was asked, sharing my experiences and understandings of the differences, there is a place for that.

I find the side by side comparison between my 4 inch F/5.4 apochromat and my 100mm F/6 Achromat quite enlightening. As much as I enjoy the achromat, as much as I love the thing, as much as I try different filters, different aperture masks and such, the difference between the two when viewing the planets is still very noticeable, nothing I have found does much in the way of closing the gap. Masking the 100mm achromat to an 80mm F/7.5 and then comparing it to my 80mm F/7 apochromat bears similar results..

Jon Isaacs




Thank you Jon, but I have Lumicon UHC, Lumicon OIII, Lumicon H-Beta, Baader 7nm H-Alpha, Baader 35nm H-Alpha, Baader 610nm Longpass, Thousand Oaks LP2, Baader Moon and Skyglow, Baader semi-apo, Baader 685nm IR Pass, and just ordered a Lumicon 640nm longpass. All of which get used actively with primarily 7nm, 610nm use.

the purpose remains the same - to bring out more detail. You can try to word it how you like, but no different in my eyes. Useful info like Mercury and Sodium lines? useful like IR data for pure visual use?

Nice try to school me about filter basics, but really you're talking to the wrong person trying to school me on it.

I'm out of the beginner section for this reason - getting snippets pulled and quoted that neglect 80% of what I'm saying only to have it worded slightly different. Have fun with it.



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rsimpkins
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6488155 - 04/25/14 03:20 PM

What a lot of great information. I am quickly becoming enamored with the idea of owning an APO refractor, largely based on the information in this thread.

Despite my desire to wait until I gain more experience before buying, I am now kicking myself for not just ponying up for the ES 127CF when it was on sale from Astronomics a couple weekends ago. I simply didn't have enough knowledge at the time to know that was a good deal. Something like that might not come along again for a very long time. Makes a person feel kind of rotten inside.

Now the long wait begins looking for the next great opportunity. I will be sure not to miss it. How often do telescopes in this price range go on sale?


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GOLGO13
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Reged: 11/05/05

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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6488208 - 04/25/14 03:39 PM

Lots of sales come up during the year. You may want to consider the carbon fiber a bit more. Not sure how the affect refractors but I understand they have some unique characteristics in use. I think just a normal tube may be better from what I have seen on here.

I see that Optcorp.com has that scope discounted. I'm more into doublets than triplets. Quicker cool down and lighter weight, but maybe do not have perfect color correction...but pretty darn close in my experience.


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Tony Flanders
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Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6488258 - 04/25/14 03:59 PM

Quote:

What a lot of great information. I am quickly becoming enamored with the idea of owning an APO refractor, largely based on the information in this thread.




APOs are wonderful, no doubt about it. But just remember that Newtonians are even more free from color, at a tiny fraction of the cost. There's a reason that Newtonians have been the tool of choice for most serious planetary observers for more than a century.


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