in comparing my modified 8-inch orion newt, i've yet to come across a refractor,APO or otherwise, that shows a crisper more detailed view of the planets.i'm curious why,aside from portability and cooldown issues, anyone would spend thousands of dollars on a 4-inch telescope.(is it just asthetics?)my newt has no false color,doesn't have a front lens to dew up, and since i installed a 3 vane curved secondary support,there are no longer any diffraction spikes. the scope is f/6,and the secondary mirror is only 1.83",so contrast isn't an issue.i've looked through many refractors, some of them high end,and while they do look nice, i've never been overly impressed with the views,considering what they cost.i also have a 120 mm short tube refractor.it's great for traveling, but i ALWAYS choose the newt when i go to my dark sky site.the views,planets and obviously deep sky are that much better. so i guess my question is, what advantages do refractors have besides being more portable and taking less time to reach outside temperature? am i missing something ? erik wilcox
reflector vs. refractor
Started by
erik
, Jan 31 2004 08:23 PM
133 replies to this topic
#1
erik
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telescope surgeon
Posted 31 January 2004 - 08:23 PM
#2
Guest_**DONOTDELETE**_*
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Posted 31 January 2004 - 09:56 PM
Newts make very good planetary scopes, as you know, better the SCTs in general and better than many refractors. Where I live, in the high desert in California, seeing is the limiting factor. Unless the seeing is VERY good and the temperature stable (temperature drops of 50 degrees overnight are not uncommon, summer or winter), when comparing the views through my APO and 8", 10" and 12" SCTs, Dobs, and Newts, most people will agree that, under the local seeing conditions, the APO provides a more pleasing image of the planets. The image is more stable with the smaller aperture, and, due to the excellent transparency in the desert, and the dark skies we observe from, the planets are not overly bright for the viewer.
Local seeing has a lot to do with living in the desert. The temperature drops thoughout the night. Larger scopes often never reach thermal equilibrium, or do so just before dawn. The refractor wins in these situations, which predominate in desert viewing. I can be doing planetary or lunar work while the big guns are still suffering from the fuzzies, even hours later.
In the desert, condensation is almost never a problem. I've only had a scope dew up (Mak, SCT, or Refractor) one time in over three years of observing from my location. Well, it wasn't dew, it was ice from a freezing ground fog, but I've never seen it before or since.
Refractors, for the most part, don't need collimation. They travel well. Newts and Dobs need collimation. Many people don't collimate their scopes regularly, so their performance suffers relative to a refractor. Mis-collimation lowers resolution and contrast.
Mirror coatings oxidize and need to be redone every few years. Many people don't do this, and their views suffer as a result.
APO refractors often have sub-1000mm focal lengths. With 2" eyepieces, this makes them ideal for open clusters and the larger nebulae. Long focal length SCTs and Maks are especially hampered in this regard. Refractors also have longer focal ratios, often around f-8 to f-10, and eyepieces, regardless of design, perform better at the slower f-ratios.
In essense, Erik, you are correct. A properly collimated, thermally stablized, curved-vaned, well baffled/flocked reflector with a secondary of less than 20% of the diameter of the primary, with a clean mirror of good figure, and good seeing will give a better view of the planets than an APO refractor. IF you have all those things, you will have a killer planetary scope and location.
Almost everyone I know owns an SCT (big secondary, long cooldown, fairly portable) or a fast Dob (big secondary, long cooldown, often poorly collimated, still portable, inexpensive) or an achromat (chromatic abberation, good optics, very portable, inexpensive). Most club members prefer the view of the planets through my APO, though.
I'll guarantee this, though. If I lived in SF or in Florida, with the nice, smooth, laminar air flow off the ocean and fairly stable temperatures, I'd have a 6" or 8" Newt, baffled or flocked or otherwise contrast-enhanced, with an undersized secondary on a curved or single-stalk spider, a low-profile helical focuser, a full set of UO HD Orthos (parfocal eyepieces are a must with low-profile, limited throw focusers), and that would be my planetary rig. I might even have two spiders, with one for deep-sky work with a big secondary and the other with a small secondary for planets.
But since I live in the desert, and have a small car, I have an APO.
Local seeing has a lot to do with living in the desert. The temperature drops thoughout the night. Larger scopes often never reach thermal equilibrium, or do so just before dawn. The refractor wins in these situations, which predominate in desert viewing. I can be doing planetary or lunar work while the big guns are still suffering from the fuzzies, even hours later.
In the desert, condensation is almost never a problem. I've only had a scope dew up (Mak, SCT, or Refractor) one time in over three years of observing from my location. Well, it wasn't dew, it was ice from a freezing ground fog, but I've never seen it before or since.
Refractors, for the most part, don't need collimation. They travel well. Newts and Dobs need collimation. Many people don't collimate their scopes regularly, so their performance suffers relative to a refractor. Mis-collimation lowers resolution and contrast.
Mirror coatings oxidize and need to be redone every few years. Many people don't do this, and their views suffer as a result.
APO refractors often have sub-1000mm focal lengths. With 2" eyepieces, this makes them ideal for open clusters and the larger nebulae. Long focal length SCTs and Maks are especially hampered in this regard. Refractors also have longer focal ratios, often around f-8 to f-10, and eyepieces, regardless of design, perform better at the slower f-ratios.
In essense, Erik, you are correct. A properly collimated, thermally stablized, curved-vaned, well baffled/flocked reflector with a secondary of less than 20% of the diameter of the primary, with a clean mirror of good figure, and good seeing will give a better view of the planets than an APO refractor. IF you have all those things, you will have a killer planetary scope and location.
Almost everyone I know owns an SCT (big secondary, long cooldown, fairly portable) or a fast Dob (big secondary, long cooldown, often poorly collimated, still portable, inexpensive) or an achromat (chromatic abberation, good optics, very portable, inexpensive). Most club members prefer the view of the planets through my APO, though.
I'll guarantee this, though. If I lived in SF or in Florida, with the nice, smooth, laminar air flow off the ocean and fairly stable temperatures, I'd have a 6" or 8" Newt, baffled or flocked or otherwise contrast-enhanced, with an undersized secondary on a curved or single-stalk spider, a low-profile helical focuser, a full set of UO HD Orthos (parfocal eyepieces are a must with low-profile, limited throw focusers), and that would be my planetary rig. I might even have two spiders, with one for deep-sky work with a big secondary and the other with a small secondary for planets.
But since I live in the desert, and have a small car, I have an APO.
#3
DenisY
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Posted 31 January 2004 - 10:41 PM
Warpd
That's one hell of a reply, there absolutly nothing i can add. It even get's me to want an APO now.
That's one hell of a reply, there absolutly nothing i can add. It even get's me to want an APO now.
#4
Guest_**DONOTDELETE**_*
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Posted 31 January 2004 - 10:49 PM
I can't add anything either besides that for me asthetics are a big part of it; I like the extreamly small size, the overall look, and the way it works. If I'm going to be spending hundreds of hours looking at the sky I might as well do it with something I like. I'm new to astronomy which is why I only have one telescope so far; eventually I will collect several more, but I still prefere the refractor.
#5
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Posted 31 January 2004 - 11:11 PM
Well, in theory, reflectors are better for the planets. But I don't know many people who can collimate and maintain them at that level of performance. For many people, it doesn't make any sense to have an APO when a Newt will work better. For me, where I live, a Newt won't work better most of the time, so I don't have one. It just depends on what you need.
#6
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Posted 31 January 2004 - 11:19 PM
One more point is that because an APO can produce an equivalent planetary image with a smaller overall size and weight, you can get good performance from a much smaller mount.
BUt I have a modified 5" Newt. Before I could afford an APO, my wife would have to pack up and leave me flat.
BUt I have a modified 5" Newt. Before I could afford an APO, my wife would have to pack up and leave me flat.
#7
jrcrilly
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Refractor wienie no more
Posted 31 January 2004 - 11:46 PM
I dunno; I can see the charm of the APO's for portability and for esthetically pleasing widefield views. For those of us who don't value portability above all else, though, the smaller ones just seem too much of a compromise. I can't visualize any conditions under which a less than 7" APO would begin to approach the planet or one degree deepsky performance of my 12.5" F/8 Newt. I know the 4" APO I had wasn't close. It was great for BIG starfields and brighter extended objects but there's only so much four inches can do.
I think we need to compare apples to apples - I'd rather have a 4" APO than a 4" Newt or Cat, but if I can have aperture I'll take that first.
I think we need to compare apples to apples - I'd rather have a 4" APO than a 4" Newt or Cat, but if I can have aperture I'll take that first.
#8
erik
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Posted 01 February 2004 - 02:14 AM
thanks for all the replies.you guys make some good points.in comparing apples to apples, i agree, a high end refractor of the same aperature as the newt will beat it every time because it suffers no light loss from the secondary obstruction. in fact, in my experiences, i think a 6 to 7 inch refractor equals a 8 inch newt or a 9 inch SCT. however, we all know what a 7 inch APO costs, and i think that if price is any consideration, the newt wins out.an 8 inch newt also weighs much less than a 7 inch refractor.and if were talking about a 4 inch APO ,as john said, theres only so much 4 inches can do.on deep sky, the newt will obliterate it, and in my opinion, it wins out on the planets as well.even when the seeing is bad,you can stop the newt down for a more pleasing view.(you can even eliminate diffraction spikes from straight vanes in this way) i think every telescope can serve a purpose, and if i had an unlimited amount of cash(and a lot of time to spend on a waiting list),i'd probably buy a nice astrophysics APO.but it wouldn't be my only scope, and i bet i'd still use the newt quite a bit.i think that a newt is just a more versatile instrument, capable of doing everything well, wheras the 4 inch refractor is more or less designed for planetary work(due to its limited aperature).having said that though, its true that newts need more maintanance and cant be banged around as much(although i dont think i'd want to bang around a $8000 refractor!)anyway, i'm sure the debate will continue. just my 2 cents.- erik wilcox
#9
pete
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Posted 01 February 2004 - 02:15 AM
I recently went for a refractor aside form all the reasons mentioned above. They look less threatening and more like a telescope. I was vacationing on a mountain overlooking a vally sometime ago with my 6" on a Dob mount. When a concerned patriot call for security becuase, they thought I was a terrorist about to fire a cannon into a town down in the vally. Bundled up in a black trench coat along with a ski mask for warmth, I was lucky not to get shot while observ. Pete
#10
Guest_**DONOTDELETE**_*
Guest_**DONOTDELETE**_*
Posted 01 February 2004 - 03:04 AM
hey all ,
gotta throw in my 2 cents here.
goin back to the original post , i must agree about
never seeing a small refractor show as pleasing a view or
as much detail as my 8 in. newt. now i can understand somewhat the photography aspects for a
refractor if thats how you make your living,
but for visual use how can anyone
justify the cost of a small apo vs a good quality 8 in newt.
seems more like toys for big kids and maybee bragging rights.
gotta throw in my 2 cents here.
goin back to the original post , i must agree about
never seeing a small refractor show as pleasing a view or
as much detail as my 8 in. newt. now i can understand somewhat the photography aspects for a
refractor if thats how you make your living,
but for visual use how can anyone
justify the cost of a small apo vs a good quality 8 in newt.
seems more like toys for big kids and maybee bragging rights.
#11
Guest_**DONOTDELETE**_*
Guest_**DONOTDELETE**_*
Posted 01 February 2004 - 08:01 AM
Hello All, 
Can`t add much to all that Warped`s astutely pointed out except maybe that, (my apologies if I missed this somewhere in the middle of Warp`s excellent post), a reflector`s tube is open at the top which can produce swirling amalgamations of hot and cold air which can interfere with the contrast, sharpness, clearness, etc., of the image in many places around the country. All such advantages, most of which were pointed out by Warped, including that many are excellent for astrophotography, can function at their full potential most of the time thereby even further providing owners with their full money`s worth which isn`t true with larger newts because of seeing conditions, etc., most are maintenance-free, can operate in almost any climate immediately when many newts suffer from tube currents, etc., as well as cooldown issues in cooler climates, retain resell value much better than newts so owners can get most of their money back should they ever decide to get rid of it, have top-notch mechanics, pinpoint stars across the ENTIRE fov, provide the best performance/inch of aperture, are literally works of art, pride of ownership, asthetics, no cool-down which is extremely important in cooler climates, portability which is extremely important to some, (Eric mentioned these last 3), etc., etc., etc., ALL figure in to the relatively high price!
Please click here for more on how a refractor can be better than a reflector under the right circumstances.
http://www.astronomi...1&t1=3&cat_id=3
Please pay attention to the grades that Astronomy Mag. gives the different sizes, types, etc., of refractors for each type of viewing.
But approaching this from a different angle and for those who didn`t read it, good 5" to 6" refractors can outperform numerous good 6"-7" and even larger reflectors on the Moon and planets, splitting binary stars and resolving globular clusters. Why? 1st, refractors show more low-contrast planetary details than many larger Newts, etc.
This shouldn`t be that difficult to understand since according to Physics, Modulation Transfer Functions show this as follows,
Let R = the Aperture of a Refractor,
Let N = the Aperture of an obstructed Newt
Let CO = the Central Obstruction
So, if R > N - CO, then the unobstructed refractor should show more low-contrast planetary detail than the obstructed newt as confirmed and explained further at all the following sites,
http://perso.club-in...bstruction.html
http://seds.lpl.ariz...s/obstruct.html
http://brayebrookobs...orum/c-o's.html
http://www.weatherman.com/knisely2.htm
http://www.laughton....fo/obs/obs.html
It should be pointed out that although the human eye may or may not be able to tell the differences in contrast between an unobstructed scope and one with a 20% obstruction in scopes of = apertures, the unobstructed scope proves that it can tell the difference by showing more low-contrast details.
But from Physics, there`s more to it than just this. Perhaps more importantly, as many experienced planetary observers know, Dawe`s Limit breaks down when it comes to viewing low-contrast planetary details as explained at Legault`s very informative site on the subject as follows,
"...The minimum size of the details that a given instrument can show must not be confused with its resolving power computed with the approximative formula:
R = 120/D (R in arcseconds, D in millimeters).
This value only works with double stars, it gives the approximative minimum separation of a couple of stars of equal magnitude that allows a given instrument to separate them visually. The fact that a planetary detail will be detected or not is very complex, it depends on many factors like its shape, color, intensity, contrast of the features on extended objects, observer`s location, seeing conditions, irradiation effects of bright objects reducing acuity of the eye, etc.
So, in good seeing, details whose size is under this stellar resolving power can be seen, etc. For ex., the size of the Cass. div. is about 0.7 arcsecond at the ends of the ring, and about 0.3 arcsecond where the ring reaches the edge of the planet. Regardless, a 9" Schmidt-Cass easily shows the Cass. div. despite the fact that it`s theoretical resolving power is only 0.55 arcseconds..."
In many newts, the CO is 20%-25%, (for ex., Eric`s is 23%.). So, sometimes R > N - CO and, in such cases, the refractor outperforms the newt on low-contrast planetary detail, etc. In addition to this CO issue, there`s a huge difference in light transmission. Unlike newts, refractors don`t have a multiple-reflection optical path causing light-scattering diffraction and internal reflections that brighten the sky background, reduce contrast, and smear images. In contrast, (Lol), refractors have the highest % of light gathered that reaches the eye. They can transmit well over 90% of the light collected while newts quite often transmit only 77%-80%.
The result of a refractor's lower diffraction and higher light transmission? In good seeing, refractors can show subtle lunar and planetary details with a more easily observed and wider contrast range with sharper images than in most newts.
Also, because the Moon and planets are all so bright, light-gathering isn`t as important as high powers. So the refractor`s smaller aperture is often an advantage for this type of viewing. Thus, it`s not uncommon to see good refractors handling powers of 80x/in., (like my C-102), and 100x/in., (like my Apos), in above ave. seeing conditions.
With all this in mind, I still have not seen a 5" newt, including high-end ones with Zambuto, etc., optics, show more planetary detail than my 4" Apo, or outperform it in any other way, except for showing a few more faint fuzzies, despite the fact that the refractor spotted them a full inch more of aperture. For that matter, I still haven`t met the 6" newt with Zambuto mirrors, etc., or otherwise that can outperform my 5" Apo in any way except for a few more faint fuzzies, despite the refractor spotting them a full inch of aperture. Many of these 6" newts couldn`t outperform the 4" Apo on planets, etc., either, despite being spotted a full 2" of aperture!
But please also keep in mind that money isn`t a telescope part. Thus, IMHO, it`s irrelevant to the telescope design. If one is trying to find out which design`s better, IMHO then, the fairest way is to compare the best scope of each design using the same apertures under the same conditions, etc. It`s then easy to see that the refractor, (other than possibly an off-axis newt), outperforms the newt in almost every optical way and in many cases, it`s not even close.
But then $$$ is mixed back in and each person must decide if a given scope is worth the money for what ever their preferences are.
That`s my opinion on it, anyway.
Please Note: Your results may vary depending on several different factors! 
If your results differ from those of mine and our other club members who helped with these tests, then so be it.
Well, that`s my $.02.
Good Luck to all and Clear, Steady Skies!
so i guess my question is, what advantages do refractors have besides being more portable and taking less time to reach outside temperature? am i missing something?
Can`t add much to all that Warped`s astutely pointed out except maybe that, (my apologies if I missed this somewhere in the middle of Warp`s excellent post), a reflector`s tube is open at the top which can produce swirling amalgamations of hot and cold air which can interfere with the contrast, sharpness, clearness, etc., of the image in many places around the country. All such advantages, most of which were pointed out by Warped, including that many are excellent for astrophotography, can function at their full potential most of the time thereby even further providing owners with their full money`s worth which isn`t true with larger newts because of seeing conditions, etc., most are maintenance-free, can operate in almost any climate immediately when many newts suffer from tube currents, etc., as well as cooldown issues in cooler climates, retain resell value much better than newts so owners can get most of their money back should they ever decide to get rid of it, have top-notch mechanics, pinpoint stars across the ENTIRE fov, provide the best performance/inch of aperture, are literally works of art, pride of ownership, asthetics, no cool-down which is extremely important in cooler climates, portability which is extremely important to some, (Eric mentioned these last 3), etc., etc., etc., ALL figure in to the relatively high price!
Please click here for more on how a refractor can be better than a reflector under the right circumstances.
http://www.astronomi...1&t1=3&cat_id=3
Please pay attention to the grades that Astronomy Mag. gives the different sizes, types, etc., of refractors for each type of viewing.
But approaching this from a different angle and for those who didn`t read it, good 5" to 6" refractors can outperform numerous good 6"-7" and even larger reflectors on the Moon and planets, splitting binary stars and resolving globular clusters. Why? 1st, refractors show more low-contrast planetary details than many larger Newts, etc.
This shouldn`t be that difficult to understand since according to Physics, Modulation Transfer Functions show this as follows,
Let R = the Aperture of a Refractor,
Let N = the Aperture of an obstructed Newt
Let CO = the Central Obstruction
So, if R > N - CO, then the unobstructed refractor should show more low-contrast planetary detail than the obstructed newt as confirmed and explained further at all the following sites,
http://perso.club-in...bstruction.html
http://seds.lpl.ariz...s/obstruct.html
http://brayebrookobs...orum/c-o's.html
http://www.weatherman.com/knisely2.htm
http://www.laughton....fo/obs/obs.html
It should be pointed out that although the human eye may or may not be able to tell the differences in contrast between an unobstructed scope and one with a 20% obstruction in scopes of = apertures, the unobstructed scope proves that it can tell the difference by showing more low-contrast details.
But from Physics, there`s more to it than just this. Perhaps more importantly, as many experienced planetary observers know, Dawe`s Limit breaks down when it comes to viewing low-contrast planetary details as explained at Legault`s very informative site on the subject as follows,
"...The minimum size of the details that a given instrument can show must not be confused with its resolving power computed with the approximative formula:
R = 120/D (R in arcseconds, D in millimeters).
This value only works with double stars, it gives the approximative minimum separation of a couple of stars of equal magnitude that allows a given instrument to separate them visually. The fact that a planetary detail will be detected or not is very complex, it depends on many factors like its shape, color, intensity, contrast of the features on extended objects, observer`s location, seeing conditions, irradiation effects of bright objects reducing acuity of the eye, etc.
So, in good seeing, details whose size is under this stellar resolving power can be seen, etc. For ex., the size of the Cass. div. is about 0.7 arcsecond at the ends of the ring, and about 0.3 arcsecond where the ring reaches the edge of the planet. Regardless, a 9" Schmidt-Cass easily shows the Cass. div. despite the fact that it`s theoretical resolving power is only 0.55 arcseconds..."
In many newts, the CO is 20%-25%, (for ex., Eric`s is 23%.). So, sometimes R > N - CO and, in such cases, the refractor outperforms the newt on low-contrast planetary detail, etc. In addition to this CO issue, there`s a huge difference in light transmission. Unlike newts, refractors don`t have a multiple-reflection optical path causing light-scattering diffraction and internal reflections that brighten the sky background, reduce contrast, and smear images. In contrast, (Lol), refractors have the highest % of light gathered that reaches the eye. They can transmit well over 90% of the light collected while newts quite often transmit only 77%-80%.
The result of a refractor's lower diffraction and higher light transmission? In good seeing, refractors can show subtle lunar and planetary details with a more easily observed and wider contrast range with sharper images than in most newts.
Also, because the Moon and planets are all so bright, light-gathering isn`t as important as high powers. So the refractor`s smaller aperture is often an advantage for this type of viewing. Thus, it`s not uncommon to see good refractors handling powers of 80x/in., (like my C-102), and 100x/in., (like my Apos), in above ave. seeing conditions.
With all this in mind, I still have not seen a 5" newt, including high-end ones with Zambuto, etc., optics, show more planetary detail than my 4" Apo, or outperform it in any other way, except for showing a few more faint fuzzies, despite the fact that the refractor spotted them a full inch more of aperture. For that matter, I still haven`t met the 6" newt with Zambuto mirrors, etc., or otherwise that can outperform my 5" Apo in any way except for a few more faint fuzzies, despite the refractor spotting them a full inch of aperture. Many of these 6" newts couldn`t outperform the 4" Apo on planets, etc., either, despite being spotted a full 2" of aperture!
But please also keep in mind that money isn`t a telescope part. Thus, IMHO, it`s irrelevant to the telescope design. If one is trying to find out which design`s better, IMHO then, the fairest way is to compare the best scope of each design using the same apertures under the same conditions, etc. It`s then easy to see that the refractor, (other than possibly an off-axis newt), outperforms the newt in almost every optical way and in many cases, it`s not even close.
But then $$$ is mixed back in and each person must decide if a given scope is worth the money for what ever their preferences are.
That`s my opinion on it, anyway.
Please Note: Your results may vary depending on several different factors!
If your results differ from those of mine and our other club members who helped with these tests, then so be it.Well, that`s my $.02.
Good Luck to all and Clear, Steady Skies!
#12
eric moerman
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Ranger 4
Posted 01 February 2004 - 08:51 AM
Dude(and al others)
the problem here is that we are not really comparing appels with appels.We are comparing 4000$+ apo with newtons around 800$.
Ofcorse the apo wil perform bether.
I think that if you take a newton that is build to the same high quality standart that al the apo's are build to it will always be as good or bether.
What we are doing now is comparing a JVC amplifier costing 150$ with a high-end amplifier costing 10000$.
The difference in sound is also big.
I dissagree that you dont need light gathering power to look at moon and planets because it comes with more aparture and you need aparture to resolve smaller details.
Ofcorse again the quality of the objectief and the rest of the telescope has to be very good to so that you can use the high powers you need to see the smal details and if seeing conditions lets you use them.
We al know that there always be refractor and reflector people and this tread can go on and on buth there is nothing else to do with al this rain anyway.
Greatings,Eric
the problem here is that we are not really comparing appels with appels.We are comparing 4000$+ apo with newtons around 800$.
Ofcorse the apo wil perform bether.
I think that if you take a newton that is build to the same high quality standart that al the apo's are build to it will always be as good or bether.
What we are doing now is comparing a JVC amplifier costing 150$ with a high-end amplifier costing 10000$.
The difference in sound is also big.
I dissagree that you dont need light gathering power to look at moon and planets because it comes with more aparture and you need aparture to resolve smaller details.
Ofcorse again the quality of the objectief and the rest of the telescope has to be very good to so that you can use the high powers you need to see the smal details and if seeing conditions lets you use them.
We al know that there always be refractor and reflector people and this tread can go on and on buth there is nothing else to do with al this rain anyway.
Greatings,Eric
#13
DenisY
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Vanguard
Posted 01 February 2004 - 09:40 AM
I recently went for a refractor aside form all the reasons mentioned above. They look less threatening and more like a telescope. I was vacationing on a mountain overlooking a vally sometime ago with my 6" on a Dob mount. When a concerned patriot call for security becuase, they thought I was a terrorist about to fire a cannon into a town down in the vally. Bundled up in a black trench coat along with a ski mask for warmth, I was lucky not to get shot while observ. Pete
Pete that happen to me once, i was in a public park, i somehow wanted to show the stars to the people passing by, then people started to sit near me, 1,2,5,10 person were sitting there looking at me, i found this pretty weird and after a while someone approched and asked me when would the firework start!!!
#14
matt
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Vendor (Scopemania)
Posted 01 February 2004 - 10:06 AM
What also happens with multi-k$ refractors is where you place your priorities, and all of you hinted towards that.
When you place, say, $3,000 for an FS102 (2,000 naked ota + 1,000 to get pointed upwards), you are not only paying for performance, you are paying for the best performance available in a 4" scope, and the comfort of not worrying about anything: no miscollimated optics or optics that cannot be collimated in case of a fall, no under- or over-greased focuser, no flexing in the focuser drawtube, etc.
You will notice there are plenty websites devoted to getting your Autostar to work or your synta mount to track, but none about tuning up (meaning: getting it to work properly) a Takahashi refractor.
It's available only to the deep-pocketed, and even the deep-pocketed might not choose to put their money there, but it makes sense, provided you are not give the bad excuses for owning one (such as saying that it would beat a $3,000 8" reflector).
When you place, say, $3,000 for an FS102 (2,000 naked ota + 1,000 to get pointed upwards), you are not only paying for performance, you are paying for the best performance available in a 4" scope, and the comfort of not worrying about anything: no miscollimated optics or optics that cannot be collimated in case of a fall, no under- or over-greased focuser, no flexing in the focuser drawtube, etc.
You will notice there are plenty websites devoted to getting your Autostar to work or your synta mount to track, but none about tuning up (meaning: getting it to work properly) a Takahashi refractor.
It's available only to the deep-pocketed, and even the deep-pocketed might not choose to put their money there, but it makes sense, provided you are not give the bad excuses for owning one (such as saying that it would beat a $3,000 8" reflector).
#15
jrcrilly
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Refractor wienie no more
Posted 01 February 2004 - 10:27 AM
When you place, say, $3,000 for an FS102 (2,000 naked ota + 1,000 to get pointed upwards), you are not only paying for performance, you are paying for the best performance available in a 4" scope, and the comfort of not worrying about anything
Hi, Matt!
Sure thing - aperture for aperture the Taks (and most of the other APO's) will give great, no-fuss performance. They'll even outperform a somewhat larger scope. I do question whether a $1000 mount will do the same; at that price level you are still firmly into the Synta and Synta clones or limited to altitude/azimuth mounts and will still have mount issues. I used to use an LXD55 mount for my 4".
I'm not against small refractors; I had a very nice 4" APO myself and will soon have one again. It's just that, like every other instrument out there, it'll be a compromise. There are times when giving up that much aperture won't make sense to me. There are also times when it's a good tradeoff in exchange for wonderful visual performance on brighter objects.
Besides, they make great finderscopes!
#16
Guest_**DONOTDELETE**_*
Guest_**DONOTDELETE**_*
Posted 01 February 2004 - 12:02 PM
Everybody has made great points. I like Dobs and Newts, but my present circumstances don't favor my owning one. Theory is a great place to start, but practicality often rears its ugly head.
One of the great things about belonging to an astronomy club is this: everybody has a scope. Our "regulars" have 8", 10" and 12" SCTs, we have a couple of Dobs, a Newt, some achros, one guy has an 18" Obsession, and I have the APO. I seldom observe alone, and my observing partner has a 10" SCT, so between us we've pretty much got everything covered.
One of the great things about belonging to an astronomy club is this: everybody has a scope. Our "regulars" have 8", 10" and 12" SCTs, we have a couple of Dobs, a Newt, some achros, one guy has an 18" Obsession, and I have the APO. I seldom observe alone, and my observing partner has a 10" SCT, so between us we've pretty much got everything covered.
#17
Guest_**DONOTDELETE**_*
Guest_**DONOTDELETE**_*
Posted 01 February 2004 - 04:04 PM
One thing that is beyond dispute in all this is that if you keep the money equal, the newt wins every time.
And it's wrong to say that money doesn't matter, or shouldn't matter. It *always* matters. Even with professional instruments it's no different.
They're all reflectors. The reason is that it would be fantastically expensive to build a refractor as large as the biggest reflectors. Imagine an 8 meter or 10 meter objective lens. Unlike a reflector, it couldn't very well be a mosaic. It would have to be one piece. Just the R&D you'd have to do to determine how the objective would be figured, and supported, to defeat sagging and adjust for changes in the scope's orientation would kill you. (You'd probably need some kind of hydraulically-activated, computer-controlled compression ring. Or maybe some super-slick adaptive optics corrector. Just guessing.)
Now, would the images be better than the 10 meter reflector? Probably. But for the money, you could probably build 100 10 meter refractors. Maybe even hook them up as some kind of super-duper interferometer.
Money always matters.
And it's wrong to say that money doesn't matter, or shouldn't matter. It *always* matters. Even with professional instruments it's no different.
They're all reflectors. The reason is that it would be fantastically expensive to build a refractor as large as the biggest reflectors. Imagine an 8 meter or 10 meter objective lens. Unlike a reflector, it couldn't very well be a mosaic. It would have to be one piece. Just the R&D you'd have to do to determine how the objective would be figured, and supported, to defeat sagging and adjust for changes in the scope's orientation would kill you. (You'd probably need some kind of hydraulically-activated, computer-controlled compression ring. Or maybe some super-slick adaptive optics corrector. Just guessing.)
Now, would the images be better than the 10 meter reflector? Probably. But for the money, you could probably build 100 10 meter refractors. Maybe even hook them up as some kind of super-duper interferometer.
Money always matters.
#18
Guest_**DONOTDELETE**_*
Guest_**DONOTDELETE**_*
Posted 01 February 2004 - 09:39 PM
Hello All,
Although this is correct, light-gathering still isn`t as important viewing planets as it is, for ex., viewing dso`s, since the planets are so bright to begin with. Thus, mag. is more important when viewing planets since higher mags. are going to make all the details visible that the scope`s able to show.
The brightness of planets can`t be emphasized enough. An excellent ex. of all this was during the Mars opposition. Some details on Mars were washed out by the combination of how bright it was and the light-gathering ability of larger apertures. The planet was so washed out in some larger scopes, it actually looked pink, while their owners scurried around trying to find the right combination of filters, etc!
Although money can always matter, it depends a great deal on what one is actually talking about.
For ex., if one is talking about what the best scope for the money is, they might get answers like the Orion ED80 refractor, the C-102HD, the XT-6 dob, the MN-56, the MK-67, the C-9.25, etc.
But if one now asks which is the best telescope out there, no one`s going to mention one of the scopes above.
Similarly, if one`s talking about the best optical performance at = apertures for the money, (strictly speaking amateur scopes 12" or smaller since TMB makes Apo refractors this large and even larger), then it certainly wouldn`t be a refractor.
But if one`s talking about the best optical performance at = apertures PERIOD!!!, then it would be the refractor.
This is certainly true. I stated my piece, etc, etc., etc! So... 
Clear, Steady Skies!
I dissagree that you dont need light gathering power to look at moon and planets because it comes with more aparture and you need aparture to resolve smaller details.
Although this is correct, light-gathering still isn`t as important viewing planets as it is, for ex., viewing dso`s, since the planets are so bright to begin with. Thus, mag. is more important when viewing planets since higher mags. are going to make all the details visible that the scope`s able to show.
The brightness of planets can`t be emphasized enough. An excellent ex. of all this was during the Mars opposition. Some details on Mars were washed out by the combination of how bright it was and the light-gathering ability of larger apertures. The planet was so washed out in some larger scopes, it actually looked pink, while their owners scurried around trying to find the right combination of filters, etc!
Money always matters.
Although money can always matter, it depends a great deal on what one is actually talking about.
For ex., if one is talking about what the best scope for the money is, they might get answers like the Orion ED80 refractor, the C-102HD, the XT-6 dob, the MN-56, the MK-67, the C-9.25, etc.
But if one now asks which is the best telescope out there, no one`s going to mention one of the scopes above.
Similarly, if one`s talking about the best optical performance at = apertures for the money, (strictly speaking amateur scopes 12" or smaller since TMB makes Apo refractors this large and even larger), then it certainly wouldn`t be a refractor.
But if one`s talking about the best optical performance at = apertures PERIOD!!!, then it would be the refractor.
this tread can go on and on
This is certainly true. I stated my piece, etc, etc., etc! So...
Clear, Steady Skies!
#19
erik
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telescope surgeon
Posted 01 February 2004 - 09:42 PM
wow, you guys have brought up a lot more good points. money does matter, and its not just about where your priorities lie.even though, in stock form, an 8 inch tube will set you back only a few hundred dollars, it literally can take many times your initial investment to get it to perform the way that you want it to. this is especially true with dobs, most of which are a work in progress.however, i think that modifying and customizing a scope is half the fun! because i wanted a 8 inch steel tube that was f/6(which nobody sold by itself), i bought an orion XT8 dob just to get the tube.then i bought an 8 inch meade LXD55 for the autostar, promptly sold the meade tube and realized that the tripod sucked too, so i bought an orion equatorial pier.after installing a 3 vane curved secondary support, pyrex primary and secondary mirrors, aluminum oversize focus knobs, a cooling fan, better tube rings, flocking the tube, modifying the focuser drawtube and much more i finally have a scope on a rock solid mount that shows more planetary and deep sky detail than any refractor or 8 inch SCT or mak that i've ever looked through.and i still spent MUCH less than a large APO would cost.and as far as it being an open tube, i've never had any problems with air swirling smearing details.and i dont think that a closed tube is immune from problems either. not only do they tend to dew up,but in light polluted areas, glare can be more of a problem, due to stray light reflecting off the lens (i've noticed this even on high end fully multi coated apo refractors)there are several articles on cloudy nights that talk about what you can see in newts compared to refractors. there is one article about making a multi aperature mask and the writer describes how he couln't even look through his 4 inch apo after the $10 modification to his newt. theres also an interesting article on the effects of central obstructions, and how the human eye can't detect anything less then 30%.it's true that mirrors do eventually need to be recoated and collimated regularly, but refractors aren't maintanance free, especially ones that use exotic flourite lens, which can be unstable and deteriorate in cold damp weather. i think that refractors advantages are portability, cooldown time and in the high end models, beauty and craftsmanship. newts advantages are more bang for the buck, easier to modify, having the eyepiece in a more comfortable location(in most cases) and being more versatile instruments.SCTs advantages are........well i guess they're more portable than newts, but they have a lot of downsides as well, including hefty cooldown times, lowest performance per inch(due to light loss from the folded light path and larger secondary obstruction) and higher cost per inch than a newt. (now i probably just **** off everyone that owns an SCT) anyway, to summarize, the differences are usually small, and i can appreciate any fine optical instrument, but , in my opinion, NEWTS RULE! - -erik wilcox - erokkarma@hotmail.com - orion 8 inch newtonian,orion 120 mm short tube refractor
#20
jrcrilly
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Refractor wienie no more
Posted 01 February 2004 - 09:57 PM
SCTs advantages are........well i guess they're more portable than newts, but they have a lot of downsides as well,
Yes, SCT's are a compromise - but the size and weight difference is quite substantial. I can't fit a 14" F/10 Newt (or my 10" F/7.5 or the 12.5" F/8) in my observatory and certainly don't want to pay for a german EQ mount that would handle either one but the 14" SCT sits in there very nicely on a compact mount. I do like Newts also but to keep the size reasonable many folks choose faster ones - and there's a compromise inherent there as well. One must choose what features to give up and what to keep.
#21
erik
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telescope surgeon
Posted 01 February 2004 - 10:26 PM
john, you're right about SCT's being portable, and i've looked through some with very good optics, but i always feel a little boxed in with the narrow FOV. also, i think there's more variance in optical quality with SCT's- like i said, i've looked through some good ones, but i've seen some, especially older models that weren't very good.it's probably because they're more difficult to make, which is one of the reasons they cost more than a newt.i haven't seen a bad one in a while though, so maybe they're getting more consistent in quality.i'm sure your LX200 is awesome, but in the smaller sizes the image always appears dim, less contrasty and not as "alive" looking as a newt with the same aperature and magnifacation. if i had the $$$ though, i probably would own an C-14 or an LX200 for what they have to offer. -erik wilcox
#22
Barry Fernelius
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Viking 1
Posted 01 February 2004 - 11:36 PM
When I owned an 8" Mag1 Portaball with a Zambuto mirror, I used to compare the views of the planets through my telescope with refractors. Over a two year period, there were a few refractors that came close to providing better views on a few exceptional nights, but I didn't find a refractor that could compete head-to-head with my reflector. (The best refractor, the one that came the closest, was an AP 155, if I recall correctly.)
I now own a 12.5" Mag1 Portaball (also with Zambuto mirror.) I'm still waiting for the night where the refractors demonstrate their clear superiority. I'm not holding my breath. Under crappy seeing conditions, I've seen the phenomena of a refractor providing what its owner called 'a more aesthetically pleasing view.' This is another way of saying when the seeing is bad, smaller aperture scopes don't see the bad seeing as well as large aperture scope. (In this type of condition, one can 'stop down' the larger scope and see the same sort of views that are seen by the refractor.)
When the seeing is good to excellent and when optical quality is excellent, aperture wins every single time. And dollar for dollar, high quality reflectors rule.
But don't take my word for it. Check out Gary Seronik's article "Four Infamous Telescope Myths" in the February 2002 issue of Sky and Telescope. You can also go to star parties and try a few experiments. Under good seeing conditions, take a look at the planetary views through a correctly collimated reflector equipped with a Zambuto, Royce, Swayze, Hall, etc. mirror. Then take a look at the views through a 6" refractor that's many times more expensive. I think that the results might surprise you.
Finally, consider this Mars image, made by Wes Higgins with a 14.5" Starmaster. In the past, when the optics in most large reflectors were mediocre at best, I believe that high quality refractors provided the best views. Now, with high quality optics readily available in large reflectors, I believe the situation has changed.
I now own a 12.5" Mag1 Portaball (also with Zambuto mirror.) I'm still waiting for the night where the refractors demonstrate their clear superiority. I'm not holding my breath. Under crappy seeing conditions, I've seen the phenomena of a refractor providing what its owner called 'a more aesthetically pleasing view.' This is another way of saying when the seeing is bad, smaller aperture scopes don't see the bad seeing as well as large aperture scope. (In this type of condition, one can 'stop down' the larger scope and see the same sort of views that are seen by the refractor.)
When the seeing is good to excellent and when optical quality is excellent, aperture wins every single time. And dollar for dollar, high quality reflectors rule.
But don't take my word for it. Check out Gary Seronik's article "Four Infamous Telescope Myths" in the February 2002 issue of Sky and Telescope. You can also go to star parties and try a few experiments. Under good seeing conditions, take a look at the planetary views through a correctly collimated reflector equipped with a Zambuto, Royce, Swayze, Hall, etc. mirror. Then take a look at the views through a 6" refractor that's many times more expensive. I think that the results might surprise you.
Finally, consider this Mars image, made by Wes Higgins with a 14.5" Starmaster. In the past, when the optics in most large reflectors were mediocre at best, I believe that high quality refractors provided the best views. Now, with high quality optics readily available in large reflectors, I believe the situation has changed.
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#23
erik
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topic starter
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telescope surgeon
Posted 02 February 2004 - 12:16 AM
barry, i agree.while i've seen a more "pleasing"view from a refractor or a large stopped down newt, i've never once seen more DETAIL in a smaller aperature. i think it's easy to perceive that you're seeing more detail if the view is less affected by the seeing, but if you were to critically compare them side by side, i would bet that the larger scope would show more or at least the same amount of detail as the smaller scope. - -erik wilcox
#24
Relativist
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Cosmos
Posted 02 February 2004 - 01:20 AM
There's no way I'd ever buy an expensive refractor, part of it is an irrational fear due to my experience with the old tasco refractor, but mostly it's the great views I've gotten from relatively inexpensive reflectors. Sorry to all you refractor fans, as long as you get more photons right?
.....Curtis
.....Curtis
#25
erik
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topic starter
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telescope surgeon
Posted 02 February 2004 - 11:06 AM
and due to simpler and easier to make design of a newt, there are less inherent things to go wrong. ther are a lot more things that refractors can suffer from(chromatic abberation, false color, glare from poorly coated lens,etc.), wheras reflectors normally provide a crisp color free view. you have to pay much more for that same view in a refractor.newts can suffer problems, like coma in faster focal ratios, and they need to be collimated regularly, but these issues are a lot easier to correct, or in the case of coma, to live with.i'd rather notice a little coma on the edge of the FOV,than a bright purple halo that fuses double stars together.you can spend another $75 on a filter that blocks some of that, but they genarally introduce an annoying greenish tint.and all refractors, except the very top of the line models, suffer from chromatic abberation to some extent.an inexpensive, well collimated newt will provide nice views right out of the box, and with a few modifications, it's easy to make them even better. just my take on things. -erik wilcox
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