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How hard is it to make a reflector as good as mid-price ED or Apo refractor?

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#1 johngwheeler

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Posted 14 April 2018 - 08:44 AM

I came back last night from an enjoyable observing evening at my club’s semi-dark site and reflected (no pun intended!) on the quality of the scopes I had looked through. It was the usual collection of SCTs, Dobsonians and 100-130mm refractors.

 

I took my own c. 2006 C8 SCT and Orion 110mm ED refractor - both of which are low-mid level scopes.

 

Chatting with the other members, many of whom own several scopes, revealed the oft-quoted impression that the refractor images are nicer, with sharper stars, but the aperture is limited. 

 

I own three refractors (the 110mm Orion ED above, a Vixen 140mm neo-achro, and a 100mm Takahashi FC100), and all can produce very sharp star images much more readily than the mass-produced reflectors that I have - SW 6” Mak, C8, SkyWatcher 8” Newtonian, GSO 10” Dobsonian. 

 

For the money I spent on them, the reflectors offer excellent value in terms of quality for the price (combined, they cost less than the Orion 110mm ED on an AVX mount ), so maybe the the quality is simply a reflection of price.

 

But it has got me to thinking about what’s invovled in creating a good quality reflecting telescope, and why we don’t seem to see many of them. I find myself consistently slightly disappointed with the images from standard Meade, Celestron and SkyWatcher reflectors (SCTs and Newts) and I’ve never looked through a reflector and thought “wow” - this is as sharp as my refractors. The best was a C8 Edge HD, which was very close and quite impressive.

 

Why is this? Is it just a market driven thing and that there is a limited desire for producing high quality premium reflectors outside of professional / research instruments?

 

I have no idea of actual numbers produced, but it seems that there one can readily buy nice refractors of 100-150mm aperture in the $1000-10,000 range, but there are few “refractor-like” reflectors in this space. Clearly there are small custom houses producing very nice instruments with precision figured mirrors that would probably meet or exceed the quality of good Apo, but there just don’t seem to be a lot them. At least I’ve never come across them, so I guess this means they are not produced in large numbers, or bought by a lot of people.  

 

It’s become a sort of quest for Holy Grail for me to find this balace of quality of aperture within the bounds of normal affordability - ideally I’d like an excellent quality reflector (both optically & mechanically) in the  10-12” range for the price of of 130mm Apo with the ssme image quality. Does it exist?


Edited by johngwheeler, 14 April 2018 - 08:50 AM.

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#2 CHASLX200

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Posted 14 April 2018 - 08:54 AM

Not hard at all.  I was never a big APO fan over 4".  Price for price a old school 8" F/8 Cave will flat out do much better than a 6" or smaller APO in my seeing for high power planet work.  A well built Newt in the 10 to 12" range will just be a better choice for deep sky as well vs a 6" APO or smaller APO.

Best to look for a used longer focus Newt or a used Dob with a great mirror.  But the APO does do things better than a Newt also, so every scope has it good and bad points.

 

Nothing beats the wide FOV of a 4" APO or even higher power views of the moon.  


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#3 SeaBee1

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Posted 14 April 2018 - 09:08 AM

I have never looked through an APO, so I can't do a comparo, but I can say that my 10 inch Royce conical housed in a structure I built gives me some incredible visual images. When seeing cooperates, Saturn is like a photo, his moons gathered around him like children, surface banding like soft pastel pajamas, his rings like a cap's brim across his brow, with a distinct black division. Is it APO like? I wish I knew...

 

Keep looking up!

 

CB


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#4 mashirts

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Posted 14 April 2018 - 09:12 AM

8 inch f/6 Zambuto mirror on CN classifieds now.  That would fit in used Orion XT8 tube with slight modification or build your own.


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#5 Mike Spooner

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Posted 14 April 2018 - 09:55 AM

"Why is this? Is it just a market driven thing and that there is a limited desire for producing high quality premium reflectors outside of professional / research instruments?"

 

 

Pretty much the market. There are Newts/DOBs out there that give sharp images.

 

Mike Spooner


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#6 B 26354

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Posted 14 April 2018 - 10:07 AM

....ideally I’d like an excellent quality reflector (both optically & mechanically) in the  10-12” range for the price of a 130mm APO with the same image quality. Does it exist?

Good question!

 

There are Newts/DOBs out there that give sharp images.

Care to offer some specifics?



#7 sg6

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Posted 14 April 2018 - 10:09 AM

They are different scopes, so in many ways the comaparison is not applicable.

Each suffer from their own problems and aberrations, being different aberrations how do you compare?

Is a broken finger better then a broken toe ?

 

Worst aspect to me involving scopes is this odd rush to get a faster one then anyone else. In some ways a good f/8 in either will perform well. Problems seem to be build an f/4 then add something ele in to correct for the shortcomings. Which I would say means you have not built a good scope, someone has produced a poor scope and then added more optics to overcome the shortfall.

 

How many will go up in a plane knowing that the engines will fail somewhere along the flight but think it's OK they have supplied a parachute for each of us?

 

To produce a good reflector or refractor likely means abandon the extreme aspects and FAST is one of them. Live with f/8. Limits the aperture you are not going to have a 10" f/8 newtonian in a dobsonian mount. Your eyeball is not going to be at the usable position much of the time. In that respect aperture limits both refractor and reflector.

 

The other aspect is how much is a good reflector?

Here a well made mirror is a lot more then a GSO item from TS Optics, and you can go order one. So they are available in effect fairly easily - Zambuto, but cost is going to higher.

 

One thing that the refractor side know is if you want apo you have to spend the money. People will try and talk themselves that an ED doublet is the same, or that a fringe killer makes it better, whereas the truth is if you want apo then go buy apo, all 3 lumbs of glass. So if you want Zambuto performance go place an order with Zambuto. 10" Zambuto mirror presently $1,600.


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#8 dgoldb

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Posted 14 April 2018 - 10:38 AM

Well, you are trying to get a FAR more capable scope for the same price as a far less capable one... 130mm of aperture versus 250-300mm?  Did you think you could double the aperture for 0$ more? Why would that make any sense? 

 

Anyway, a 130mm apo triplet will run you at least 2k.  Add a tripod/mount for at least another 300 or so and you're at 2.3k.   For 3.6k, you can get a lightholder optics 10" mirror in a teeter structure.  Top of the line.  That is 56% more money for 90% more aperture.  If you want to save even more, you can buy used or go with something like a Dobstuff.


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#9 theKCW

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Posted 14 April 2018 - 10:57 AM

One reason for the contrast loss on reflectors is the secondary mirror. A smaller secondary mirror helps improve contrast - that's one reason a Mak seems sharper than an SCT. However, in order to get a smaller secondary mirror that still reflects the full light cone from the primary, you need a higher f ratio. Look at "planetary" dobs for some examples. Another is the diffraction spikes from the spider vanes. Some people use curved spider vanes that spread out the diffraction so that it doesn't make the "cross" pattern, instead making a slight glow around objects.

#10 Asbytec

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Posted 14 April 2018 - 11:51 AM

I forget who did it, but he built an optimized 6" Newt that rivaled a 6" APO including the use of an optical window to eliminate diffraction spikes. He did it to prove the point. The article was a few years ago on CN, I believe.
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#11 Astro88

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Posted 14 April 2018 - 12:25 PM

I forget who did it, but he built an optimized 6" Newt that rivaled a 6" APO including the use of an optical window to eliminate diffraction spikes. He did it to prove the point. The article was a few years ago on CN, I believe.

I think it was Ed Turco.  Here is a link to the discussion.


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#12 Jeff Morgan

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Posted 14 April 2018 - 01:50 PM

You can certainly get great Newt images by sweating the details.

 

But there are still two things inherent in the design that assure the Newtonian will always lose an equal aperture comparison:

 

1) The central obstruction. It takes a portion of the signal and dumps it from signal (Airy Disk) to noise (diffraction ring). You never get that back. 

 

2) The primary mirror sits close to the ground. There is usually a sharp temperature gradient there, and the light has to traverse this twice.


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#13 Jon Isaacs

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Posted 14 April 2018 - 02:31 PM

You can certainly get great Newt images by sweating the details.

 

But there are still two things inherent in the design that assure the Newtonian will always lose an equal aperture comparison:

 

1) The central obstruction. It takes a portion of the signal and dumps it from signal (Airy Disk) to noise (diffraction ring). You never get that back. 

 

2) The primary mirror sits close to the ground. There is usually a sharp temperature gradient there, and the light has to traverse this twice.

 

If one is comparing scopes of equivalent apertures,  the the diffraction of a central obstruction cannot be recovered. 

 

But most often one is comparing a larger aperture Newtonian with a smaller aperture refractor and in that case the situation is reversed . The diffraction effects of the smaller aperture mean the airy disk is larger and this has a greater impact than a reasonably sized central obstruction .

 

My questions for John:

 

How much attention do you pay to the details? 

 

Are you a stickler for precise collimation ?

 

Are you a stickler for thremal equilibrium ? 

 

Do you understand the effects lesser quality seeing in larger apertures? The effects of the brighter star images . My 22 inch is about 3.7 magnitudes brighter than a 4 inch.  Think that a magnitude 3 star looks like Sirius in a 4 inch ..

 

Do you have the eyepieces that are appropriate for a scope of the focal ratio ?

 

Are you correcting for coma ?

 

My standard 15 year old GSO 10 inch Dob provides essentially perfect views , stars that are clean and sharp across the field , nice round , in focus stars.  

 

Such views require an attention to detail and understanding. 

 

My TeleVue NP-101 provides as perfect a view as there is,  it's F/5.4 and unlike most refractors,  its corrected for field curvature. . But without the good eyepieces (think 31 mm Nagler ) the views suffer . The GSO Dob is just the same .

 

Newtonians are telescopes for tinkerers .  The devil is in the details .

 

Jon


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#14 glend

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Posted 14 April 2018 - 03:01 PM

Have a look at the Skywatcher MN190 Mak-Newt, it is the perfect scope you seek. At f5.3, and perfectly corrected, this flat field astrograpgh/visual scope ticks all the boxes at 1000mm fl.  No pesky diffraction spikes, thanks to the small secondary mounted directly on the front corrector. Always in collimation, offset factory set. The tube is heavily baffled. It delivers large APO like performance and contrast, with true colour rendition, at 1/3 the cost of an APO of comparable size. Unlike SCTs it does not fog up, the thick Ohara front corrector just needs a single heat strap around it to maintain clear operation in the most trying conditions. I have owned mine for three + years and it gets used more than anything else i own, with nothing on the market that compares at that price point.


Edited by glend, 14 April 2018 - 03:04 PM.

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#15 johngwheeler

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Posted 14 April 2018 - 05:33 PM

Well, you are trying to get a FAR more capable scope for the same price as a far less capable one... 130mm of aperture versus 250-300mm?  Did you think you could double the aperture for 0$ more? Why would that make any sense? 

 

Anyway, a 130mm apo triplet will run you at least 2k.  Add a tripod/mount for at least another 300 or so and you're at 2.3k.   For 3.6k, you can get a lightholder optics 10" mirror in a teeter structure.  Top of the line.  That is 56% more money for 90% more aperture.  If you want to save even more, you can buy used or go with something like a Dobstuff.

That’s a fair point, but imagine one of the advantages of the reflector is that even a top of the line mirror should be much cheaper than the a good doublet or triplet lens of the same aperture.

 

I’ve never had the opportunity to look through a premium Newt/Dob, but I have heard good things about Teeter. Probably hard to get hold of in Australia though, without a nervewracking shipping option!



#16 johngwheeler

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Posted 14 April 2018 - 05:38 PM

To produce a good reflector or refractor likely means abandon the extreme aspects and FAST is one of them. Live with f/8. Limits the aperture you are not going to have a 10" f/8 newtonian in a dobsonian mount. Your eyeball is not going to be at the usable position much of the time. In that respect aperture limits both refractor and reflector.

 
 

One reason for the contrast loss on reflectors is the secondary mirror. A smaller secondary mirror helps improve contrast - that's one reason a Mak seems sharper than an SCT. However, in order to get a smaller secondary mirror that still reflects the full light cone from the primary, you need a higher f ratio. Look at "planetary" dobs for some examples.


I hadn’t thought of this and it makes sense. I don’t think I’ve ever seen an f/8 Newt in the field, and the quality of most f/8-f/10 SCTs that I’ve seen left me wanting (although as previously metnioned Celestron Edge HD is pretty good)

#17 johngwheeler

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Posted 14 April 2018 - 05:59 PM

If one is comparing scopes of equivalent apertures,  the the diffraction of a central obstruction cannot be recovered. 
 
But most often one is comparing a larger aperture Newtonian with a smaller aperture refractor and in that case the situation is reversed . The diffraction effects of the smaller aperture mean the airy disk is larger and this has a greater impact than a reasonably sized central obstruction .
 
My questions for John:
 
How much attention do you pay to the details? 
 
Are you a stickler for precise collimation ?
 
Are you a stickler for thremal equilibrium ? 
 
Do you understand the effects lesser quality seeing in larger apertures? The effects of the brighter star images . My 22 inch is about 3.7 magnitudes brighter than a 4 inch.  Think that a magnitude 3 star looks like Sirius in a 4 inch ..
 
Do you have the eyepieces that are appropriate for a scope of the focal ratio ?
 
Are you correcting for coma ?
 
My standard 15 year old GSO 10 inch Dob provides essentially perfect views , stars that are clean and sharp across the field , nice round , in focus stars.  
 
Such views require an attention to detail and understanding. 
 
My TeleVue NP-101 provides as perfect a view as there is,  it's F/5.4 and unlike most refractors,  its corrected for field curvature. . But without the good eyepieces (think 31 mm Nagler ) the views suffer . The GSO Dob is just the same .
 
Newtonians are telescopes for tinkerers .  The devil is in the details .
 
Jon


Thanks for the well considered answer. Yes, some attention to detail is to be expected with a Newtonian with resepect to collimation, thermal management, coma correction and the choice of eyepieces.

I guess my fundamental question is “does the fundamental design of reflecting telescopes (of any design) prevent achieving the same optical quality of a lens telescope”? I thinking in terms of Strehl values, dot sizes and the other parameters that opticians use to determine absolute image fidelity. Do we have to accept a compromise if we want a larger telescope?

Probably the answer is “it depends”, and you can never really compare apples to apples if one sets a 5” Apo against a 10” Newtonaian.

#18 johngwheeler

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Posted 14 April 2018 - 06:01 PM

Have a look at the Skywatcher MN190 Mak-Newt, it is the perfect scope you seek. At f5.3, and perfectly corrected, this flat field astrograpgh/visual scope ticks all the boxes at 1000mm fl.  No pesky diffraction spikes, thanks to the small secondary mounted directly on the front corrector. Always in collimation, offset factory set. The tube is heavily baffled. It delivers large APO like performance and contrast, with true colour rendition, at 1/3 the cost of an APO of comparable size. Unlike SCTs it does not fog up, the thick Ohara front corrector just needs a single heat strap around it to maintain clear operation in the most trying conditions. I have owned mine for three + years and it gets used more than anything else i own, with nothing on the market that compares at that price point.


Thanks for this. The MN-190 is a scope that has intrigued me, although I’ve never seen one.

It does sound close to what I’ve looking for if the optical quality is as good as you say it is!

#19 Mike Spooner

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Posted 14 April 2018 - 09:19 PM

Good question!

 

Care to offer some specifics?

I was simply addressing the ability of Newtonians to provide satisfying views. Granted not all do. As with many things, execution of a design requires some care and effort to insure success. I am of the perhaps not unbiased opinion that extreme aperture difference is not required to provide equal opportunity for one design over another. I'm referring to on axis images and realize the benefits of design for camera imaging. 

The OP also addressed mechanicals and this may be an even more uncommon denominator especially in the sizes mentioned. Material availability, fit and finish really don't scale easily given the typical budget ranges applied. My personal favorite scopes all have glass or ceramic glass substrates not typically found in amateur Newtonians. The scopes themselves are not eye candy. To get a nice tube for a small refractor might be a challenge but workable - scaling that up to a much larger design is not a linear problem (or cost) at least in my experience. My expertise is not in production design but I've addressed those issues that bothered me and judging by the number of threads on issues with new scopes, there is plenty of room for improvement in commercial offerings. Anyone else ever wonder why refractors are touted as having basically a nonissue with collimation but after a few hundred years the Newtonian still is called on the carpet for that limitation? Yes initial collimation requires some effort but to have to resort to a frustrating battle night after night points to design failure. After 50 years I maybe understand a bit about collimation but I wanted to drive somewhere and set up my smaller Dobs and observe.

 

To get more specific would perhaps involve more non objective promotion than I'm comfortable with - most of it has been hashed over and gets into areas of personal preferences that run the gamut. 

 

Best,

Mike Spooner 


Edited by Mike Spooner, 14 April 2018 - 09:22 PM.

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#20 Mike Lockwood

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Posted 14 April 2018 - 09:27 PM

Worst aspect to me involving scopes is this odd rush to get a faster one then anyone else. In some ways a good f/8 in either will perform well. Problems seem to be build an f/4 then add something ele in to correct for the shortcomings. Which I would say means you have not built a good scope, someone has produced a poor scope and then added more optics to overcome the shortfall.
How many will go up in a plane knowing that the engines will fail somewhere along the flight but think it's OK they have supplied a parachute for each of us?

Do you troll often, or is it just an occasional hobby?
 

To produce a good reflector or refractor likely means abandon the extreme aspects and FAST is one of them. Live with f/8. Limits the aperture you are not going to have a 10" f/8 newtonian in a dobsonian mount. Your eyeball is not going to be at the usable position much of the time. In that respect aperture limits both refractor and reflector.

Sounds like someone has some unresolved fast telescope issues.

 

A good reflector needs quality optics, good mechanics, and thermal management.  Do those right, and f/# doesn't really matter.  I'll take a 20" f/4.0 because it will eat a 10" f/8 for lunch with twice the resolution and four times the light gathering.  And that 10" f/8 will beat a 6" refractor.


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#21 Asbytec

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Posted 14 April 2018 - 09:33 PM

I guess my fundamental question is “does the fundamental design of reflecting telescopes (of any design) prevent achieving the same optical quality of a lens telescope”? I thinking in terms of Strehl values, dot sizes and the other parameters that opticians use to determine absolute image fidelity. Do we have to accept a compromise if we want a larger telescope?

 

 

I think the short answer is yes. We cannot avoid the added diffraction and obscuration of the central obstruction. You can take steps to minimize the effects by reducing the obstruction and increasing the Strehl. We can "optimize" a Newt so that the differences become less noticeable, say with an obstruction of 20% or less. We can also get a slightly larger aperture to pack energy into a smaller angular diameter. But, the effects are still there. The only remaining question is how much, including residual color in an APO. 

 

I tend to believe, having observed with a decent scope in some amazing seeing, the question really should be how good does our scope need to be in order to show you what's there to be seen? Even a premium APO will not have a "perfect" Strehl across all wavelengths. The closest you might get to perfection is a premium mirror, but then it'll be obstructed to some degree. So, the question really boils to how good it has to be to knock your socks off, including the real world environment of seeing, collimation, thermal management, and even the observer paying attention to the image. 

 

I like the term "sensibly perfect" in that it implies this is as good as it gets and it's hard to tell the difference from a perfect optic. You'll get sensibly perfect images with a fine APO and a premium mirror even if there is some color in the former and a modest obstruction in the latter. But, I tend to think a good scope we'd be happy to use will be "sensibly good" enough. Remember, in anything less that nearly perfect seeing, few scopes are delivering "diffraction limited" images to the focal plane. Smaller apertures are more immune to seeing and can retain "diffraction limited" performance (and despite the controversy over what that means) which I consider to be "sensibly good" enough. 

 

In my opinion only, I think if a scope can /approach/ the intent of the Rayleigh criterion it will be "sensibly good." The Rayleigh criterion, as I understand it's intent, is the equivalent of presumably smooth 1/4 pvw of LSA offering a Strehl of 0.8 or slightly better at RMS of 1/14 waves (Strehl 0.82) at the Marechal criterion. This is the optical aberration, and we have to consider the obstruction. So, when we combine both the aberration and obstruction, we still need to meet the criterion of achieving 0.8 Strehl-like figure in the final image on the focal plane. A good modest aperture scope with a 0.95 Strehl and a 30% obstruction meets this criterion to be "sensibly good" when seeing is also diffraction limited. In my experience.

 

A premium scope *will* be better, but the above level of performance will allow you to see what's there to be seen save some low contrast detail on small scales near the first diffraction ring, give or take. This is the tiny realm of obstruction effects where APOs and premium mirrors with modest obstructions shine. And, as for paying attention to detail and appreciating the telescopic image, so much depends on the observer to pick out detail that can be seen. It's not the scope's responsibility to hand us a nice image on a silver platter. Observing requires some effort from the observer to enjoy the image fully. Seeing everything that is there to be seen requires work, observing is enjoyable...but it's also difficult. Difficult and rewarding. 

 

A premium scope with a Strehl of 0.98 and 20% obstruction puts Strehl 0.98 * Obstruction (1 - co^2)^2 * 0.84 of the maximum = 76% of it's gathered light into the Airy Disc. A good mass produced scope, as above with 30% obstruction, puts Strehl 0.95 * Obstruction (1 - co^2)^2 * 0.84 of the maximum available light = 66% of all the light gathered into the Airy disc on the focal plane. This is not as good as the former premium example, but at 0.66/0.84 = 0.78 Strehl-like performance on the focal plane close to the "diffraction limit" approaching the Marechal criterion and will be "sensibly good." When the obstruction becomes smaller, Strehl can fall a little to and still achieve this level of performance when seeing does not degrade the image appreciably.  


Edited by Asbytec, 14 April 2018 - 09:38 PM.


#22 havasman

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Posted 14 April 2018 - 11:36 PM

One reason for the contrast loss on reflectors is the secondary mirror. A smaller secondary mirror helps improve contrast - that's one reason a Mak seems sharper than an SCT. However, in order to get a smaller secondary mirror that still reflects the full light cone from the primary, you need a higher f ratio. Look at "planetary" dobs for some examples. Another is the diffraction spikes from the spider vanes. Some people use curved spider vanes that spread out the diffraction so that it doesn't make the "cross" pattern, instead making a slight glow around objects.

The second sentence is an oversimplification as regards Dobs. I can’t look it up for you now but see Mel Bartel’s site for more complete and expert data.


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#23 Codbear

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Posted 15 April 2018 - 03:16 AM

A lot depends on where you live/observe... Where I live in Northern California, the temperature variation is usually about 20 degrees; my $4,000 11" Teeter Newt with a Zambuto mirror blows away my AP130GT that cost 150% of the price 11" price with no cool down issues to speak of.

 

While the 11" Zambuto isn't nearly as portable as the AP130 refractor, it isn't that far off my 16" GSO dob, that so happens to have a 1/10th wave mirror. I've never had to turn on the fans of either dob, which is a very important thermal consideration, depending on where you live. 

 

You don't need to pay apo refractor prices to get apo performance...a premium dob with about twice the diameter mirror as the apo objective for about the same price will perform tremendously better in my opinion.


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#24 Jon Isaacs

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Posted 15 April 2018 - 04:43 AM

Thanks for the well considered answer. Yes, some attention to detail is to be expected with a Newtonian with resepect to collimation, thermal management, coma correction and the choice of eyepieces.

I guess my fundamental question is “does the fundamental design of reflecting telescopes (of any design) prevent achieving the same optical quality of a lens telescope”? I thinking in terms of Strehl values, dot sizes and the other parameters that opticians use to determine absolute image fidelity. Do we have to accept a compromise if we want a larger telescope?

Probably the answer is “it depends”, and you can never really compare apples to apples if one sets a 5” Apo against a 10” Newtonaian.

 

John:

 

The original observation in this thread was that many observers seem to think that refractors provide sharper stars than reflectors.  I think one needs to consider this more carefully.  Why is this?  Understanding perceptions is important. 

 

In terms of comparing spot sizes and Strehl values, are you comparing a 5 inch apo against and 10 inch Newtonian or a 10 inch apo versus a 10 inch Newtonian?  

 

The first is the more common comparison and more realistic comparison because it's one that is within in the realm of reality.  

 

In that comparison, the fine scale contrast can be much better in the Newtonian, the angular spot sizes at identical magnifications, they can be much smaller with the Newtonian.  This is why a 10 inch Newtonian can cleanly split double stars that unsplittable with a 5 inch refractor.

 

Both Mike Spooner and Mike Lockwood are highly skilled opticians.  Looking through their telescopes, that is very likely a different experience than looking through a mass produced telescope..

 

Attention to detail.  

 

Jon


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#25 nashvillebill

nashvillebill

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Posted 15 April 2018 - 09:36 AM

At some point aren't a few folks taking things to the point of absurdity?

 

I'm reading The History of the Telescope now and in reality, the inexpensive mass-produced scopes we have available today will outperform ANYTHING available up until the mid 1800's..For example, it appears that the mark of a good scope in those days was to resolve the four stars in M42's Trapezium.  Not E or F, only the first 4.  Yet my el cheapo 10 inch dob resolves E and F....whereas the old-time astronomers were hassling with tubes supported by towers and ropes (aerial scopes), re-polishing their speculum mirrors, and dealing with "optical" glass that was full of defects.  Somehow though they made some incredible observations....

 

Just trying to inject a sanity check here.


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