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MKV
Carpal Tunnel
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Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: robboski2004]
      #5596632 - 12/30/12 05:47 PM Attachment (11 downloads)

Quote:

The lens design , Roland Christen published in the Sky and Telescope , was later corrected , due to being over-corrected
for spherical and not optimised for colour.

These glasses are capable of producing, what in 1981, was considered apo correction. i.e green , red , blue within the airy disc



Hi Ian, well, below is a testimony of Christen's correction (April 1982). It's now better corrected for spherical aberration, but (a) it has introduced coma, (b) it has lost its symmetry the 1981 article boasted about, and (c) it is not corrected for red, green and blue, not even on-axis, so it doesn't qualify as an APO, but it was offered as one!

It was intended to cover an impressive 52 mm FOV (because that's where it would have outperformed any Newotnian without additional optics) but, as you can see, it didn't do such a good job. Incidentally, Sky & Telescope did not publish spot diagrams, just the configuration parameters. I think the reason is clear.

All other subsequent configurations are proprietary. BY 1985 Christen was offering (hopefully more optimized) 6-inch f/8 APO OTA on an equatorial mount for $2,595 (figure out what that's worth in 2012 dollars!).

Regards,
Mladen


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wh48gs
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Re: Optimized Newts vs APOs new [Re: MKV]
      #5596636 - 12/30/12 05:49 PM

Mladen,

Quote:

Vla, the OP proposed a windowed Newtonian. If the tube is sealed for all practical purposes, and the optics cleaned and collimated prior to a comparative test, speaking of dirt accumilation on the mirrors is moot.




If we talk about optimized Newtonian, we are starting with the standard configuration. The window is commonly thought of as the mean of avoiding spider vane effect, but real-life data suggest that it is probably even more important for added protection of mirror surfaces. However, even windowed Newtonian is still not as well protected from airborne contaminants as an apo, especially if using prism diagonal. In addition, transmitting coatings are not only more than fourfold smaller error source than reflecting coating for given thickness variation, they are also generally more durable to decay. Considering the effect that likely limited exposure to airborne contaminants and dirt have on observatory mirrors, it is only beneficial to take this into account.

Quote:

If the Newt were to be made specifically for this comparative study, as proposed, then speaking of 3-year old coating is also moot. There are Questars 3.5 still in use that were made in 1964 (there is a NASA report on this), and their mirrors are still in excellent condition, no doubt because the tube is sealed.




I'd like to hear some specifics on that "excellent" attribute. Again, as the observatory measurement imply, the effect to exposure is significantly smaller with respect to reflectivity, than scatter. As for the one-time purpose of a telescope, I'm pretty sure that everyone is interested in optimizing performance in a prolonged period of time.

Quote:

We could just as easily look for image degrading factors in objective lenses as well...for the sake of fairness. We can assume less then perfect baffling, or dirt on the lens, fingerprints, what have you, etc.




I know my post was long, and you may have missed it, but I did exactly that. The three factors considered were larger-scale surface roughness and surface dirt/contamination (the two most significant degradation factors in the Newtonian, the last counted only for one mirror, since the front lens surface is also exposed (in all fairness, it is considerably easier to keep clean than reflecting coating, and also deteriorating at a considerably slower pace), as well as roughness due to coating unevenness (the least significant with properly applied, relatively fresh coating, but it shouldn't be assumed).

Vla


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bratislav
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Reged: 09/07/06

Re: Optimized Newts vs APOs new [Re: Daniel Mounsey]
      #5596651 - 12/30/12 06:05 PM

Yes, a well made 13" Newtonian will better smaller APOs any day. Actually, make that SOME days. That full thickness primary will take a long time to radiate heat out. 10 kilos of Pyrex store an awful amount of heat. Try it during rapidly falling temperatures (after a sunset).

You see, it is easy to remember ONE best of everything. I still vividly remember a night when my Mak was so painfully sharp on Saturn that I kept piling the magnification until I ran out of eyepieces (that was at 650x, in a little 180mm Mak!!!). It was the night I tried to capture elusive Encke in smallest instrument to date. I failed (I am now convinced it takes at least 10 inches and perfect seeing to see it as I've never seen it in anything smaller than 12").

But most OTHER nights Mak is an exercise in frustration. As is my SCT, my Newtonians, Schiefspieglers and all other reflective scopes I know and use. APO is far from perfect, and it won't make great seeing from a mediocre night. But it WILL show you what atmosphere allows much more often than any other type. Optimized or not.

Bottom line - yes, a Newtonian (Maksutov/Schiefspiegler/Yolo/whatever) CAN match visually an equal aperture APO on planets.

Once or twice per year where I live.
If I'm lucky.


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wh48gs
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Re: Optimized Newts vs APOs new [Re: bratislav]
      #5596654 - 12/30/12 06:07 PM

Quote:

What I think is even more damaging to reflectors is thermal behavior.




I've noticed that from your previous post. That is also a factor that generally benefits an apo and may, indeed, be the most significant factor (so we have errors due to thermals, obstruction, larger-scale roughness, surface contamination, coatings, all favoring the refractor). Its effect can be minimized in the Newtonian, but will remain larger. At the same time, cooling the mirror diminishes mirror surface protection by the window, so that also has its quid pro quo.

Quote:


And before anyone suggests more 'optimizing', have a good look at my Maksutov.




Can you estimate how much time you've spent just looking at it

Vla


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mikey cee
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Re: Optimized Newts vs APOs new [Re: wh48gs]
      #5596668 - 12/30/12 06:16 PM



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bratislav
sage


Reged: 09/07/06

Re: Optimized Newts vs APOs new [Re: wh48gs]
      #5596669 - 12/30/12 06:16 PM Attachment (9 downloads)

Quote:


Can you estimate how much time you've spent just looking at it

Vla




Hey, if you got it, flaunt it
It is a telescope p*rn after all


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MKV
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Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: Jeff Morgan]
      #5596691 - 12/30/12 06:31 PM

Quote:

Quote:

As general comment, not aimed at the post I quoted, I see the usual list of famous guys that use APOs, but even with my limited experience, I recognize people who have skin in the game and/or a possible financial stake in the APO.



The theory in Psychology is called Cognitive Dissonance. When the guy setting up next to you is getting the same performance while only committing 5% of the resources you did, my bet is you will experience it.



Spot on, guys. Thankfully, we have digital imagery so we c an all "share" in this experience. Enjoy!

6-inch acrhomat vs 6-inch Newotnian

Jupiter 10-inch APO (yeah my pictures of Jupiter were really "horrible"!)

Here is another 6-inch view of Jupiter

Jupiter in an 8-inch APO

Jupiter - 5-inch refractor

Jupiter in Questar 3.5 (price tag ~ $5,000! Buy, hey, it's a Questar!)

Saturn, 5-inch APO (Christen's 5-inch f/6 1985 was selling for $1500 - which is $3856 in 2011 dollars!). Definitely worth it...for some.

I rest my case. Those who want to believe in super telescopes they may.

Mladen


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bratislav
sage


Reged: 09/07/06

Re: Optimized Newts vs APOs new [Re: MKV]
      #5596752 - 12/30/12 07:03 PM

Oh wow, you really give a new meaning to a phrase "building a straw man" !
Maybe you should start learning the differences between planetary imaging (as in stacking of 1000s of selected images) and visual observation.

Actually your second link is useful - people can see what an 'at the eyepiece' view through a 10" APO looks like. I can only wish my 10" Newtonian and 11" SCT are that steady every night.

I've got a video footage of Saturn through 1m Pic du Midi during night of nearly perfect seeing (way too large to attach here). It is spellbinding. I've asked a guy who sent it to me how often they have seeing like that. He responded "nowhere near as we'd like!". This is a purpose built planetary instrument at one of the best (if not THE best) locations in Europe. Right at the peak of the mountain, slick dome with no turbulence creating slits or other discontinuities, figured by one of the best opticians on the planet. Yes, it is capable of staggeringly good planetary images (plenty of them on the web). But have a look what happens at less than perfect night (scroll to the bottom)
http://astro2009.futura-sciences.com/astronomie/2009/07/30/impact-sur-jupiter...

You can find a bad example for just about any telescope if you look around and do that with an axe to grind.


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cheapersleeper
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Re: Optimized Newts vs APOs new [Re: bratislav]
      #5596779 - 12/30/12 07:21 PM

The 10" TMB was very good for afocal.

I don't think Youtube is an authoritative source in this case.


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MKV
Carpal Tunnel
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Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: bratislav]
      #5596810 - 12/30/12 07:36 PM

Quote:

Oh wow, you really give a new meaning to a phrase "building a straw man" ! Maybe you should start learning the differences between planetary imaging (as in stacking of 1000s of selected images) and visual observation...Actually your second link is useful - people can see what an 'at the eyepiece' view through a 10" APO looks like. I can only wish my 10" Newtonian and 11" SCT are that steady every night...You can find a bad example for just about any telescope if you look around if you do that with an axe to grind.



I am beginning to think you didn't read the introductory post. It was clear from the beginning that this was about visual comparison Ed was porposing. Did you miss that?

Photoshop art is a magic method of tempering with evidence. Raw images are the only objective way to compare different telescopes, side by side.

And, by the way, my 8-inch example shows that APOs are also subject to atmospheric turbulence. Just watch that video long enough and see Jupiter disappear.

Yes, "bad" examples are a plenty, but when you put two telescopes together it doesn't matter! They are both imaging the same thing, at the same time, and under the same conditions, and any difference between them is the difference in their performance. It's relative!

What you will see in such a case is that (a) either one is better than the other or (b) there is no difference. If the difference is slight or there is no difference, you may want to ask yourself: why should I pay 20 times more for the other one?

Mladen


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MKV
Carpal Tunnel
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Re: Optimized Newts vs APOs new [Re: wh48gs]
      #5596820 - 12/30/12 07:42 PM

Quote:

I'd like to hear some specifics on that "excellent" attribute.



I'd love to find it for you but I didn't save the link. If I stumble upon it again, I'll send it to you via PM. The author didn't go into details, just stated the coating on all surfaces was still good after 17 or so years.

Mladen


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bratislav
sage


Reged: 09/07/06

Re: Optimized Newts vs APOs new [Re: MKV]
      #5596869 - 12/30/12 08:11 PM

Quote:


I am beginning to think you didn't read the introductory post. It was clear from the beginning that this was about visual comparison Ed was porposing. Did you miss that?

Photoshop art is a magic method of tempering with evidence. Raw images are the only objective way to compare different telescopes, side by side.

And, by the way, my 8-inch example shows that APOs are also subject to atmospheric turbulence. Just watch that video long enough and see Jupiter disappear.

Yes, "bad" examples are a plenty, but when you put two telescopes together it doesn't matter! They are both imaging the same thing, at the same time, and under the same conditions, and any difference between them is the difference in their performance. It's relative!

What you will see in such a case is that (a) either one is better than the other or (b) there is no difference. If the difference is slight or there is no difference, you may want to ask yourself: why should I pay 20 times more for the other one?

Mladen




I give up. Noone stated that APOs are immune to atmospheric turbulence. Where did you read that ???

BTW, what makes you think that in your example of 8" APO a nearby 8" Newtonian would do any better ? In fact, based on my direct experience (which you continue to evade and ignore), it would be worse. Most likely quite a bit worse. How do I know that ? I actually have observed, side by side, with APO and similar size reflector. Many times. Under different seeing conditions, different temperatures, different objects. My own eyes. No imagery, no internet, no cameras of any sort.

Let me repeat the questions that you keep ignoring :

How many high quality APOs did you look through and did the said comparison YOURSELF (Youtube can hardly be taken as pinnacle of truth(tm) when it comes to 'evidence' )?

How many of those comparisons that you keep mentioning were done by a person who owns and has made BOTH instruments in question (an APO and a reflector) as to be unquestionably free from any bias ?

When you answer those questions (to yourself, primarily), we may have something to discuss.
In the meantime it is like discussing religion, which I have absolutely no interest to do.

Actually I just remembered, I have a Herschel prism to finish, and Sun is out. Much more interesting, and far more productive.


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MKV
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Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: bratislav]
      #5596957 - 12/30/12 09:33 PM

Quote:

BTW, what makes you think that in your example of 8" APO a nearby 8" Newtonian would do any better



Where did you read I wrote it would?

You think it would fare worse based on your direct experience? Are we talking the same focal ratio, and windowed Newotnian with 12% CO? If not then you're off the topic, because Ed'schallenege clearly all things being equal save for the windows and 12% CO.

You observed side by side telescopes many times, and with your own eyes, no "imagery, no internet, no cameras of any sort." Are you suggesting you're free of bias, but cameras are not?

It's irrelevant how many APOs anyone looked through. What matters is hard evidence and you don't offer any, yet.

You say "Youtube can hardly be taken as pinnacle of truth(tm) when it comes to 'evidence'", but anecdotal accounts can? Interesting way of thinking, I must admit.

Then you ask "How many of those comparisons that you keep mentioning were done by a person who owns and has made BOTH instruments in question (an APO and a reflector) as to be unquestionably free from any bias ?" Let's just see the images. That should be easy.

As to your invitation "When you answer those questions (to yourself, primarily), we may have something to discuss, " I must say, certainly, as soon as you provide some images. And then let's get down to the implicit effect of such a comparison, namely the 20X price difference. That's a minimum $10,000 question.

Mladen


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Dave O
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Reged: 12/21/11

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Re: Optimized Newts vs APOs new [Re: MKV]
      #5597130 - 12/30/12 11:24 PM

Quote:

Quote:

And perhaps herein lies the problem Mladen ... have you ever looked at Jupiter through a fine APO? If so, and if the view looked the same to you as that in a similar aperture Newtonian, then I agree ... an APO would pretty much be a waste of money for you.



Dave O, no need to change the goalposts. Just tell me have you ever looked through an optimized 6-inch f/10 windowed Newotnian with a 12% obstruction? Neither have I. So neither one of us really knows what difference would be, and what price you and I would be willing to attach to it.




Not changing goal posts, just trying to determine if you know what you are talking about. I have made no claims in this thread about the performance of Newts (optimized or not), nor APOs; I have only remarked on what I've seen through a 3 1/2" Questar, which I use regularly, in response to a posting of images by you earlier in this thread.

For further clarification (and to address your later comments), back in post #5586578 you stated:

Quote:

Using Aberrator(R), I constructed this collection of Jupiter shots starting from 0% obstruction (APO) all the way to 45% (for Newotnians). I intentionally chose a picture that resembles the kind of image reaching the eye rather than the Photoshop(R) art that is commonly used. I think this is a much more realistic portrayal of what an observer can expect to see.

The only thing I did not include are the atmospheric effects at this magnification which would make these images all but stable.




From the above, it was my understanding that the pictures that followed were indicative of the views you've had of Jupiter through a telescope. My only claim was that these images are very poor representations of what can be seen visually at the eyepiece, and are nothing like what I see when looking through a relatively small, obstructed telescope. The conclusion that I arrived at (based upon that post), is that either 1) you have never looked at Jupiter through a quality telescope; 2) your visual acuity is much less than most; or 3) the images you posted do not truly represent the views that you see at the eyepiece in spite of your claims to the contrary. I suspect the latter ...

*Edit (for clarification) -- I am not claiming that images taken through my Questar are better than the posted images; rather I am claiming that what I see at the eyepiece through my Questar is better than the posted images.

As to my other posts in this thread ... I have simply been trying to keep the target centered on the 'challenge' as proposed by Ed -- which was for equal apertures (among other things). In this regard, I've 'reminded' you that the proposed CO was 12% (vice the 15% that you reported later).

Later, I took a moment to refute your analysis using Dawes Limit to determine the resolution of extended objects.

You've accused others of making 'wild claims' on numerous occasions; yet, it seems that you've made some 'wild claims' yourself.

FWIW, I am a big fan of Newts. I am not as certain as Ed (or you for that matter), that they can go toe-to-toe with a fine APO of EQUAL aperture; but, even if they are only slightly larger, they will give an APO a run for the money. That (in my mind) is the true advantage of the Newt -- aperture -- when the seeing is excellent, aperture wins.

I am not certain of the benefits of an optical window on a Newt (I am of the opinion a curved spider is good enough); I am also one who thinks a 17% CO is good enough (in a larger aperture of course). I am certain that some can see a difference in contrast, but I am not certain that difference really matters ...

Edited by Dave O (12/31/12 12:19 AM)


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Daniel Mounsey
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Re: Optimized Newts vs APOs new [Re: Asbytec]
      #5597242 - 12/31/12 12:37 AM Attachment (10 downloads)

Quote:

I optimized my own scope by reducing the CO by about 9% of its diameter. The first and most apparent improvement was to the stellar diffraction pattern. Light in the rings was immediately reduced just as science said it would be. In fact, the number of rings visible was reduced by 1 on the brightest stars. (In fact the third ring is gone and the second ring is now barely visible on Aldebaran.) Reduced diffraction effects on the moon were also noticeably reduced.

Turning to Jupiter, however, it took a good long time of close scrutiny (sketching) to begin to realize improvement must have occurred. It was not immediately apparent even with that much reduction of the CO. The results simply showed up on the sketches over time. So, if I can extrapolate experience with a 9% reduction in CO by diameter, then it's reasonable to conclude a 4% contrast change induced by a 15% CO will be difficult, depending on the target and the real world conditions you correctly speak to.





Norme,
Your ability to notice or even appreciate the difference is quite remarkable, so obviously you have really dedicated some time at the eyepiece. I also like and use Orthos. Perhaps you may wish to share some thoughts here. Central obstruction is indeed a fascinating issue. With that said, I would like to elaborate on p.94 of the 1st edition of Backyard Astronomers Guide, which you may already recall. Using a 7" Starfire under good seeing conditions, the authors suspended 14, 21 and 29 percent obstructions. Both indicated that no real noticeable effects were present in the images.

Interestingly even with a 43 percent obstruction under good seeing on all accounts,they described the image as a reduction in contrast, but by no means, anything less than very good. That's actually quite remarkable. It may be fun for us to have another look to see how aberrator interprets the airy disc and diffraction patterns in each scenario here.

On paper, we should most likely see some differences worth noting, but in reality while observing in the field, the authors feel confident that the issue is superseded by a combination of effects such collimation (to which SCT's and fast Newtonians are especially sensitive to), stray light suppression, scattered light from minor surface roughness, tube currents and system wavefront error, which tend to appear less common with refractors.

In this example, I've seen brief moments where my 14.5" reflector with "excellent" optics surpassed my 6" apo on planets, but once again "only" during brief moments for reasons similar to what the authors described. You and I both know, that a larger reflector on a good day with proper setup (that 14.5" is not setup properly) and seeing will overwhelm the apo on planets, but that was not the case.

COMPARISON

With the Ceravolo HD145 I have, I think the obstruction is something like 18%, but even though I've used it on countless occasions, never once have I even been reminded of a central obstruction nor have I even noticed it. I treat it as an unobstructed telescopes because the contrast is indistinguishable from any refractor as long as it's acclimated.

Edited by Daniel Mounsey (12/31/12 12:08 PM)


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Daniel Mounsey
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Re: Optimized Newts vs APOs new [Re: Daniel Mounsey]
      #5597248 - 12/31/12 12:43 AM Attachment (11 downloads)

In my opinion, the greatest achilles heel of the reflective design is "thermals" by far. This reflector looks okay when it's not acclimated, but
I dare anyone to tell the difference from an apo of equal aperture once its acclimated.


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Daniel Mounsey
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Re: Optimized Newts vs APOs new [Re: MKV]
      #5597261 - 12/31/12 01:03 AM

Quote:

Quote:

Quote:

As general comment, not aimed at the post I quoted, I see the usual list of famous guys that use APOs, but even with my limited experience, I recognize people who have skin in the game and/or a possible financial stake in the APO.



The theory in Psychology is called Cognitive Dissonance. When the guy setting up next to you is getting the same performance while only committing 5% of the resources you did, my bet is you will experience it.



Spot on, guys. Thankfully, we have digital imagery so we c an all "share" in this experience. Enjoy!

6-inch acrhomat vs 6-inch Newotnian

Jupiter 10-inch APO (yeah my pictures of Jupiter were really "horrible"!)

Here is another 6-inch view of Jupiter

Jupiter in an 8-inch APO

Jupiter - 5-inch refractor

Jupiter in Questar 3.5 (price tag ~ $5,000! Buy, hey, it's a Questar!)

Saturn, 5-inch APO (Christen's 5-inch f/6 1985 was selling for $1500 - which is $3856 in 2011 dollars!). Definitely worth it...for some.

I rest my case. Those who want to believe in super telescopes they may.

Mladen




Are these images on par with what some of you are seeing at the eyepiece?


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Pinbout
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Re: Optimized Newts vs APOs new [Re: Daniel Mounsey]
      #5597273 - 12/31/12 01:17 AM

Quote:

CONCLUSIONS

Every dob owner should have a refractor and every refractor owner should have a dob. To disregard either design is a closed minded approach to the hobby








do you have any pics of the back end of the ceravolo?


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MKV
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Re: Optimized Newts vs APOs new [Re: Dave O]
      #5597285 - 12/31/12 01:29 AM

Quote:

My only claim was that these images are very poor representations of what can be seen visually at the eyepiece, and are nothing like what I see when looking through a relatively small, obstructed telescope... the images you posted do not truly represent the views that you see at the eyepiece in spite of your claims to the contrary.



Hi Dave O. The image qulaity is irrelveant because you are comparing two telescope under identical conditions. If the image is poor it will be poor in both scopes. But it may be poorer in one of them, or it may be equal in both. Either way, one must ultimately ask the question if the difference is worth the 20X difference in cost.

I suspect you may have missed my post above of the videos of Jupiter with various scopes - including Q3.5. They all seem poor. That's because "raw" images are not Photoshoped. You can make Jupiter look crystal clear is you stack 1000 frames using Questar 3.5, but don't tell anyone that's what you see through the eyepiece!

Despite the $5K price tag of Q3.5, it's still a telescope the size of many finder scopes. The price tag doesn't make it magically perform like an 8-inch. Claiming that it does is a pretty wild claim.

Mladen


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MKV
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Re: Optimized Newts vs APOs new [Re: Daniel Mounsey]
      #5597288 - 12/31/12 01:33 AM

Quote:

Are these images on par with what some of you are seeing at the eyepiece?



I have seen better. But obviously this is what some people see and even think worth recording. What you see at the eyepiece is not what you see in the Photoshoped images and brochures.

BTW, that's a very shiny tube you've got. Maybe some baffles would do a lot of good.

Mladen

Edited by MKV (12/31/12 01:38 AM)


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