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bino/quadroculars?

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#151 GlennLeDrew

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Posted 15 September 2017 - 01:58 PM

In the absence of aperture masking, the Fresnel pattern remains unchanged for two-eyed vs one-eyed viewing. If the Airy disk appears to shrink, but the rings have the same diameter, this would suggest a dimming. Conversely, a brightening would make the Airy disk 'fatten' up. With bino vision, the seeming improvement in resolving power should be nulled by the seeming increase in brightness, resulting in a Fresnel pattern that has the same Airy disk diameter with respect to the ring dimension. At least, I've never seen anything different enough from this.

 

The reference to the medical study's figure of a resolution increase of some 16% is perfectly in line with the 18.9% suggested by signal theory alone. Again, this is *not* a result of the optics; it's purely occurring in one's brain, whereby the noise in each eye's image is reduced in summation. In other words, both eyes together see what each alone sees, just a bit less noisily, and hence more 'cleanly'. That's it.

 

As pointed out, a parallax increase via a larger objective separation does result, for scenery close enough, in an increase in resolution of depth. Resolution in depth is completely different from resolution in detail.

 

Our brains cannot integrate images in the manner of long baseline interferometry because the two images cannot retain phase coherence, for starters. And even if we could, it would pertain at any one instant over a very tiny angle of order the Fresnel pattern (if I understand correctly--I've never read anything mentioning field size for usefulness.)



#152 SPastroneby

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Posted 19 September 2017 - 05:48 PM

Pffheeeww! Didn't come here for the last week, and my thread has grown into something big like this. At the very least it shows there's an interest in it. And as a second one wonders why no extensive testing has been done, if there's still so much dispute about it. There are a few papers being mentioned here and a few there (in favor of 1,41 or not), but there doesn't seem to be a smoking gun. To be honest, the papers suggesting it's 1,41 have a bit more meat to it than the reverse, concerning actual data.

 

But I find it strange it seems so difficult to prove it one way or another.  Couldn't one just use lasers to simulate different magnitudes of very weak stars, and/or images that pertains to resolution. Then you either have a camera looking at it (or you let a statistically relevant group of, say, 100+ people watch through it), with an 8", then a bino of 2 x 8", then one of x1,19 bigger, and then one of 1,41 bigger aperture, and you compare them all. the results closest to each other would indicate the most similar apparatus, at least in actual observing power.

 

It would rapidly lead to an *actual* measurement of it, instead of all the theoretical talk, which -as we can see - can go on endlessly without ever being truly conclusive.

 

 

 

That's not what the people who built the Large Binocular Telescope are saying. BTW, NASA confirms the 1,41x factor...

 

Peter

 

The LBT uses two mirrors and interferometry to establish a long baseline.  This is not the case with any amateur telescope.  And I think the factor along that single axis is greater than 1.41x.  

 

'nuff said.

 

Jon 

 

 

One second. As far as I'm aware, the binocular design of the Large Binocular Telescope (LBT) has two identical 8.4 m telescopes mounted side-by-side on a common altitude-azimuth mounting for a combined collecting area of a single 11.8 m telescope. They just talk about the lightgathering being equal to one 11,8m telescope here, NOT that they use interferometry. When they DO talk about interferometry, they say this: The two primary mirrors are separated by 14.4 m center-to-center and provide an interferometric baseline of 22.8 m edge-to-edge.

 

It's clear for me, that the interferometry deals with *the resolution*, thus, which takes into account the distances *between* the mirror. It has no relevance to the 11,8m number.

 

Amateur astronomers, sadly, have no expensive interferometry as of yet, true, but this does not mean anything to the equivalent surface area one gets. Now, I know you're going to respond by saying that's because they both have a focal point / "eye", but I'll respond to that at the end of my post.

 

 

 

No, 1,41 is the factor of linear size as confirmed by all sources except Zanewski, which seems to be the only one you quote. S-N just adds to that, as demonstrated by Meese et al. and offers binoscope performance up to 1,8x its diameter. 

 

Try to put a 100mm binocular (with changeable eyepieces to get similar mag) next to a C8 and you'll see what a hard time the latter has in trying to outperform. 

 

The same goes for resolution. Two eyes resolve better than one, just like a composite telescope resolves better than a mono, as demonstrated by the LBT. NASA states that the 8m LBT performs like a 11,2m mono on light gathering power, i.e. 1,41x linear. One brain or one CCD... it makes no difference.

 

Peter

 

I think the counter is, that a CDD can merge the pictures in a way the eye/brain can't. I don't know to what extend this is tested and proven, though. I mean, we all know a CCD is better in many respects, but why would *the principle* of the matter differ, if you look at it in comparison. Why would it drop to 1,19? And even if it were true, then it would still mean, that the 1,41 would be correct if it's about AP and one IS using a CCD. But then, if that is the result of effectively having more light-input and/or resolution, or noise-reduction (aka, objectively, physical causes), and not merely imaginary /brain /subjective, then it's difficult to understand why it would drop so much.

 

 

 

 

 

NASA's statement that the 8m LBT has the light grasp of an 11.2m mono scope is quite true. But they're most assuredly not suggesting this would be the result if it could be used as a visual binocular.

 

The actual light grasp of two optical systems when used as a visual binocular does NOT simply add together to make the image in one's visual cortex equal to a monoscope of the same total aperture area (and hence 1.41X larger in diameter.)

 

I think you may have misconstrued the meaning of the factor 1.41, it relating to *area*, not diameter, where aperture equivalence is concerned.

 

When comparing performance of a smaller binocular to a larger monoscope, it's *imperative* that the test be done at the same exit pupil, not the same magnification. Just as an instrument permits to see fainter stars and eak out more detail as magnification is increased (up until the exit pupil has shrunk to about 1mm), by boosting the smaller instrument's magnification you are giving it an artificial enhancement; that's cheating, if you will. What if the monoscope is already at a 1mm exit pupil? Do you push the bino to smaller than this into 'empty magnification' territory in the incorrect quest for similar magnification? For then the bino would look to be the poorer performer by virtue of pushing it too far.

 

To take this to an extreme. A monoscope is working at a 7mm exit pupil, and a bino is working at a 1mm exit pupil (its resolution limit). In terms of actual, discernible detail, the bino could have an aperture as small as 1/7 that of the monoscope for a nicely bright target. And if we take a 1mm exit pupil as permitting to see stars 2 magnitudes (a factor of 6.3) fainter than with a 7mm exit pupil, the bino aperture *area* could be about 1/6.3 that of the monoscope, which is a linear aperture ratio of SQRT(6.3), meaning the bino could have a 2.5X smaller aperture. That's the kinds of disparity in aperture that can result when seeking comparable resolution or depth of penetration on point sources where the exit pupils vary.

 

But when we compare instruments at the same exit pupil, the performance of the monoscope is equal to that of the bino when its aperture area/diameter is 1.414/1.189 that of the bino aperture.

Yes, the two optical system thingy. I've seen you argue this before, but I've been thinking about this...

 

What about the GMT, then? *CLEARLY* this has only one focal point, and only one 'eye'; all the mirrors come to the same 'eye'. Yet, there too, they use the 1,41 figure, and say it's equivalent to a 22.0 m one. But in this case, one can't say it's due to having two lenses/eyepieces/optical systems. So...are you now saying, when a human would look through it, the lightgathering power would be suddenly reduced to 1,19? This makes no sense, because essentially, it IS the same as a 22m one, with one focal point (apart from some minor losses of the space lost between the mirrors, of course). There is no CCD merging of two or more optical systems, here: all light is gathered in the same place, before it reaches any CCD.

 

So, let's take this - logically - further: a human looks into the eyepiece of a solid, one-piece 22m mirror telescope... surely he sees all the lightgathering power, resolution, etc. OF a 22m mirror telescope...right? Now, divide the same mirror into segments with the same area, but that still convert all light in that same eyepiece; why would he now only see 8,4m x 1,19 x 1,19 x etc increase?

 

It makes no sense to say that a mirror equivalent of a 22 mirror (thus, calculated with 1,41) would suddenly turn into a far less capable telescope (with 1,19) because you're looking through it as a human, while the same mirror with the same area but in a monolithic block, would again yield the same results as a full 22m mirror (since it *would* be a single 22m mirror).


Edited by SPastroneby, 20 September 2017 - 11:02 AM.


#153 GlennLeDrew

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Posted 19 September 2017 - 09:13 PM

If you divide a mirror into a bunch of segments, the total light gathering is still the same (minus the loss due to any gaps.) If divided into, say, 12 equal-area segments, each will collect 1/12 the light of the total.

 

Of course, the gaps will introduce much diffraction, in the manner of a complex spider, which impairs small-scale contrast. Hence the desirability of the contiguous surface of a one-piece mirror.

 

Back to the 'quadrocular'.

 

We know that combining two systems via a beamsplitter results in an actual loss. That's out.

 

We can try to direct the images from two standalone telescopes of the usual form, meaning the primary mirrors are axisymmetric, so as merge into one image. Can't be done without a beamsplitter, else at least one must be tilted, resulting in astigmatism.

 

And so we're left with the MMT approach, which means the two mirrors *must* share the same optical axis. Meaning that at least one is not axisymmetric; a not easy task to figure well. And this means the exit pupil will actually be two pupils exactly representing in miniature the two separated objectives. Which in turn means a bit more diffraction than for the same-area single mirror. And don't forget the requirement for alignment to a fraction of an arcsecond, lest resolution suffer, or double images result.

 

If these hurdles are overcome, the two objectives delivering to one eye will have the image twice as bright. Resolving power perpendicular to the axis connecting the mirrors will be as for one mirror, but along the connecting axis will be that for an aperture of diameter equal to the separation between opposite edges of the pair. But again, for the light grasp there will be more prominent diffraction, and the Fresnel pattern will be a bit odd looking.


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#154 Gleb1964

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Posted 20 September 2017 - 03:51 AM

If these hurdles are overcome, the two objectives delivering to one eye will have the image twice as bright. Resolving power perpendicular to the axis connecting the mirrors will be as for one mirror, but along the connecting axis will be that for an aperture of diameter equal to the separation between opposite edges of the pair. But again, for the light grasp there will be more prominent diffraction, and the Fresnel pattern will be a bit odd looking.

Glenn, just a few comments. When combining two apertures to contribute to one image in not coherent way, the image would be twice as bright and diffraction limit the same as a single aperture. With coherent combining of two apertures the image would be 4 times brighter, as amplitudes of electromagnetic wave double, and intensities are the squares of amplitudes. Because of energy conservation law that means the twice less illuminated area, because airy disc, corresponding to single aperture, would be dissected by dark stripes of destructive interference, reducing efficient area twice. Of cause, it is for monochrome light. As interference structure scaled proportional to wavelength, on polychromatic (white) light it would be vanished on a short distances from null fringe. On extended object the fringes would not be observed as different fringes would overlap each other. So, with polychromatic light and extended objects intensities would just double like by not-coherent combining and no benefit of resolution can be found.

Second comment - I would be careful talking about resolution gain regarding by visual observation with interferometer-like imaging even with monochrome light. Resolution gain is not so straightforward, it is more "mathematical" option. Human brain is not evolved for that. Higher resolution can be derived mathematically under certain circumstances. Interferometer amplifying just selected spatial frequencies corresponding to it's base (distance between combined apertures), so on a monochrome MTF graph it rise just some area on high frequencies.


Edited by Gleb1964, 20 September 2017 - 03:52 AM.


#155 GlennLeDrew

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Posted 20 September 2017 - 07:54 AM

Gleb,

What I'm describing would be like doing this. Take, say, a 16" Newt, and install a mask having two holes of diameter 6" (and separated by 4"), located on opposite sides of the optical axis. This would be just like an 'MMT' comprised of two 6" mirrors. Compare views with one hole open against two holes open. With one hole the exit pupil would be a single (off-axis) disk; with both holes the exit pupil would be two (off-axis) disks separated by 2/3 the disk diameter. Now imagine the Fresnel pattern seen at high power.



#156 SPastroneby

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Posted 20 September 2017 - 12:15 PM

Zarenski was the one who misinterpreted the 1,41x factor, that seems to be clear now. It would also be impossible to do an exact limiting magnitude test because humans are too easily biased and are poor at assessing which star we have seen and which we haven't. Any such test would have a poor result.

 

Therefore I prefer to stick to the "impression" that I get, how unscientific that may sound. You have to admit that a 18% linear diameter increase, as you are suggesting to be the norm between mono and bino, would result in a hardly noticeable improvement at the eyepiece. A C8 against a C9.5. Yet anyone who's ever observed with binoculars, small or large binoscopes and who's compared one against two eyes vision will tell you that that is pure nonsense and that the difference is significant, to say the least.

 

As I wrote in my article, people who'd observed Stephan’s Quintet through my binoscope, were so amazed that they ran off to their photographer friends at the other side of the observing field in order to inform them. The latter didn't want to believe at first so I had to return to Stephan’s Quintet another two times to show it to them as well. In the 20", the Quintet was faint and the faintest members were difficult to see. In the binoscope you didn't need averted vision at all... they were all just there and with structural details too. Where's the math behind this? Honestly, I don't know. I only want to show you that sometimes you have to leave the math behind and simply believe what you are seeing.

 

Hmm... I'm sort of agreeing with Glennledrew on this one, even though I have the impression the 1,19 factor is wrong, and the 1,41 is more correct, based on the data thus far. But that data is pretty meager. But he's right when he says: "However. If you feel a ~0.3m gain is under-represented in your case, can you tell us just what is your own personal improvement in limiting stellar magnitude for bino vision at fixed exit pupil? I ask because I see thus far only non-quantified impressions, which in any scientific context are to be accorded low weighting.

 

I focus on stellar limiting magnitude because it's the easiest means of assessing comparative depth of penetration. And it's a valid indicator of aperture equivalence for point sources since, after all, we predict to good effect stellar magnitude limits based on aperture."

 

Now, I do not doubt you speak true when claiming you see far better - but scientifically spoken, anecdotal impressions are worthless. This should be tested out properly, in actual experimentation. It will also need this, to let the issue be solved once and for good. I also don't understand why this isn't researched to it's final conclusion, with actual experiment. It seems to me, a lab could easily set this up, and to counter the 'subjectivity' one could just use a CCD, imho. Yes, they're more sensitive and what not, but *the principle* would still be valid: if you take the same eyepiece with the same CCD and the same conditions (such as exposure-time), one would still be able to determine (with lasers/false stars of exact magnitudes) if the resolution power, lightgathering power, etc would be more akin to the 1,19 number or the 1,41 one.

 

Alternatively, one could just go for the statistical approach with humans, in a double blind test. You let, say, 100 people look at 10 different patterns and count how much stars or details they can see, then, if a significant difference (in the scientific sense of the word) is found for one way or the other (for equivalent aperture-size) you have a high statistical likelihood you are correct. Statistical analysis using the scientific methodology brings worth to anecdotal evidence and observations, after all.

 

This is why I'm slightly leaning towards the 1,41 number, because the most data is collected there, even if it's not conclusive. But for the 1,19 number, there is even less.

 

I really wished someone - maybe an amateur or pro-astronomer - would make his thesis about it, or a dissertation-paper.


Edited by SPastroneby, 20 September 2017 - 12:15 PM.


#157 SPastroneby

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Posted 20 September 2017 - 12:28 PM

 

 ...there's also a significant gain in resolution.

 

Hi Peter,

 

I would rather call it "a significant gain in perceived resolution", because our brain just uses our eyes as photon-collecting sensors. However, as everybody knows, it's not the eyes that "see"  -  it's our brain which does.

 

The size of the Airy-disk projected on the retina certainly doesn't change in either eye just because there is another eye collecting photons next door. But binocularly the brain has two independent sensors at its disposal providing more information to analyze in order to finally synthesize a better image.

 

But how exactly the brain merges and analyzes the two incoming streams of information in order to calculate a more informative image than one-eyed only, is still quite unexplored shrug.gif .

 

There still are phenomena which can't be quantified just by using simple formulas...

 

Chris

 

 

Yes, well... that's all good and well, but what about the objectively measured increase, then?

 

I see a lot of this 'the brain is weird in composing images/seeing things', but somehow, this seems to bypass the central question of how much gain it *actually* has. What would be the result if one used CCD's, instead of human eyes/brain, for instance?

 

Or...what can people *actually* differentiate? I mean, let's assume eyes/the brain does weird things, but than the question still begs: working weird as it may, how much better can it perceive things through a bino? (aka, the statistical approach).

 

I don't see any research/data that has done this. (Though I see "Campbell and Green" mentioned a lot, but didn't see any link; does anyone have a link to it?)



#158 SPastroneby

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Posted 20 September 2017 - 02:58 PM

Sorry if I seem to mass-post a bit, but I've been away from this chan for a week, and my thread has become so huge I'm backlogging, and kinda answering them in reverse (though my multi-quotes should be in chronological order, more or less).

 

 

 

That's all very interesting and I already knew that seeing isn't such an issue with binocular viewing since I got my first binoviewer. 

 

However, you haven't answered my question. Who says that our brain doesn't combine both images in the same way as the LBT does? 

 

Seeing was particularly calm when I made my observations and in both cases the airy disks were well defined. So how do you explain that observing with both eyes showed more black between both components or, in the case of STF2696, I only saw one elongated star with one eye and both stars well defined with binocular vision?

 

I refuse to accept that this is simply due to seeing, just like you can read a text from a further distance with both eyes. Unless I see some relevant scientific evidence, which up till now no-one has presented.

 

Peter

Peter, with detection of electromagnetic wave in visible range the fase information would be lost. There is no such fast enough detectors for visible, IR and even far IR range. If step down in frequency by 3-4 orders to therahertz range, there are detectors which can detect both fase and amplitude, those used in radio interferometry (like VLBI), where it is possible to interfere signals after detection by correlating recorded signals. But in shorter range, including visible, information about fase would be lost, detector fixing only signal's intensity (square of amplitude). So interferometry in visible range required only coherent mixing of light before detection. The same valid for eye, it only provide intensity distribution, no fase to correlate signals in brain, no way. No gain in resolution above limit defined by difraction of every single aperture is possible, no change in size of airy disc.

I thought I have explained exactly that before.

 

I have been wondering, Gleb, why this is the case. I'm aware optical interferometry has come long after radio-wave interferometry, because, as I assume, the waves are much shorter. Thus, it entails more technical challenges, I understand that. However, I don't see any physical law prohibiting doing the same thing with visible wavelengths as one can do with radio-waves; both are electromagnetic waves, after all. So why, with modern progress in optica and computerisation, couldn't we make a mixing of light AFTER detection, just as we already can for radio-waves. There does not seem to be some inherent impossibility to it, so is it only a matter of technical prowess in resolving the equally technical difficulties?

 

It would seem to me, that a lot of annoying issues and complxity at the telescope's side would be gone if one could simply make the light of different telescopes coherent *after* they are collected. After all, isn't it just data, in its essence?

 

Take adaptive optics, for instance. They now use deformable secondary mirrors to counter airdisturbances, based on the data given by a fake star (laser) as a reference for the variables. I've always wondered why they have to do that. Wouldn't it be far simpler to just record the exact data of the phase-shifts of the light coming into the mirror, and record that. And then record the exact data of the fake star as well. And then 'play back' both data and change the waves accordingly from one dataset in regard to the other?

 

Basically: why can't the incoming wavefront, when recorded, not be corrected by the (data of) the wavefront sensor, AFTER the light (and it's varying wavefront) went in and was recorded? I don't understand why they need a mirror to do the work beforehand. It's just data, essentially. One can  do the processing later, no?

 

Can you shed any light (pun intended ;-) on this?

 

 

@kunuma:

 

"I don't think you're reading that post correctly. Multi mirror telescopes are not used visually. I would think the resolution of an 18" binoscope in binocular visual mode is exactly that of a single 18" mirror.  This looks like a never ending thread...."

 

I agree with you on the resolution -front, but I can't understand how it would not double the lightgathering power. When the LBT says it's equal to a 11,8m telescope, they're not talking about resolution. Glenn made a valiant effort to explain it, and I sort of understand what he's saying, but I have difficulty in following him through completely. For instance, does it really matter whether there is coherency/interferometry in regard to light-gathering power? Let's say there's not in principle, because you still have double the are of lightgathering that you had before, so what does it matter if it's coherent light or not, or whether it hits an eye or a CCD? I mean, obviously both mirrors or lenses would need to be in focus, but if they were, in, say, one eye, whether this is a human eye or not, two 'buckets of light' should gather double to amount of light. There might be issues of focus, of coherence, of fresnel paaterns, of whatever, but 2 times a given (mirror)area would mean two times as much light that is gathered.  I can't see how this would be logically disputed.

 

Yet, I seem to remember someone here saying, in my example of a quadroscope, the first two (joined as a binocular) telescopes (for instance, the two on the left), would yield no better result, since the image would get 'merged'. And the 1,41 betterment would only show up when the two eyes were used (that's to say, one eye for the left telescope(s) and the other from the right telescope(s). Was he in error, or am I missing something here? Is it because the human eye can't discern it? (and with a CCD one can?). This seems weird to me, as a single mirror with exactly the same area, the difference would definitely by noticeable with a human eye.

 

So what would be needed to make a hypothetical quadroscope work on its best? First the light of the left and right side telescopes merge (coherent? or would there be improvement even if not?), and then guiding it to one eye each (from the left and the right)? Or an additional merging coherent/inteferometrically once again in one point/eye? And what with CCD's for AP? Just one in each telescope, and letting it work like the MMT?

 

I'm wondering what configuration would give the worst outcome (but while still working), and what the best.

 

 


Peter:

 

A binocular telescope does not behave exactly as telescope of twice the aperture.  If it were a twin objective telescope or segmented mirror  telescope like the Kecks, where objective or mirror contributes to the overall aperture then it would perform according to the combined aperture.

 

But a binocular telescope does work that way, it's two separate objectives that are not linked.  It produces a pair of identical Airy disks, one in each eye and the eye has no way of combining them to reduce their size.  

 

Jon

 

 

Ok. But is that due to the imperfect merging in the brain? If that same binocular was used by two CCD's instead of eyes, and the image merged then, would it then behave exactly as a telescope twice the aperture?

 

Peter,

Are you certain as to what the 1.41 factor applies? It's signal to noise, which corresponds to the area of the equivalent aperture, not the diameter.

This I had a question with as well. Surely there is a direct correlation between diameter and the area of the equivalent aperture? Granted, a doubling of the diameter will be far more than a doubling of the light gathering power (it would double the resolution, but make it four times better in light gathering). But a doubling of the area would still be doubling the light gathering, no? And wouldn't that result in an equivalent diameter of 1,41 times that of the original diameter (when the same area is doubled)? So isn't the 1,41 factor directly related to the diameter, just *because* there was a doubling of the area?

 

 

Peter,

I still haven't received that paper, so thanks for the summary...

 

So, we see that some investigators obtain a detection boost of about root two (1.41), but here we see a result of 1.7. That latter figure would then correspond to a linear aperture ratio of SQRT(1.7) = 1.3. For example, a 130mm aperture monoscope would be about equal to a 100mm binocular--at the same exit pupil.

 

It would seem that the point source result of around 0.3-0.35 magnitude derived by numerous amateurs using stars would indicate a smaller improvement n binocular detection than that obtained by a resolved pattern of cyclical variation.

 

There might be a bit of a boost in detection when a repeating pattern is involved versus a single patch or blob. This *might* in part account for the larger-than-1.41 detection ratio.

Thanks for the explanation. I was reading the conclusion (a few times), but found it hard to understand in a pragmatic way. Not sure why they went for a scale of decibels..

 

 

"The innate need to quantify things leads to an attempt to put the gain into numbers. Like many others, I was content to accept the simplistic root two gain based on signal theory, which was widely enough promulgated. And it closely enough accorded with my own impressions and determinations.


Your correspondent noted the amateur's fetishistic need to find equivalences.  How true! [wink.gif] Given the wide variation in subject brightness, size and form, it's probably foolhardy to try and pin things down to one value. But if one has to do so in order to give *some* idea, being a bit on the conservative side has merit. For the beginner who might observe the brighter stuff, a smaller aperture equivalence would apply. Moreover, there's less chance to set up potentially unrealistic expectation. The more experienced folk who work in the realm of threshold observation can realize a larger gain and hence aperture equivalence."

 

The need to find equivalences... indeed, indeed. smile.gif  Also, it could have practical implementations and results too, in an economic sense, IF it were proven once and for all what (and how much) the advantages are, at least objectively. As said, when I started the thread it was with the idea that, if the 1,41 number was right, a binoscope of two smaller apertures would equal that of one bigger one to the point, where the threshold is reached that it becomes economically more interesting (for a certain, given (large) size of aperture). This is, because prices of telescopes (and certainly APO's) do not go up linearly.  For instance, two 180mm APO's would cost 50000 EUR together, while the equivalent 254mm one costs 77000 EUR. Quite a steep difference of 27000 EUR.

 

That is, IF that 1,41 number holds up. The lower it gets, the less use it has, economically speaking.


Edited by SPastroneby, 21 September 2017 - 11:44 AM.


#159 PeterDob

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Posted 21 September 2017 - 03:33 AM

Right. Yesterday evening the sky was perfect again so I tried Gleb's (brilliant) idea and masked the binos down to 10cm and pointed at a fairly bright star (Alpheratz) which would allow me to study the diffraction pattern at 507x.

 

20170920_221056.jpg

 

Michelson and Morley once conducted an experiment that became world-famous... because it completely failed. I'm sort of in the same position here and must humbly admit that the skeptics were right, as far as resolution's concerned, and that the airy disk changed bugger all. So my apologies for having insisted so much, but the difference when observing those doubles was really striking and led me to believe that resolution effectively changed. Now it would probably be fair to say that binocular observation works like stacking photos, but nothing more

 

HOWEVER...

 

Coming back to SPastroneby's original question, all scientific studies that have been conducted so far agree that (I've previously posted all the links):

 

- There is no such thing as a single binocular summation factor and that summation improves when conditions worsen (Pirenne, 1949)

- The extent of summation depends on stimulus contrast and duration (Bearse and Freeman, 1994)

- There is significant summation at low contrast (Banton and Levi, 1991)

- At low contrast, the level of summation is greater than could be expected by probability summation alone (Simmons and Kingdom, 1988)

- Summation depends on the complexity of the task, with simple tasks (detection) displaying far greater summation than complicated ones (pattern recognition) (Frisen and Lindblom, 1988)

 

Therefore, it appears that Zarenski's quite alone with his 1.19x diameter increase, which he merely derived from the "standard" 1.41 summation factor by Campbell and Green, which wasn't meant for low-contrast observations in the total dark at all. Since Zarenski's can hardly be called a scientific study, his statement is completely irrelevant against all of the studies I mentioned.

 

So, what exactly is the real binocular summation factor of a binoscope? Honestly, I don't know and I don't think anyone could put a number on it. Perhaps it also depends from person to person? Doing a limiting magnitude test would be difficult, if not impossible because which stars will you use as a reference? You'd also need a lot of people to get a scientifically relevant result.

 

I risk becoming tedious here, but about 20 people confirmed that a 20" is no match for an 18" binoscope, whereas according to Zarenski they would be more or less equal. A 27" may be slightly superior as regards to light gathering power, the increased binocular contrast of the binoscope made it a pretty close call (I know... only confirmed by me and the other telescope's owner).

 

I could also link to a very interesting article, written by someone who's used big, astronomical binoculars for decades and has published many articles on the subject. In one of these, he compares 100mm Miyauchi binos to a 150mm short-tube APO. Unfortunately it's in Italian (can send it on request if you like), but it is interesting as it compares the same aperture difference as my 18" binos against a 27" mono and... he comes to exactly the same conclusions. The APO lets you go slightly deeper (also because the Miyauchi aren't designed for high power), but binocular contrast makes it a very close call on faint, extended objects. Therefore, if you insist on having a number, my best guess is that a pair of binos perform like a monocular telescope 1.4x its diameter, as I've always stated. I know that "impressions" don't mean much, but the difference with closing one eye is simply too great and certainly much more than the hardly visible 1.19x. Faint stars for instance suddenly disappear or become very hard to see. With both eyes M104's dust lane suddenly appears full of structures, which fade to a dark band with monocular vision. With both eyes I see the Pillars of Creation in M16, whereas they're invisible with one eye (under my SQM20.9 sky and with my eyes). Nebulae appear so much brighter and richer in detail, faint galaxy clusters suddenly become easy, "impossible" objects such as the extremely faint planetary ARO215 suddenly become possible... An aperture increase of only 19%? Nah, I don't buy it.

 

That's my opinion. I will no longer bother you with my bickerings from now on, since I have some star gazing to do. grin.gif

 

Cheers,

 

Peter


Edited by PeterDob, 21 September 2017 - 04:09 AM.

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#160 Gleb1964

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Posted 21 September 2017 - 03:51 AM

Gleb,

What I'm describing would be like doing this. Take, say, a 16" Newt, and install a mask having two holes of diameter 6" (and separated by 4"), located on opposite sides of the optical axis. This would be just like an 'MMT' comprised of two 6" mirrors. Compare views with one hole open against two holes open. With one hole the exit pupil would be a single (off-axis) disk; with both holes the exit pupil would be two (off-axis) disks separated by 2/3 the disk diameter. Now imagine the Fresnel pattern seen at high power.

Ok Glenn, that is how it looks by Zemax simulation.

polychromatic Huygens PSF full aperture 400 700nm
Polychromatic PSF of initial 16 inch aperture

 

polychromatic Huygens PSF single hole 1x6in 400 700nm
PSF after adding 1 6 inch hole

 

polychromatic Huygens PSF combined aperture 2x6in base10in 400 700nm
2x 6 inch holes, separated 4 inch (10 inch center-center)

 

polychromatic MTF full aperture Vs aperture mask with 2holes 400 700nm

Polychromatic MTF graph of initial 16 inch aperture and with added 2 holes mask above, making it interferometer-like. The MTF of combined of 2 holes aperture drops down middle spatial frequencies, but it superior for some range of higher frequencies, correspondent to interferometer baseline. In orthogonal direction to baseline MTF is the same, as single 6inch hole has.

 

Would be on sky sinus-shaped object, like test objects used in labs, it possible to benefit on increased contrast performance on certain frequencies. But for normal extended objects visual performance would be bad. It is similar to degradation of performance with using huge central obscuration.


Edited by Gleb1964, 21 September 2017 - 03:52 AM.

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#161 GlennLeDrew

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Posted 21 September 2017 - 07:58 AM

Peter,

Comparing performance on intrincally 'high' contrast targets like stars, most folks find a limiting magnitude gain of around 0.3m or so when both eyes are open vs one. Signal theory's gain in S/N of 1.41, which means an aperture equivalent linear aperture ratio of 1.19, suggests we should expect a magnitude limit difference of 0.37. That real world results are somewhat poorer naturally means a slightly smaller than 1.19 linear aperture equivalence. For stars. And so Zarenski's propounding of the 1.19 figure is not at all unrealistic, based on actual results obtained for stars, which was his sole criterion. Perhaps he naively extended this across the board, as I was inclined to due to no pressing reason that suggested itself to me.

 

Of course for the more difficult detection of details in low contrast extended objects a larger aperture equivalence ratio is indeed suggested and supported. And so we are more clearly seeing that there's a continuum.

 

Gleb,

Thanks for the inclusion of the Zemax plots. Just for clarity, I take it that in the MTF graph the two curves for the 6" apertures has response plotted for the orthogonal axes, one for the poorer resolution perpendicular to the line joining the two apertures, and the other for the better resolution along the line joining the two apertures.



#162 PeterDob

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Posted 21 September 2017 - 08:14 AM

Come on... How on Earth did he come by that magic number 0.31 magnitude which so coincidentally coincides with the 1.41 C&G summation factor? Which stars did he use as a reference? How many people were involved? Who were involved? Please, that number is just nonsense.

Besides, he was NOT looking at high brightness/contrast objects but at the faintest visible stars which implies a maximum summation factor as per the studies I've mentioned.

Peter

#163 Gleb1964

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Posted 21 September 2017 - 09:13 AM

Peter,
Comparing performance on intrincally 'high' contrast targets like stars, most folks find a limiting magnitude gain of around 0.3m or so when both eyes are open vs one. Signal theory's gain in S/N of 1.41, which means an aperture equivalent linear aperture ratio of 1.19, suggests we should expect a magnitude limit difference of 0.37. That real world results are somewhat poorer naturally means a slightly smaller than 1.19 linear aperture equivalence. For stars. And so Zarenski's propounding of the 1.19 figure is not at all unrealistic, based on actual results obtained for stars, which was his sole criterion. Perhaps he naively extended this across the board, as I was inclined to due to no pressing reason that suggested itself to me.

Of course for the more difficult detection of details in low contrast extended objects a larger aperture equivalence ratio is indeed suggested and supported. And so we are more clearly seeing that there's a continuum.

Until good seeing condition and stars are diffraction limited, increasing linear aperture by factor of 1.19 decrease size of diffraction by the same factor, so aperture collect 1.41 more light on the 1.41 less area. That means 2 times light density, signal noise ration improved 1.41, detection limit improved by the same factor, and that factor would match bino performance.

In case of poor seeing condition when stars are seeing limited and looks like extended objects, large aperture collect more light, but can't concentrate it in a smaller spot. You need increase aperture by higher factor, to match bino performance, especially on detection of faintest stars, were bino would have factor up to 1.7-1.8. At bad seeing condition single aperture should be increased by linear of factor 1.3-1.34 to match bino on faint star detection. The same factor one can calculate for any low contrast extended objects.

Having different objects in the field of view at the same time, brighter objects would benefit less, then faint in bino. If one would derive one digit, need agree which of objects have to be selected.

 

Gleb,

Thanks for the inclusion of the Zemax plots. Just for clarity, I take it that in the MTF graph the two curves for the 6" apertures has response plotted for the orthogonal axes, one for the poorer resolution perpendicular to the line joining the two apertures, and the other for the better resolution along the line joining the two apertures.

Yes Glenn, you are right, and MTF for poorer resolution direction is exactly as MTF of a single hole. 



#164 PeterDob

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Posted 21 September 2017 - 09:30 AM

 

 

Until good seeing condition and stars are diffraction limited, increasing linear aperture by factor of 1.19 decrease size of diffraction by the same factor, so aperture collect 1.41 more light on the 1.41 less area. That means 2 times light density, signal noise ration improved 1.41, detection limit improved by the same factor, and that factor would match bino performance.

In case of poor seeing condition when stars are seeing limited and looks like extended objects, large aperture collect more light, but can't concentrate it in a smaller spot. You need increase aperture by higher factor, to match bino performance, especially on detection of faintest stars, were bino would have factor up to 1.7-1.8. At bad seeing condition single aperture should be increased by linear of factor 1.3-1.34 to match bino on faint star detection. The same factor one can calculate for any low contrast extended objects.

 

 

 

Says who???

 

Really... who established all of this? BTW, Gleb, have you ever observed through a binoscope and done a limiting magnitude test? I'd challenge anyone to see the difference between a mag. 17 and a mag. 17.3 star. Heck... I can't even get two equal results when trying to guess the naked-eye limiting magnitude.

 

But who am I to question Zarenski's law? I'm just and old bugger that happens to observe with a binoscope all the time...

 

Peter 



#165 daquad

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Posted 21 September 2017 - 11:03 AM

Peter, glad to see you tried that experiment.  I assume your results confirmed that the star's Airy disc remained the same size.  However, I was hoping you could tell whether or not the shape of the Airy disc changed to look more oval, with the minor axis of the oval being along the line joining the two apertures.  (I say oval, because I am not sure if the cross section of the disc would be an ellipse.)

 

BTW, to reinforce your claim regarding magnitude detection difference, most people will have difficulty detecting a magnitude difference less than 1/3 magnitude.  Experienced variable star observers can get to 1/10 magnitude using the fractional and/or step method, but this takes a lot of practice, whereas 1/5 magnitude is more likely to be realized using these methods.

 

Dom Q.



#166 Eddgie

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Posted 21 September 2017 - 11:46 AM

This conversation has drifted a bit but in the context of the OPs question, I would say that a lot of what has been covered suggests that the gain in a binocular telescope is very real (and my experience is that this is true because a 100mm binocular will do much better than a 100mm refractor of similar focal length and quality.

 

But the question to me is would a quad scope  be better than building a binocular that had the same size and weight, and would this be better than a single aperture of the same size and weight using a binoviewer (even if it were custom designed for the application).

 

See, the binoviewer dims the image, but you still get the resolution of the native aperture.

The binocular telescope  at the beginning of this article weighs 330 lbs and only the builder knows how much it cost. It is impractical to move so it takes a dedicated space, or an observer that is way more patient than most of us would be if it required moving. 

 

Now lets say we were talking about building a quad scope with four 6" refractors.  That would be a very complex and quite heavy telescope (not to mention expensive is you used 4 Apos.

 

So the question to me (and the one the OP should ask himself) is whether he could expect a result better than he could get with a standard 18" telescope using a binoviewer.

 

We get wrapped up in these theory questions, but often the raw truth is that an increase in aperture is a sledgehammer approach that generally works. 

 

Since the OP posted in a refractor forum though, My guess is that he thinks an Apo Quad scope would be this magnificent beast that would blow everything else away.

 

Building it though would be insanetly expensive and difficult, and in the end, it would probably not be able to provide a better view than a single 18" Newt with a Binoviewer. 

 

I am still waiting to see the design..   That is when the reality of the feasibility of this will start to come through.  It is all theory and unless there is a design in mind, it is just a lot of talk.  

Show me the money.   Let's see the conceptual design.   That is where we can say "WOW!" or we can say "Yeah, but....." 

 

I love a good theory discussion, but sometimes, we loose sight of the fact that the proposal itself is simply one that can't be easily executed so is unlikely to happen or sometimes there is simply a better way to get to the goal.  

 


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#167 PeterDob

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Posted 21 September 2017 - 12:06 PM

Hello Dom! To be honest, I didn't see the slightest difference in the airy disk between mono and bino. There wasn't even a hint of an oval... :( But thanks for conferming my point. I'd really be interested to know how on Earth Zarenski claimed the limiting magnitude increase of 0.3 with binocular vision. I suspect it was not derived from actual observations but merely a calculation based on the useless (in this case) C&G summation factor.

 

Cheers,

 

Peter



#168 SPastroneby

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Posted 21 September 2017 - 01:54 PM

This conversation has drifted a bit but in the context of the OPs question, I would say that a lot of what has been covered suggests that the gain in a binocular telescope is very real (and my experience is that this is true because a 100mm binocular will do much better than a 100mm refractor of similar focal length and quality.

 

But the question to me is would a quad scope  be better than building a binocular that had the same size and weight, and would this be better than a single aperture of the same size and weight using a binoviewer (even if it were custom designed for the application).

 

See, the binoviewer dims the image, but you still get the resolution of the native aperture.

The binocular telescope  at the beginning of this article weighs 330 lbs and only the builder knows how much it cost. It is impractical to move so it takes a dedicated space, or an observer that is way more patient than most of us would be if it required moving. 

 

Now lets say we were talking about building a quad scope with four 6" refractors.  That would be a very complex and quite heavy telescope (not to mention expensive is you used 4 Apos.

 

So the question to me (and the one the OP should ask himself) is whether he could expect a result better than he could get with a standard 18" telescope using a binoviewer.

 

We get wrapped up in these theory questions, but often the raw truth is that an increase in aperture is a sledgehammer approach that generally works. 

 

Since the OP posted in a refractor forum though, My guess is that he thinks an Apo Quad scope would be this magnificent beast that would blow everything else away.

 

Building it though would be insanetly expensive and difficult, and in the end, it would probably not be able to provide a better view than a single 18" Newt with a Binoviewer. 

 

I am still waiting to see the design..   That is when the reality of the feasibility of this will start to come through.  It is all theory and unless there is a design in mind, it is just a lot of talk.  

Show me the money.   Let's see the conceptual design.   That is where we can say "WOW!" or we can say "Yeah, but....." 

 

I love a good theory discussion, but sometimes, we loose sight of the fact that the proposal itself is simply one that can't be easily executed so is unlikely to happen or sometimes there is simply a better way to get to the goal.  

 

 

Granted, a binoscoop, and certainly a quadroscoop, would be too heavy and too complex to easily go on star-parties with it, and set it up at the fly there. But I already agreed so in an earlier post, and also, I never started from that premise anyway. I mean, I didn't imply it was meant to be used 'mobile'.

 

But, you have amateur-astronomers who have small (or large) bought - or self-made - observatories too, and let's assume it's for that purpose, which makes the whole issue of your first part of the post irrelevant in that particular aspect.

 

Truth be told, in the department of 18" to 25" , even without bino's, the mobility decreases anyhow. So, let's start with the premise it's for a fixed place.

 

The REAL issue for me was, that, given those conditions, whether or not it would be beneficial - in cost/benefit terms - of having a bino or quadro (of 2 or 4 smaller apertures) compared to the more-expensive one-piece telescope of equivalent aperture. This is, if the cost of 2-4 smaller scopes would have similar capacity of one bigger one, but for far less money. If that were possible, was the underlying question. If the 1,41 number were true, then it would seem that it *should* be possible, seen the prices augment non-linearly at a certain threshold of aperture.

 

The reason I took refractors instead of reflectors isn't a defining issue, I merely took refractors as an example because: 1)there was even less data or examples of it, and I like the unusual out-of-the-box thinking the most - and a quadro refractor is highly unorthodox, I think we can all agree on this, 2)there is no or less need for collimation in refractors, 3)I know the prices best of refractors, and it's clear APO's are in a segment where prices drastically augment from a given aperture (about 150mm). But, if reflectors also have this drastic increase starting from a certain aperture, in principle, this holds true regardless.

 

I was NOT trying to claim or indicate you could get the best bang for your bucks by using refractors (bino or quadro) instead of reflectors. Obviously, it you just go for "with a given budget, with what can I get the most light-gathering prowess", then reflectors always win, from 10cm onward.

 

No, my post specifically deals with the question whether a bino or quadro could trump the equivalent mono - whether it's refractors or reflectors - in cost/benefit terms. And why, if the 1,41 number was right, did that not show itself in the field? And whether or not that continues the more telescopes you add. Obviously, if it did, then 4 x a smaller diameter would equal a far larger diameter, but for a fraction of the price. If that were true, I find the lack of enthusiasm for it strange. So either something is off, or the number isn't right (which led to this whole theoretical discussion), or, as the proponents of bino's said, the fact that there is a bias and people (wrongly, according to them) use the 1,19 number instead of the 1,41, led to no enthusiasm from the amateur-astronomer to want to buy it or try it out, and consequently, also to very meager enthusiasm of manufacturers. To them, the lack of more bino's/quadro's is a sort of self-fulfilling prophesy, since most amateur astronomers consider the 1,19 number as true, and thus non-viable or at least not wortwhile, few are interested in it, and since few are interested, few manufacturers are interested in selling them, making the exceptions unduly expensive, which leads to even less enthusiasm, etc. Rince, repeat. I'm not saying this is correct, but it is a possible answer for the lack of bino's/etc. This is why a definite answer to what a bino or quadro equals to is important, because it would break open (or let it rest for good) the issue for such systems.

 

That's the underlying question, here. As I've repeatedly said in my past posts, it's not a "I want to make a quadroscope"-proposal. It's a "Why aren't there more bino/quadroscopes around if the number of 1,41 is right, and my logic holds of the price-benefit comparison?" (an alternative explanation would have been that the 1,41 number was right, but the added complexity (and thus price of the needed optical systems) of merging the images would cost more than it would gain, and thus it would never have a better cost-benefit factor than buying a mono, for instance. But, strangely enough, I didn't see that extensively being used as a counter, at least not with some indication of what actually would be needed, and what it would actually cost.)

 

Most of the counterarguments dealt with the question of the 1,41, though. And indeed, if it was 1,19, the economical benefit/incentive would be far less, which would underscore the lack of commercial mass-produced available bino's or even quadro's. The discussion which number IS right, and what equivalent may be used, led to this whole theoretical discussion in this thread - and at the end, we're still not quite sure, is what I gather from it.

 

As for your specific question about how a quadro would work; well; I don't know. WOULD it work to begin with? You have 4 lenses, 2 on the left (L1, L2) and two on the right (R1, R2). I would assume one would first merge the light from both sides (L1 + L2 and R1 + R2) and then reflect it with small flat mirrors into the left and right eye, accordingly, as you would with a bino. Whether it would or could work, is exactly my question. And if not, is it due to technical problems (aka, it's possible in principle) or is it fundamental?

 

For instance, if it's true that having two lenses or mirrors (aka, double the area) - say L1 and L2 - and you merge the image, you have NO benefit at all (nor in resolution, nor in light-gathering) when it reaches you're left eye (or CCD, if you're doing AP), compared to one such lens of mirror (aka, half the area)... then obviously, the concept wouldn't make sense at all. But, as said in earlier posts, I find the notion of doubling your area (and thus light-gathering bucket) and having NO additional benefit at all, difficult to comprehend.

 

IF that is the case which is being made against it, but I'm not even sure it is. As said, the question thus far mainly boiled down to the 1,41 vs 1,19 debate. And with good right, because IF the 1,19 is right, then there would almost be no incentive to go for a binoscope, let alone a quadroscope instead of the equivalent mono.


Edited by SPastroneby, 21 September 2017 - 02:30 PM.


#169 Gleb1964

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Posted 21 September 2017 - 05:36 PM

 

Until good seeing condition and stars are diffraction limited, increasing linear aperture by factor of 1.19 decrease size of diffraction by the same factor, so aperture collect 1.41 more light on the 1.41 less area. That means 2 times light density, signal noise ration improved 1.41, detection limit improved by the same factor, and that factor would match bino performance.
In case of poor seeing condition when stars are seeing limited and looks like extended objects, large aperture collect more light, but can't concentrate it in a smaller spot. You need increase aperture by higher factor, to match bino performance, especially on detection of faintest stars, were bino would have factor up to 1.7-1.8. At bad seeing condition single aperture should be increased by linear of factor 1.3-1.34 to match bino on faint star detection. The same factor one can calculate for any low contrast extended objects.

Says who???
 
Really... who established all of this? BTW, Gleb, have you ever observed through a binoscope and done a limiting magnitude test? I'd challenge anyone to see the difference between a mag. 17 and a mag. 17.3 star. Heck... I can't even get two equal results when trying to guess the naked-eye limiting magnitude.
But who am I to question Zarenski's law? I'm just and old bugger that happens to observe with a binoscope all the time...
 
Peter

 

Peter, no needs to complicate things. The question, we discussing, can be formulated like: How much human gain by observing the same scene with one or with two eyes? Really, no need in binoscope, no need to look on stars.

A point source in a dark room, adapted to darkness observer, tape-measure to measure distance from observer eyes to point source - that is all what need to conduct experiment. The distance to point source works as precise attenuation factor. It is need only to find distances when observer begin to detect source with both eyes or with left/right eyes open. Gaining factor for point source can be found as relation of squares of measured distances.

Additional conditions - observer can use eyeglasses, if need seeing correction. Light source power supply should be stable. Light source preferably white, like incandescent lamp, with continuous spectrum and even angular distribution. A tiny hole in aluminum foil with ground glass diffuser highlighted behind.

Experiment setup can be modified to define performance gain on extended objects. In that case observer located on a fixed distance from test-object, illuminated by weak source. Test-object brightness attenuated by changing distance from source to test-object. Need to find maximum distance when detection of test-object is still possible and compare square of that distance for both eyes against one.

Still no needs for a binoscope yet. Of course, if we want to stop down eye, as often a cause with using optics with output pupil smaller then eye, then need some complication. But until we are not measuring eye resolution there is no need in such complications. I thinks, described above experiment setup can deliver efficiency of brain merging two eye. Having that digits it is possible to calculate efficient aperture gain regarding to binoscope.


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#170 GlennLeDrew

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Posted 21 September 2017 - 06:22 PM

Gleb,

Your previous post brilliantly outlines a limiting magnitude test, under *controlled* conditions. Several measurements of threshold distance should average out the small individual variations of such things as fluctuating iris aperture.

 

I'd add this. Do not do this in complete darkness. A person's visual system becomes utterly dominated by noise. A lighter environment, of brightness more like that of a fairly bright night sky (surface brightness roughly 19-20 MPSAS) would be far preferable.

 

By the way. In an earlier post you brought up the matter of concentration of light via a smaller Fresnel pattern via a larger aperture. For at least the case where the exit pupil is insufficient to resolve diffraction, this is irrelevant. We see an unresolved point, and so *only* total brightness matters. In such case, the magnitude limit scales exactly as anticipated, where a 0.37m gain corresponds to an aperture equivalence of 1.189 by diameter.

 

Peter,

It's not 'Zarenski's Law.' And I'm pretty sure he conducted numerous tests on actual stars. And 1/3 magnitude is not insignificant, nor so difficult to discern. Try it yourself while binoviewing. Use a star cluster having good magnitudes to fainter than your limit. See how faint *you* can go when using both eyes vs one, at some fixed magnification.



#171 PeterDob

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Posted 22 September 2017 - 04:31 AM

@SPastroneby: The reason why there aren't more binoscope's around is pretty simple:

 

1. They're very bulky, as you said, and more difficult to manage. You can still assemble a 25" mono on your own, whereas this is impossible for an 18" bino.

 

2. Not everyone is able to observe with both eyes.

 

3. (and most importantly) A binoscope is commercially not feasible. Mr. Otte must be one of the very few that still has them on offer. He told me that, regardless of all his experience, every new binoscope he builds is an adventure and you're never sure where it will end. He initially said that he could deliver mine in 4-5 months. In the end it took him 13 months due to alignment problems, too unstable primary mounts and redesigning the tertiary mounts. In the end, he said, if he counts all of his working hours he'd earn about €2 an hour!

 

That being said, my 18" binos cost me quite a bit less than a 25" Obsession (counting in shipping to Europe and import duties).

 

 

@Gleb: Actually, what you're suggesting has already been done many times and the results are quite inconclusive (I've already mentioned some of these studies twice). Meese et al. (2006) mentioned 1.7x (not in the total dark) whereas if you follow Pirenne's original graph (1949) you'd arrive at 2x. Other studies refuse to put a number on it but all say that the level of summation increases dramatically with reduced light/contrast. 

 

@Glenn: This is why I suspect Zarenski never did any real star test and that he merely calculated the actual magnitude gain from the C&G standard summation factor. His results simply don't match laboratory studies nor experience in the field. Which star cluster would you use? In my case, an 18" telescope has a theoretical limit of mag. 17. So you'd need a star cluster that contains stars of mag. 17.0, 17.1, 17.2, 17.3 and so on. But what does "I've seen it" mean anyway? You've seen it or you THINK you've seen it? Remember, we're talking about tenths of magnitudes difference on 17th magnitude stars! You claim you can see the difference? Well, in that case you must be Superman because I'm pretty sure that no-one can do this, as Dom confirmed.

 

To see how difficult it is, install the popular mobile phone app "Loss of the Night" and try it out under urban skies. Now try to get the same result twice.

 

An 18" has a limit of 17.0. A 25" of 17.7. At this faintness this 0.7 difference would be extremely hard to detect. Yet, a 25" has a whole different "feel" than an 18" and suddenly objects are becoming so much easier to see. Now THAT is exactly what the binoscope also delivers and that is why I claim that the difference can't possibly be a miserable 19% aperture gain. The C8 vs. a C9.5. No, we're talking about much more. I'd invite any 25" owner to come and pay me a visit. I'm sure they'll go home frustrated.

 

Peter



#172 GlennLeDrew

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Posted 22 September 2017 - 01:17 PM

Peter,

When one conducts NELM estimates, on a good night 5.9m might be achieved, but on a slightly poorer night 5.7m might be the limit. On another night, 5.8m. Variable star estimates, by eye or telescope, with a bit of practice, can be reliable enough to 0.1m.

 

The actual magnitudes before telescopic amplification has no bearing; it's the apparent brightness to the eye. A 17m star in the eyepiece is just like, say, a 6m star seen naked eye. Stars in the eyepiece that differ by, say, 0.2m have the same brightness ratio as naked eye stars differing by 0.2m.

 

The magnitude scale is logarithmic, not linear. And so a given magnitude difference, whether the stars be in the dim or bright regime, results in the same brightness ratio.

 

One has no difficulty in perceiving a 0.3m difference. Else visual star observation to 0.1m levels--which is routinely done--would be impossible.

 

First, how about testing NELM with one eye vs two? As stressed above, the result in magnitude delta here is *precisely* the same as when using a bino, small or large. Because in the end it all boils down to your eyes/visual cortex. Placing optics ahead of the eyes makes NO difference.

 

If you want to use your big bino to test the difference, I know that if some online utility--such as the Vizier plotting service at the CDS--can use the GAIA data, an accurate-in-brightness chart to well fainter than 17m should be able to be cooked up.



#173 SPastroneby

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Posted 30 September 2017 - 02:29 PM

I did find this site: http://www.avalon-in...ducts/binoscope .

 

Are there others who make (well, sell) binoscopes professionally?



#174 PeterDob

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Posted 01 October 2017 - 03:52 AM

The link you posted only refers to smaller binoscopes, comparable to large binoculars. Apart from a few home-builders such as Bruce Sayre, I only know of two who make large binoscopes (i.e. a double reverse Dobsonian):

-JMI http://www.jimsmobile.com/buy_rb.htm

- Otte http://arieotte-binoscopes.nl/

Cheers,

Peter

#175 PETER DREW

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Posted 01 October 2017 - 08:38 AM

I still build refracting and reflecting binoscopes, mainly by commission to fund the next project as I am now "retired" from commercial activity. So far this year I have made 4 150mm aperture refracting units, 1 102mm and 1 80mm APO unit. Also 1 200mm reflecting binoscope. , and 1


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