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, 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?
"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.
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.
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?
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?
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!  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. 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.