No, I didn't. I don't own a binocular, and even then I would have to compare it with a mono of 1,19 and/or 1,42 bigger. I feel I otherwise wouldn't be sure how much 'better' it would be, certainly not if in practice it would be between the 1,19 and 1,42. Maybe you can gauge such a thing accurately, but clearly there is a high subjectivity in it, seen the descriptions and assertions of others with a binobsodian. I'm pretty sure those guys are seasoned sky-watchers too, but clearly they come to another appreciation of it. And...well... they DO have the most data to show for as of yet, which doesn't mean they couldn't be subject to some form of subjectivity themselves - I'm not blind to that possibility.
Maybe someone can make a paper about this, some day? It would be nice to have such an experiment repeaedt, but then with double-blind tests that are statistically relevant, and maybe with a measure apparatus that can note the differences more objectively.
"I take it by your silence that you are in agreement."
It's rather because I was at work, and also because I can't answer to everything. ;-) Though Glennledrew made basically the same argument before you, and I answered him. In short, I think it's only partially because of the technical limitations, and for a bigger part, just about the cost... and the cost-benefit argument was one that I made as well.
There is something not quite right in the claim that pro's use segmented mirrors because they can't do anything else because of *technical* limitations. Look at your and Glennledrew's examples. He said that the MMT used 6 x 1,8 mirrors, because it wasn't technical possible in that time (late 70ies) to make a mirror of 6,5 meter. First of all, even that is a bit doubtful, since the BTA of 6,05 meter was already built in the beginnings of the 70ies. But, let's, for arguments sake, say that was right, and it was impossible to make a 6,5meter one back then. Ok. But if one claims pro's want the biggest mono's they can get, and it was only because of technical limitations the 6,5 meter wasn't built... then why didn't they built 4 x 4m class mirrors? Because 4 meter was CERTAINLY "technical possible". And surely, 4 x 4meters would have been better - and being bigger mono's - then 6 x 1,8 meter. Using logic, this points to the fact it was not - at least not primarily - a *technical limitation*, but a cost limitation. They had a certain budget they couldn't pass over. And 3 or 4 meter telescopes were technical possible alright, but they were too expensive. A single 1,8 meter would have been the cheapest of course, but would also meant the least scientific return.
What they did, thus - and this was/is one of my arguments - is to make a cost benefit analysis. "What's the most we can get with the budget we have." And lo and behold, they used 6 small diameter mirrors in conjunction to get the equivalent of a 4,5 meter one. Why not directly a 4,5 meter one, then - that WAS technically possible, after all? Well, exactly because of what I said: cost. It was cheaper to have 6 mirrors of 1,8 meter than one of 4,5 meter. Which is exactly my point. Think about it. If a 4,5 meter is better, is technical possible AND you have the budget for it, and you claim pro's always go for the bigger mono instead of the smaller segmented, than *there is no reason* why they would have chosen the 6 x 1,8 meters ones, now is there?
I'm just using logical sense here. It's a fact a 4,5 meter telescope was already technically possible before the 50ies, let alone late 70ies. So that CAN NOT have been the determining factor. This leaves cost/budget. Which means they thought 6 x 1,8meter telescopes would be a better cost-benefit approach than one 4,5meter one, contrary to what you claim.
Idem with your example of the Keck. I'm not sure what you try to show, in fact, since it seems rather speaking against your conclusion. Maybe you wanted to say 'well, the minimum is 72", so you see how big it is'...yes, but they also have big budgets. No-one is denying one monolithic mirror is better then several smaller for the same aperture, it's a matter of cost-benefit that is the point here. If they *really* wanted big monolithic mirrors at any cost, there is absolutely no reason to go for small (in their eyes and budget) mirrors like that. No, they would have gone for a handful of very large mirrors, like the GMT has as concept.
This, thus, in effect once again shows it's not about technical possibilities, or that pro's will always choose bigger mirrors if it's technically possible, but that there is a cost-benefit trade-off. Of course, that trade-off (the threshold I spoke of) lays far higher, financially, than that of an amateur astronomer, which is why 72" mirrors is 'small' for them, even when it's huge for us. That's relative to the budget one has, however, not relative to the merits of the underlying principle.
Now, are you and Glennledrew wrong in every instance? No. Your argument holds, imho, where there really IS a technical limitation. You two would be right, for instance, with the example of the GMT. There, we see they use 7 x 8,4 meter mirrors, giving it the equivalent of (resolving power of) a 24.5 m (80.4 ft) primary mirror and collecting area equivalent to a 22.0 m one.
Why didn't they go for a 25m monolithic one? THERE you are right: because it's a technical limitation. For the longest time now, since the 90ies, the largest single mirrors that can and have been made, are between 8 and 8,5 meters. Even the future telescopes, like the GMT, which indeed goes for the largest mono's, has that limitation, and thus goes for 7 of them used in conjuction. It's currently impossible to create one large 25meter mirror; there is not a manufacturer that can make such a thing right now. You won't find any telescope mono-mirror in the world which is larger than 8,5 meter. All the ones that have bigger aperture, are segmented. So your argument holds there. Because the 8,4 meter limitation is there, and that's a technical limitation for the time being. This clearly isn't valid for all pro observatories that have a (total) aperture that is less than 8,4 meters, obviously - since one *can* make a mono of 8,4m. There, it's a matter of cost/benefit.
Am I saying something outrageous here? I don't think so. I'm only applying logic.
There are two separate problems.
First, suppose two telescopes of 100mm each combined into a single (monocular) eyepiece. Their light gathering ability would be equal to a single 142mm telescope (here is the area which matter).
Second, supposte two telescope of 100mm each used to make a binoscope (i.e. one eye--> one telescope). Here the binocular summation apply, and their light gathering (for visual use obviously) could be considered equivalent to a 119mm monocular telescope.
Third, suppose 4 telescopes, joined two by two in a binoscope. Then their light gathering ability would be equal to:
A much more efficient way to increase the light ability is to concentrate the lights of all 4 telescopes into a single eyepiece: 100mm*1.41*1.41=200mm. If a kind of reverse beam-splitter could be made, with 4 100mm ED doublet you obtain a 200mm ED telescope - cost saving, yes! But the optics to merge the light of 4 telescopes intoa single eyepiece would be super difficult.
What they do in real life is a different application: 4 telescopes with 4 cameras (and many more).
Dragonfly is an innovative, multi-lens array designed for ultra-low surface brightness astronomy at visible wavelengths. Commissioned in 2013 with only three lenses, the array is growing in size and proving capable of detecting extremely faint, complex structure around galaxies. The most recent upgrade—completed in 2016—saw Dragonfly grow to 48 lenses in two clusters.
Wow! Riccardo, this is about exactly what I was looking for and envisaging how big such a thing could grow, like a fly's eye (though they apparently called it a dragonfly's eye). Thanks for the link, I'll be sure to check up on it! But cursory glancing the article already seem to indicate they definitely do it for the advantages it gives (though I'd have to delve deeper to see the economics of such a thing). Why would they make it, if it would be more advantaguous in price and/or capabilities, if they could use a big mono-lens or mirror, after all?
It's pretty interesting they got the same basic idea as I, but in effect manage to make one. If you have any other links/info/specs about it, feel free to give it! :-)
Also, thanks for explaining things further, your explanation was pretty clear and succinct.
Edited by SPastroneby, 24 August 2017 - 12:52 PM.