Commercial Dragonfly array

[xelasnave]

If stray light is something so concerning why dont they have baffled extention tubes, like the Hubble approach (and mine) to reduce stray light reaching the lens.
I still have no comparrison shots, with and without, because I am busy still setting up.
But in my case at least the unit must help stop stray light from the street light nearby.
If Hubble uses this approach is that not a decent pointer to there being something to the idea.
Alex

[rally]

Hi Bojan,

What they claim is that the almost total lack of reflections and scattering that you would otherwise get on every other optical surface of a reflector or ordinary refractor telescope in existence gives rise to a theoretical limit on the resolving capability of 28 magnitudes.

That is the SNR gain they are taking advantage of.
Their optics dont have this problem so they can go down to 32 magnitudes.

That is to say that the optical noise produced by the minute amount of reflection and scattering at the wavelength level of imperfection on ordinary glass surfaces is enough to limit their ability at 28 magnitudes
Theirs doesnt have this thanks to Canons process.

Thats their SNR magic bullet !

The result of Canon's "nano fabrication coating" is that the surface of the optical elements is to all intents and purposes perfectly "smooth" because it is well below the length/height of any of the wavelengths of light they are interested in and thus in effect invisible to the optical system.
As a result of this they have reduced the inherent optical noise so that they can resolve down to 32 magnitudes.

All the rest of the stacking just helps with ordinary sensor and data collection noise reduction and improved integration time - more light for in same time. Its nothing special at all - but just as necessary as normal to imporve SNR, remove sensor and processing noise etc etc

As soon as others are capable of coating their surfaces in the same manner, I guess their technical advantage disappears and Im sure that might happen, but there may well be some manufcaturing and technical limitations (and patents) that make this difficult or impossible for larger elements such as big refractors and mirrors.

In answer to your question "what is the difference (apart from saving time) between stacking subframes taken by array of telescopes and stacking frames taken sequentially by a single telescope? "
There is no difference whatsoever ! - you seem to miss the point - the gain they claim in their papers (and their published results appear to support it) is their ability to avoid the increased noise of surface imperfections that exist on other optics.

I do not believe they are using 1980's technology, my understanding is that its latest technology, some published articles list the actual model number of the lens, current retail pricing is about $10kUS and that corresponds with their costed model.

Hope that makes sense.

For an amateur maybe $2k or $10k for a lens is a lot but for a research project that is finding and discovering what they are uncovering - its not really a big investment, just a matter of them getting appropriate funding to go further and based on their findings - I would be surprised if they didnt get funding for their 480 lens system.

They did all this on a baby Paramount with photographic lenses not a Magellan or a Hubble !

I just started at their website and a few press releases and then started reading the links that progressively went further into the actual research papers. Its all discussed openly and details presented.

[bojan]

Rally,
Here is service manual for EF lens , optical formula (number of elements, their shape etc.) is the same as (my) '80-es model. Of course there are improvements, most likely in details, like coatings. And focus motors etc.
I haven't tried anything with this (newer) model, but if it so good as they claim, it would have been known already in our community... and that is not the case (OK - the price may be the factor here... but because some of us are more than ready to open their valets for high quality, the whole story somehow doesn't fit).

Again, I appreciate the saving in time needed for single observation.
Everything else (to me) is .. well.. .a bit overblown.

BTW, the magnitude limit is 28 magnitudes per square arc sec. And they are talking about 32... this is 4 magnitudes more, 0r ~32x lower intensity difference. This means dynamical resolution must be 5-bit higher....

[rally]

Hi Bojan,

Its not the same technology today as it was nearly 40 years ago !
I dont need to read a service manual to know this.

They would have better glass, better rpoduction techniques, better quality control, better grinding equipment and better testing equipment and certainly better coating technologies - since that is the specific area that they attribute their claims.
Canon has many patents on this - Google them to read about it.
But one striking difference between this nano coating is that its a single coating - not a series of multi layer coatings like those used in normal optics. One coatiing does it all.

Simplified - Canons Nano Coating technology produces a crystalline surface coating that has a variable comparative density. The base is a high density, the surface is lighter.
Its done with holes that are approximately 1/4 the wavelength of the light of interest.
The coating starts out life as a fluid spin coating process of 5-10 nanometer sized Al2O3 which is dried and then is reaquafied and dried out again, during which stage it recrystallises and produces the variable density coating with the right sized and ratio of hole sizes.
The fluid and process they use is their black art !

Their Patents were only lodged in the last few years and this technology did not exist in 1980.

Old film lenses are well known and understood for their lack of antireflective coatings - its generally why a cheap kit lens of today performs better than most of the best glass from the film era (with some rare exceptions)

Film didnt reflect light to the same extent that CCD sensors do and hence why the old lenses didnt perform very well with CCDs
Standard film grain structure was also a limit they built their lenses around whereas CCDs can resolve down to smaller pixels/grains needing better resolving lenses and Im pretty sure that needs to be across a wider spectral bandwidth than film was sensitive to.

As to why one person didnt discover what another person discovered - I cannot tell you - the world is full of discovery - someone has to be first !

Its a question of recognising the merit in what you have discovered and then after all the unexpected discoveries they realise just what the ramifications are of their initial discovery.
They certainly didnt expect it and so I doubt anyone else could have.

You can't do that if you are stuck in the mud of old fashioned paradigms . . . and that is what they did - looked outside the box by going back to basics and using a ready made solution.

Up till now, Im guessing most amateurs werent specifically interested in this field of low surface brightness objects.
The fact that Dragonfly has now discovered so much that is new and a lot of what they have found simply defies the current theories and explanations of galaxy formation etc will no doubt stimulate some interest in the amateur fraternity.

Pretty sure 4 magnitudes is a factor of 39.8 ?
I rounded it up to 40x earlier

Im not sure they are necessarily claiming they have 5 bits of higher dynamic range - they are just able to see the extra 'bits' below 28mag that everyone else has lost, buried in the noise of their optics !!
They can get their dynamic range expansion same as we do by stacking different length subexposures.

Anyway - there is lots to read about what they claim and over 200 approaching 300 papers out there that document their discoveries arising from their observations in such a short space of time from grants only provided in 2013, 2014 and 2016 - so its an amazing amount of discovery in such a short time.
No matter how they have achieved it.

[AstroApprentice (Jason)]

First there was McGregor v Mayweather, now there is Bojan v Rally!
I'm finding the latter fight very informative and more interesting to follow...
Next Round!

[bojan]

Eh...
No, it's not Bojan vs Rally..
It is just clearing the understanding of basics, as I want to know what is this about this dragon fly and reasons for going for it.
Personally, I am not someone who would take other people's things for granted, that is why I am posting the questions, after all this is what makes difference between science and "science".. Science correct itself through checking and re-checking, the other is not.

As to optical design differences between FD and EF 400mm f/2.8L lens, I only stated the optical system is the same - details like coatings etc may be different of course. Is this is THE detail that makes all the difference, that remains to be seen. Alex's baffling comes to mind..
And yes, Rally is right, 2.512^4 = 39.8, my calculation was very coarse.

I am reading further.. but it will take some time for the next round

[rally]

Goodness - people reading the posts because they think its a fight !!

Bojan and I have communicated on and off forum many times about lots of things - he wants the info to back it up and I'm happy to provide what I can and why - afterall Im the one making the claims !! - hardly adversarial.
I am sure he is enjoying the process as much as me, forces us both to question our beliefs.

But yes, I do agree its a really interesting development that seems to have floated under the radar for a while and the reason why I keep adding to it.
I reckon we should understand more about it and how they did it - because I reckon there will be some amateurs who will potentially be interested to go down the same route albeit more cheaply just so they can go 40x deeper than before !
A 3 lens system isnt necessarily out of the question and Im sure there will be other nano coated lenses coming out soon - or maybe Takahashi will borrow some technology from Canon as I believe they already do now ?

Most of everything I have referred to can be found on their website, but you need to follow to a few external links (and chains) and read a bit to get the full story.

I think the Dragonfly site just assumes everyone doesnt need to have all the relevant details and that if its in a paper or 200 then its all there.
Canons patents are about as descriptive as a Kodak CCD spec sheet really ! - Im sure its done that way deliberately - but one of the big-name photographic journalists got a factory tour and an interview at the Canon lens factory where they make these and he got a good scoop on it - so that was more interesting and enlightening to read !

If I can refind that link after so long I'll post it up too.

[bojan]

Originally Posted by rally

... Im not sure they are necessarily claiming they have 5 bits of higher dynamic range - they are just able to see the extra 'bits' below 28mag that everyone else has lost, buried in the noise of their optics !!
They can get their dynamic range expansion same as we do by stacking different length subexposures.

They claim they are seeing intensity 4 mag below some previously established threshold.. and that threshold (probably camera noise, skyglow at dark site plus scatter in optics etc) can be reached very quickly with f/2.8 lens (couple of minutes exposure at ISO3200 will do.).
I made a quick calculation (adding magnitudes, 0 and 4... ) and mag difference (contribution) between old threshold (28m /arcsec sq) and new one is -0.027 mag, or ~2.45% brighter in linear terms.

If I am not mistaken, 'normal' camera with 14-bit resolution should be able to see 0.012% intensity difference. This is valid in the linear range of the sensor, and no camera noise accounted for.
So. yes... no need for 5 bits more, but averaging (stacking) is definitely a key here.

[rally]

Bojan,

Cant find the patent !
But here's the journalists Canon interview

http://www.imaging-resource.com/news...tour-interview