Telephoto array finds dark matter galaxies.

[jamaeolus]

Apparently an innovative group of astronomers at yale decided to use an array of telephoto lenses instead of traditional telescopes in their research.



Prices are sure to shoot up now, dammit.

[Attila]

wow

[Lightshow]

http://www.astro.caltech.edu/~ycao/B&ETalks/vandokkum_bne.pdf

[luisalegria]

Thats one of my Soligors, middle row, second from the left.
.....
I kid, I kid!

[exaklaus]

That's an interesting project.
Well explained even for me, who knows not very much about this theme!
And they seem to know what they are doing (when not choosing Soligors )

[l9magen]

Really interesting!!! Puts my sky-watching to shame.

[buerokratiehasser]

JFTR Arrays + deconvolution (virtual apertures) have been used for decades now. Dont ask me for details, please - I only read about it somewhere, I dont work in that field. Maybe I should have. :<

It is still impressive (can you say cloud- I mean skybuster?) and it is working in the 500 nm area I understand (virtual telescopes are often radio)

[jamaeolus]

I have considered making an array of cheap second hand point and shoot digital cams and stitching the result. So many ideas so little time!

[Gerald]

Without a doubt, the array of 10 super telephoto lenses Canon 400mm F2.8, which cost $10,000 each, is very impressive. Much more impressive, for example than an array of 10 Pentacon 135mm F2.8 telephoto lenses.

Speaking seriously, the price of $100k they paid for the set of Canon lenses was a bargain for an important scientific experiment. Just to give an idea of the costs of science today, the budget of CERN in 2016 is 1127.2 billion CHF, what corresponds to more than 3 million a day!

I have little doubt that the results were significant to unravel the mysteries of the universe. Moreover, those scientists were very smart in using "cheap" (!) commercial photographic lenses instead of an exceedingly expensive telescope specially designed for the experiment. By the way, the inspiration probably came from a team member with experience in birding. You know, 400mm F2.8 lenses are very popular with bird photographers.

Some additional observations:

1) The scientists "discovered" that the Canon lens produces less light scatter then the big reflecting telescopes used by the professional astronomers. Not a big news, to be true. Photographers have long known that the so-called catadioptric lenses, aka "mirror lenses", produce images with less contrast than normal photographic lenses.

2) The goal of using an array with 10 telephoto lenses was only to increase the capability of detecting astronomical subjects of extremely small light intensity. The telephoto array did not increase, for example, the resolution or the angle of coverage compared with a single lens. In principle, the same result they achieved could be obtained with only one lens and an exposure time ten times larger. Nonetheless, the scientific setup would be much less impressive.

3) The scientists praised in several articles the nano-coating(s) of the Canon lens. They considered it an important factor for the success of the experiment. IMHO, scientists bought the marketing of Canon and other lens manufacturers, who like to talk about the "miraculous" properties of the lens coatings. Ken Rockwell says a lot of BS, I know, but I totally agree with him when he comments on the Nikon 400mm F2.8 lens, which is equivalent to the Canon lens used in the experiment:

"N: Magic Nano-crystal coating, meaning a coating which varies its index of refraction continuously to achieve even greater reflection reduction. It's probably only on one surface, and is used mostly for marketing purposes."
http://www.kenrockwell.com/nikon/400mm-f28-fl.htm

Indeed, the Canon lenses used in the experiment have 17 elements in 13 optical groups. There are 26 air-glass surfaces, so it should be evident that one or two surfaces with nano-coating have negligible impact on the performance compared with a lens with only traditional multicoated surfaces.


Bibliographical Reference:
https://arxiv.org/pdf/1401.5473v1.pdf

[Lightshow]

Canon has stated that that they use the best coating on the surfaces that need it the most, so it will likely only be needed on only one or two surfaces, they also said that these nano coatings will give the designers more freedom in lens design, the biggest down side is that the nano coatings are very soft.

[Gerald]

[buerokratiehasser]

Certainly, coatings not perfect. (1-imperfection)^(2*lenses)

But is it a fair test to look at a tilted angle into a lens? Plus interior of lenses is usually really black to eat stray light.

[Lightshow]

[jamaeolus]

After doing some research into coatings I found that early uncoated lenses lose about 4% of available light at each air glass interface. That is the main reason early lenses tended to mostly be triplets. With more complex optical schemes F numbers dropped so quickly and contrast became so poor that they weren't a reasonable answer to improved optical construction. With the discovery by astronomers! that old lenses in telescopes performed better research ensued to discover why. Coatings by specialty chemicals were far better than the film of haze left by evaporating lubricants. Modern lenses can have lots of coatings. There are 2 main effects by which coatings improve optical performance. The first is that the coating will have an index of refraction between that of interface materials (air to glass for single coatings, and air to coating to coating to glass for multi coated). The second effect is interference. By making the thickness of the coating 1/4 the wavelength of the light the cancellation by destructive interference improves performance. Many lenses today will have 10 to 15 elements.

[Gerald]

[jamaeolus]

Gerald what a great test! I would have expected a bit more improvement as well. But just with routine experience and not a carefully controlled test my hunch was that the Super-Takumar's were very close to or as good as the Super Multi Coated. It would appear that most of the improvement is with the first coating.

[Lightshow]

I wasn't sure if my humor would show through with out any emoticons.
I can see a difference between my Super-Taks and my S-M-C lenses, is it huge? no, do I see it in every situation? no, but the difference is still there.
And I do agree that there are diminishing returns.

[ZoneV]