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Depth of field for a normal camera is a function of the relative aperture size (f-number), focal length and distance to the subject. This camera is able to crea

Depth of field for a normal camera is a function of the relative aperture size (f-number), focal length and distance to the subject. This camera is able to create a huge depth of field with a far smaller aperture than would be expected with a conventional camera. So how does it break the laws of physics? Well it doesn't; it cheats by not preserving the phase of the light. In a normal lens, the phase of the light is preserved. Light that must travel further to reach the point of focus travels faster as it passes through less lens material (where it travels slower than the speed of light). The lens is also made on a flat disc a little bit like a Fresnel lens. The difference with this lens is that it doesn't have a single point of focus, instead light is focused onto many planes, simultaneously with equal power of light focused onto each plane. In this paper the planes were chosen to be between 5 and 1200mm. A clever computer algorithm calculates the exact shape of the lens to get this distribution given a specific wavelength of light. The end result is a lens which has amazing depth of field but the trade off of only operating well at a single frequency and poor efficiency. Most of the incoming light is being focused on a plane that the sensor isn't on. Indeed at 1200mm it has an equivalent f-number of 555 requiring some insanely bright lighting and long exposure time to get a good image. I can't see many real world applications of this camera given the downsides but in a world of more computational photography this could be one part of a better imaging system.

pedrovhb 7y ago
Thanks for the understandable breakdown. This is very interesting indeed, but at an equivalent f/555 I don't see many practical applications for this either. For context, usual photography uses apertures from f/1.2 to f/11, with lower numbers letting being a larger aperture and thus more light in. It'd require a massive amount of light to get a usable image. Maybe the images could be sharper with this lens, or have very good macro? As you stop down (increase the aperture number) images become sharper up to a point where the diffraction limit steps in and quality degrades; usually this happens at f/9 to f/11 (which is why I mentioned f/11 as the lower range of commonly used apertures; although almost all lenses can go smaller, for pixel-peeping quality you'd want to use an ND filter and f/11 aperture).
blattimwind 7y ago
Wondering how diffraction applies to this one. Certainly not to the equivalent aperture, because any f/555 lens would resolve essentially nothing (probably measured in mm/lp, not lp/mm; edit: not quite, about 3.5 lp/mm).
hinkley 7y ago
This sounds an awful lot like Lytro's technology, perhaps with a different mechanism to achieve a Fresnel lens. [edit: Wait, Wikipedia lists Horowitz and Andreesen as founders of Lytro? I thought they were just investors?]
thaumasiotes 7y ago
> The end result is a lens which has amazing depth of field but the trade off of only operating well at a single frequency and poor efficiency. Most of the incoming light is being focused on a plane that the sensor isn't on. Indeed at 1200mm it has an equivalent f-number of 555 requiring some insanely bright lighting and long exposure time to get a good image. How does this compare to a pinhole camera, which (ideally) has perfect depth of field and focuses all incoming light onto the plane of the sensor, but which achieves that at the cost of admitting very little incoming light? (Thus requiring insanely bright lighting and long exposures.) It seems like the exact same tradeoff.
abortz 7y ago
> Most of the incoming light is being focused on a plane that the sensor isn't on. Indeed at 1200mm it has an equivalent f-number of 555 requiring some insanely bright lighting and long exposure time to get a good image. I'm don't think that's why the lens has such a high f-number at large focal lengths. Rather, it's simply because they only manufactured a very small (1.8mm diameter) lens. Given the exotic shape and manufacturing of the lens I'm not surprised it's so small, and I suspect scaling this to larger lenses would be a very serious barrier to practicality. It's also not clear why they chose that particular focal range, so there may be some other issues I didn't notice. But on the whole this is very interesting work! The fundamental observation (not caring about the phase of light at the focal plane) that makes this work is more interesting to me tbh. The authors' previous work uses a similar technique to produce a thin, single element apochromatic lens -- something that normally takes 3 thick lenses and expensive glass formulations.
yummypaint 7y ago
Clearly there are limitations for standard color photography, but lasers provide abundant and cheap monochromatic light. If the scene doesn't depend on natural lighting the exposure problems could be overcome.

pedrovhb 7y ago

Thanks for the understandable breakdown. This is very interesting indeed, but at an equivalent f/555 I don't see many practical applications for this either. For context, usual photography uses apertures from f/1.2 to f/11, with lower numbers letting being a larger aperture and thus more light in. It'd require a massive amount of light to get a usable image. Maybe the images could be sharper with this lens, or have very good macro? As you stop down (increase the aperture number) images become sharper up to a point where the diffraction limit steps in and quality degrades; usually this happens at f/9 to f/11 (which is why I mentioned f/11 as the lower range of commonly used apertures; although almost all lenses can go smaller, for pixel-peeping quality you'd want to use an ND filter and f/11 aperture).

blattimwind 7y ago

Wondering how diffraction applies to this one. Certainly not to the equivalent aperture, because any f/555 lens would resolve essentially nothing (probably measured in mm/lp, not lp/mm; edit: not quite, about 3.5 lp/mm).

hinkley 7y ago

This sounds an awful lot like Lytro's technology, perhaps with a different mechanism to achieve a Fresnel lens. [edit: Wait, Wikipedia lists Horowitz and Andreesen as founders of Lytro? I thought they were just investors?]

thaumasiotes 7y ago

> The end result is a lens which has amazing depth of field but the trade off of only operating well at a single frequency and poor efficiency. Most of the incoming light is being focused on a plane that the sensor isn't on. Indeed at 1200mm it has an equivalent f-number of 555 requiring some insanely bright lighting and long exposure time to get a good image. How does this compare to a pinhole camera, which (ideally) has perfect depth of field and focuses all incoming light onto the plane of the sensor, but which achieves that at the cost of admitting very little incoming light? (Thus requiring insanely bright lighting and long exposures.) It seems like the exact same tradeoff.

abortz 7y ago

> Most of the incoming light is being focused on a plane that the sensor isn't on. Indeed at 1200mm it has an equivalent f-number of 555 requiring some insanely bright lighting and long exposure time to get a good image. I'm don't think that's why the lens has such a high f-number at large focal lengths. Rather, it's simply because they only manufactured a very small (1.8mm diameter) lens. Given the exotic shape and manufacturing of the lens I'm not surprised it's so small, and I suspect scaling this to larger lenses would be a very serious barrier to practicality. It's also not clear why they chose that particular focal range, so there may be some other issues I didn't notice. But on the whole this is very interesting work! The fundamental observation (not caring about the phase of light at the focal plane) that makes this work is more interesting to me tbh. The authors' previous work uses a similar technique to produce a thin, single element apochromatic lens -- something that normally takes 3 thick lenses and expensive glass formulations.

yummypaint 7y ago

Clearly there are limitations for standard color photography, but lasers provide abundant and cheap monochromatic light. If the scene doesn't depend on natural lighting the exposure problems could be overcome.