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Thread: Focus on focus

  1. #1
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    Focus on focus

    New technology being unveiled that will allow the focus to change after the image has been taken!

    Here tis.
    We know time flies, we just can't see its wings.

  2. #2
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    Works fine on a 13 megapixel image reproduced at internet resolution. Start with a 13 meg image. Use lenses over CCD pixels so some focus closer, some farther and you have a totally out of focus image. Now use software to display the image that selects the close focus or far focus or in-between focus pixels. This is an over simplified version but basically what it does from what I've read. Won't remove coma that usually goes with curved field of view. For astro images if taken slightly out of focus just reproduce at a smaller scale. Final results would be similar and probably better than this system.

    Google Plenoptic Cameras for more on this.

    In short, I'm not impressed. I want to use all the photons collected not a rather small fraction of them.

    Rick

  3. #3
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    Quote Originally Posted by RickJ View Post
    For astro images...
    I see no reason why you'd ever use this technology for astronomical imaging.

  4. #4
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    I certainly could be mistaken, but I suspect greater potential exists with this concept even for astronomy. For instance, it should have some capacity to adjust for atmospheric problems almost automatically, assuming respectable processing power. Lunar images don't require high megapixel sensors so, in the future, the higher resolution sensors might work well with this technology.
    We know time flies, we just can't see its wings.

  5. #5
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    I don't see it helping seeing one iota for planetary imaging. Really the same thing we do now with software picking the best frames or even best parts of frames. Here all pixels are used preserving full resolution. You can't do better than that. To get the same resolution with such a camera you'd need many times the focal length or far smaller pixels and thus a far longer exposure that can't freeze seeing. Pixel movement during these longer exposures would be deadly to resolution.

    Rick

  6. #6
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    I should probably check my facts 'afore replying, but don't plenoptics only work when the scene has depth, ie a measurable focus range, so that the sets of data it captures includes an 'offset' that depends on the object's distance?

    I understood that it relies on the slight variance in angle of light rays coming from objects at differing distances as the key to allowing the .. er.. plenopting.. If that's correct, the stars and planets (with their effective infinity-only focus) wouldn't give the camera anything to work with - all parallel lines...

    And if it's incorrect, I will learn something!

  7. #7
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    Quote Originally Posted by chrlzs View Post
    I understood that it relies on the slight variance in angle of light rays coming from objects at differing distances as the key to allowing the .. er.. plenopting.. If that's correct, the stars and planets (with their effective infinity-only focus) wouldn't give the camera anything to work with - all parallel lines...
    I agree that it doesn't seem all that interesting for astronomy if only because it reduces the fraction of sensor area detecting the light you want. However, what the sensor is exposed to isn't directly the light from the astronomical targets, but their light after going through a (possibly involved) train of optical elements, which can perfectly well (all by themselves and against our will) be out of focus, have a non-flat focal surface and so on. Since the atmosphere also becomes an optical element, I could see where this kind of approach could be made to work as a sort of after-the-fact adaptive optics for bright enough objects. (No idea whether it would be economically competitive with the existing flavor, though).

    The image/object distinction through a telescope tripped up Percival Lowell in one of his arguments about twinning of Martian canals - he failed to recognize that what the eye focuses on is not the planet, but its image millimeters in front of the eyeball, so the eye can focus either in front of or beyond that image.

  8. #8
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    I can't see any benefit to improving seeing, just the opposite in fact. AO as used by amateurs follows the prism action of the atmosphere moving the field around. By reacting at a 10hz rate it attempts to follow this motion keeping the field steady. This would still be needed with these cameras as they do nothing for this. They correct for focus by making several images, each with a different focus. This greatly reduces the resolution of the image. Reduce a standard image the same amount and the minor focus differences seeing creates would again be invisible. If I image a 3" per pixel I don't worry at all about anything seeing does to me. It is a problem at 1" per pixel of course. But such a camera would only be capable of 3" resolution at best on my system. So no gain on nights of average to poor seeing and a loss on nights of good seeing. For me to see a benefit I'd need not an 11K chip but a 40K chip with super small pixels that would require very long exposure time or a very large aperture, far beyond what I could afford.

    Rick

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