focal length

Discussion in 'General Electronics Chat' started by bhuvanesh, Jan 17, 2015.

  1. bhuvanesh

    Thread Starter Member

    Aug 10, 2013
    268
    2
    we all know that focal length of our eyes is 22m and of mobile camera is around 33 to one or 200 mm.yet if we see through mobile the image is not sharp as we see from our eyes.Why is that so.Thank you in advance
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,789
    945
    digital resolution is the limiting factor

    the camera converts the visual image to a finite set of pixels. the larger the number of pixels the greater the close up resolution of the image becomes.
     
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  3. MagicMatt

    Member

    Sep 30, 2013
    117
    14
    Right idea, but largely the wrong culprit. Some digital sensors are a lot better than others, and it's not as straightforward as "it's always this". Having used thermally cooled CCD cameras, I can assure you that it's not only possible to achieve resolution and dynamic range as good as our eyes, but often far better.

    Digital resolution is often not the main issue, but the quality of the optics in front of the sensor. Take the same sensor from your mobile and replace the crap glass lens with a nice high quality Leica lens, and the difference in the captured image is astounding... but who wants a large Leica lens sticking out of their mobile!?

    The human eye is surprisingly poor too - around 7 megapixels with a blind spot in the centre... but the eye doesn't take a single snapshot, it's a video stream with a very powerful processor behind it. The eye takes literally thousands of snapshots and (for want of a better term) "stacks" them, making the realistic resolution of your normal 90 degree field of view the equivalent of around 450 megapixels, and for your full field of view, closer to 600 megapixels.

    Yes, if you used your mobile the same way, with a good quality lens instead of the supplied one, taking thousands of images and stacking them in something like Registax, you could achieve much the same image, or even better.

    There's also the whole "Circle Of Confusion" scenario, which I really only recommend you read if you want a full-on scientific answer to your question. It's a fairly easy concept once you understand it, but not immediately obvious.
     
  4. bhuvanesh

    Thread Starter Member

    Aug 10, 2013
    268
    2
    visual image is converted to finite set of pixels rather that not having what it has.its is for the sake limited storage?
     
  5. bhuvanesh

    Thread Starter Member

    Aug 10, 2013
    268
    2
    what is the use of it since our eye don't have capability to feel beyond qualities(our eyes is 450 megapixels so it cant feel the 600 megapixel image) or we can say like it never seen 600 megapixel image.am i making point?

    human eye is around 500 megapixel.is it not?

    eye capture video in 1000 frames per second?
    ful field of view mean i dont understand
     
    Last edited: Jan 17, 2015
  6. MagicMatt

    Member

    Sep 30, 2013
    117
    14
    Ummmm... what? Sorry, I can't understand what you are trying to say. Are you asking why we don't all have 600 megapixel cameras in our mobile phones?

    1 - Cost.
    2 - Size of optics.
    3 - Processing power needed to take and stack all those images.
    4 - Memory required to process the images.
    5 - Speed and capacity of temporary storage needed for the initial video feed.
    6 - Storage requirements for the final file.
    7 - Processor power and memory capacity needed to decode and display such a large image.

    Uncompressed, each image would be about 2.25Gb ... as a JPEG it would still run into hundreds of megabytes.

    The point of taking an image at a higher quality than our eyes can see is that you are then able to see those things later by simple enlarging the image. Another approach i to zoom in and take the image. A bit like this:
    http://lroc.sese.asu.edu/images/gigapan/

    Closer to 600 megapixels.
    http://www.clarkvision.com/articles/eye-resolution.html

    Brains and eyes do not really work that way. Our eyes capture images on the outside of our vision far better than in the centre, which they can't see at all (blind spot). We do not record video, we produce memories which retain some visual information.

    Your eyes do not stay still. To see what is right in front of you, your eyes need to move around a bit to counter-act the issue of having a blind spot right in the centre of your vision. Your full field of view is therefore slightly larger than a stationary camera would be with the same optics. This is why, when we do astronomy, we often talk about looking at things using averted vision - you can quite literally fail to see something that is right in front of you.
     
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