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| krokodyle... |
 Posted: Tue Nov 10, 2009 2:58 pm |
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anyone here knows (even approximately):
1. the typical focal length of the objective
2. the size of the detector
3. how do the pixels look like (spacing, aspect ratio, size)
I understand that 8 megapixels cellphones and even more
are now available.
answers, refs, links appreciated.
thank you very much. |
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| Richard J Kinch... |
| Posted: Tue Nov 10, 2009 5:09 pm |
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krokodyle writes:
[quote]anyone here knows (even approximately):
1. the typical focal length of the objective
2. the size of the detector
3. how do the pixels look like (spacing, aspect ratio, size)
[/quote]
It is odd that the cheaper and smaller these things get, that such
characteristics are treated as if they don't matter and aren't worth
talking about.
Given the the tiny scale they must be really small in conventional terms,
smaller than webcams. One would expect a focal length of a few mm and a
sensor size of similar dimension.
But really, we all have a drawer full of dead or obsolete cellphones, so
why not tear one apart and have a look? |
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| Helpful person |
| Posted: Wed Nov 11, 2009 3:49 am |
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Joined: 22 Jun 2004
Posts: 873
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On Nov 10, 2:58 pm, "krokodyle" <[e^i*pi=-1] at (no spam) euler.com> wrote:
[quote]
I understand that 8 megapixels cellphones and even more
are now available.
[/quote]
An interesting application where more megapixels yields poorer
perfomance. Marketing rules!
www.richardfisher.com |
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| Helpful person |
| Posted: Wed Nov 11, 2009 10:11 am |
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Joined: 22 Jun 2004
Posts: 873
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On Nov 11, 1:53 pm, "krokodyle" <[e^i*pi=-1] at (no spam) euler.com> wrote:
[quote]
At the end of the article holography is mentioned, which seems to me pure
PR hype as I do not see how (among many other things) any meaningful info
could thus be obtained much less transmitted (even at 12 megapixels).
[/quote]
Holographic recording of microscopic data is a an excellent method to
obtain data from a low quality optical system as found in a cell
phone. Although not familiar with the specific device I would expect
the main chalenge would be in the digital processing.
www.richardfisher.com |
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| Don Stauffer... |
| Posted: Wed Nov 11, 2009 10:12 am |
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krokodyle wrote:
[quote]anyone here knows (even approximately):
1. the typical focal length of the objective
2. the size of the detector
3. how do the pixels look like (spacing, aspect ratio, size)
I understand that 8 megapixels cellphones and even more
are now available.
answers, refs, links appreciated.
thank you very much.
Don't know specific answers for questions 1 and 2. However, answers to[/quote]
3 depend on 2. If you know the size and number of pixels you can easily
compute the pitch of the detectors. The size is essentially the inverse
of the pitch. It is a little hard to say exactly, because if you plot
the response vs position, the response is not necessarily a step
function. The response within a pixel may vary with position a bit.
That is, it is not neccessarily a sharp boundary between pixels. Aspect
ratio is also a bit hard to determine because of this. However, aspect
ratio of actual sensitive area has very little effect on performance.
You might consider the size and aspect ratio questions in terms of fill
factor- what fraction of a pixel in each direction is actually
sensitive. Fill factor does have a slight effect on the mtf at higher
spatial frequencies, but is, again, not a real big factor. |
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| krokodyle... |
| Posted: Wed Nov 11, 2009 1:53 pm |
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"Helpful person" <rrllff at (no spam) yahoo.com> wrote
On Nov 10, 2:58 pm, "krokodyle" <[e^i*pi=-1] at (no spam) euler.com> wrote:
[quote]
I understand that 8 megapixels cellphones and even more
are now available.
[/quote]
An interesting application where more megapixels yields poorer
perfomance. Marketing rules!
www.richardfisher.com
===================================================
Maybe. In fact I just read about a new 12 megapixels phone to be released
shortly.
My own cellphone has I think perhaps 4 to 5 megapixels and I am
rather surprised at the quality of the pictures thus obtained...
(true at first my expectations were low).
No, I do not have yet another cellphone to demolish (prior suggestion). :-(
The New York Times had an article on how to turn a cellphone into a
microscope (allegedly):
http://www.nytimes.com/2009/11/08/business/08novel.html
At the end of the article holography is mentioned, which seems to me pure
PR hype as I do not see how (among many other things) any meaningful info
could thus be obtained much less transmitted (even at 12 megapixels). |
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| krokodyle... |
| Posted: Wed Nov 11, 2009 3:28 pm |
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"Helpful person" <rrllff at (no spam) yahoo.com> wrote
On Nov 11, 1:53 pm, "krokodyle" <[e^i*pi=-1] at (no spam) euler.com> wrote:
http://www.nytimes.com/2009/11/08/business/08novel.html
[quote]At the end of the article holography is mentioned, which seems to me pure
PR hype as I do not see how (among many other things) any meaningful info
could thus be obtained much less transmitted (even at 12 megapixels).
[/quote]
Holographic recording of microscopic data is a an excellent method to
obtain data from a low quality optical system as found in a cell
phone. Although not familiar with the specific device I would expect
the main chalenge would be in the digital processing.
www.richardfisher.com
=====================================================
Thanks.
I thought that holography required enormous amounts of data in order
to obtain meaningful results, in the present situation I can see additional
difficulties such as the fact that any reconstruction requires having access
to the phase (and not the intensity of an image.)
But I could be mistaken or not up to date with the latest developments. |
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