low light

Discussion in 'Digital Photography' started by ipy2006, Mar 7, 2007.

  1. "acl" <> wrote:
    > On Mar 16, 6:29 am, "David J. Littleboy" <> wrote:
    >
    >> I think you guys are talking past each other here.
    >>
    >> I think John is arguing that _for a sensor of a given size_, larger
    >> pixels
    >> aren't any better.

    >
    > But doesn't this make him a "crop fan" for you?


    No. I think what John is saying is orthogonal to sensor size arguments. He's
    arguing that for a given sensor size, one wants as many pixels as one can
    get. Roger is arguing that for a given number of pixels, one wants the
    largest sensor you can get.

    I suspect that they're both right.

    David J. Littleboy
    Tokyo, Japan
     
    David J. Littleboy, Mar 16, 2007
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  2. ipy2006

    acl Guest

    On Mar 16, 3:46 pm, "Roger N. Clark (change username to rnclark)"
    <> wrote:
    > acl wrote:
    > > On Mar 16, 7:04 am, "Roger N. Clark (change username to rnclark)"
    > > <> wrote:

    >
    > >> 2) There is a difference. The signal you record has added
    > >> read noise. A larger pixel collects more photons
    > >> so the signal is larger compared to the read noise.
    > >> Thus you can detect fainter things, or have better high
    > >> ISO performance. If you sum the signal from a smaller
    > >> pixels to equal the area of a larger pixel size,
    > >> you are also adding read noise, so you don't gain
    > >> as much as having the larger pixel with one read noise.

    >
    > > Is read noise fixed per pixel, per unit area, or something else?

    >
    > Read noise is per pixel. Say you had 2 sensors, one with half
    > the pixel size, so you needed to add 4 pixels to equal the area
    > of the larger pixel. Lats say both had great read noise of
    > 4 electrons. The larger pixel gets: X + 4 electrons noise.
    > The smaller pixel sensor, adding 4 pixels gets:
    > X + sqrt(4)*4 = X + 8, so the read noise is effectively
    > doubled.
    >


    Yes of course if the noise is independent of pixel size. This is why I
    asked.

    > Read noise for a given sensor is dependent on the design of the sensor
    > and how the readout is configured. Read ranges from just under 4
    > to about 30 electrons and is not dependent on pixel size.
    > For example, see Figure 3 at;http://www.clarkvision.com/imagedetail/digital.sensor.performance.sum...
    >
    > At low ISO, and low bit count (e.g. 12 bits) and noise in the A/D converter
    > contributes greater noise than the true read noise from the sensor.
    >


    OK thanks. That explains why it is independent of pixel size. I'd have
    thought that, except for noise coming from amplifiers and the readout
    circuitry, the rest (things like thermal noise) should scale with the
    detector area. But on second thought, this is far more complicated
    than the simplistic model I have, there are capacitors, surface states
    (for these small sizes) etc.

    But personally I hope this kind of noise could go down enough so we
    can have high pixel density sensors which will give more flexibility
    in trading off noise for resolution. Hopefully with built-in binning
    for the raw files too, as always having 60MB raw files seems a bit
    wasteful (but the again 300KB for an executable seemed huge to me in
    1988).
     
    acl, Mar 16, 2007
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  3. ipy2006

    John Sheehy Guest

    "Pat" <> wrote in
    news::


    > At the risk of pissing off all of the "purists" out there, you might
    > want to consider the original Canon Digital Rebel (the good old 300).
    > That would get you a useable body for not much money. Then add the
    > Russian operating system to get to ISO of 3200. It's a bit grainy but
    > sometimes grainy is better than nothing.


    ISO 3200 on the 10D and the 300D with the hack is nothing but ISO 1600
    metered for a stop of under-exposure.

    The 10D and 300D are worse performers at high ISO than any of the APS-sized
    Canon DSLRs to come after them. The 10D/300D have about 4x the read noise
    in the deepest shadows as the 20D and 30D and more than 2x the XTi pushed
    to 3200.

    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    John Sheehy, Mar 16, 2007
  4. David J. Littleboy wrote:

    > No. I think what John is saying is orthogonal to sensor size arguments. He's
    > arguing that for a given sensor size, one wants as many pixels as one can
    > get. Roger is arguing that for a given number of pixels, one wants the
    > largest sensor you can get.
    >
    > I suspect that they're both right.



    It is certainly not true that for a given sensor size, one wants
    as many pixels as possible. One does not want pixels so small that
    no or very very few lenses can make use of the resulting sensor
    resolution, because smaller pixels result in worse very low light
    noise. This only occurs when the square root of the number of
    photons is smaller than the read noise.

    For sensitivity, one does want, for a given number of pixels,
    the largest sensor size possible. Of course, to use this one
    needs large, fast, expensive lenses ... and the concommittent
    loss of depth of field.

    Doug McDonald
     
    Doug McDonald, Mar 16, 2007
  5. ipy2006

    John Sheehy Guest

    "acl" <> wrote in
    news::

    > On Mar 15, 2:31 pm, John Sheehy <> wrote:
    >> that standard deviation is only *one* factor in the noise equation;
    >> magnification is another, and the low noise of big pixels is visually
    >> magnified when the pixels are magnified along with the subject.

    >
    > Exactly, and if you don't need the extra pixels you can bin.


    Yes, but I think it is very important to stress that there is no need to
    bin to get the benefit. Often, the situation is described in such a way
    that binning or downsampling are *necessary* to get the benefit. There
    is a cult of pixel-for-pixel's sake that misses the forest (image or
    subject) for the trees (pixels), IMO. To me, the most important quality
    factors in descending importance are:

    1) SQ (subject quality)

    2) IQ (image quality)

    3) PQ (pixel quality)

    If #3 doesn't also help #1, it is in vein.

    >> 2) slight benefit in photons collection rate per unit of sensor area
    >> due
    >> to less wasted space on the sensor (not always realized, however; my
    >> 1.97u FZ50, for example, collects about the same number of photons per
    >> unit of area as the 1DmkII, at RAW saturation for the same ISO).


    > Well, as long as there are no constant noise sources (eg 10 electrons/
    > pixel independent of the area). I have no idea if there are or not.


    Blackframe read noise on my FZ50 is about 3.34 electrons at ISO 100 (4800
    electrons at saturation), and about 2.71 electrons at ISO 1600 (about 300
    electrons at saturation). Binned down 3x3 (to DSLR size), that's about
    0.9 and 1.11 electrons (43,200 and 2700 max), respectively.

    These values are derived from multiplying the standard deviation of FZ50
    blackframes by 1.66, since the Panasonic RAW files, unfortunately, are
    clipped at the blackpoint, a very bad idea that most camera manufacturers
    engage in. Canon is one of the few that leave a bias in the RAW data
    with a full symmetrical noise histogram with positive and negative noise.
    Clipping at black means bright, noise-clouded blacks with minute signals
    clipped. Blackpoint clipping should not occur, IMO, until your RAW
    conversion needs to enter a gamma-adjusted state (where negative signal
    or noise are meaningless). All white-balancing, resampling, and
    demosaicing should be done before the clipping, to maintain black blacks,
    and a minimum of noise. I would guess that most converters don't
    maintain this state, but clip Canons at black immediately upon loading
    RAW data to get it in the same state as most other cameras. In my own
    hand-conversions in IRIS and in PS with filtermeister and RAW linear
    greyscale sources, I have made conversions with much less color tint and
    bright haze in the deepest shadows. In fact, I have even promoted images
    to a higher bit-depth before any interpolative actions, for more
    precision. RAW converters, generally, are taking a lot of short-cuts,
    IMO, and are not delivering what they can in these areas. They seem
    focused mainly on the post-processing values like skin color and tonal
    curves in the highlight areas, etc.

    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    John Sheehy, Mar 16, 2007
  6. ipy2006

    acl Guest

    On Mar 16, 3:55 pm, "David J. Littleboy" <> wrote:
    > "acl" <> wrote:
    > > On Mar 16, 6:29 am, "David J. Littleboy" <> wrote:

    >
    > >> I think you guys are talking past each other here.

    >
    > >> I think John is arguing that _for a sensor of a given size_, larger
    > >> pixels
    > >> aren't any better.

    >
    > > But doesn't this make him a "crop fan" for you?

    >
    > No. I think what John is saying is orthogonal to sensor size arguments. He's
    > arguing that for a given sensor size, one wants as many pixels as one can
    > get. Roger is arguing that for a given number of pixels, one wants the
    > largest sensor you can get.
    >
    > I suspect that they're both right.


    Well Roger's argument is that read noise is independent of pixel size,
    in which case there is a pixel size that optimizes the resolution/
    noise tradeoff (it depends on where you set your threshold for noise
    tolerance and on the noise properties of the sensor and electronics).

    But anyway I was referring to the fact that, from reading your
    previous posts, I'd have expected you to make some derogatory remark.
    At least, that's what you seemed to do every time someone else
    mentioned higher pixel density as an advantage for a sensor. But it
    seems that now, for some reason, you decided to think before
    ridiculing, and I was forced to conclude that it has to do with the
    messenger rather than the message.
     
    acl, Mar 16, 2007
  7. ipy2006

    Pat Guest

    On Mar 16, 12:15 pm, John Sheehy <> wrote:
    > "Pat" <> wrote innews::
    >
    > > At the risk of pissing off all of the "purists" out there, you might
    > > want to consider the original Canon Digital Rebel (the good old 300).
    > > That would get you a useable body for not much money. Then add the
    > > Russian operating system to get to ISO of 3200. It's a bit grainy but
    > > sometimes grainy is better than nothing.

    >
    > ISO 3200 on the 10D and the 300D with the hack is nothing but ISO 1600
    > metered for a stop of under-exposure.
    >
    > The 10D and 300D are worse performers at high ISO than any of the APS-sized
    > Canon DSLRs to come after them. The 10D/300D have about 4x the read noise
    > in the deepest shadows as the 20D and 30D and more than 2x the XTi pushed
    > to 3200.
    >
    > --
    >
    > <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    > John P Sheehy <>
    > ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><



    Yeah, and .....

    The OP's best bet would be a Hasselblad, a few banks of soft boxes,
    and a crew of gaffers. But, like your ideas, it doesn't take into
    account the OP's budget. You want to start with a $1200 camera when
    the persons budget is $1000. Ain't going to happen.

    So if you don't like my idea -- which I'm not sure I even like my idea
    -- what dSLR would you suggest for the OP with a $1000 budget (don't
    forget sales tax and shipping)?
     
    Pat, Mar 16, 2007
  8. ipy2006

    John Sheehy Guest

    "Pat" <> wrote in
    news::

    > So if you don't like my idea -- which I'm not sure I even like my idea
    > -- what dSLR would you suggest for the OP with a $1000 budget (don't
    > forget sales tax and shipping)?


    A used 20D or a used Rebel XT.

    With lenses, might run a little bit more than a used 300D, but will be far
    faster in operation, and better in low light. Sometimes it's worth going a
    little over budget to get something a notch or two better.

    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    John Sheehy, Mar 16, 2007
  9. ipy2006

    John Sheehy Guest

    "acl" <> wrote in
    news::

    > On Mar 16, 7:04 am, "Roger N. Clark (change username to rnclark)"
    > <> wrote:
    >
    >> 2) There is a difference. The signal you record has added
    >> read noise. A larger pixel collects more photons
    >> so the signal is larger compared to the read noise.
    >> Thus you can detect fainter things, or have better high
    >> ISO performance. If you sum the signal from a smaller
    >> pixels to equal the area of a larger pixel size,
    >> you are also adding read noise, so you don't gain
    >> as much as having the larger pixel with one read noise.
    >>

    >
    > Is read noise fixed per pixel, per unit area, or something else?


    It's something that happens when reading the pixels, and has more to do
    with the electronics involved than anything else. It includes noise from
    all parts of the readout chain (at the pixel, in the amplifier, in the
    readout wiring, in the ADC, etc. Canon is very good at keeping it low,
    relative to signal, at high ISOs compared to most other companies, which
    seem to just amplify the same noise to a higher amplitude.

    There are basically three categories in the read noise vs ISO category;
    Cameras like Canon DSLRs that have less read noise at ISO 1600 than ISO
    100, in electrons, cameras like the Pentax K10D which have the same read
    noise in electrons at all ISOs, and cameras like my FZ50, which does a
    very good job of readout at ISO 100, but gets more read noise in
    electrons at ISO 100.

    Of course, the most relevant part of read noise at the pixel level, as
    measured in units of electrons, is the ratio of the maximum number of
    electrons digitized at the ISO, and the read noise in electrons. That
    determines the lowest signal level, relative to saturation, where a 1:1
    S/N could be obtained, if blackframe read noise was the only noise.

    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    John Sheehy, Mar 16, 2007
  10. ipy2006

    John Sheehy Guest

    John Sheehy <> wrote in
    news:Xns98F58CDA865F2jpsnokomm@130.81.64.196:

    > Blackframe read noise on my FZ50 is about 3.34 electrons at ISO 100
    > (4800 electrons at saturation), and about 2.71 electrons at ISO 1600
    > (about 300 electrons at saturation). Binned down 3x3 (to DSLR size),
    > that's about 0.9 and 1.11 electrons (43,200 and 2700 max),
    > respectively.


    Sorry, I had just woken up after an 18-hour emergency shift at work.

    I divided by three when I should have multiplied by three. I was thinking
    in terms of the noise-to-signal ratio, and applied it to absolute photon
    counts.

    That should have read:

    Blackframe read noise on my FZ50 is about 3.34 electrons at ISO 100
    (4800 electrons at saturation), and about 2.71 electrons at ISO 1600
    (about 300 electrons at saturation). Binned down 3x3 (to DSLR size),
    that's about 8.1 and 10 electrons (43,200 and 2700 max),
    respectively.


    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    John Sheehy, Mar 16, 2007
  11. ipy2006

    acl Guest

    On Mar 16, 8:53 pm, John Sheehy <> wrote:
    > "acl" <> wrote innews::
    >
    > > On Mar 16, 7:04 am, "Roger N. Clark (change username to rnclark)"
    > > <> wrote:

    >
    > >> 2) There is a difference. The signal you record has added
    > >> read noise. A larger pixel collects more photons
    > >> so the signal is larger compared to the read noise.
    > >> Thus you can detect fainter things, or have better high
    > >> ISO performance. If you sum the signal from a smaller
    > >> pixels to equal the area of a larger pixel size,
    > >> you are also adding read noise, so you don't gain
    > >> as much as having the larger pixel with one read noise.

    >
    > > Is read noise fixed per pixel, per unit area, or something else?

    >
    > It's something that happens when reading the pixels, and has more to do
    > with the electronics involved than anything else. It includes noise from
    > all parts of the readout chain (at the pixel, in the amplifier, in the
    > readout wiring, in the ADC, etc. Canon is very good at keeping it low,
    > relative to signal, at high ISOs compared to most other companies, which
    > seem to just amplify the same noise to a higher amplitude.


    Maybe I didn't phrase my question carefully: Is it dependent on the
    area of the pixel? For example, something like thermal noise should be
    proportional to the active volume of the photodetector (to a first
    approximation at least), while noise which is produced by the
    amplifier should be independent of the actual area. The point of the
    question is to find out whether it will scale down with the pixels or
    not, and if it does, do we gain or lose? eg if it was proportional to
    the volume, then scaling down to half the linear dimensions would
    increase the s/n ratio, as the number of photons detected would be 1/4
    but the noise would be 1/8 (this is supposed to be a sketch to explain
    what I mean, not a serious argument).

    Of course it is obvious that eventually there's a limit, for small
    enough structures everything changes, but this should be at the scale
    of a few nm at most, not microns, so irrelevant for us.

    >
    > There are basically three categories in the read noise vs ISO category;
    > Cameras like Canon DSLRs that have less read noise at ISO 1600 than ISO
    > 100, in electrons, cameras like the Pentax K10D which have the same read
    > noise in electrons at all ISOs, and cameras like my FZ50, which does a
    > very good job of readout at ISO 100, but gets more read noise in
    > electrons at ISO 100.
    >
    > Of course, the most relevant part of read noise at the pixel level, as
    > measured in units of electrons, is the ratio of the maximum number of
    > electrons digitized at the ISO, and the read noise in electrons. That
    > determines the lowest signal level, relative to saturation, where a 1:1
    > S/N could be obtained, if blackframe read noise was the only noise.
    >


    Yes and the question relevant to our subject is how the two scale. The
    signal scales with the square of the linear size, but the noise? That
    is the point.
     
    acl, Mar 16, 2007
  12. ipy2006

    John Sheehy Guest

    "Roger N. Clark (change username to rnclark)" <> wrote
    in news::

    > If you sum the signal from a smaller
    > pixels to equal the area of a larger pixel size,
    > you are also adding read noise, so you don't gain
    > as much as having the larger pixel with one read noise.


    No. Read noise doesn't add linearly. 9 pixels binned into one triples the
    pixel read noise in electrons, while multiplying the signal electrons by 9,
    resulting in 3x the signal-to-readnoise ratio. Have you ever binned
    blackframes?

    With CCDs, on-chip binning can actually increase the ratio further, as they
    can add the same read noise to 4 pixels as they can to one pixel. There's
    a Dalsa paper about this technique. Such hardware binning is the only
    reason besides storage/speed issues to do the binning in-camera, IMO;
    otherwise, more and smaller pixels are better (especially if RAW data is
    not clipped at the blackpoint).

    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    John Sheehy, Mar 16, 2007
  13. ipy2006

    John Sheehy Guest

    "acl" <> wrote in
    news::

    > But personally I hope this kind of noise could go down enough so we
    > can have high pixel density sensors which will give more flexibility
    > in trading off noise for resolution. Hopefully with built-in binning
    > for the raw files too, as always having 60MB raw files seems a bit
    > wasteful (but the again 300KB for an executable seemed huge to me in
    > 1988).


    The smaller the pixels become, the less bit depth you need to record them
    at the same level of accuracy.

    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    John Sheehy, Mar 16, 2007
  14. ipy2006

    acl Guest

    On Mar 16, 6:50 pm, John Sheehy <> wrote:
    > "acl" <> wrote innews::
    >
    > > On Mar 15, 2:31 pm, John Sheehy <> wrote:
    > >> that standard deviation is only *one* factor in the noise equation;
    > >> magnification is another, and the low noise of big pixels is visually
    > >> magnified when the pixels are magnified along with the subject.

    >
    > > Exactly, and if you don't need the extra pixels you can bin.

    >
    > Yes, but I think it is very important to stress that there is no need to
    > bin to get the benefit. Often, the situation is described in such a way
    > that binning or downsampling are *necessary* to get the benefit. There
    > is a cult of pixel-for-pixel's sake that misses the forest (image or
    > subject) for the trees (pixels), IMO. To me, the most important quality
    > factors in descending importance are:
    >
    > 1) SQ (subject quality)
    >
    > 2) IQ (image quality)
    >
    > 3) PQ (pixel quality)
    >
    > If #3 doesn't also help #1, it is in vein.
    >
    > >> 2) slight benefit in photons collection rate per unit of sensor area
    > >> due
    > >> to less wasted space on the sensor (not always realized, however; my
    > >> 1.97u FZ50, for example, collects about the same number of photons per
    > >> unit of area as the 1DmkII, at RAW saturation for the same ISO).

    > > Well, as long as there are no constant noise sources (eg 10 electrons/
    > > pixel independent of the area). I have no idea if there are or not.

    >
    > Blackframe read noise on my FZ50 is about 3.34 electrons at ISO 100 (4800
    > electrons at saturation), and about 2.71 electrons at ISO 1600 (about 300
    > electrons at saturation). Binned down 3x3 (to DSLR size), that's about
    > 0.9 and 1.11 electrons (43,200 and 2700 max), respectively.


    I don't understand, why are you dividing by three? for noise r, you
    want sqrt(9*r^2)=3r, ie around 10 and 9 electrons or so. Or am I
    missing something?

    >
    > These values are derived from multiplying the standard deviation of FZ50
    > blackframes by 1.66, since the Panasonic RAW files, unfortunately, are
    > clipped at the blackpoint, a very bad idea that most camera manufacturers
    > engage in. Canon is one of the few that leave a bias in the RAW data
    > with a full symmetrical noise histogram with positive and negative noise.


    Yes I think Nikon does this too I didn't check in detail though, just
    an impression I got from looking at blackframes in IRIS some time ago;
    but maybe it is also dcraw's handling of the data, I don't know. The
    standard deviation of the noise was slightly higher at slightly larger
    raw values (5 or so) than at 0; so I thought that it is simply
    clipping the left edge of the noise distribution. But I didn't
    specifically check.

    > Clipping at black means bright, noise-clouded blacks with minute signals
    > clipped. Blackpoint clipping should not occur, IMO, until your RAW
    > conversion needs to enter a gamma-adjusted state (where negative signal
    > or noise are meaningless). All white-balancing, resampling, and
    > demosaicing should be done before the clipping, to maintain black blacks,
    > and a minimum of noise. I would guess that most converters don't
    > maintain this state, but clip Canons at black immediately upon loading
    > RAW data to get it in the same state as most other cameras. In my own
    > hand-conversions in IRIS and in PS with filtermeister and RAW linear
    > greyscale sources, I have made conversions with much less color tint and
    > bright haze in the deepest shadows. In fact, I have even promoted images
    > to a higher bit-depth before any interpolative actions, for more
    > precision. RAW converters, generally, are taking a lot of short-cuts,
    > IMO, and are not delivering what they can in these areas. They seem
    > focused mainly on the post-processing values like skin color and tonal
    > curves in the highlight areas, etc.


    I must admit that I cannot imagine that this clipping will have any
    serious consequences, except maybe if you do binning (it'll lighten
    the black), but I'm not sure how important it would be. But maybe if
    it's really noise then it will have an effect. I can't check, though.
    Could you post examples with and without this when you get time? I am
    curious.
     
    acl, Mar 16, 2007
  15. ipy2006

    acl Guest

    On Mar 16, 9:18 pm, John Sheehy <> wrote:
    > "acl" <> wrote innews::
    >
    > > But personally I hope this kind of noise could go down enough so we
    > > can have high pixel density sensors which will give more flexibility
    > > in trading off noise for resolution. Hopefully with built-in binning
    > > for the raw files too, as always having 60MB raw files seems a bit
    > > wasteful (but the again 300KB for an executable seemed huge to me in
    > > 1988).

    >
    > The smaller the pixels become, the less bit depth you need to record them
    > at the same level of accuracy.
    >


    Yes you're right. If the full well capacity is proportional to pixel
    area (and it must be something like that), then the size of a raw file
    should in principle remain roughly constant as we decrease the pixel
    size (until edge effects take over and it is not useful to miniaturise
    any more due to the fill factor not being 1).

    Nice to know that we won't be needing 100GB cards soon.
     
    acl, Mar 16, 2007
  16. ipy2006

    acl Guest

    On Mar 16, 9:03 pm, John Sheehy <> wrote:
    > Sorry, I had just woken up after an 18-hour emergency shift at work.
    >
    > I divided by three when I should have multiplied by three. I was thinking
    > in terms of the noise-to-signal ratio, and applied it to absolute photon
    > counts.
    >
    > That should have read:
    >
    > Blackframe read noise on my FZ50 is about 3.34 electrons at ISO 100
    > (4800 electrons at saturation), and about 2.71 electrons at ISO 1600
    > (about 300 electrons at saturation). Binned down 3x3 (to DSLR size),
    > that's about 8.1 and 10 electrons (43,200 and 2700 max),
    > respectively.
    >


    OK, I missed this post before, that explains it. Thanks.
     
    acl, Mar 16, 2007
  17. ipy2006

    John Sheehy Guest

    Lionel <> wrote in
    news::

    > On Fri, 16 Mar 2007 12:29:52 +0900, "David J. Littleboy"
    > <> wrote:
    >
    >>I think you guys are talking past each other here.
    >>
    >>I think John is arguing that _for a sensor of a given size_, larger
    >>pixels aren't any better.

    >
    > But they /are/ better! - That's why the sensor designers are
    > constantly trying to improve the fill-factor, ie; make the pixels (or,
    > more accurately, the actual photo diode surface, which is smaller than
    > the pixel size) bigger for a given sensor size/resolution ratio. This
    > is because the bigger the suface of the photodiode (as a proportion of
    > the size of that pixel on the sensor), the more photons it'll collect
    > for a given exposure. And, all else being equal, more photons equals a
    > better signal to noise ratio.


    Bigger pixels capture more photons per *PIXEL*; not per unit of sensor
    area, which is much more relevant. Noise per pixel is just a myopic,
    "missing-the-forest-for-the-trees" academic curiosity with no direct
    relationship to practical photography, in terms of pixel density.

    Think hard about this, if you think large pixels give better images, for
    shot noise reasons:

    Imagine that you had 16 square containers, and you gave them to an
    assistant, to place in a tight 4x4 array out in a field, to measure
    rainfall during a certain period of time.

    Your assistant is me, and I decide to replace the 16 containers with 64
    square containers, 4 of which fit in the same space as 1 of yours. I come
    back to you with a list of results from 64 smaller containers, instead of
    the 16 you asked for. The list is longer, and the total count is the
    same as it would be if I used your original containers, but have I
    created any *NOISE*?

    Of course not, but many people believe so for capturing photons instead
    of raindrops!

    The fact is, the smaller pixels give you more detail about where the
    raindrops (or photons) fell. That is not *NOISE*.

    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    John Sheehy, Mar 16, 2007
  18. ipy2006

    Pat Guest

    On Mar 16, 2:38 pm, John Sheehy <> wrote:
    > "Pat" <> wrote innews::
    >
    > > So if you don't like my idea -- which I'm not sure I even like my idea
    > > -- what dSLR would you suggest for the OP with a $1000 budget (don't
    > > forget sales tax and shipping)?

    >
    > A used 20D or a used Rebel XT.
    >
    > With lenses, might run a little bit more than a used 300D, but will be far
    > faster in operation, and better in low light. Sometimes it's worth going a
    > little over budget to get something a notch or two better.
    >
    > --
    >
    > <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    > John P Sheehy <>
    > ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><



    I don't necessarily disagree with that, but then $1000 would really be
    the budget then, would it.
     
    Pat, Mar 16, 2007
  19. ipy2006

    John Sheehy Guest

    "David J. Littleboy" <> wrote in
    news:etebdm$lv6$:

    > No. I think what John is saying is orthogonal to sensor size
    > arguments. He's arguing that for a given sensor size, one wants as
    > many pixels as one can get. Roger is arguing that for a given number
    > of pixels, one wants the largest sensor you can get.
    >
    > I suspect that they're both right.


    Yes, if that is what Roger is arguing. There are legions of people,
    however, in other web forums that quote Roger as proof that bigger pixels
    are always better, in all situations, and that the "megapixel race" is a
    race to nowhere. He could be clearer if he means what you say, but I get
    the impression that he does believe that subdividing a given pixel real-
    estate into smaller pixels lowers the bottom line in image quality.

    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    John Sheehy, Mar 16, 2007
  20. ipy2006

    John Sheehy Guest

    John Sheehy <> wrote in news:Xns98F5A1C552A9Fjpsnokomm@
    130.81.64.196:

    > There are basically three categories in the read noise vs ISO category;
    > Cameras like Canon DSLRs that have less read noise at ISO 1600 than ISO
    > 100, in electrons, cameras like the Pentax K10D which have the same read
    > noise in electrons at all ISOs, and cameras like my FZ50, which does a
    > very good job of readout at ISO 100, but gets more read noise in
    > electrons at ISO 100.


    That should have been "at ISO 1600" in the last line.

    Does usenet have editing yet? :)

    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    John Sheehy, Mar 16, 2007
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