ISO 20,000 revisited: Night and Low Light Photography with DigitalCameras

Discussion in 'Digital Photography' started by Roger N. Clark (change username to rnclark), Feb 27, 2006.

  1. A few weeks ago we had a long discussion on a new
    announcement of an ISO 20,000 sensor followed by
    discussion of intensified sensors. Some of us
    pointed out that digital cameras already had quantum
    efficiencies in the tens of percent with very low read
    noise. Kennedy didn't think low noise DSLRs could
    detect very low light levels amounting to less than
    one photon per pixel per frame.

    I've done an extensive analysis of my Canon 1D Mark II
    and performed tests to see what could be done. I determined
    the quantum efficiency of the 1D Mark II sensor is
    about 28% and the system read noise is only 3.9
    electrons. (The 20D has similar low read noise, and
    probably similar QE.)

    This performance results in great low signal detections and
    I show on a new web page detecting image detail with
    only 0.1 photon per pixel per frame in low light conditions
    such as 0.00016 lux, and providing credible signal detection
    when combining only 64 frames.
    See:

    Night and Low Light Photography with Digital Cameras
    http://www.clarkvision.com/photoinfo/night.and.low.light.photography

    A detailed evaluation of the Canon 1D Mark II read noise,
    full well capacity, and dynamic range as a function of ISO
    is at:

    Procedures for Evaluating Digital Camera Noise and Full
    Well Capacities; Canon 1D Mark II Analysis
    http://www.clarkvision.com/imagedetail/evaluation-1d2

    The determination of quantum efficiency is at:

    Digital Cameras: Counting Photons, Photometry, and Quantum Efficiency
    http://www.clarkvision.com/imagedetail/digital.photons.and.qe

    The bottom line is that if one removed the Bayer filter from
    current DSLRs and used the full range of the CMOS/CCD sensor,
    the performance we now have in color at ISO 1,600 we would have
    at ISO 16,000 in black and white (but with images like infrared film).
    So claims of a new higher sensitivity sensor that is orders of
    magnitude more sensitive than current DSLRs is bogus from all
    the data I've seen as well as investigated on the above pages.

    Roger
     
    Roger N. Clark (change username to rnclark), Feb 27, 2006
    #1
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  2. Roger N. Clark (change username to rnclark)

    ASAAR Guest

    Re: ISO 20,000 revisited: Night and Low Light Photography with Digital Cameras

    On Sun, 26 Feb 2006 22:46:46 -0800, Roger N. Clark (change username
    to rnclark) wrote:

    > A few weeks ago we had a long discussion on a new
    > announcement of an ISO 20,000 sensor followed by
    > discussion of intensified sensors.
    >
    > . . .
    >
    > The bottom line is that if one removed the Bayer filter from
    > current DSLRs and used the full range of the CMOS/CCD sensor,
    > the performance we now have in color at ISO 1,600 we would have
    > at ISO 16,000 in black and white (but with images like infrared film).
    > So claims of a new higher sensitivity sensor that is orders of
    > magnitude more sensitive than current DSLRs is bogus from all
    > the data I've seen as well as investigated on the above pages.


    An ISO of 20,000 isn't an order of magnitude greater than 16,000,
    but did you really mean "20,000"? The thread you mentioned referred
    to an ISO an order of magnitude higher than that. So if the
    respective sensors are 16,000 and 200,000, that would be slightly
    more than an order of magnitude difference, but less than "orders",
    which would need a super sensor of at least 1,600,000 ISO.

    There's another point I'm not clear on. The OP from that thread
    says that the sensor's sensitivity is 2000X. (2000 x 100 ==
    200,000). That would seem to imply that it was based on a
    comparison with the more or less universally accepted value of ISO
    100 for the native sensitivity of today's typical camera. I
    understand why you chose to compare ISO 16,000 with ISO 20,000 (or
    200,000) but is that fair? I didn't read the news item posted in
    the OP. Did it claim that the sensor had an effective ISO only for
    B&W? If it did, your results may be more or less valid. But even
    if so, from reading your messages it seems that you might not be a
    disinterested observer, and instead of trying to determine what the
    Korean sensor is actually capable of producing, seem to be looking
    mainly for ways to back your earlier assertions that it can't be as
    good as claimed. And if you accidentally used ISO 20,000 instead of
    the claimed ISO 200,000, then the Korean sensor's ISO more than
    meets the 10x improvement which you previously said is bogus.

    Here's a clip from one of your replies in that thread:

    > Message-ID: <>
    > Date: Sun, 29 Jan 2006 11:03:01 -0800
    > From: "Roger N. Clark (change username to rnclark)"
    > Newsgroups: rec.photo.digital
    > Subject: Re: ISO 200000 ?
    > . . .
    >
    >> Even if the claimed
    >> "2000X light sensitivity" can't be attained, most people would be
    >> giddy if only a 500X improvement could be achieved. The first
    >> result would be that cameras would no longer need to include
    >> flashes, so only external units would be sold. Bye bye red-eye,
    >> unless as the OP asked, it turns out to be too good to be true. :)
    >>

    >
    > But the point is that even 500x is bogus, so is 10x. The quantum
    > efficiency is already 20 to 30% in consumer systems. You can up it
    > 3 to 5x if you could get to ~100% quantum efficiency. That is for
    > the high signal case (more than about 50 to 100 photons). For the
    > low signal case, read noise dominates. Best systems are already in
    > the 3 to 4 electron read noise range, so you see big gains in photon
    > detection below a few photons. That is a regime that doesn't
    > make photographs. That was the point of the tables I posted.
     
    ASAAR, Feb 27, 2006
    #2
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  3. ASAAR wrote:

    > On Sun, 26 Feb 2006 22:46:46 -0800, Roger N. Clark (change username
    > to rnclark) wrote:


    >>A few weeks ago we had a long discussion on a new
    >>announcement of an ISO 20,000 sensor followed by
    >>discussion of intensified sensors.


    >>
    >>The bottom line is that if one removed the Bayer filter from
    >>current DSLRs and used the full range of the CMOS/CCD sensor,
    >>the performance we now have in color at ISO 1,600 we would have
    >>at ISO 16,000 in black and white (but with images like infrared film).
    >>So claims of a new higher sensitivity sensor that is orders of
    >>magnitude more sensitive than current DSLRs is bogus from all
    >>the data I've seen as well as investigated on the above pages.

    >
    > An ISO of 20,000 isn't an order of magnitude greater than 16,000,
    > but did you really mean "20,000"? The thread you mentioned referred
    > to an ISO an order of magnitude higher than that. So if the
    > respective sensors are 16,000 and 200,000, that would be slightly
    > more than an order of magnitude difference, but less than "orders",
    > which would need a super sensor of at least 1,600,000 ISO.


    Your are right. I mean to write 200,000.

    > There's another point I'm not clear on. The OP from that thread
    > says that the sensor's sensitivity is 2000X. (2000 x 100 ==
    > 200,000). That would seem to imply that it was based on a
    > comparison with the more or less universally accepted value of ISO
    > 100 for the native sensitivity of today's typical camera. I
    > understand why you chose to compare ISO 16,000 with ISO 20,000 (or
    > 200,000) but is that fair?


    I think you are missing the point. Sensitivity is expressed as
    photon conversion efficiency, called the quantum efficiency (QE).
    Important too is low electronics noise (low read noise).
    Current QE of DSLRs are in the 20 to 35+% range and backside illuminated
    CCDs are in the 90+% range. So sensor sensitivity of current
    DSLRs can only be improved 3 to 4x to be perfect. So any claim
    of "orders of magnitude" improvement was bogus from the start for
    a high signals tens of photons and greater.

    One person argued that it was not the high level signal that is
    the improvement but the low signal regime, including less than
    a photon per pixel per frame. I posted astronomical images
    that I new went deep, recording low numbers of photons.
    But I had no information on how low that really was compared
    to the E2V sensors whose web sites showed terrestrial night
    scenes and lab images where the photons recorded were less than
    one photon per pixel per frame. So no one really knew how low
    a DSLR could go.

    From my experience with other sensors, and with DSLRs in astronomical
    imaging, I knew one could record signals less than the system noise,
    but I did not have any hard data at the below one photon per pixel
    level. So I was challenged to show what could be done with DSLRs.

    After these new tests, it proves that DSLRs can record signals less
    than 1 photon per pixel per frame. In fact the performance is
    significantly better than I thought. In a terrestrial night,
    fraction of a second image, DSLRs record less than a photon
    per pixel per frame per fraction of a second. In astronomical
    imaging, that level gets pushed lower: less than a photon per
    pixel per frame per minute(s).

    I didn't read the news item posted in
    > the OP. Did it claim that the sensor had an effective ISO only for
    > B&W? If it did, your results may be more or less valid. But even
    > if so, from reading your messages it seems that you might not be a
    > disinterested observer, and instead of trying to determine what the
    > Korean sensor is actually capable of producing, seem to be looking
    > mainly for ways to back your earlier assertions that it can't be as
    > good as claimed. And if you accidentally used ISO 20,000 instead of
    > the claimed ISO 200,000, then the Korean sensor's ISO more than
    > meets the 10x improvement which you previously said is bogus.


    Regardless of what number they claim, 10x, 100x, ISO 20,000, ISO 200,000,
    there is no actual sensitivity gain beyond improvement in quantum
    efficiency of 3 to 4x. More than that is like digital zoom to magnify an
    image! Call digital ISO zoom. The sensitivity is the Quantum efficiency.
    The read noise is low enough in the better DSLRs such that
    photon noise is still a significant factor in the lowest signals.

    If the Korean sensor claims ISO 200,000, it must be using different
    specifications than is used in DSLRs, and correspondingly
    different noise specs. Digital ISO zoom. You can
    do that now in photoshop.

    The main improvement in the sub one photon per pixel case of the
    intensified sensors is lowering read noise, but you still have
    photon noise and in the case I show on the web page of a moonlit
    scene, the zero read noise sensor would show only about a 2x improvement
    in image signal-to-noise ratio over current DSLRs.

    Yes, the 200,000 ISO claim is bogus, and current DSLRs are performing
    very well indeed.

    Roger
     
    Roger N. Clark (change username to rnclark), Feb 27, 2006
    #3
  4. Roger N. Clark (change username to rnclark)

    ASAAR Guest

    Re: ISO 20,000 revisited: Night and Low Light Photography with Digital Cameras

    On Mon, 27 Feb 2006 08:00:37 -0700, Roger N. Clark (change username
    to rnclark) wrote:

    > The main improvement in the sub one photon per pixel case of the
    > intensified sensors is lowering read noise, but you still have
    > photon noise and in the case I show on the web page of a moonlit
    > scene, the zero read noise sensor would show only about a 2x improvement
    > in image signal-to-noise ratio over current DSLRs.
    >
    > Yes, the 200,000 ISO claim is bogus, and current DSLRs are performing
    > very well indeed.


    If everything you claim is correct, you raise an interesting point
    nearly as significant as the claims made for the Korean sensor. What
    is involved with using "the full range of the CMOS/CCD sensor"? You
    say that when that is combined with removing the Bayer filter, the
    color ISO 1,600 performance could be boosted to b&w ISO 16,000
    performance (with images resembling infrared film). As a fairly
    large number of people would love to be able to have an infrared
    sensitive camera having performance comparable to ISO 16, why aren't
    cameras given this capability? Security concerns? If the only
    change was to remove the Bayer filter, where do you estimate the
    increased ISO would fall between 1,600 and 16,000?
     
    ASAAR, Feb 27, 2006
    #4
  5. Re: ISO 20,000 revisited: Night and Low Light Photography with Digital Cameras

    In article <>, "Roger N. Clark (change
    username to rnclark)" <> writes
    >A few weeks ago we had a long discussion on a new
    >announcement of an ISO 20,000 sensor followed by
    >discussion of intensified sensors. Some of us
    >pointed out that digital cameras already had quantum
    >efficiencies in the tens of percent with very low read
    >noise. Kennedy didn't think low noise DSLRs could
    >detect very low light levels amounting to less than
    >one photon per pixel per frame.
    >

    Actually Roger, as I suspect you are aware, that is not what I said. In
    fact it was another correspondent in that thread who claimed that less
    than one photon per pixel per frame was impossible to achieve. In fact,
    not only did I state that this was possible but provided evidence of
    intensifiers which did achieve this.

    My comment was that digital SLRs were unable to achieve a useful image
    in 10^-4 lux (overcast starlight) illumination in an exposure of 1/50th
    of a second with any amount of post processing - which is what the
    intensified camera achieved and which is also what high ISO would
    achieve. None of your examples on your page come close to that - the
    1/20 sec moonlit single frames appear to be about a factor of almost 700
    wide of the target, based on the illumination level and the exposure you
    used.

    Close, but no cheese this time. ;-)
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
     
    Kennedy McEwen, Feb 27, 2006
    #5
  6. Re: ISO 20,000 revisited: Night and Low Light Photography with Digital Cameras

    In article <>, "Roger N. Clark (change
    username to rnclark)" <> writes
    >
    >I think you are missing the point. Sensitivity is expressed as
    >photon conversion efficiency, called the quantum efficiency (QE).
    >

    Actually Roger, I think *you* are missing the point, still. Sensitivity
    isn't *just* quantum efficiency! For example, those digital cameras
    which achieve ISO3200 today don't have a QE that is 4x better than the
    cameras that have only ISO800. In fact, both detectors have pretty much
    the same QE.

    >Yes, the 200,000 ISO claim is bogus, and current DSLRs are performing
    >very well indeed.
    >

    Your 1/20sec exposures in quarter moonlight, are still more than two
    orders of magnitude away from the objective, using the data on your
    page, an objective that intensifiers and LLTV sensors achieve every day,
    well, night actually. ;-)
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
     
    Kennedy McEwen, Feb 27, 2006
    #6
  7. Roger N. Clark (change username to rnclark)

    Guest

    Re: ISO 20,000 revisited: Night and Low Light Photography with Digital Cameras

    ASAAR wrote:

    > If everything you claim is correct, you raise an interesting point
    > nearly as significant as the claims made for the Korean sensor. What
    > is involved with using "the full range of the CMOS/CCD sensor"?


    Stripping out the CFA, back-illumination, and upsizing the pixel. Read
    noise reduction via L3CCD techniques (start writing those checks to
    TI), super-fast pixel rates (for DR), etc.

    > You
    > say that when that is combined with removing the Bayer filter, the
    > color ISO 1,600 performance could be boosted to b&w ISO 16,000
    > performance (with images resembling infrared film).
    > As a fairly
    > large number of people would love to be able to have an infrared
    > sensitive camera having performance comparable to ISO 16, why aren't
    > cameras given this capability?


    N people want an IR camera. C*N people want a color camera. C is a
    very large constant (probably over a thousand, probably even higher).
    Special fab run for a few photographic kooks? Maybe some day. Not
    even the 20Da got a CFA-less sensor, since it was likely too big a hit
    to the production costs ("Why buy this $4k un-cooled camera when I can
    get a fancy-ass cooled one from SBIG for a bit more?")

    > Security concerns?


    Despite the claims of some here, it's already far too late for that.
    Not that this will keep El Presidente from withdrawing the Poisson
    distribution from the public sphere....

    > If the only change was to remove the Bayer filter, where do you estimate the
    > increased ISO would fall between 1,600 and 16,000?


    I can't find a definitive spectrum of "overcast starlight". However:

    http://arxiv.org/PS_cache/astro-ph/pdf/9909/9909153.pdf

    (and others of the genre)

    may be representative (ignore some of the spikes in the visual due to
    so-called civilization). Note the large increase in intensity at the
    near infrared, and also recall that as the wavelength increases, energy
    per photon decreases, so the number of photons available scales even
    more. Now recall that the Bayer CFA puts essentially tight (but lossy)
    passbands in the visual [[look at the spectrum again: UBVRI passbands
    are shown: B=blue, V=green, R=red]] and there is a deep IR filter
    beforehand (this IR filter is needed because the dye filters in the
    typical photographic cameras are can be transparent to longer IR).
    The exact number needs an integration, but we can expect at least a
    factor of 2 (just for bandwidth), but clearly there is much more to be
    gained.

    In the end, the game is converting photons. This is what "quantum
    efficiency" is all about: sensitivity. The labels we attach to these
    photons -- what photographers call "ISO" -- are beside the point.
    Anyone who claims or says otherwise needs to present new physics to
    back up their statements, because current, known, physics 'explains'
    all existing cameras. Even soooper-dooper secret decoder ring level
    cameras.
     
    , Feb 28, 2006
    #7
  8. ASAAR wrote:
    > On Mon, 27 Feb 2006 08:00:37 -0700, Roger N. Clark (change username
    > to rnclark) wrote:
    >
    >
    >>The main improvement in the sub one photon per pixel case of the
    >>intensified sensors is lowering read noise, but you still have
    >>photon noise and in the case I show on the web page of a moonlit
    >>scene, the zero read noise sensor would show only about a 2x improvement
    >>in image signal-to-noise ratio over current DSLRs.
    >>
    >>Yes, the 200,000 ISO claim is bogus, and current DSLRs are performing
    >>very well indeed.

    >
    >
    > If everything you claim is correct, you raise an interesting point
    > nearly as significant as the claims made for the Korean sensor. What
    > is involved with using "the full range of the CMOS/CCD sensor"? You
    > say that when that is combined with removing the Bayer filter, the
    > color ISO 1,600 performance could be boosted to b&w ISO 16,000
    > performance (with images resembling infrared film). As a fairly
    > large number of people would love to be able to have an infrared
    > sensitive camera having performance comparable to ISO 16, why aren't
    > cameras given this capability? Security concerns? If the only
    > change was to remove the Bayer filter, where do you estimate the
    > increased ISO would fall between 1,600 and 16,000?
    >

    Consider that CMOS and CCD sensors have response from less than
    4000 angstroms to about 10,000 angstroms, with a full width
    at half maximum from about 3800 to 8500 angstroms. Full Width
    at Half Maximum (FWHM) is the point at which the response
    of a system falls by a factor of two from the peak response.
    The FWHM is a good approximation of the throughput of a system.
    So the FWHM is ~ 8500 - 3800 = 4700 angstroms.

    But the green filter has a full width at half maximum from
    about 5000 to 5770 angstroms, so a FWHM of only about 770 angstroms.
    Then the green filter is somewhat less than 100% transmission.

    The FWHM ratio of the sensor and green filter is ~4700/770 ~ 6.
    Multiplying in transmission due to the color filter times
    the transmission of the IR blocking filter (somewhere
    from 80% to less than 25% seem to be numbers in documents (but
    that may include detector quantum efficiency). If the transmission
    is as high as 80%, the effect of removing the filters would let
    6/0.8 = 7.5x more light in. If the transmission is 25%, the
    improvement would be 6/.25 = 24! A factor of 10 seems
    to be consistent with other data I've seen in scientific papers.

    It is a good question why it hasn't been done. Amateur astronomers
    have removed the IR blocking filter and replaced them with
    filters than block less IR light (google Heutech: they do it for
    a fee), then Canon did it with the 20Da. But for someone
    wanting a black and white sensor, lenses working over such a large
    wavelength range would be an issue, but a more modest design
    could replace the IR + color filter that only allowed light
    from the UV to about 7000 angstroms, and gaining some 6x in
    speed should be easy. You would also need to put in a compensating
    piece of glass in place of the color filter so the focal point
    doesn't change (so the AF system maintains accuracy).

    Example spectral response functions:
    http://www.graftek.com/pdf/Manuals/basler/A600fmanual.pdf
    see figures 1-3 and 1-4 which shows QE spectral response and
    filter transmission.

    If you are interested, you might contact Heutech and see if they
    would do a modification for you. (I have no affiliation with
    them nor have I bought anything from them).

    Roger
     
    Roger N. Clark (change username to rnclark), Feb 28, 2006
    #8
  9. Kennedy McEwen wrote:

    > In article <>, "Roger N. Clark (change
    > username to rnclark)" <> writes
    >
    >> I think you are missing the point. Sensitivity is expressed as
    >> photon conversion efficiency, called the quantum efficiency (QE).
    >>

    > Actually Roger, I think *you* are missing the point, still. Sensitivity
    > isn't *just* quantum efficiency! For example, those digital cameras
    > which achieve ISO3200 today don't have a QE that is 4x better than the
    > cameras that have only ISO800. In fact, both detectors have pretty much
    > the same QE.


    Ahah! Finally an admission. I've been saying that for quite
    a while. Let's normalize the test conditions.

    >> Yes, the 200,000 ISO claim is bogus, and current DSLRs are performing
    >> very well indeed.
    >>

    > Your 1/20sec exposures in quarter moonlight, are still more than two
    > orders of magnitude away from the objective, using the data on your
    > page, an objective that intensifiers and LLTV sensors achieve every day,
    > well, night actually. ;-)


    Let's normalize the conditions between sensors to see what the
    true difference in the sensors really is.

    The LLTV intensified sensors in your test are

    1) Black and white, with no color filters, and no IR blocking filter.
    This is a huge factor, about 10x between the bandwidth difference
    and the transmission loss of the filters.
    2) They are back side illuminated with QE >~ 90%, so about
    3.4x higher sensitivity than DSLRs.
    3) The videos on the E2V site use f/1.4 lenses, I only have
    and f/1.8 lens, so another factor of 1.7x difference.
    4) Like you admit above with different digital cameras achieve
    different ISOs, which is due to pixel size, the E2V sensors
    are much larger than DSLR pixels. If I remember right, it
    was something like 25x35 microns compared to 8.2 microns
    for the Canon 1D Mark II. The area ratio is then about
    13x for those numbers.

    So equalizing the two systems, there is 10*3.4*1.7*13 ~ 750x
    difference. Now of that 750x, only 3.4x is actual sensitivity
    differences between the two systems. 750/3.4 = 220 in optical
    differences.

    With the DSLR results showing it the sensor can detect
    and provide image information at the <1 photon per pixel per
    frame and normalizing the test conditions, proves there are
    not "orders of magnitude" improvement by using the intensified
    sensors.

    So the lab test showed detecting 0.1 photon per pixel per frame
    in a 0.00016 lux 1-second exposure. That equals (multiply
    by 220 and divide by 1.6 then another 50 (to get to your
    1/50 second exposure:

    = 0.1 *220/1.6/50

    = 0.27 photon, per pixel per frame per 1/50 second,
    which is above the detection threshold already
    established.

    In this low light condition, the E2V back side illuminated sensor
    would get 0.27 * 3.4 ~ 0.9 photon per pixel per frame. With
    its lower read noise, photon noise would dominate any image
    made, thus would be another ~2x lower noise over the bare DSLR
    sensor. So between effectively zero read noise, and the QE,
    the sensor would perform about 7x better than the DSLR,
    not "orders of magnitude." The no course as light levels
    increase to a few tens of photons, then performance is only
    the QE difference.

    QED

    Roger
     
    Roger N. Clark (change username to rnclark), Feb 28, 2006
    #9
  10. Kennedy McEwen wrote:
    > In article <>, "Roger N. Clark (change
    > username to rnclark)" <> writes
    >
    >> A few weeks ago we had a long discussion on a new
    >> announcement of an ISO 20,000 sensor followed by
    >> discussion of intensified sensors. Some of us
    >> pointed out that digital cameras already had quantum
    >> efficiencies in the tens of percent with very low read
    >> noise. Kennedy didn't think low noise DSLRs could
    >> detect very low light levels amounting to less than
    >> one photon per pixel per frame.
    >>

    > Actually Roger, as I suspect you are aware, that is not what I said. In
    > fact it was another correspondent in that thread who claimed that less
    > than one photon per pixel per frame was impossible to achieve.



    I guess I misunderstood when you said:
    Kennedy McEwen wrote (Re: ISO 200000 ?), 1/24/2006 3:04 PM:
    > However that 0.5 phot/pix/frame is now substantially
    > lower than the read noise which is applied to *every* pixel. Hence my
    > insistence that the read noise you quote for the Canon device of 3
    > photons is much higher than a useful signal level.


    Kennedy McEwen wrote (Re: ISO 200000 ?), 1/26/2006 4:01 PM:
    > What I am not convinced of is that
    > the example you referenced is a tougher challenge than the one I gave -
    > NOT the issue about detecting signals in SNRs of less than unity.


    Kennedy McEwen wrote (Re: ISO 200000 ?), 1/23/2006 2:31 PM:
    > How is the integration of several frames with a noise
    > floor of >1 phot/pix/frame equal to <1 phot/pix/frame?


    Kennedy McEwen wrote (Re: ISO 200000 ?), 1/28/2006 7:49 PM:
    > Limitations which are still orders of magnitude
    > beyond what can be achieved with a DSLR sensor.


    Kennedy McEwen wrote (Re: ISO 200000 ?), 1/29/2006 1:55 PM
    > the Korean press release made it quite clear why they are
    > interested in such sensor improvements, and they are only
    > claiming useful images in 0.1lux.


    (Note the moonlit scene test with a DSLR got images at 0.06 lux,
    and the lab test 0.00016 lux).

    In fact,
    > not only did I state that this was possible but provided evidence of
    > intensifiers which did achieve this.
    >
    > My comment was that digital SLRs were unable to achieve a useful image
    > in 10^-4 lux (overcast starlight) illumination in an exposure of 1/50th
    > of a second with any amount of post processing - which is what the
    > intensified camera achieved and which is also what high ISO would
    > achieve. None of your examples on your page come close to that - the
    > 1/20 sec moonlit single frames appear to be about a factor of almost 700
    > wide of the target, based on the illumination level and the exposure you
    > used.


    See my other post. The optics difference (color filters on the
    DSLR, bare sensor on your intensified sensor, very large pixel size)
    means an optical difference of about 220. The .06 lux scene
    would then be equivalent to .00027 lux scene when the sensor
    sensitivities are directly compared. That makes the difference
    to 0.0001 lux and 1/50 second only a factor of 6.7, 3.4 of that
    is the QE difference (>90% for the intensified sensor, versus
    about 28% for the DSLR). So now we have a remaining 2x which
    is the real improvement in this test case: the lower read noise
    of the intensified sensor.
    >
    > Close, but no cheese this time. ;-)


    Yep, for you.

    Roger
     
    Roger N. Clark (change username to rnclark), Feb 28, 2006
    #10
  11. Roger N. Clark (change username to rnclark)

    ASAAR Guest

    Re: ISO 20,000 revisited: Night and Low Light Photography with Digital Cameras

    On Mon, 27 Feb 2006 19:26:40 -0800, Roger N. Clark (change username
    to rnclark) wrote:

    > It is a good question why it hasn't been done. Amateur astronomers
    > have removed the IR blocking filter and replaced them with
    > filters than block less IR light (google Heutech: they do it for
    > a fee), then Canon did it with the 20Da. But for someone
    > wanting a black and white sensor, lenses working over such a large
    > wavelength range would be an issue, but a more modest design
    > could replace the IR + color filter that only allowed light
    > from the UV to about 7000 angstroms, and gaining some 6x in
    > speed should be easy. You would also need to put in a compensating
    > piece of glass in place of the color filter so the focal point
    > doesn't change (so the AF system maintains accuracy).
    >
    > Example spectral response functions:
    > http://www.graftek.com/pdf/Manuals/basler/A600fmanual.pdf
    > see figures 1-3 and 1-4 which shows QE spectral response and
    > filter transmission.
    >
    > If you are interested, you might contact Heutech and see if they
    > would do a modification for you. (I have no affiliation with
    > them nor have I bought anything from them).


    Thanks for the information. While I haven't been actively
    considering such a modification, if the price isn't too outrageous I
    might use it to extend the life of my next retired camera. Unless,
    that is, it causes AF problems, and is not appropriate for cameras
    such as mine that can focus manually, but not easily.
     
    ASAAR, Feb 28, 2006
    #11
  12. Re: ISO 20,000 revisited: Night and Low Light Photography with Digital Cameras

    In article <>, "Roger N. Clark (change
    username to rnclark)" <> writes
    >Kennedy McEwen wrote:
    >> In article <>, "Roger N. Clark (change
    >>username to rnclark)" <> writes
    >>
    >>> A few weeks ago we had a long discussion on a new
    >>> announcement of an ISO 20,000 sensor followed by
    >>> discussion of intensified sensors. Some of us
    >>> pointed out that digital cameras already had quantum
    >>> efficiencies in the tens of percent with very low read
    >>> noise. Kennedy didn't think low noise DSLRs could
    >>> detect very low light levels amounting to less than
    >>> one photon per pixel per frame.
    >>>

    >> Actually Roger, as I suspect you are aware, that is not what I said.
    >>In fact it was another correspondent in that thread who claimed that
    >>less than one photon per pixel per frame was impossible to achieve.

    >
    >
    >I guess I misunderstood when you said:


    I guess you did since none of your quoted references address what you
    now claim I said. In fact, I had already addressed your
    misunderstanding quite clearly and succinctly when I responded to your
    post on 25th January with:
    Roger:
    >You seem to not believe that a signal can be dug out of the noise.

    Kennedy:
    >Not at all, that was my original argument - which you suggested was
    >trickery!


    This followed previous discussions on the topic on 23rd January:
    Roger:
    >You can detect <1 photon per pixel per frame if the noise floor
    >is above one photon too.

    Kennedy>
    >Of course you can, but you have spent the last few days telling us all
    >that detection at less than <1photon per pixel per frame is impossible!


    and on 24th January:
    Roger>
    >You keep repeating the < 1 photon per pixel per frame, but I have
    >not understood from what you have written, how many total photons
    >you would consider a detection.

    Kennedy>
    >Typically, 50% probability of detection would occur at a PSNR (ie.
    >after any frame & spatial integration) of 2.25.


    We can continue posting references to previous discussions till hell
    freezes, but at no time did I claim or infer what you are now stating I
    did. In fact, when I thought you had misinterpreted my comments in that
    way I specifically attempted to corrected your interpretation and, on
    the 24th January post referenced above spelled out precisely what I
    considered the limit to be.

    I don't think I could have been any clearer, but I am not responsible
    for your interpretations.
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
     
    Kennedy McEwen, Mar 2, 2006
    #12
  13. Re: ISO 20,000 revisited: Night and Low Light Photography with Digital Cameras

    In article <>, "Roger N. Clark (change
    username to rnclark)" <> writes
    >Kennedy McEwen wrote:
    >
    >> In article <>, "Roger N. Clark (change
    >>username to rnclark)" <> writes
    >>
    >>> I think you are missing the point. Sensitivity is expressed as
    >>> photon conversion efficiency, called the quantum efficiency (QE).
    >>>

    >> Actually Roger, I think *you* are missing the point, still.
    >>Sensitivity isn't *just* quantum efficiency! For example, those
    >>digital cameras which achieve ISO3200 today don't have a QE that is
    >>4x better than the cameras that have only ISO800. In fact, both
    >>detectors have pretty much the same QE.

    >
    >Ahah! Finally an admission. I've been saying that for quite
    >a while.


    Really? I am pretty sure that this is the first time that any
    comparison of ISO levels in different consumer cameras has been
    mentioned in this thread or the previous one. That doesn't mean you
    haven't been saying it for some time, but you certainly haven't been
    saying it in this discussion. In fact, in the previous thread on this
    topic I raised the issue several times that ISO wasn't just QE, hoping
    you would bite - you didn't, and you still, apparently, don't get it.
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
     
    Kennedy McEwen, Mar 2, 2006
    #13
  14. Kennedy McEwen wrote:

    > In fact, in the previous thread on this
    > topic I raised the issue several times that ISO wasn't just QE, hoping
    > you would bite - you didn't, and you still, apparently, don't get it.


    I'm not sure what you mean here. Sensors have only one QE, on my
    QE web page I only derive one QE per sensor (per color/wavelength):

    Digital Cameras: Counting Photons, Photometry, and Quantum Efficiency
    http://www.clarkvision.com/imagedetail/digital.photons.and.qe

    Then I have shown digital cameras like the 1D Mark II follow
    a simple noise model, equation 2 at:
    http://www.clarkvision.com/imagedetail/evaluation-1d2

    N = (P + r^2 + t^2)^(1/2),

    Where N = total noise in electrons,
    P = number of converted photons,
    r = read noise in electrons, and
    t = thermal noise in electrons (~0 for short exposures).

    So Signal-to-noise ratio = P/N

    This applies to the intensified sensors also, just r ~0.

    If you have a different definition of sensitivity and achievable
    Signal-to-noise ratios, please give specifics, instead of
    personal attacks like you just don't get it.

    Roger
     
    Roger N. Clark (change username to rnclark), Mar 6, 2006
    #14
  15. Kennedy McEwen wrote:

    > Roger:
    >> You seem to not believe that a signal can be dug out of the noise.

    > Kennedy:
    > >Not at all, that was my original argument - which you suggested was
    > >trickery!


    Please cite where I said it was trickery. If you look through the
    usenet archives for the last year, you will see I have said
    that signals can be dug out of the noise because I was doing it.
    I do not believe I said any such thing about trickery.

    > Roger:\
    >> You can detect <1 photon per pixel per frame if the noise floor
    >> is above one photon too.

    > Kennedy>
    > >Of course you can, but you have spent the last few days telling us all
    > >that detection at less than <1photon per pixel per frame is impossible!


    Where did I say it was impossible? Again I do not believe I
    said any such thing.

    > We can continue posting references to previous discussions till hell
    > freezes, but at no time did I claim or infer what you are now stating I
    > did.


    Kennedy, I am not trying to be obstinant, and I don't
    think you are either. We clearly have a communication problem,
    probably due different paradigms from which we are coming.
    But if we can talk specifics using equations, as I did in my
    other post tonight, perhaps we can avoid unfortunate
    name calling.

    Roger
     
    Roger N. Clark (change username to rnclark), Mar 6, 2006
    #15
  16. Kennedy McEwen wrote:

    > Roger:
    >> You seem to not believe that a signal can be dug out of the noise.

    > Kennedy:
    > >Not at all, that was my original argument - which you suggested was
    > >trickery!


    Please cite where I said it was trickery. If you look through the
    usenet archives for the last year, you will see I have said
    that signals can be dug out of the noise because I was doing it.
    I do not believe I said any such thing about trickery.

    > Roger:\
    >> You can detect <1 photon per pixel per frame if the noise floor
    >> is above one photon too.

    > Kennedy>
    > >Of course you can, but you have spent the last few days telling us all
    > >that detection at less than <1photon per pixel per frame is impossible!


    Where did I say it was impossible? Again I do not believe I
    said any such thing.

    > We can continue posting references to previous discussions till hell
    > freezes, but at no time did I claim or infer what you are now stating I
    > did.


    Kennedy, I am not trying to be obstinant, and I don't
    think you are either. We clearly have a communication problem,
    probably due different paradigms from which we are coming.
    But if we can talk specifics using equations, as I did in my
    other post tonight, perhaps we can avoid unfortunate
    name calling.

    Roger
     
    Roger N. Clark (change username to rnclark), Mar 6, 2006
    #16
  17. Kennedy McEwen wrote:

    > Roger:
    >> You seem to not believe that a signal can be dug out of the noise.

    > Kennedy:
    > >Not at all, that was my original argument - which you suggested was
    > >trickery!


    Please cite where I said it was trickery. If you look through the
    usenet archives for the last year, you will see I have said
    that signals can be dug out of the noise because I was doing it.
    I do not believe I said any such thing about trickery.

    > Roger:\
    >> You can detect <1 photon per pixel per frame if the noise floor
    >> is above one photon too.

    > Kennedy>
    > >Of course you can, but you have spent the last few days telling us all
    > >that detection at less than <1photon per pixel per frame is impossible!


    Where did I say it was impossible? Again I do not believe I
    said any such thing.

    > We can continue posting references to previous discussions till hell
    > freezes, but at no time did I claim or infer what you are now stating I
    > did.


    Kennedy, I am not trying to be obstinant, and I don't
    think you are either. We clearly have a communication problem,
    probably due different paradigms from which we are coming.
    But if we can talk specifics using equations, as I did in my
    other post tonight, perhaps we can avoid unfortunate
    name calling.

    Roger
     
    Roger N. Clark (change username to rnclark), Mar 6, 2006
    #17
  18. Re: ISO 20,000 revisited: Night and Low Light Photography with Digital Cameras

    In article <>, "Roger N. Clark (change
    username to rnclark)" <> writes
    >Kennedy McEwen wrote:
    >
    >> Roger:
    >>> You seem to not believe that a signal can be dug out of the noise.

    >> Kennedy:
    >> >Not at all, that was my original argument - which you suggested was
    >> >trickery!

    >
    >Please cite where I said it was trickery.


    The post which that quote specifically responded to! Viz: Sat, Jan 21
    2006 9:43 am "Kennedy is tricking you"

    Just to jog your memory, that was the same post in which you
    acknowledged that:
    "Kennedy has alluded to less than 1 photon per pixel per frame and
    implied that 1 photon was useful."
    .... which would appear to be in direct contradiction of your opening
    statement in this thread!
    >
    >Kennedy, I am not trying to be obstinant, and I don't
    >think you are either. We clearly have a communication problem,
    >probably due different paradigms from which we are coming.


    It would seem so. The lines that you now object to were quoted word for
    word from posts in the previous thread on this topic. They were not new
    statements and, at the time they were made, you didn't have any
    objection - possibly because your own statements were fresh in your
    mind, so there was less possibility of misunderstanding.

    Just as I objected to you misinterpreting my words, you are objecting to
    me quoting yours.
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
     
    Kennedy McEwen, Mar 6, 2006
    #18
  19. Kennedy McEwen wrote:

    > In article <>, "Roger N. Clark (change
    > username to rnclark)" <> writes
    >
    >> Kennedy McEwen wrote:
    >>
    >>> Roger:
    >>>
    >>>> You seem to not believe that a signal can be dug out of the noise.
    >>>
    >>> Kennedy:
    >>> >Not at all, that was my original argument - which you suggested was
    >>> >trickery!

    >>
    >>
    >> Please cite where I said it was trickery.

    >
    >
    > The post which that quote specifically responded to! Viz: Sat, Jan 21
    > 2006 9:43 am "Kennedy is tricking you"
    >
    > Just to jog your memory, that was the same post in which you
    > acknowledged that:
    > "Kennedy has alluded to less than 1 photon per pixel per frame and
    > implied that 1 photon was useful."
    > ... which would appear to be in direct contradiction of your opening
    > statement in this thread!
    >
    >>
    >> Kennedy, I am not trying to be obstinant, and I don't
    >> think you are either. We clearly have a communication problem,
    >> probably due different paradigms from which we are coming.

    >
    >
    > It would seem so. The lines that you now object to were quoted word for
    > word from posts in the previous thread on this topic. They were not new
    > statements and, at the time they were made, you didn't have any
    > objection - possibly because your own statements were fresh in your
    > mind, so there was less possibility of misunderstanding.
    >
    > Just as I objected to you misinterpreting my words, you are objecting to
    > me quoting yours.


    This is typical of many of your posts. You take things out of
    context and then do personal attacks. If you go back and actually
    read the exchanges, people were confused by your <1 photon/pixel
    statements. It took quite a while for people to understand
    that you meant combining multiple pixels either by multiple frames
    or multiple pixels combined (summed, averaged, etc). People
    took that to mean the multiple photons were being acquired, where
    we first thought you meant <1. The problem originated in that you said
    <1 photon per pixel per frame, but failed to say that pixels or
    frames are combined to improve the signal-to-noise.

    The rest of the exchange, which you left out, and took out of context
    is: Sat, Jan 21 2006 9:43, Roger said:
    > What he failed to clarify is that in none of the references,
    > do people actually claim a detection with one photon. For example,
    > in one of the papers they integrated for 160 seconds. If, for example,
    > there was 1 photon per pixel per frame, and 1/50 second frames, then
    > they would accumulate 50*160 = 8000 photons. The other way that is alluded to
    > making detections is many pixels summed together (either mathematically,
    > or by the eye to make the appearance of a fuzzy blob) with each pixel
    > getting 1 photon. So again, the image and object being detected
    > is MANY photons, not 1.


    Later in that same post I said:
    > Detecting a signal less than the noise is done all the time.


    and, again in the same post:
    > So, in summary, 1 photon per pixel per frame IS useful, if you
    > sum many pixels to get many photons. Whether you do that with
    > pixel summing and one frame or multiple frames is irrelevant, but
    > you need multiple photons, and in all cases, your maximum signal-to-noise
    > ratio is the square root of the number of pixels you counted.


    So please stop taking phrases out of context without reading the complete
    message.

    You need to clarify you meaning better.
    Not that I don't need to either, but I try and stay
    on topic and continue to answer questions and make further
    clarifications. This thread is another one typical along this
    line--get off topic and start personal attacks.

    How about getting back on topic?

    I posted a model for the noise in a camera system. Do you agree?
    If not, how would you modify it?

    I've also shown that the Canon 1D Mark II has 3.9 electron read noise
    and frames can be combined to detect <1 photon per pixel per frame.
    Do you agree with the analysis? If not why not?

    Roger
     
    Roger N. Clark (change username to rnclark), Mar 7, 2006
    #19
  20. Re: ISO 20,000 revisited: Night and Low Light Photography with DigitalCameras

    wrote:

    > I can't find a definitive spectrum of "overcast starlight". However:
    >
    > http://arxiv.org/PS_cache/astro-ph/pdf/9909/9909153.pdf
    >

    That spectrum is the night sky background (airglow, galactic light,
    interplanetary dust), but excludes most starlight. A better
    approximation, I think, is that it would be similar to overcast
    daylight. Stars go from much bluer to much redder than our
    sun, so the average might be somewhat similar. Probably totaling
    up the brightest 100 stars would be a good approximation to see
    if the sun represents an average (get the average spectral type,
    then look up the spectrum for that spectral type). Of course,
    averaging a bunch of spectra would likely smooth out the
    emission and absorption lines.

    Roger
     
    Roger N. Clark (change username to rnclark), Mar 7, 2006
    #20
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