Under-exposure Versus Higher ISO?

Discussion in 'Digital Photography' started by Mardon, May 5, 2006.

  1. Mardon

    Mardon Guest

    Suppose that I'm using a Canon 20D and shooting in RAW, with the
    slowest shutter speed and largest aperture that I can use for a given
    situation. I'm at ISO800 ant the photo is still being under-exposed.
    How bad must the under-exposure become before it's better to up the
    ISO to 1600? Same question if I'm already at 1600. How bad must the
    under-exposure be before I'm better off to up the ISO to 3200?

    I know that the answer to this question can be complicated by
    suggesting flash and other such things to increase the light but
    that's not my point. I'm hoping to get a simple response about the
    final picture quality that can be achieved when evaluating the trade-
    off between under-exposing versus using a higher ISO while shooting
    RAW.
     
    Mardon, May 5, 2006
    #1
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  2. Mardon

    Ed Ruf Guest

    On Fri, 05 May 2006 14:54:35 GMT, in rec.photo.digital Mardon
    <> wrote:

    >Suppose that I'm using a Canon 20D and shooting in RAW, with the
    >slowest shutter speed and largest aperture that I can use for a given
    >situation. I'm at ISO800 ant the photo is still being under-exposed.
    >How bad must the under-exposure become before it's better to up the
    >ISO to 1600? Same question if I'm already at 1600. How bad must the
    >under-exposure be before I'm better off to up the ISO to 3200?


    I believe it's always better to properly expose with higher iso to
    increase the signal to noise ratio. I think it is then easier to
    filter the noise. One thing to consider is are the extreme higher isos
    real. Or are they just iso1600 pushed with analog amplification? That
    is the case with my D200 above 1600. I recently used 3200 to get some
    shots of some herons doing a mating dance when I had no other
    alternative. I didn't have time to try 1600. This was shot across a
    creek at twilight with a 200mm lens + 2x TC, so I needed everything I
    could to get shutter speeds up. I haven't made a 1:1 comparison of
    1600 lighted later vs 3200 yet, so I haven't got any hard evidence of
    which is better.
    ________________________________________________________
    Ed Ruf Lifetime AMA# 344007 ()
    http://EdwardGRuf.com
     
    Ed Ruf, May 5, 2006
    #2
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  3. Today Mardon commented courteously on the subject at hand

    > Suppose that I'm using a Canon 20D and shooting in RAW,
    > with the slowest shutter speed and largest aperture that I
    > can use for a given situation. I'm at ISO800 ant the photo
    > is still being under-exposed. How bad must the
    > under-exposure become before it's better to up the ISO to
    > 1600? Same question if I'm already at 1600. How bad must
    > the under-exposure be before I'm better off to up the ISO
    > to 3200?


    I can't speak to the 20D but in the case of my Rebel XT, I
    would stay at ISO 800 because the Rebel is quite noisy at that
    "speed" and is useless to me at 1600.

    So, without your saying what you percieve your 20D noise to be
    at 400, 800, 1600, and 3200, isn't this a theoretical question
    that you could answer by taking some controlled test shots
    varying not only the ISO but appropriate other photometric
    settings?

    > I know that the answer to this question can be complicated
    > by suggesting flash and other such things to increase the
    > light but that's not my point. I'm hoping to get a simple
    > response about the final picture quality that can be
    > achieved when evaluating the trade- off between
    > under-exposing versus using a higher ISO while shooting
    > RAW.


    Yes, flash would not only complicated the issue, it would
    invalidate it unless you were intending to expose the main
    subject with the flash and slave(s) if any, and using the high
    ISO to bring up the background exposure.

    But, in the final analysis, it is yours, and only your opinion
    that matters, given the type of subject(s) you shoot, what
    dynamic range and DOF you wish to achieve, and your tolerance
    for noise.

    --
    ATM, aka Jerry

    "Go ahead, make my day", Dirty Harry in the movie "Sudden
    Impact"
     
    All Things Mopar, May 5, 2006
    #3
  4. Mardon

    Guest

    Ed Ruf wrote:
    > One thing to consider is are the extreme higher isos
    > real. Or are they just iso1600 pushed with analog amplification?


    They're not really real : they're digital ;o).

    A sensor has only one 'real' sensibility (generally the lower one), the
    others are made by a signal amplification - that, more or less,
    amplifies also noise.

    The only differences i can see are :
    - some S/N optimization algorithm may also be applied after
    amplification, but would it be better in-camera than what you can do in
    post-processing with those neat ninjas of denoiser softs?
    - if the analog/digital conversion is made after amplification (likely,
    isn't it?), the higher-ISO signal contains more signal levels than the
    underexposed one... but I'd think that in the high ISO (and 16-bit)
    case, both are limited by noise?

    So, my personal conclusion would be 'six of one and half a dozen of the
    other' between underexposing and cranking ISO setting (while RAW of
    course)...
    Any different input would be of course gladly welcome!
     
    , May 5, 2006
    #4
  5. Mardon

    Mardon Guest

    All Things Mopar <> wrote:

    > I can't speak to the 20D but in the case of my Rebel XT, I
    > would stay at ISO 800 because the Rebel is quite noisy at that
    > "speed" and is useless to me at 1600.


    The 20D is quite usable at ISO1600 but some noise is certainly
    visible. ISO3200 works on the 20D but it is too noisy for most
    purposes.

    > So, without your saying what you percieve your 20D noise to be
    > at 400, 800, 1600, and 3200, isn't this a theoretical question
    > that you could answer by taking some controlled test shots
    > varying not only the ISO but appropriate other photometric
    > settings?


    I was hoping that someone had already performed the sort of
    'experiment' that you describe and that they would post their results
    in response to my question. Performing these theoretical tests that
    require controlling several variable combinations isn't really 'my
    thing'. My impression based on my everyday experience is that if a
    RAW image is underexposed by more than a full f stop, then it's
    probably better to go to the higher ISO. If the underexposure is
    less than a full stop, I think it's better to shoot at the lower ISO
    and use Noise Ninja or some other noise filter to reduce the noise.
    (BTW, I find Noise Ninja better than the noise reduction filter built
    into PS CS2.) I'm not sure of this conclusion , however, and wanted
    to find out what others think.
     
    Mardon, May 5, 2006
    #5
  6. Mardon

    Scott W Guest

    wrote:
    > Ed Ruf wrote:
    > > One thing to consider is are the extreme higher isos
    > > real. Or are they just iso1600 pushed with analog amplification?

    >
    > They're not really real : they're digital ;o).
    >
    > A sensor has only one 'real' sensibility (generally the lower one), the
    > others are made by a signal amplification - that, more or less,
    > amplifies also noise.
    >
    > The only differences i can see are :
    > - some S/N optimization algorithm may also be applied after
    > amplification, but would it be better in-camera than what you can do in
    > post-processing with those neat ninjas of denoiser softs?
    > - if the analog/digital conversion is made after amplification (likely,
    > isn't it?), the higher-ISO signal contains more signal levels than the
    > underexposed one... but I'd think that in the high ISO (and 16-bit)
    > case, both are limited by noise?
    >
    > So, my personal conclusion would be 'six of one and half a dozen of the
    > other' between underexposing and cranking ISO setting (while RAW of
    > course)...


    A quick test with a Rebel XT shows a lot less noise in the ISO 400 shot
    then the 100, when both are taken at the same aperture and shutter
    speeds.

    So at least between iso 100 and 400 it is much better to use iso 400
    then simply underexpose

    Scott
     
    Scott W, May 5, 2006
    #6
  7. Mardon

    ASAAR Guest

    On Fri, 05 May 2006 11:03:25 -0400, Ed Ruf wrote:

    >> Suppose that I'm using a Canon 20D and shooting in RAW, with the
    >> slowest shutter speed and largest aperture that I can use for a given
    >> situation. I'm at ISO800 ant the photo is still being under-exposed.
    >> How bad must the under-exposure become before it's better to up the
    >> ISO to 1600? Same question if I'm already at 1600. How bad must the
    >> under-exposure be before I'm better off to up the ISO to 3200?

    >
    > I believe it's always better to properly expose with higher iso to
    > increase the signal to noise ratio. I think it is then easier to
    > filter the noise. One thing to consider is are the extreme higher isos
    > real. Or are they just iso1600 pushed with analog amplification?


    Why would that be? I'd think that you'd have more to work with if
    the lowest ISO was used. Consider a shot taken at ISO 100 that
    requires for proper exposure a shutter speed of 1/60 sec at f/4. If
    the same shot is taken with the camera set to ISO 400, the camera
    might use 1/250 sec at f/4 or 1/60 sec at f/8, but the final image
    will appear to be the same, still underexposed, but with the
    addition of a bit of added noise. But the first shot captured more
    light. Four times as many photons, so wouldn't you be able to
    manipulate the RAW file with software to bring out more of the
    shadow detail, which isn't buried in as much noise? Continuing
    along this line, there could be a problem with highlights in the
    same shot being blown, as more individual sensor cells might have
    filled to their capacity. But this would be more of a problem if
    the original problem was overexposure, not underexposure.

    Note: I'm basing this on the OP's saying that he's using the slowest
    shutter speed and largest aperture "for a given situation", and that
    means that the limit is his, not the camera's. For instance, the
    camera might be capable of using f/1.4, but he isn't willing to
    sacrifice DOF by opening beyond f/4, or the camera can use a shutter
    speed of 1/'15 sec, but that wouldn't be fast enough to eliminate
    subject movement. It could be a different matter if the limitation
    was the camera's. For example, if he's using shutter priority mode
    because he requires a shutter speed of no slower than 1/60 sec for a
    particular shot, but at that speed a proper exposure would require
    an f/2 lens but the maximum available aperture is only f/4,
    underexposure would be the result. But in this case, a higher ISO
    would allow for a proper exposure.

    Your example of the twilight heron shots seems to be an example of
    the latter case, where you required a fast shutter speed and the
    camera's lens probably didn't have a wide enough aperture for the
    available light, so the higher ISO was appropriate. So while the
    shutter speed was determined by you (not limited by the camera),
    with the aperture, you ran into a physical limit of the lens.

    Whether I'm right or wrong about this, I hope I've explained it
    clearly enough to be followed, and whether I'm right also depends on
    my understanding of whether the OP's exposure limits are created by
    his requirements, or if they are limited by the camera's hardware.
     
    ASAAR, May 5, 2006
    #7
  8. Mardon

    Mardon Guest

    ASAAR <> wrote:

    > Whether I'm right or wrong about this, I hope I've explained
    > it
    > clearly enough to be followed, and whether I'm right also
    > depends on my understanding of whether the OP's exposure limits
    > are created by his requirements, or if they are limited by the
    > camera's hardware.


    I posted the question in the context of doing macro photos of live
    'bugs' that are 1 mm to 3 mm long. The lens is an f/3.5 180mmL and
    the camera a 20D. I have to keep the shutter speed up because the
    bugs are alive and moving. I can't open the apature too much because
    there is almost no depth of field anyway with these extreme close-
    ups. The lens can stop down to f/45 but I prefer to shoot the
    'bugs' in natural light and f/45 at 1/250 sec just doesn't give
    enough light even at ISO1600. I generally wind up at about ISO1600
    f/22 at 1/250 or 1/320. I can use ISO800 but it underexposes. That
    is the basis of my question.
     
    Mardon, May 5, 2006
    #8
  9. Today Mardon attempted to dazzle everyone with this profound
    linguistic utterance

    > The 20D is quite usable at ISO1600 but some noise is
    > certainly visible. ISO3200 works on the 20D but it is too
    > noisy for most purposes.


    How would you judge 20D noise vs. Rebel XT? I am beginning to
    think I shoulda popped the bucks for the 20D and just suffered
    with the larger size and weight. My available light tests show
    that ISO 400 is the highest I like, I can deal with 800 with
    lots of work, but 1600 is useless (to me).

    >> So, without your saying what you percieve your 20D noise
    >> to be at 400, 800, 1600, and 3200, isn't this a
    >> theoretical question that you could answer by taking some
    >> controlled test shots varying not only the ISO but
    >> appropriate other photometric settings?

    >
    > I was hoping that someone had already performed the sort of
    > 'experiment' that you describe and that they would post
    > their results in response to my question. Performing these
    > theoretical tests that require controlling several variable
    > combinations isn't really 'my thing'. My impression based
    > on my everyday experience is that if a RAW image is
    > underexposed by more than a full f stop, then it's probably
    > better to go to the higher ISO. If the underexposure is
    > less than a full stop, I think it's better to shoot at the
    > lower ISO and use Noise Ninja or some other noise filter to
    > reduce the noise. (BTW, I find Noise Ninja better than the
    > noise reduction filter built into PS CS2.) I'm not sure of
    > this conclusion , however, and wanted to find out what
    > others think.
    >

    I understand what a "controlled test" is and what it involves.
    I have used "design of experiments" techniques to do digital
    camera testing, principally when evaluating a Nikon 8400 last
    year, which I took back, and my current Rebel XT which I kept.

    One f/stop is only half as bright, which is easily corrected.
    Yes, it will produce noise, but not nearly as much as a 2,3,5
    stop under, as often happens.

    The opinions/experience of others can be valuable, but hardly
    definitive. e.g., whether this is "your thing" or not, how
    would you know what my results are or anyone elses without
    knowing what "controlled conditions" any of us used? Besides
    the variables you already discussed, and my clarifying
    comments and questions, personal preference is the real
    deciding factor, but subject type and the full gamut of
    lighting is also of paramount importance.

    Then, there's the general issue of hand-held vs. tripod or
    monopod ...

    --
    ATM, aka Jerry

    "I came, I saw, I conquered" - Alexander The Great
     
    All Things Mopar, May 5, 2006
    #9
  10. Today Mardon attempted to dazzle everyone with this profound
    linguistic utterance

    > I posted the question in the context of doing macro photos
    > of live 'bugs' that are 1 mm to 3 mm long. The lens is an
    > f/3.5 180mmL and the camera a 20D. I have to keep the
    > shutter speed up because the bugs are alive and moving. I
    > can't open the apature too much because there is almost no
    > depth of field anyway with these extreme close- ups. The
    > lens can stop down to f/45 but I prefer to shoot the 'bugs'
    > in natural light and f/45 at 1/250 sec just doesn't give
    > enough light even at ISO1600. I generally wind up at about
    > ISO1600 f/22 at 1/250 or 1/320. I can use ISO800 but it
    > underexposes. That is the basis of my question.


    I must've missed this part. There is a world of difference
    between macro anything and general photography, or specialized
    subjects such as sports, architectural, portaits, fine detail
    such as cars or objects d'art, etc. using the same camera.

    --
    ATM, aka Jerry

    "I came, I saw, I conquered" - Alexander The Great
     
    All Things Mopar, May 5, 2006
    #10
  11. Mardon

    Scott W Guest

    Mardon wrote:
    > ASAAR <> wrote:
    >
    > > Whether I'm right or wrong about this, I hope I've explained
    > > it
    > > clearly enough to be followed, and whether I'm right also
    > > depends on my understanding of whether the OP's exposure limits
    > > are created by his requirements, or if they are limited by the
    > > camera's hardware.

    >
    > I posted the question in the context of doing macro photos of live
    > 'bugs' that are 1 mm to 3 mm long. The lens is an f/3.5 180mmL and
    > the camera a 20D. I have to keep the shutter speed up because the
    > bugs are alive and moving. I can't open the apature too much because
    > there is almost no depth of field anyway with these extreme close-
    > ups. The lens can stop down to f/45 but I prefer to shoot the
    > 'bugs' in natural light and f/45 at 1/250 sec just doesn't give
    > enough light even at ISO1600. I generally wind up at about ISO1600
    > f/22 at 1/250 or 1/320. I can use ISO800 but it underexposes. That
    > is the basis of my question.


    I would say you need more light.

    But as to your question do a test and see, shoot the same shot at ISO
    800 and 1600 and see if there is less noise in the 1600 shot.

    I did this test between iso 100 and 400 and the 400 shot had less
    noise, not sure what the out come between 800 and 1600 would be but it
    is an easy test.
    http://www.pbase.com/konascott/isotest

    Scott
     
    Scott W, May 5, 2006
    #11
  12. Mardon

    Scott W Guest

    All Things Mopar wrote:
    > Today Mardon attempted to dazzle everyone with this profound
    > linguistic utterance
    >
    > > The 20D is quite usable at ISO1600 but some noise is
    > > certainly visible. ISO3200 works on the 20D but it is too
    > > noisy for most purposes.

    >
    > How would you judge 20D noise vs. Rebel XT? I am beginning to
    > think I shoulda popped the bucks for the 20D and just suffered
    > with the larger size and weight. My available light tests show
    > that ISO 400 is the highest I like, I can deal with 800 with
    > lots of work, but 1600 is useless (to me).
    >


    The 20D has a fair bit less noise at high ISO, I will try and get some
    test shots done.
    I don't think it is a full stop worth but not too far from it.

    With the 20D I happily shoot at ISO 400 and will go up to ISO 800, with
    the XT I happlily shoot at ISO 200 and will go up to ISO 400. For both
    cameras when forced I will go higher but I really don't like the noise.

    Scott

    Scott
     
    Scott W, May 5, 2006
    #12
  13. Today Scott W attempted to dazzle everyone with this profound
    linguistic utterance

    >> How would you judge 20D noise vs. Rebel XT? I am beginning
    >> to think I shoulda popped the bucks for the 20D and just
    >> suffered with the larger size and weight. My available
    >> light tests show that ISO 400 is the highest I like, I can
    >> deal with 800 with lots of work, but 1600 is useless (to
    >> me).

    >
    > The 20D has a fair bit less noise at high ISO, I will try
    > and get some test shots done.


    This comment doesn't make sense to me wrt to your last
    paragraph. I am not insulting you, but this sounds close to
    non sequitor to me.

    > I don't think it is a full stop worth but not too far from
    > it.


    > With the 20D I happily shoot at ISO 400 and will go up to
    > ISO 800, with the XT I happlily shoot at ISO 200 and will
    > go up to ISO 400. For both cameras when forced I will go
    > higher but I really don't like the noise.
    >

    Being that ISO in a digital isn't real, it is signal
    amplification, I don't understand your description of "full
    f/stop worth" even with this example. To my question, it would
    seem that you feel 1600 and 3200 are unacceptably noise to
    you. Please explain, as I would like to learn this stuff in
    DSLR terms vs. my old Nikon FTN 35mm terms.

    A single ISO "upgrade" isn't all that significant to me, but I
    can see your point-of-view.

    --
    ATM, aka Jerry

    "I came, I saw, I conquered" - Alexander The Great
     
    All Things Mopar, May 5, 2006
    #13
  14. Mardon

    Paul Rubin Guest

    All Things Mopar <> writes:
    > Being that ISO in a digital isn't real, it is signal
    > amplification, I don't understand your description of "full
    > f/stop worth" even with this example. To my question, it would
    > seem that you feel 1600 and 3200 are unacceptably noise to
    > you. Please explain, as I would like to learn this stuff in
    > DSLR terms vs. my old Nikon FTN 35mm terms.


    In FTN 35mm terms, you can shoot Tri-X at 800, 1600, 3200, etc. by
    push processing, but the results get worse and worse as you go higher
    in speed. Maybe Tri-X looks ok at 800 and looks like crap at 1600,
    while TMZ still looks ok at 1600, a full stop faster than 800. That's
    where the "full stop" description comes from.

    DSLR vs FTN terms: "Signal amplification" is sort of like push processing.
     
    Paul Rubin, May 5, 2006
    #14
  15. Mardon

    ASAAR Guest

    On Fri, 05 May 2006 18:21:17 GMT, Mardon wrote:

    > I generally wind up at about ISO1600 f/22 at 1/250 or 1/320. I can use
    > ISO800 but it underexposes. That is the basis of my question.


    Ah, thanks for the additional information. In this case I'd say
    that you're probably better off shooting with ISO 1600, but there
    are a couple of things you can do that may help.

    First, even though it's a big expense, a camera having a more
    noise-free sensor, such as Canon's 5D may allow you to get good
    exposures even at ISO 400. Even if buying one is out of the
    question, it may be worthwhile borrowing or renting one for a day to
    see how it performs. Because of the larger sensor, though, and
    assuming that the f/3.5 180mmL can work with the 5D's full sized
    sensor, its field of view will be less than what it is on the 20D.
    It will also have a slightly shallower DOF, but you might still be
    able to get a good exposure at f/45 with a faster shutter speed.

    The second thing to consider is whether you can reduce the ambient
    temperature sufficient to slow the bugs to 1/2 their normal speed.
    If so, you could use the 20D at ISO 800 with f/22 and a 1/125 sec.
    shutter speed. You might be able to slow them down much more than
    this without having to cool the bugs down to refrigerator
    temperatures. Instead of cooling the entire room, you may only need
    a $5.00 Styrofoam cooler containing a bag of ice (or dry ice) with
    the bugs raised on a platform that's several inches below the top of
    the cooler.

    The last thing to consider would be whether using a ring light (or
    the equivalent that spaces several small flashes around the lens)
    would provide a light sufficiently natural for your purposes. I
    don't think that it's the color temperature that's the problem (RAW
    correctable anyway), but attaining an even, shadow free
    illumination. It's also an extra expense, but much less than a 5D,
    and would allow you to use the lens's smallest aperture and be able
    to stop even much faster moving bugs in their tracks without having
    to resort to using RAID. :)
     
    ASAAR, May 5, 2006
    #15
  16. Today Paul Rubin attempted to dazzle everyone with this
    profound linguistic utterance

    > All Things Mopar <> writes:
    >> Being that ISO in a digital isn't real, it is signal
    >> amplification, I don't understand your description of
    >> "full f/stop worth" even with this example. To my
    >> question, it would seem that you feel 1600 and 3200 are
    >> unacceptably noise to you. Please explain, as I would like
    >> to learn this stuff in DSLR terms vs. my old Nikon FTN
    >> 35mm terms.

    >
    > In FTN 35mm terms, you can shoot Tri-X at 800, 1600, 3200,
    > etc. by push processing, but the results get worse and
    > worse as you go higher in speed. Maybe Tri-X looks ok at
    > 800 and looks like crap at 1600, while TMZ still looks ok
    > at 1600, a full stop faster than 800. That's where the
    > "full stop" description comes from.
    >
    > DSLR vs FTN terms: "Signal amplification" is sort of like
    > push processing.


    I understand your analogy. In fact, I did exactly what you
    describe and got exactly the results you predict.

    I hope to hear more from the person I asked this question of so
    I can "calibrate" their expectations of ISO vs noise in the
    context of this thread.

    --
    ATM, aka Jerry

    "I came, I saw, I conquered" - Alexander The Great
     
    All Things Mopar, May 5, 2006
    #16
  17. Mardon

    Mardon Guest

    For anyone following this thread, I'm providing two recent images to
    show the kind of macro work I'm doing. Macro is all new to me, so I
    have lots yet to learn. Nothwithstanding my OP, I know how to add
    light with flash; I just prefer not too and want to know if high ISO
    or lower ISO with a slight under sxposure is better.

    I have two Speedlite 850EX units and an ST-E2 transmitter that allows
    me to fire both flash units off-camera. I'm considering buying a MT-
    24EX macro Twin Lite but even if I had that specialized flash, I'd
    still prefer to take my photos without a flash whenever that's
    reasonably possible.

    Here's two samples of my macro photos from yesterday and today. The
    beetle was taken with a flash and the spider without. The beetle was
    over 2.5x as long as the spider so take that into account when
    comparing the images. The spider is crawling on the plastic lid of a
    peanut butter jar that I used to catch him her.

    8 mm long beetle photographed at f/32, 1/250 sec. ISO800 & single
    off-camera Speedlite 580EX:
    http://www.justphotos.ca/oldphotos/macro/images/8269Top.jpg

    3 mm long spider photographed at f/22, 1/320 sec, ISO1600 and no
    flash:
    http://www.justphotos.ca/oldphotos/macro/images/8224.jpg
     
    Mardon, May 5, 2006
    #17
  18. Mardon

    Kaz Kylheku Guest

    Mardon wrote:
    > Suppose that I'm using a Canon 20D and shooting in RAW, with the
    > slowest shutter speed and largest aperture that I can use for a given
    > situation. I'm at ISO800 ant the photo is still being under-exposed.
    > How bad must the under-exposure become before it's better to up the
    > ISO to 1600? Same question if I'm already at 1600. How bad must the
    > under-exposure be before I'm better off to up the ISO to 3200?


    But, since photography is an art, you might just want to experiment and
    subjectively evaluate the image quality, right?

    An under-exposed picture doesn't take advantage of the dynamic range.
    You should always sample signals using enough gain so that you take
    advantage of the sampling resolution. If you can can sample a signal to
    a number between 0 and 255, say, but the instrumentation gain is set
    such that there is no value above 63, then you are down from 8 bits to
    6. Quantization from analog to digital is also noise! Even if you
    perfectly sample a noise-free signal, the sampling introduces noise of
    its own, and sampling 6 bits introduces more distortion than 8 bits.

    If you crank up the sensitivity so that you can use 0 to 255, you can
    always divide everything by 4 to get it back in 0-63 range. That also
    cuts the noise amplitude by 4. So in other words, even if the greater
    sensitivity brings in more noise, it's probably worth it.

    I say probably, because the way amplification works is complex.
    Amplifiers use negative feedback to reduce gain, which also has the
    effect of reducing noise. Cranking up the gain means that noise grows
    in greater proportion than the signal, because the noise-reducing
    effect of negative feedback is diminished. The amplifier is less
    stable, less linear and the signal/noise ratio goes down.

    In order for the tradeoff to be worth it, you have to get a bigger
    decrease in quantization noise than an increase in analog noise.

    And that assumes that the two noises are equal from a subjective,
    esthetic point of view, which they are not. That brings us back to
    experimentation.

    > I know that the answer to this question can be complicated by
    > suggesting flash and other such things to increase the light but
    > that's not my point.


    Among "other such things" would be a lens with more light gathering
    power.
     
    Kaz Kylheku, May 5, 2006
    #18
  19. Mardon

    ASAAR Guest

    On 5 May 2006 15:06:10 -0700, Kaz Kylheku wrote:

    >> I know that the answer to this question can be complicated by
    >> suggesting flash and other such things to increase the light but
    >> that's not my point.

    >
    > Among "other such things" would be a lens with more light gathering
    > power.


    That would work in many cases, but not here, where the smallest
    possible aperture is required in order to maximize DOF.
     
    ASAAR, May 5, 2006
    #19
  20. Today Mardon attempted to dazzle everyone with this profound
    linguistic utterance

    > For anyone following this thread, I'm providing two recent
    > images to show the kind of macro work I'm doing. Macro is
    > all new to me, so I have lots yet to learn.
    > Nothwithstanding my OP, I know how to add light with flash;
    > I just prefer not too and want to know if high ISO or lower
    > ISO with a slight under sxposure is better.
    >
    > I have two Speedlite 850EX units and an ST-E2 transmitter
    > that allows me to fire both flash units off-camera. I'm
    > considering buying a MT- 24EX macro Twin Lite but even if I
    > had that specialized flash, I'd still prefer to take my
    > photos without a flash whenever that's reasonably possible.
    >
    > Here's two samples of my macro photos from yesterday and
    > today. The beetle was taken with a flash and the spider
    > without. The beetle was over 2.5x as long as the spider so
    > take that into account when comparing the images. The
    > spider is crawling on the plastic lid of a peanut butter
    > jar that I used to catch him her.
    >
    > 8 mm long beetle photographed at f/32, 1/250 sec. ISO800 &
    > single off-camera Speedlite 580EX:


    I have a 430EX which works up to 30 feet for me shooting car
    pictures at ISO 100-200. I imagine you will use your big gun
    for much longer shooting than beetles - which is like swatting
    mosquitoes with a 100 mega ton bomb! <grin> I complement you
    on your excellent ramp up using slave flash so well.

    > http://www.justphotos.ca/oldphotos/macro/images/8269Top.jpg


    Looks OK, Mardon, but somewhat washed out to me.

    > 3 mm long spider photographed at f/22, 1/320 sec, ISO1600
    > and no flash:
    > http://www.justphotos.ca/oldphotos/macro/images/8224.jpg


    Outstanding.

    Please keep in mind that I have never done digital macro work
    and haven't done any with a 35mm since my early Nikon FTN
    days, circa 1969-1975.

    --
    ATM, aka Jerry

    "I came, I saw, I conquered" - Alexander The Great
     
    All Things Mopar, May 5, 2006
    #20
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