Using Flash Beyond The Guide Number Distance.

Discussion in 'Digital Photography' started by Mardon, Feb 2, 2007.

  1. Mardon

    Mardon Guest

    At 105mm & ISO100 my Canon Speedlite 580EX has a guide number of 58
    (meters). At ISO3200 (maximum ISO of the Canon 20D) the 'effective' guide
    number becomes 328. My lens has a maximum aperture of f/2.8. This
    indicates that in darkness, the maximum distance from the flash, at ISO3200
    and f/2.8, is 117 meters for a 'properly' exposed photo. My question is
    how far beyond this distance is a flash useful at night? The other night I
    photographed a piece of snow removal equipment at 200 meters, f/2.8,
    ISO3200, but it was badly underexposed. Even though the equipment was
    still well beyond the guide number distance of my 580EX, would the use of
    my flash have helped?.

    Related question for the 'oldies'. I seem to recall that the large
    flashbulbs I used back in the '60s really packed a wallop. I can't recall
    the guide numbers of those things. Does anyone know? I suspect they were
    well over 100 at ISO100 (expressed in the equivalent ASA in those days,of
    course.)
    Mardon, Feb 2, 2007
    #1
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  2. Mardon

    Steve Wolfe Guest

    > At 105mm & ISO100 my Canon Speedlite 580EX has a guide number of 58
    > (meters). At ISO3200 (maximum ISO of the Canon 20D) the 'effective' guide
    > number becomes 328. My lens has a maximum aperture of f/2.8. This
    > indicates that in darkness, the maximum distance from the flash, at
    > ISO3200
    > and f/2.8, is 117 meters for a 'properly' exposed photo. My question is
    > how far beyond this distance is a flash useful at night? The other night
    > I
    > photographed a piece of snow removal equipment at 200 meters, f/2.8,
    > ISO3200, but it was badly underexposed. Even though the equipment was
    > still well beyond the guide number distance of my 580EX, would the use of
    > my flash have helped?.


    A little, but not a lot. Double the distance, quarter the power, so your
    flash would have been roughly two stops less than needed. If you *really*
    need to reach out and touch someone, get a "better beamer".

    steve
    Steve Wolfe, Feb 2, 2007
    #2
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  3. Mardon

    HEMI-Powered Guest

    Today, Mardon made these interesting comments ...

    > At 105mm & ISO100 my Canon Speedlite 580EX has a guide number
    > of 58 (meters). At ISO3200 (maximum ISO of the Canon 20D) the
    > 'effective' guide number becomes 328. My lens has a maximum
    > aperture of f/2.8. This indicates that in darkness, the
    > maximum distance from the flash, at ISO3200 and f/2.8, is 117
    > meters for a 'properly' exposed photo. My question is how far
    > beyond this distance is a flash useful at night? The other
    > night I photographed a piece of snow removal equipment at 200
    > meters, f/2.8, ISO3200, but it was badly underexposed. Even
    > though the equipment was still well beyond the guide number
    > distance of my 580EX, would the use of my flash have helped?.
    >
    > Related question for the 'oldies'. I seem to recall that the
    > large flashbulbs I used back in the '60s really packed a
    > wallop. I can't recall the guide numbers of those things.
    > Does anyone know? I suspect they were well over 100 at ISO100
    > (expressed in the equivalent ASA in those days,of course.)
    >

    The light power of flash (or any light source) varies as the
    square of the increased distance, so if you double the distance,
    you'd get 1/4 the light from your external flash. In photographic
    terms, each increase or decrease of 2x results in one f/stop, so
    doubling distance at night would reduce your exposure by 2
    f/stops. Whether that is or is not significant depends on ambient
    lighting of the subject you are shooting, surrounding areas, and
    your own definition of "good" and "bad".

    I would expect the noise in your photos to increase
    significantly, however. ISO 3200 may be noisy even when properly
    exposed, I don't know. I have a Canon Rebel XT and its noise
    becomes quite apparent at ISO 400 and its max ISO 1600 is pretty
    much useless to me as it is so noisy that it is virtually
    impossible to fix post-processing in PSP 9.

    --
    HP, aka Jerry
    HEMI-Powered, Feb 2, 2007
    #3
  4. Mardon

    Mardon Guest

    "HEMI-Powered" <> wrote:

    > I would expect the noise in your photos to increase
    > significantly, however. ISO 3200 may be noisy even when properly
    > exposed, I don't know. I have a Canon Rebel XT and its noise
    > becomes quite apparent at ISO 400 and its max ISO 1600 is pretty
    > much useless to me as it is so noisy that it is virtually
    > impossible to fix post-processing in PSP 9.


    Thanks for your comments. The night photo that I mentioned in my OP was
    pretty poor; both under-exposed and noisy at ISO3200 with my 20D. In case
    you're curious about how bad it really was, I've put a copy here:
    http://www.JustPhotos.ca/misc/images/025479.jpg
    The metadata is embedded.
    Mardon, Feb 2, 2007
    #4
  5. Mardon

    Neil Ellwood Guest

    On Fri, 02 Feb 2007 15:25:12 +0000, Mardon wrote:

    > At 105mm & ISO100 my Canon Speedlite 580EX has a guide number of 58
    > (meters). At ISO3200 (maximum ISO of the Canon 20D) the 'effective' guide
    > number becomes 328. My lens has a maximum aperture of f/2.8. This
    > indicates that in darkness, the maximum distance from the flash, at ISO3200
    > and f/2.8, is 117 meters for a 'properly' exposed photo. My question is
    > how far beyond this distance is a flash useful at night? The other night I
    > photographed a piece of snow removal equipment at 200 meters, f/2.8,
    > ISO3200, but it was badly underexposed. Even though the equipment was
    > still well beyond the guide number distance of my 580EX, would the use of
    > my flash have helped?.
    >
    > Related question for the 'oldies'. I seem to recall that the large
    > flashbulbs I used back in the '60s really packed a wallop. I can't recall
    > the guide numbers of those things. Does anyone know? I suspect they were
    > well over 100 at ISO100 (expressed in the equivalent ASA in those days,of
    > course.)


    No.

    --
    Neil
    Reverse 'r' and 'a', delete 'l' for email.
    Neil Ellwood, Feb 2, 2007
    #5
  6. Mardon wrote:
    > "HEMI-Powered" <> wrote:
    >
    >> I would expect the noise in your photos to increase
    >> significantly, however. ISO 3200 may be noisy even when properly
    >> exposed, I don't know. I have a Canon Rebel XT and its noise
    >> becomes quite apparent at ISO 400 and its max ISO 1600 is pretty
    >> much useless to me as it is so noisy that it is virtually
    >> impossible to fix post-processing in PSP 9.

    >
    > Thanks for your comments. The night photo that I mentioned in my OP was
    > pretty poor; both under-exposed and noisy at ISO3200 with my 20D. In case
    > you're curious about how bad it really was, I've put a copy here:
    > http://www.JustPhotos.ca/misc/images/025479.jpg
    > The metadata is embedded.


    What I find interesting is that the only thing that *appears to be
    illuminated by the flash is the top pedestrian sign- or is that
    self-illuminated?

    What about trying same shot, wide open, at say 1/10th, with and without
    flash?

    It's almost certain the flash wasn't going off full. Try also full
    manual on the flash.

    *knowing appearances are deceiving.....<s>


    --
    John McWilliams
    John McWilliams, Feb 2, 2007
    #6
  7. Mardon

    Mardon Guest

    John McWilliams <> wrote in
    news::

    > What I find interesting is that the only thing that *appears to be
    > illuminated by the flash is the top pedestrian sign- or is that
    > self-illuminated?


    Thanks for the comments. You're right in your what you say but wrong in
    your assumption. I did not have any flash with me, so that's why you can't
    detect any effects of one being used for the image. The sign was self-
    illuminated.

    > What about trying same shot, wide open, at say 1/10th, with and without
    > flash?


    I wasn't out looking to take any photos, so I didn't have a tripod with me
    either. I hand-held the camera at 1/160 which is about as slow as I
    figured I could go with a 200mm focal length and a 1.6x crop, even with the
    IS lens.
    Mardon, Feb 2, 2007
    #7
  8. Mardon

    Pat Guest

    On Feb 2, 12:47 pm, Mardon <> wrote:
    > "HEMI-Powered" <> wrote:
    > > I would expect the noise in your photos to increase
    > > significantly, however. ISO 3200 may be noisy even when properly
    > > exposed, I don't know. I have a Canon Rebel XT and its noise
    > > becomes quite apparent at ISO 400 and its max ISO 1600 is pretty
    > > much useless to me as it is so noisy that it is virtually
    > > impossible to fix post-processing in PSP 9.

    >
    > Thanks for your comments. The night photo that I mentioned in my OP was
    > pretty poor; both under-exposed and noisy at ISO3200 with my 20D. In case
    > you're curious about how bad it really was, I've put a copy here:http://www.JustPhotos.ca/misc/images/025479.jpg
    > The metadata is embedded.



    It might have helped, but it wouldn't have given the results you
    wanted. That big pile of snow would be a pretty good white and the
    distance would have faded out to near black (or near that it was).
    You can overshoot your flash a little (and it's one of the very few
    times I would suggest shooting in RAW), but you will get a bright area
    up close to you.

    For what you are doing, a tripod is probably a better idea. Shoot a
    longer exposure.

    Another option, but quite a bit more expensive, is to hide a few
    flashed around the image to light up what you want. Your flash can be
    used as a master to fire either dedicated to dumb slaves that are down
    near your subject.
    Pat, Feb 2, 2007
    #8
  9. Mardon wrote:
    > John McWilliams <> wrote in
    > news::
    >
    >> What I find interesting is that the only thing that *appears to be
    >> illuminated by the flash is the top pedestrian sign- or is that
    >> self-illuminated?

    >
    > Thanks for the comments. You're right in your what you say but wrong in
    > your assumption. I did not have any flash with me, so that's why you can't
    > detect any effects of one being used for the image. The sign was self-
    > illuminated.


    I see now where I missed the sentence in the o.p., but was blinded by
    the light of the Subject line.....<s>

    >> What about trying same shot, wide open, at say 1/10th, with and without
    >> flash?

    >
    > I wasn't out looking to take any photos, so I didn't have a tripod with me
    > either. I hand-held the camera at 1/160 which is about as slow as I
    > figured I could go with a 200mm focal length and a 1.6x crop, even with the
    > IS lens.


    O.K., again, I was focussed on the questions of flash, etc. but you did
    have a couple more stops available.

    --
    john mcwilliams
    John McWilliams, Feb 2, 2007
    #9
  10. Mardon

    HEMI-Powered Guest

    Today, Mardon made these interesting comments ...

    > "HEMI-Powered" <> wrote:
    >
    >> I would expect the noise in your photos to increase
    >> significantly, however. ISO 3200 may be noisy even when
    >> properly exposed, I don't know. I have a Canon Rebel XT and
    >> its noise becomes quite apparent at ISO 400 and its max ISO
    >> 1600 is pretty much useless to me as it is so noisy that it
    >> is virtually impossible to fix post-processing in PSP 9.

    >
    > Thanks for your comments. The night photo that I mentioned in
    > my OP was pretty poor; both under-exposed and noisy at ISO3200
    > with my 20D. In case you're curious about how bad it really
    > was, I've put a copy here:
    > http://www.JustPhotos.ca/misc/images/025479.jpg The metadata
    > is embedded.
    >

    It is said that "beauty is in the eyes of the beholder", and so is
    picture quality. You are the best - and only real - judge of how
    good your night shots are. I imagine they are noisy and have other
    defects, but the only other way for you to get the shot would be to
    mount the camera on a tripod and use a long exposure, perhaps
    multiple seconds. Tripod night shots are particuarly problematic,
    as I'm sure you're aware.

    --
    HP, aka Jerry
    HEMI-Powered, Feb 2, 2007
    #10
  11. Mardon

    AustinMN Guest

    On Feb 2, 1:39 pm, "Pat" <> wrote:
    <snip>
    >
    > Another option, but quite a bit more expensive, is to hide a few
    > flashed around the image to light up what you want. Your flash can be
    > used as a master to fire either dedicated to dumb slaves that are down
    > near your subject.


    One combination I have used is a tripod and manual flash. With any
    exposure longer than the flash recycle time, you can fire the flash
    twice. With even longer exposures, you can fire the flash many
    times. Keep in mind that you have to fire the flash (at full power)
    four times to double the distance. I've even been known (in my
    younger days) to run to a new location while the flash was recycling.

    The technique works OK, (not really well) because noise still
    accumulates with the long exposure.

    Austin
    AustinMN, Feb 2, 2007
    #11
  12. Mardon wrote:
    > At 105mm & ISO100 my Canon Speedlite 580EX has a guide number of 58
    > (meters). At ISO3200 (maximum ISO of the Canon 20D) the 'effective' guide
    > number becomes 328. My lens has a maximum aperture of f/2.8. This
    > indicates that in darkness, the maximum distance from the flash, at ISO3200
    > and f/2.8, is 117 meters for a 'properly' exposed photo. My question is
    > how far beyond this distance is a flash useful at night? The other night I
    > photographed a piece of snow removal equipment at 200 meters, f/2.8,
    > ISO3200, but it was badly underexposed. Even though the equipment was
    > still well beyond the guide number distance of my 580EX, would the use of
    > my flash have helped?.
    >
    > Related question for the 'oldies'. I seem to recall that the large
    > flashbulbs I used back in the '60s really packed a wallop. I can't recall
    > the guide numbers of those things. Does anyone know? I suspect they were
    > well over 100 at ISO100 (expressed in the equivalent ASA in those days,of
    > course.)
    >


    Tripod, beanbag, or use self-timer to trip shutter with least camera shake.

    Morton
    Morton Linder, Feb 3, 2007
    #12
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