Canon PowerShots not fully manual?

Discussion in 'Digital Photography' started by Dogger the Filmgoblin, Jul 20, 2004.

  1. I just discovered that my Canon PowerShot A75 is not *fully* manual
    even when I operate in manual (M) mode.

    When pointed at a very bright light source that overwhelms the frame,
    the camera will stop down to f/8.0, even though I am trying to take
    the picture at f/2.8, it won't let me; it insists on trying to expose
    the picture more normally. But that's not what I'm after. I WANT the
    light source to overwhelm the frame (not that it's important, but I'm
    shooting a window and I want the light from it to bloom as much as
    possible for effect). When I put a camera in manual mode, I really
    mean it. I don't want a babysitter.

    You can recreate this effect by putting the camera in manual mode,
    zoomed all the way out, point it very close to a light source and try
    to shoot it without having your aperture forced shut -- you can't.

    The same think happens in Aperture Mode, in which I am supposed to
    have full control of the aperture.

    Does anyone know how I can force this camera to do what I want it to
    do?

    DB.
     
    Dogger the Filmgoblin, Jul 20, 2004
    #1
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  2. Send it to obedience training classes at the camera store. If that doesn't
    work, use a small pipe wrench on the lens and crank it open to the 2.8 you
    want.
     
    Daniel Dravot, Jul 20, 2004
    #2
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  3. Dogger the Filmgoblin

    chibitul Guest

    Perhaps the bright light soure is too bright, i.e. even the faster
    shutter (1/2000 s or so?) would still overexpose, and you may damage the
    sensor. Perhaps the camera is trying to protect itself? Try a newutral
    density filter if this is the case. let us know.
     
    chibitul, Jul 21, 2004
    #3
  4. Don't quit your day job.

    DB.
     
    Dogger the Filmgoblin, Jul 21, 2004
    #4
  5. Well, I want it overexposed, that's the whole point. But what you say
    is interesting. I didn't know it was possible actually to damage the
    sensor with light. Can anyone confirm this? It seems doubtful to me.
    My interim soolution has been to half-press the shutter on a dark
    background, and then point at the light I want overexposed before
    taking the pic -- this seems to sidestep the forced-iris closing, but
    if this is going to damage my CCD, I won't do it anymore.

    Can anyone shed any light? (no pun intended)

    DB.
     
    Dogger the Filmgoblin, Jul 21, 2004
    #5
  6. Dogger the Filmgoblin

    chibitul Guest

    [snip]
    Well, anything can be damaged by too much light. Think of a "landscape"
    of the Sun (focus at infinity) where the shutter is open for a few
    seconds and the lens is open all the way. the Sun will be focused on the
    sensor and it will burn the sensor. You can light a fire using the
    focusing the Sun onto a match or paper. Sure the sensor will be damaged
    this way.

    What you should do is take a picture and then analyze the shutter speed.
    if the shutter is 1/2000s (or whatever the maximum shutter speed is on
    your camera), then it seems this is what is going on. if on the other
    hand the shutter is much slower, then I don't know what is going on. are
    you sure you are in manual mode??? is there some sort of custom setting
    on your camera? maybe that does something strange???
     
    chibitul, Jul 22, 2004
    #6
  7. Dogger the Filmgoblin

    chibitul Guest

    One more thing: check the EXIF data, make sure you are in manual mode.
    perhaps the dial on your camera is broken, it appears to be in Manual
    mode but the camera is actually in other mode?
     
    chibitul, Jul 22, 2004
    #7
  8. Dogger the Filmgoblin

    Milan Guest

    The lens is not focused to a single point like you do when trying to
    start a fire with a magnifying glasss. If there is a shutter that only
    opens when you take the picture, what is sensing the image that is
    displayed on the LCD before you take the picture. I don't think the sun
    will hurt the sensor.
     
    Milan, Jul 22, 2004
    #8
  9. The shutter speed is 1/60, manually set, and does not vary from
    whatever choice I make, nor does the white balance or ISO or anything
    else. Only the f/stop is forced shut in response to an overblown frame
    -- even in manual mode (and also in Aperture Av mode, by the way, in
    which I should have total control of the iris but apparently don't in
    extreme exposures).

    I have checked the EXIF data. Everything is as expected. My dial isn't
    broken, it switches modes perfectly as indicated on the LCD; it isn't
    even loose. This A75 is less than 3 weeks old and works perfectly. I
    believe this behaviour is built in to the firmware of the camera.
    Anyone else with an A75 (and probably other A-series) could probably
    duplicate the behaviour by setting the cam to f/2.8 in manual mode,
    and pointing it directly at a light bulb in close-up: watch the f/stop
    jump. As I have said, there is a work-around by half-pressing the
    shutter before pointing at what I want overblown, but this is not a
    'fully' manual camera. But since most people will not ever try to
    massively overexpose a major part of the frame for effect, they will
    never notice.

    I find the idea of the Sun damaging the sensor difficult to believe
    but I am still open to more evidence/argumentation along this line.

    DB.
     
    Dogger the Filmgoblin, Jul 22, 2004
    #9
  10. I've been doing more tests, and I'm finding this overexposure nanny to
    be more and more intrusive. It's not just overblown frames; if I'm
    shooting outdoors and trying to keep the iris open to maintain a
    narrow depth of field (for interesting macro work), the camera forces
    a middle exposure; it won't let me push the exposure even a little bit
    for a high-key look; again unless I point at something dark or cover
    the lens with my hand while I half-press the shutter (and again in
    full manual 'M' mode as indicated on the LCD).

    I would be interested as to whether other A-series owners can
    replicate this issue; I'm willing to bet that they can.

    DB.
     
    Dogger the Filmgoblin, Jul 22, 2004
    #10
  11. Dogger the Filmgoblin

    chibitul Guest

    [snip]
    It's up to you what you believe or not. I know that my film SLR manual
    says not to point the lens to the Sun and lock up the mirror since this
    way I might burn the shutter curtains. I do believe in some cases (not
    always) you can damage the sensor or something...
     
    chibitul, Jul 23, 2004
    #11
  12. Dogger the Filmgoblin

    Carl Miller Guest

    Too late.
     
    Carl Miller, Jul 24, 2004
    #12
  13. I just tried my A80. It does give me absolute control in manual mode.
    I tried shooting a desk lamp on my desk. In Av, with aperture set to
    f/2.8 and at ISO 50, the evaluative metering chose an exposure of 1/400
    sec. This left the fluorescent tube in the lamp itself somewhat
    overexposed, but details of the surrounding reflector visible. The
    rest of the frame was near black. Then I switched to manual and tried
    exposures of 1/8 second and then 1 second. The camera shot both images
    as instructed, even the one that's 9 stops overexposed.
    Well, so far we've heard only of your camera doing this. Does Canon
    mention this in the manual anywhere? (Have you read the manual
    cover-to-cover? Canon is usually pretty thorough about mentioning
    camera eccentricities somewhere in the manual.)

    The A75 definitely has different firmware than the A80. For example,
    the A75 has the ability to superimpose the shooting date or time *in
    the image area*, a feature of no other Canon camera I've looked at the
    manual for.

    Dave
     
    Dave Martindale, Jul 24, 2004
    #13
  14. The sun is a danger to sensors. Focused sunlight from a f/2.8 lens (the
    focal length doesn't matter; it's the f/number that determines light
    intensity in the image) can burn paper or wood. Applied to a Bayer
    sensor, it could fade the colour filters if they are organic dyes. It
    could overheat the silicon itself to the point of damaging it, or
    melting something in contact with it like the filter layer or lenslet
    array. This could also be an issue with extremely bright artificial
    light sources, such as a carbon arc or Xenon arc lamp (e.g. in a video
    or movie projector). On the other hand, an ordinary desk lamp isn't
    going to be a risk.

    Trivia: semiconductors like silicon and germanium get *very* hot when
    exposed to sunlight, hotter than surrounding objects. Truly black
    objects absorb energy at all wavelengths, but they also radiate
    longwave IR well, so incoming energy is radiated back to the world.
    Fully white and transparent objects are poor radiators, but they don't
    absorb much energy in the first place, so they stay relatively cool.

    On the other hand, silicon and germanium look close to black at visible
    light wavelengths, so they absorb visible light and near-IR efficiently
    and convert it to heat. But they are pretty much transparent in the
    far-IR, which makes them very poor radiators of heat. So these
    materials absorb energy, get hot, can't re-radiate the heat, and thus
    get very hot. Don't leave a piece of raw silicon sitting on your car
    dashboard in the summer.

    A Google search for "sun damage to CCD" also gives some
    interesting-looking links.

    Dave
     
    Dave Martindale, Jul 24, 2004
    #14
  15. You make a good argument for why 'prolonged' exposure to sunlight
    might damage the camera, but you haven't said anything that shows
    there is any danger of heat damage at the fraction-of-a-second shutter
    speeds we're talking about here.

    I did do some Google searching, but -- forgive me for this -- your
    search terms are biased. Why? Because you're much less likely to find
    the phrase 'sun damage' on a page where is an argument is made that
    brief sun exposure is safe for the CCD. It's like searching for the
    conclusion that I want to read. Instead I chose to search for more
    neutral terms like CCD and "direct sunlight" (including quotes) and
    came up with some interesting results.

    First of all, there are varying opinions out there, like on anything.
    But whenever an actual camera manual is directly quoted (and it they
    are quoted very often on this point on USENET), it ALWAYS indicates to
    avoid *prolonged* exposure to sun or *leaving* the camera pointing or
    sitting in the sun. I could find no quotation by anyone that
    recommends against pointing into the sun long enough to snap a single
    shot. From my own manual:

    "Do not aim the camera directly into the sun or at other intense light
    sources which could damage your eyesight."

    Nothing there about damaging the camera at all. They're just warning
    you against looking into the sun with your eye.

    And a little later:

    "Avoid using, placing or storing the equipment in places subject to
    strong sunlight or high temperatures."

    Obviously they mean for a prolonged period here, since it's ludicrous
    not to even *use* the camera in direct sunlight. They don't write very
    precisely do they? And funny how they're always vague on the side of
    overwarning you ridiculously. Lawyers.

    Don't get me wrong. I am still open to this argument. But I would like
    to see even one somewhat authoritative reference (not just a user's
    opinion pulled out of nowhere), just one, from some manufacturer or
    lab, that *specifically* states that the CCD or colour filters (not my
    eye! that isn't the issue!) can be damaged by being pointed at the sun
    for the short time necessary to compose and take a single shot. I have
    been searching, through pages and pages of google results, and I can't
    find a single such reference. And indeed, common sense dictates that
    nothing could heat up significantly in such a short time, even with a
    magnifying glass focusing sunlight to a point on it. Have you ever
    burned anything with a magnifying glass? It takes quite a while even
    focused to a point MUCH smaller than my CCD.

    DB.
     
    Dogger the Filmgoblin, Jul 25, 2004
    #15
  16. Quick follow-up (I have posted another far more detailed message
    simultaneously with this one, but USENET being odd that way who knows
    which will show up in the thread first)...

    Here is the link to the *only* source about brief (not prolonged) CCD
    exposure to direct sunlight that I have found: every other reference I
    have found is just a user's opinion posted somewhere. This is an
    actual PC magazine article, and it says there is no danger to the
    camera in framing and shooting a shot into the sun. I don't consider
    this very authoritative at all; but it's as authoritative as I can
    possibly find. When I see a camera manufacturer or a professional
    testing lab claim that the brief exposure from framing and snapping a
    single shot of the sun can damage my camera, I will consider changing
    my ways. Anyone got one? If this is really true, there *should* be
    such a specific reference, not just vague near-miss camera manual
    quotes about heating up the camera body or protecting your vision.
    Until I see such a reference, I'll continue in my habits of keeping
    the camera protected from heat and sunlight but allowing the sun to
    hit the lens occasionally for the 5 to 20 seconds it takes to compose
    a nice solar flare shot; these habits have served me well for quite a
    while through several CCDs with no ill effects I could ever detect.

    DB.
     
    Dogger the Filmgoblin, Jul 25, 2004
    #16
  17. Dogger the Filmgoblin, Jul 25, 2004
    #17
  18. Do you use the LCD display for previewing the exposure? If not, then
    the CCD is only exposed for a fraction of a second, and I agree there is
    minimal chance of CCD damage.

    But most people do use the LCD display, and that requires the shutter to
    sit there open until just before the exposure.
    Well, you're not going to take anything I say as an authoritative
    answer, so I don't know why I bother, but: Have you ever tried burning
    something using the focused sunlight from a f/2.8 camera lens? A
    magnifying glass is often a higher f/number (just divide focal length by
    diameter) and is a single-element uncorrected lens. A camera lens is
    well-corrected and focuses the light into a nice round image of the sun.

    And the image *will* be quite small. The sun covers an angle of about
    0.5 degree. The wide-angle focal length of the A80's lens is about 7
    mm, so the focused image of the sun is 7 * tan(0.5) = 0.06 mm or about
    2.4 thousandths of an inch in diameter. The A70/A75 have a smaller CCD
    and even shorter FL lens. If the camera is stationary (on a tripod) the
    same pixels get that energy on a continuing basis while you compose the
    shot.

    Let me suggest an experiment: Take any f/2.8 camera lens, or a larger
    aperture stopped down to f/2.8. A 50 mm FL lens collects a lot more
    total energy at f/2.8 than a 7 mm lens, but both produce an image with
    the same number of watts per square mm - the longer FL lens just covers
    more area with the image. Using the lens, focus an image of the sun on
    your finger. How long can you do this for? Now reflect that your
    finger isn't as efficient at absorbing light as the CCD, so it won't get
    as hot.

    Dave
     
    Dave Martindale, Jul 26, 2004
    #18
  19. Good point about the LCD preview ... I hadn't thought of that.
    Well, I'll certainly listen to an argument or chain of reasoning based
    upon mutually agreeable facts (see above), but I usually won't just
    accept untested a plain assertion unsupported by reference to some
    creditable source that something is true or isn't true, from a
    stranger. No offence, and I certainly don't think your opinion is
    worthless. It's just the nature of essentially anonymous conversation.
    I see where you're going with this reasoning, and maybe I am wrong and
    a camera lens does produce a stronger effect than a magnifying glass
    .... but your logic is a little bit odd. The angle of the sky covered
    by the sun can't really be a factor. If I zoomed in on the sun making
    it take up the whole frame, by your logic it would be less dangerous.
    I find that odd. Surely the issue is not the size of the sun but the
    amount of convergence (and therefore concentration) that is produced
    in its rays on any particular substance; that is what will produce
    rapid heating. It's a plain uncontestable fact that a camera will not
    produce as much convergence on the film plane or CCD as a magnifying
    glass focused to a point on something, because if it did it would be
    useless in capturing an image (every image would consist of a single
    point!)
    Well ... this experiment can be misleading ... again, if I am focusing
    all of the light-gathering power of the lens upon a single point, then
    I am concentrating a lot more heat than a film lens does on a the film
    plane. I don't have a separate lens to try it with, but I'm not sure
    of the value of this experiment for the reasons I've stated. I'll
    stipulate that a camera lens may transfer more the sun's heat than a
    magnifying glass, but keep in mind that the fastest lens is no lens at
    all. Remove the glass or the lens and you have the widest f-stop
    possible, with all of the sunlight hitting the material. The real
    issue is how tightly the rays are converging. Maybe for a 1/3 of an
    inch CCD they are converging tightly enough to be an issue, especially
    along with your excellent point about the LCD preview being on meaning
    the light is in fact getting to the sensor.

    But I'd still like to see some manufacturer just come right out and
    say it, instead of vaguely inapplicable manual warnings about my eyes.

    DB.
     
    Dogger the Filmgoblin, Jul 26, 2004
    #19
  20. No, my point was that the light intensity at the surface is determined
    by the f/number. If you have a constant-aperture zoom, the brightness
    of the image is the same at any focal length. On the other hand, with
    the more typical variable-aperture zoom, brightness goes down as you
    zoom in. (This is all assuming the camera's on a tripod. If it's
    handheld, the wideangle lens is probably less dangerous simply because
    it produces a small image that you can't keep aimed at the same spot all
    the time.)
    I'll contest that! You seem to be under the impression that a
    magnifying glass somehow magically focuses the light from the sun to a
    point. It does not. No optical device can do that, since the sun isn't
    a point source. A magnifying glass focuses the sun's light to a circle
    that is an image of the sun, with the diameter of the circle
    proportional to the focal length of the magnifying glass. Most
    magnifiers have focal length somewhere between 50 and 250 mm. A 50 mm
    camera lens will produce exactly the same size lens as a 50 mm hand
    magnifier (which would be labelled 5X).

    The very best a lens can do is focus all the light from one point on the
    sun to one point on the image of the sun, and a well-corrected camera
    lens comes very close to that idea. A magnifying glass has poorer
    optics, gives a fuzzier image, and spreads the same energy over a
    slightly larger area - even when the focal length is the same. The only
    time a magnifying glass, or a lens, focuses light to anything
    approaching a point is when the light comes from a point source such as
    a distant star (not the sun), or the coherent light from a laser.
    No lens can focus light from the sun on a single point.
    But with no convergence at all. This corresponds to an infinite
    focal length and infinite f/number. Any positive lens will do better.
    Which is determined entirely by the f/number of the lens!
    CCD size doesn't matter. DSLRs are less vulnerable simply because they
    don't have LCD preview.

    Did you see this movie, which someone else posted recently?
    http://ireid.home.cern.ch/ireid/images/JuraSunset.wmv
    Note the effect after the sun passes a point on the CCD.

    Dave
     
    Dave Martindale, Jul 27, 2004
    #20
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