Need help with some basics ...

Discussion in 'Digital SLR' started by Cockpit Colin, Jul 17, 2005.

  1. Hi all,

    Being new to DSLR photography I'd like to think that I'm slowly coming to
    terms with the basics, but playing with my 350D tonight I've come across
    something I don't understand.

    Can someone help me out here? ...

    If I set the camera to FULL AUTO and take a picture across the room the
    flash pops up and the camera selects 1/60 Sec - F4.0 - ISO400 - no probs

    On PROGRAM Mode - same parameters.

    On SHUTTER PRIORITY however, with 1/60 - ISO 400 set the Aperature indicator
    is flashing to say "out of range" (it's only an F4.0 lens), and I have to
    come down to 1/30 of a sec to keep it happy (flash is primed for all of
    these tests by the way).

    On APERATURE PRIORITY it again wants a shutter speed of 1/30 Sec for correct

    So ...

    With ISO set to 400 for all tests and flash primed, WHY is the camera happy
    with an 1/60 + F4.0 combo on AUTO or PROGRAM modes, but insisting on 1/30 +
    F4.0 in Tv or Av modes?

    I don't get it.

    Any help apreciated.

    Many thanks,

    Cockpit Colin, Jul 17, 2005
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  2. Cockpit Colin

    dylan Guest

    It's warning you that you need more aperture, it obviously needs f2.8 which
    isn't available on your lens.
    basically it's metering without compensating for the flash and telling you
    it's too dark.
    As above
    Presumably in AUTO it knows it's going to use flash.
    Sounds like the camera needs a bit more logic to tell it you are going to
    use flash.
    My 10D is identical.
    dylan, Jul 17, 2005
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  3. I doubt that it's not considering the flash because in addition to the flash
    being primed, it's also showing the flash symbol in the view finder.
    Not quite I don't think - in AUTO it'll raise and fire the flash as/when
    required - in other modes it has to be manually deployed - but should still
    be considered when it IS manually deployed.

    With some further testing, I think the issue is to do with with AUTO
    exposure - I did a series of tests - on AUTO it seems under-exposed, whereas
    at 1/15 everything looks a lot brighter (and more correctly exposed).

    Does anyone know of an issue where AUTO or PROGRAM modes under-expose?
    Cockpit Colin, Jul 17, 2005
  4. This is indeed odd. I have tried this on my 350D at ISO 200 and with flash
    raised (and registered in the viewfinder) in all cases:

    In P mode: 1/60, f4

    In Tv mode: 1/60 set, f4 flashing but taken anyway. Exposure on the result
    identical to P mode.

    In Av mode: f4 set, camera set and took at 1/6! Over exposure on the result.

    I do not have an answer but at least we are all have the same issue.

    Mike Bernstein
    Mike Bernstein, Jul 17, 2005
  5. Cockpit Colin

    dylan Guest

    On my 10D deploying or not deploying the flash makes no difference to the
    meter reading, apart form the flash symbol, so where's it considering it ?
    dylan, Jul 17, 2005
  6. Common problem with these cameras. Even some dedicated Speedlights will
    underexpose. Take to camera back to Canon and ask them to adjust the
    flash exposure. It's a warranty repair and fairly quick to do.
    The Studio of Foto Ryadia, Jul 17, 2005
  7. On my 10D deploying or not deploying the flash makes no difference to the
    Good point. I'm left with the feeling that this is either a major bug, or
    I'm just not understanding how it's supposed to work.
    Cockpit Colin, Jul 17, 2005
  8. I do not consider mine (350D) underexposed.

    Mike Bernstein
    Mike Bernstein, Jul 17, 2005
  9. Cockpit Colin

    JPS Guest

    In message <whpCe.1174$>,
    That proves nothing. Both my 10D and 20D ignore the fact that the flash
    is going to fire in Av and Tv modes, when choosing the floating
    JPS, Jul 17, 2005
  10. Cockpit Colin

    David Hardin Guest

    With the flash engaged, which it will do automatically in full auto or if
    you manually engage it in P mode, the camera thinks that the flash will be
    the main source of light and takes over setting the exposure. However, in
    Tv, Av, or M mode the camera thinks the flash will be used only for fill and
    takes its exposure settings from available light then adjusts the flash
    duration for the amount of dialed-in fill.
    David Hardin, Jul 17, 2005
  11. Thanks David,

    I think you've hit the nail on the head.

    Is there any resource that you can point me to that would give me more info
    on this? (I couldn't immediately see the answers in the user manual)


    Cockpit Colin, Jul 18, 2005
  12. Cockpit Colin

    Chrlz Guest

    and he and Justin are the only correct respondents!! I don't own a
    Canon, but this is a pretty basic concept and I would be very surprised
    if other DSLR's didn't act similarly. My prosumer does it too, and *so
    it should*..
    Chrlz, Jul 18, 2005
  13. Cockpit Colin

    David Hardin Guest

    David Hardin, Jul 18, 2005
  14. I stand a suitably humbled man - on the upside, that's about 3 things I've
    learned from the group already :)

    .... at least I've heard of the term "fill in flash"!
    Cockpit Colin, Jul 18, 2005
  15. It's working a treat - thanks for that - I think it's going to cover
    EVERYTHING I need to know for now (and some time to come!)


    Cockpit Colin, Jul 18, 2005
  16. Cockpit Colin

    Colin D Guest

    In Av or Tv mode, the camera will attempt to expose for the ambient
    light, whereas in auto or P mode it only exposes for the flash. The
    typical use for Av or Tv is outdoor exposures in dull light or at night
    where you want to capture some of the background. The manual should go
    into this for you.
    Colin D, Jul 18, 2005
  17. Cockpit Colin

    Colin D Guest

    No bug. Read the book.

    Colin D, Jul 18, 2005
  18. Herewith the section from the 350D manual. I do not personally think the
    manual deals with this quite as described in this group, although the last
    paragraph may have something to do with it.

    For fully automatic flash photography. The shutter speed (1/60 sec. - 1/200
    sec.) and aperture value are set automatically, just as in <1> (Full Auto)

    Enables you to set the desired shutter speed (30 sec. - 1/200 sec.). The
    camera then automatically sets the flash aperture value to obtain the proper
    exposure at the shutter speed you have set.

    Enables you to set the desired aperture value. The camera then automatically
    sets the shutter speed (30 sec. - 1/200 sec.) to obtain the proper exposure
    at the aperture you have set.
    Against dark backgrounds such as the night scenes, slow-sync shooting will
    be set so that both the subject and background are exposed correctly. The
    main subject is exposed with the flash, and the background is exposured with
    a slow shutter speed. Because automatic slow-sync shooting uses a slow
    shutter speed, always use a tripod. If you do not want a slow shutter speed
    to be set, set C.Fn-3 [Flash sync. speed in Av mode] to [1: 1/200sec.

    Mike Bernstein
    Mike Bernstein, Jul 18, 2005
  19. Cockpit Colin

    james Guest

    So what's to be done about it? I can't imagine that putting a Canon
    flash on a Canon camera takes us back to the days of manual exposure.
    james, Jul 18, 2005
  20. Cockpit Colin

    Chrlz Guest

    I stand a suitably humbled man - on the upside,
    I wasn't intending to humble you, but I was a little surprised at some
    of the replies!

    So to summarise - as soon as you step into A and S modes, the camera
    should (and obviously did) go into 'you're the boss' mode, along with
    'meter the scene only' mode.

    In P and Auto modes, it pretty much assumes you're a dummy, and you
    just want the camera to give you a well-lit exposure. So if it thinks
    the scene is too dim for a hand-held shot, it decides to do the whole
    lighting thing itself with the flash as the light source.

    In A and S (or Av and Tv) modes, it just meters the scene and assumes
    you know what you are doing - and if the flash is up/on, the camera
    logic will dial it down to just *fill* the exposure.

    Which is all probably *exactly* what you want..!
    Chrlz, Jul 19, 2005
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