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Thread: Flash Questions

  1. #1

    Flash Questions

    This may seem a really basic question but search as I might I cannot find an answer that gives it straight.

    I have a 450D and a 430EX II speedlight. If I shoot in Av mode outdoors in daylight do I need to AE lock on the background every time. In what sort of situation would I benefit from using AE lock. This leads to a second question with the 450D if I try to use AE lock when the flash is attached (eg focus, AE lock background then recompose) the camera says I am using FE lock. What is the difference between AE lock and FE lock. I am pretty sure I need AE lock for fill flash does anyone know how I lock AE when the speedlight is mounted on a 450D.

    And finally the easy solution would be to use P mode so why does this seem to be frowned upon. Are there situations when P mode will not cope?

    Sorry for the rapid fire questions but it is driving me mad at present I want to to get the very basics of using fill flash and then start to experiment when I am confident with the basics. I thought about asking on POTN but I have a feeling I would come away with a shopping list for 20,000 of lighting equipment a top of the range DSLR and an inferiority complex about my meagre equipment. Having sold the cat, the my liver and my Wombles albums to obtain the POTN starter kit I still would not have a clue where to begin so please treat my questions as you would an 8 year old

  2. #2

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    Re: Flash Questions

    I have a 450D and a 430EX II speedlight. If I shoot in Av mode outdoors in daylight do I need to AE lock on the background every time. In what sort of situation would I benefit from using AE lock. This leads to a second question with the 450D if I try to use AE lock when the flash is attached (eg focus, AE lock background then recompose) the camera says I am using FE lock. What is the difference between AE lock and FE lock. I am pretty sure I need AE lock for fill flash does anyone know how I lock AE when the speedlight is mounted on a 450D.
    Why not just go try it both ways????

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    Re: Flash Questions

    Quote Originally Posted by Wirefox View Post
    I have a 450D and a 430EX II speedlight. If I shoot in Av mode outdoors in daylight do I need to AE lock on the background every time.
    No.

    That was easy

    In Av mode with a flash you've got two things going on ...

    1. The camera will adjust the shutterspeed to correctly adjust the background exposure (unfortunately, if there's not much light this may result in a shutterspeed so low that camera shake becomes a problem). If you want to bias the background exposure with EC (Exposure compensation) you can.

    2. The camera will adjust the flash output for correct foreground exposure. If you want to bias the foreground exposure with FEC (Flash Exposure Compensation) you can.

    Often I find that the easiest way to grasp the concept of what's going on (and to give you more control) is to put the camera in manual mode (just start by selecting a shutterspeed and aperture that's the same as what the camera would have chosen in Av mode, and go from there).

    N K Guy wrote what is considered to be the "bible" of Canon EOS Flash. There's a lot that won't apply to what your asking (so just skip over it), but a LOT that will, so it's well worth a read.

    You can find it here.

    Hope this helps

  4. #4

    Re: Flash Questions

    Colin

    You have made things much clearer. An excellent link too. I find one of the problems with the internet is too much information (and a lot of that is conflicting or confusing). I find your primers very useful indeed...hows that book coming along

    Again many thanks

    Steve

  5. #5

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    Re: Flash Questions

    Quote Originally Posted by Wirefox View Post
    This leads to a second question with the 450D if I try to use AE lock when the flash is attached (eg focus, AE lock background then recompose) the camera says I am using FE lock. What is the difference between AE lock and FE lock. I am pretty sure I need AE lock for fill flash does anyone know how I lock AE when the speedlight is mounted on a 450D.
    When flash is being used AE lock (if it was available) would refer to the ambient light that is illuminating the background, whereas FE lock refers to the flash light that is illuminating the subject. When you're using flash, the function of the * button changes from AE lock to FE lock. One way around this if you still want to perform AE lock is to set the metering mode (probably centre weighted average, partial or spot - see below), go to manual mode, half press the shutter to wake the camera up (if necessary), set the aperture that you want and adjust the shutter speed while observing the metering display in the viewfinder until you get the background exposure that you're after. Then recompose, focus and shoot.

    Quote Originally Posted by Wirefox View Post
    If I shoot in Av mode outdoors in daylight do I need to AE lock on the background every time. In what sort of situation would I benefit from using AE lock.
    The circumstances under which you would need to use this kind of pseudo AE lock when using flash are similar to the circumstances under which you would otherwise use AE lock, i.e. when the evaluative algorithms don't give you the result that you want. Typically this would be when you want to partial or spot meter off something in the background. This could be necessary sometimes, but would not usually be the case. You would have to be careful that you don't end up making it impossible for the camera to get a good subject exposure if the subject is already brightly illuminated by the ambient light, since the flash can only add more light. The automatic algorithms try to allow for this sort of thing (pretty well usually). That's probably why the camera design makes it awkward to lock AE when using flash.

    Quote Originally Posted by Wirefox View Post
    And finally the easy solution would be to use P mode so why does this seem to be frowned upon. Are there situations when P mode will not cope?
    P mode is oriented towards getting the shutter fast enough that you get a steady hand-held shot, even if this means underexposure of the background. Also it sets both aperture and shutter speed, i.e. it does not allow you to lock in the aperture independently, so you get less direct control over the appearance of the result (with respect to depth of field and background blur). It's a kind of compromise that tries to get some sort of reasonable shot, but maybe not exactly the one you want. Also it's right next to the green box, which is an even bigger compromise. Whether there's anything wrong with any of this is a matter of circumstances.

    Will

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    Re: Flash Questions

    Personally, I don't do much flashing; but when I have to, with my 40D, I prefer to use manual settings as I also tend to end up confused and over exposed.

    Most of my flash use is with macro photography so I use the same principles for general flash photography and it usually ends up OK - eventually!

    I just decide upon the possible shutter speeds (say 125 to 200 range) then pick a suitable aperture (like F8 or F11) then pick and mix with whatever ISO setting gives me the best result. A couple of test shots are a good idea but after a while you can guess reasonably close. For small variations in light or excessively light or dark clothing etc, I just plus or minus the shutter speed or aperature as required.

  7. #7

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    Re: Flash Questions

    Quote Originally Posted by Geoff F View Post
    Personally, I don't do much flashing
    Glad to hear it!

    ("Flashing" means something else in these parts!)

  8. #8

    Re: Flash Questions

    as I also tend to end up confused and over exposed.


    What small minds we have.

    Seriously though, Geoff, Will, Colin and Kevin (your are right of course) your help has been invaluable to me. I have started to get some passable results but it is still very hit and miss. I just need plenty of practice. This image is still a little patchy but I am heading the right way.

    Flash Questions

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