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manual flash and light metering

Why when using manual flash, if you need to set say an aperture of f3.5 on your camera and your lightmeter says f7.1, why would the 7.1 be too much light, given that the wider the aperture, the greater the amount of light entering the sensor?

Comments

  • TrevTrev Moderator
    edited December 2015

    MrH,

    You have it about face, the f7.1 is not too much light, the meter is telling you that f3.5 is too much light for the settings (shutter/ISO) you have and you need to put the aperture to f7.1 to stop it down.

    So, you need to make sure you have your ISO and your Shutter speed set on the light meter the same as the camera, then you get a reading for the aperture. If you want to change it about, and want an Aperture set to a specific setting, you need to juggle ISO and shutter until the meter gives you that setting, eg: f3.5, you will need to keep adjusting the shutter/ISO (make sure you put those values in the meter) until it reads f3.5

    However, the quick way is once you take a light meter reading, in your case it read f7.1, you can then usually rotate the wheel on the meter until you reach f3.5, then see what the shutter is then saying on the meter, so merely set that and you don't even need to fire another shot. If you cannot achieve that check that ISO is not too high, change that, with the reading still in place and you will also see the aperture value change along with it.

    One shot is all it takes, then rotate wheel on meter so the aperture reads what you want, then change the settings on the camera to what the values on the meter now shows.

    The other side to it would be if using flash (manual only), and you needed to be at or just under sync speed, you set the camera shutter ISO and fstop you want, say to get a background so it looks like you want, then you need to take a shot with the flash on, take a reading, and then merely adjust the power of the flash up/down until you get the aperture value making sure of course you entered the Shutter/ISO on the meter the same as the camera.

    The easy way to change then would be to 'count the clicks' on the flash (if it dials up/down in 1/3rd increments), so you want f11, meter gives you f8, then 3 clicks more power to get to it quickly.

    Learning to 'count in 3's' (each click is a 1/3rd of a stop, so the 3 clicks is a full stop) is a great way to learn without a huge pile of test shots. Just make sure you have the camera and the light meter set up so the increments are in 1/3rd stop values, as you can change to 1/2 and even full stop values, so setting that correctly at the start will stop a lot of head scratching.

    Trev




  • Neil vNNeil vN Administrator
    You have answered your own question. Step back a little bit and think this one through again. I think you're on the verge of this ... 


    If the light-meter tells you the flash is giving you f/7.1 ... if you open your aperture wider, you will be allowing too much light to hit the sensor. Hence, over-exposure.  

    It is exactly as you have it here:  " ... given that the wider the aperture, the greater the amount of light entering the sensor?"
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