Another DoF Question

Discussion in 'Beyond the Basics' started by fotogenik, Aug 1, 2006.

  1. fotogenik

    fotogenik TPF Noob!

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    Ok,

    I understand the basics of establishing depth of field. lower the aperture (smaller number, larger opening) gives a more shallow depth of field, but when I try it in the studio I take my meter reading, set the camera and them bump the aperture down a couple of notches to get a more shallow depth of field.

    What end up happening is the picture blows out and is utter crappiness.

    Any help or advise on this?
     
  2. Digital Matt

    Digital Matt alter ego: Analog Matt

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    I'm assuming you are using studio flashes. Correct me if I'm wrong.

    You have to adjust your lights to suit the aperture that you would like to use. In a studio setting, using strobes, the aperture is the only thing that controls the light. If you meter at f/8, and then open up to f/4 for a more shallow depth of field, you'll be overexposed by 2 stops. What you should do is use a handheld flash meter, and set it to shutter priority. If you are hand holding, pick a fast shutter speed, preferrably your sync speed, which is probably 1/250. Then, having your meter trigger the flashes, check the aperture that it's giving you. If the meter tells you f/8, and you want a shallow depth of field, you'll have to lessen the output power of the lights, so that it requires a wider aperture to let in the same light. You would lower your lights by 3 stops to get to 2.8, for instance.
     
  3. fotogenik

    fotogenik TPF Noob!

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    ok, camera sync speed is 1/500th.

    So set meter to 1/500th and trigger the flashes. Assume I got a reading of f8. Set camera to 5.6 for instance to get a more shallow depth of field and drop light output by 3 stops to get what I am looking for?

    Is that about right?
     
  4. Philip Weir

    Philip Weir TPF Noob!

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    Turn off your flash heads. Shoot available light or just the modelling lamps and shoot a series of exposures at different apertures so you can see what the various apertures do, then you will know what aperture you want to shoot at. just a thought.
     
  5. Digital Matt

    Digital Matt alter ego: Analog Matt

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    Not exactly. f/8 to f/5.6 is only one stop. You need to adjust the output of the lights by the amount of depth of field you want. If you get f/8, and you want 5.6, drop the power of the lights, and meter again. Continue to meter and adjust the lights until it says 5.6, or whatever aperture you want. Sometimes you want more depth of field, and you would increase the power of the lights, until you get a reading of f/16. You should meter each time though, until the meter tells you that the flash power is correct. Even though a flash may have a scale on the back, and you are dialing it back a certain number of stops, it may not be exact, and that's why you should always meter to make sure.
     
  6. Christie Photo

    Christie Photo No longer a newbie, moving up!

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    This is exactly right. Remember... the duration of the flash is faster than the shutter. So, changing the shutter speed will not affect exposure. When using strobes, the exposure is varied by the power of the flash OR aperature.

    To re-state, if you want to shoot with a larger aperature, you have to reduce the output of the strobes.

    Pete
     

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