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Best advice to set exposure in Manual mode while using flash?

Discussion in 'Lighting Forum' started by jambaj0e, Sep 6, 2010.

  1. jambaj0e

    jambaj0e Mu-43 Top Veteran

    Aug 31, 2010
    Quick question with using flash:

    As an intermediate level user, I've been fairly successful with using manual mode to get proper exposure without flash, but I'm having trouble trying to figure out how to calibrate shutter speeds when I'm using flash. How do I know how fast I can use the shutter speed at any given f-stop when using flash, since the exposure meter doesn't reflect actual exposure when using flash?
  2. photoSmart42

    photoSmart42 Mu-43 Top Veteran

    Feb 12, 2010
    San Diego, CA
    The short answer is that you tell the flash the settings you want to shoot at, and it meters and adjusts the output automatically to match. With a manual flash like my Vivitar 285HV, the settings are fully manual. I can set the ASA (i.e. ISO), f-stop, and power output I desire out of the flash to compensate for the image as metered by my camera. I still use the settings I want on my camera in terms of shutter speed (up to the flash sync), aperture, etc. - all the parameters that are dictated by the composition - but I allow the flash to add the extra light I need to expose the scene properly given my composition parameters.

    With modern TTL flash units, and especially with ones designed for Panasonic/Olympus cameras that have advanced features like FP-TTL and HSS, the camera the flash what to do to expose the scene properly.

    If you want to get into flash photography more, I'd suggest starting with Strobist. It's a fantastic resource for learning how to work with flash, and you can grow from there. Lighting is a whole 'nother aspect of photography once you master the basics of composition.
  3. G1 User

    G1 User Mu-43 Veteran

    Jul 20, 2010
    Question 1
    Does the flash have an "auto eye"?

    If it does, the flash will have a few "Auto f/stop" choices to pick from. Like f/4, f/5.6, f/8, f/11... it will at least have 2 anyway...

    Set the flash on an "auto f/stop" and then use that f/stop on the lens. The fastest shutter Shutter speed will be what the manual says you can use... 1/160 is common. Make sure to look on the flash for the near/far distance at the f/stop your using.

    • Side Note: Slower Shutter Speeds will effect how bright the background can get, the subject exposure won't change. This is called "dragging the shutter", Outdoors, this will allow a normal background that is not too dark.

    This is the easiest way.....

    For a full manual flash with no guide, you need to know the power output..(Guide Number) example: GN 100 at 10 feet.....

    1. Focus on your subject
    2. use this formula.... GN-100 / #feet = f/stop... the pink 100 an example, use the guide number from your flash
    GN100 / 10feet = f/10
    GN100 / 6 feet = f/16.5
    GN100 / 16 feet = f/5.6 (about) f/7.2 may be better (f/6.2 is the actual f/stop, but no camera has that setting)
    GN100 / 25 feet = f/4

    Set the Lens to your answer, or closest f/stop to the answer.
  4. twalker294

    twalker294 Mu-43 Top Veteran

    Aug 18, 2010
    When using a flash as your main light source, the shutter speed only controls how much the ambient light (available light,) is allowed to contribute to the exposure. It has nothing to do with the exposure of your main subject.

    Try this -- in a normally lit room, set your camera to a set aperture, say f/5.6. Set your shutter speed to 1/50 and take a picture. Now set your shutter to 1/200 but leave the aperture at 5.6 and take another picture. When you look at both you will see the the main subject is lit the same but in the 1/50 picture you can see what's going on in the background of the shot. However in the 1/200 picture, everything other than the subject will be almost black.
  5. isabel95

    isabel95 Mu-43 Top Veteran

    An Excellent Source for Learning about Flash...

    Is the book from Lumiquest: "Flash: The Most Available Light".

    It's been discontinued but I found it used on Amazon. Abebooks.com is another super source of used books.


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