Using a flash

Discussion in 'Beyond the Basics' started by matbathome, Jul 4, 2009.

  1. matbathome

    matbathome TPF Noob!

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    Hi:

    I'm new here.

    I also just started using a flash. I am pretty experienced in using non flash, so I'm struggling with getting the right picture at times.

    Here's the latest shoot I did:
    SimpleViewer

    You will notice that some of the photos have motion blur to them (in particular, the first one). As someone who always shot without the flash, I always knew not to go below 1/60. Is that the same for flash photography?

    What can I do to avoid the motion blur? Still shoot at 800 or 1600 ISO?

    Also, I've noticed some of my reds have come out kind of "hot" or too strong. I shot the above set set on cloudy wb. Should I have changed that to indoor lighting wb?
     
  2. KmH

    KmH Helping photographers learn to fish Supporting Member

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    What camera? Yes. you should have selected incandesent or flouresent depending on the light source and your cameras capabilities.

    P A R T I

    Most DSLR's have a flash sync speed of 1/200 or 1/250.

    The sync speed is the fastest shutter speed that still allows the shutter to be fully open.

    The shutter mechanism is made of 2 curtains. Nikon calls the curtains front and rear and Canon calls them first and second.

    The sequence is the front/first curtain opens fully, and at that instant the flash unit fires. The duration of the flash is about 1/40,000 sec........and will stop motion very well, unless......

    What is happening in your images is that because of your slow shutter speed (1/60) all the motion blur is being captured with ambient light well after the flash unit has fired and before the rear/second curtain has closed.

    What you are doing with your shutter speed at 1/60 is called 'dragging the shutter'.

    P A R T II




    There are 2 ways to fix your situation.
    • Increase your shutter speed to your cameras sync speed 1/200 or 1/250.​
    • Go into your menus and select rear/second curtain sync so your flash unit fires just at the instant the rear/second curtain starts to close, insteadd of firing as soon as the front/first curtain is fully open.​
    When you use flash you can actually control 2 different exposures in the same frame/image. Shutter speed will control the density/exposure of the background and aperture will control the density/exposure of the foreground which is usually your subject.​




    It takes a little thought and visualization to wrap your head around how this all works but the key is that the shutter has 2 curtains.​



    At shutter speeds above your cameras sync speed the shutter is never fully open. It is just a slit of varying width. The faster the shutter speed the narrower the slit. So, if you try and use the flash with a shutter speed higher than the sync speed you get images with part of the frame blacked out because one or both of the curtains was in the way.​



    Well, that's some of the basics, but using flash takes a little more thought and a more thorough understanding of how your camera works.

    All new photographers go through the same learning curve and figure it all out, and so will you. :thumbup:​
     
    Last edited: Jul 4, 2009
  3. matbathome

    matbathome TPF Noob!

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    Thanks. I have a Nikon D40x and it does have the rear curtain sync option. I will try that next time.
     
  4. Andrew Boyd

    Andrew Boyd TPF Noob!

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    Your photos are not that far off. Looks like you're bouncing off the ceiling for most of these, which is a fine approach. Couple of points to keep in mind:
    Your flash outputs daylight-balanced light--5500 degrees Kelvin. The room that you're in--which is still contributing to the exposure--look flourescently lit, I'm guessing. That's a wierd wavelength but lower and different from your flash, usually about 4300K. If you want to balance these, you need to get a bit of flourescent gel to GO OVER your strobe. Now you can put the camera on the Flourescent light balance setting and everything matches!
    Rosco and Lee both make the gel material:
    I buy this stuff from a place in New York, The Set Shop. Here's the page for the gel.
    I know this sounds complicated but you obviously are interesting in improving, so good luck!
    Andrew Boyd
    TheDiscerningPhotographer.com
     

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