• Welcome to ScubaBoard


  1. Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

    Benefits of registering include

    • Ability to post and comment on topics and discussions.
    • A Free photo gallery to share your dive photos with the world.
    • You can make this box go away

    Joining is quick and easy. Login or Register now by clicking on the button

Q: Regarding Ext.Flash Auto

Discussion in 'SeaLife' started by GwFresh, Nov 24, 2008.

  1. GwFresh

    GwFresh New

    # of Dives: 500 - 999
    Location: Ontario, Canada
    2
    0
    I've been doing some above-water testing with a new DC800 just to get used to how it functions, and I'm having trouble understanding the logic behind how it exposes in External Flash Auto mode. My experiments were directed specifically at using the flash to balance foreground/background lighting in a given scene (typically referred to as balanced or fill flash), but I'm having trouble getting the camera to correctly read and expose for the background light conditions when in this mode.

    My test scene was a window with plants on the ledge, sunlight steaming in (bright & hot outside). First I wanted to establish the proper exposure for this hot background, then would add the flash to fill in the (outlined and underexposed) foreground plants.

    With the camera set to Program AE, (the flash turned off) the LCD and histogram respond to changes in light, as well as changes to Exposure compensation (EV Ž± 2 stops), and the affects of any changes can be seen in the final picture. So a series of images can be taken while bracketing, allowing you to get the desired exposure. Everything behaves the way you would expect, similar to many other digital cameras.

    If however, I switch to Ext.Fl.Auto, (also with the flash turned off) the LCD and histogram show changes in the lighting within the scene, or changes to exposure compensation (as in Program AE), BUT, when the picture is taken, those changes don't translate to the final image. It is drastically underexposed (2.5 to 3 stops), and no amount of adjustment is possible to bring it within range.

    So basically, I'm asking, is there any way to get the camera to expose for the background automatically, (given a little nudging one way or the other with exposure comp.)? Or am I forced to go to External Flash Manual to get the system to do want I want?
     
  2. Former Sealife Employee

    Former Sealife Employee Contributor

    # of Dives: 0 - 24
    Location: New Jersey
    181
    0
    In Ext Flash Auto, the camera will adjust automatically to the background, but the automatic exposure program is much different from the Program AE mode because it is designed primarily for underwater slave-strobe photography.

    The fastest shutter speed in Ext Flash Auto mode is 1/500 seconds, while Program AE can reach a shutter speed of 1/2000. If Ext Flash Auto shutter speed exceeds 1/500, it will be too fast for the Digital Pro Flash to synchronize (or deploy the full load/duration of the flash). That explains why the bright background in your picture test is overexposed.

    In Ext Flash Auto, you can make adjust the exposure using the FLASH button on the back of the camera housing. Push the button once and the camera is set to Macro Flash mode and reduces the cameras exposure. Macro Flash will always use f5.6 while the shutter speeds adjust automatically (up to 1/500 sec). Push the FLASH button again and the camera is set to Far Flash mode. Far Flash will always use f2.7 while the shutter speeds adjust automatically (up to 1/500 sec). Push the FLASH button again and the camera is set back to the original default setting called Normal Flash. In Normal Flash the camera will automatically select the aperture and shutter speed depending on the ambient light.

    Hope that helps.
     
  3. GwFresh

    GwFresh New

    # of Dives: 500 - 999
    Location: Ontario, Canada
    2
    0
    Thank-you so much for your reply. It's too bad that sort of info isn't in the manual. (I don't suppose there's some sort of reference chart available that shows what shutter speeds, f-stops, and ISO values the camera is limited to in the various modes? That would be useful.)

    I do have some other questions if possible:
    - You gave the upper end of the shutter speed range (in Ext Flash Auto), but what's the slowest shutter speed that the camera selects in that mode?
    - The SL961 manual, recommends setting the ISO on auto and the EV compensation to "0" (when in Ext Flash Auto), however, can you change those settings, or does changing those defeat auto modes?
    - Are there any plans to bring out a wide-angle lens specifically for the DC800 camera?

    Again, thanks for your help.
    Gerry
     
  4. Former Sealife Employee

    Former Sealife Employee Contributor

    # of Dives: 0 - 24
    Location: New Jersey
    181
    0
    Sorry, no chart is available.

    The slowest shutter speed in Ext Flash mode is 1/90 sec.

    The default ISO in Ext Flash mode is 64. You can change it, however we strongly recommend leaving it at 64 for the sharpest image quality. Increasing the ISO value makes the CCD sensor more sensitive to white noise and results in a grainier image. Changing the EV compensation in Ext Flash mode is no effect.

    No. The DC800 has a 28mm wide angle lens. We developed some wide angle lens prototype designs with the intention of introducing the a lens for the DC800, but the results were not acceptable.
     
  5. paulmila

    paulmila Scuba Media & Publications

    # of Dives: 200 - 499
    Location: Carle Place, New York
    53
    0

    Hi Denise,
    I wish SeaLife would design a separate wide-angle lens capability. It is kind of nice to build it into the camera, as with the DC800, so you don't have to buy and lug around more stuff. But when I compare it to my DC600 with separate wide-angle lens, the DC600 with separate wide-angle lens gives a better wide-angle view.
     
  6. paulmila

    paulmila Scuba Media & Publications

    # of Dives: 200 - 499
    Location: Carle Place, New York
    53
    0
    I've found that it's a bit difficult to test the below-water modes when on land because the UW settings are designed to compensate for the UW environment and look different when not under water. These cameras seem to do a great job without tweaking the settings, so I usually leave them on the auto settings and get good results.
     

Share This Page