Non-TTL Flash Questions

Discussion in '35mm Cameras' started by narke, Jan 10, 2005.

  1. narke

    narke Guest

    I got a flash unit without TTL capability, it equips with an AUTO mode
    of course. The GN number of this Flash unit is 20 (ISO 100 in meter).
    In the back side of the unit, there is a sheet, which said, in it's
    auto-mode, the aperture has to be f/5.6 for a ISO 100 film.

    Supposing in the following two scenes, I equiped with a camera with
    smallest aperture of f/16, a roll of ISO 100 film and no any other
    material on hand. So, how should I use the flash unit to get correct
    exposure in each scene?

    1) I want to shoot a subject one meter away. The ambient light is main
    light (sunlight come thru the window nearby), the front side of the
    subject fall in deep shadow. So I want to use the flash to fill some
    light to the front but keep the background in the mood. And, I can
    image that the fill light should be one stop less than normal. How do
    I do?

    2) A subject in darkness, so in this time the flash light gets
    dominate. But I am not well sure the exactly distance between camera
    and subject, I just know the distance should not strike the
    speedlight's upper range. So I think I can rely on the flash unit's
    AUTO mode, for the simple reason that the sensor build in the
    speedlight will cut off the speedlight automatically when it received
    enough amout. However, there is a problem, for the AUTO mode, the speed
    light always ask for a fixed aperture, in this case, that is a f/5.6.
    But I dont want f/5.6! I actually need f/8 for some reason.

    -
    narke
     
    narke, Jan 10, 2005
    #1
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  2. narke

    Nick Zentena Guest

    Set the camera to F/8.

    I'm guessing you can tell the flash what film speed you're using? Lie to
    the flash. Set the flash to a film speed one stop slower.

    Nick
     
    Nick Zentena, Jan 10, 2005
    #2
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  3. narke

    chemliftbake Guest

    Narke:

    If your guide number is 20, the closest you can shoot a subject at
    f16 with 100 film is 20 / 16 = 1.25 meters. If you want only half of
    this power to reach the subject for fill flash, you multiply this
    distance by the square root of 2, 1.414. So 1.25 meters x 1.414 = 1.77
    meters.

    If your flash requires an aperture of 5.6 and you want to shoot f8,
    then you need to trick the flash into producing twice as much power as
    it normally would. You need to set the flash to ISO 50 film instead of
    ISO 100. Good luck.

    Bob C.
     
    chemliftbake, Jan 10, 2005
    #3
  4. narke

    narke Guest

    If your guide number is 20, the closest you can shoot a subject at
    If I can not shoot for such a long distance (because the subject will
    become
    too small in the frame), is there any other method? Does a diffuser on
    flash
    unit help that? I means I still shoot from one meter away, but use some
    material as diffuser which covered on the bulb of the flash unit. I
    think this
    may effectly reduce the GN. Am I right? If so, do you get any suggetion
    on the
    material of a DIY diffuser? Thanks.
    My flash unit is Ricon Speedlight 200, which has only a sheet on the
    back of it
    which tells the combinations of ISO/Distance/Apperture. I do not find
    any way I
    can set a ISO number for it. That simply tells me for a ISO 100, I
    should use
    a f/5.6, for a ISO 50 I should use f/4, for a ISO 200 I should use f/8,
    and so
    on. For the speedlight itself, it just don't need know the film speed
    anyway.
    In fact, I beleive that on one can use any method to fool a speedlight
    to force
    it produce tweice power as it maixmized.
     
    narke, Jan 10, 2005
    #4
  5. narke

    narke Guest

    Nikck,

    Please check my reply to chemliftb, thanks!
     
    narke, Jan 10, 2005
    #5
  6. narke

    Nick Zentena Guest

    The sensor will handle this. It'll turn off the flash when enough light
    hits it. The problem is it seems to have only one F/stop. So it's not the
    most control. If you cover the flash with something then the flash will put
    out more light until it's happy. All you'll manage to do is waste battery
    power. You might get some softer light.



    If you're metering of the scene fits those numbers you're okay. If not the
    flash won't work very well for fill flash. If you meter and the scene needs
    F/8 at ISO 100 then set the camera for F/8. The flash will assume you've set
    the camera at F/5.6 and let out one stop less light. The only control you
    seem to have is with playing with the cameras's sync speed. But odds are
    you'll have trouble using slower speeds outdoors.

    You might want to keep an eye out for a newer used flash then that
    Ricoh 200. Which camera are you using?

    Nick
     
    Nick Zentena, Jan 10, 2005
    #6
  7. << I got a flash unit without TTL capability, it equips with an AUTO mode
    of course. The GN number of this Flash unit is 20 (ISO 100 in meter).
    In the back side of the unit, there is a sheet, which said, in it's
    auto-mode, the aperture has to be f/5.6 for a ISO 100 film. >>

    Narke-

    In either case, you need to figure the maximum shutter speed for flash
    synchronization into your computations. In the case of bright ambient light
    (sunlight), the shutter speed may not be fast enough to match the f/stop
    required by the flash.

    In case 1, you may need to sacrifice the background and let it be over exposed.
    Use manual mode, set the aperture to f/16 (since you don't have f/22) and set
    shutter speed to the maximum for flash. The guide number (20) divided by
    distance (1 meter) equals the ideal f/stop, f/20.

    If by chance, the background light would require a shutter speed slower than
    the maximum flash speed, then you can balance foreground and background
    lighting by choice of shutter speed.

    In case 2, you can't get around the f/5.6 limitation in automatic flash mode.
    If you choose any other ISO, it will not affect the flash output, only the
    f/stop recomended on the calculator dial. (That said, f/8 would only be one
    stop off, and may be adequate - give it a try.)

    For ideal exposure, you would use the flash in manual mode, divide 20 by
    subject-to-camera distance in meters and use that as your f/stop. Working
    backwards for f/8, your subject must be approximately 20/8 = 2.5 meters away
    from the flash for proper exposure.

    This assumes shutter speed does not exceed the camera's maximum flash sync
    speed. If there happens to be some ambient light, you could adjust the shutter
    speed downward to take advantage of it.

    Fred
     
    Fred McKenzie, Jan 10, 2005
    #7
  8. narke

    narke Guest

    The sensor will handle this. It'll turn off the flash when enough
    light
    In my understand, the sensor has nothing to do with this scene when the
    flash was set to manual mode, right? A Non-TTL flash will emit fixed
    amount of light regardless if or not the subject get enought
    illumination, wouldn't it? If my guess is right, some material covered
    on the bulb will effectlly block some light and sequencely reduce the
    GN number of the flash unit.

    Am I right? Thanks

    Again, what will happen if I use the manual mode of the flash?
    How to play with the sync speed? what's the tricks? Thanks.

    My camera body is Contax Arial. How much the Ricoh Speedlight 200 cost
    about now? I hate it and want to sell it now :-(


    Narke
     
    narke, Jan 11, 2005
    #8
  9. narke

    narke Guest

    In case 1, you may need to sacrifice the background and let it be
    over exposed.
    So ... the subject will get one stop more light because in this
    distance it ask for a f/22 but I give it f/16, right? That's the
    subject itselft not only the background will get overexposure.
    .... but the more the aperture is opened up, the more the subject will
    get illuminated by the flash (in manual mode), so the far I leave away
    from my purpose. I did not recognize where is the point of balance.
     
    narke, Jan 11, 2005
    #9
  10. << ... but the more the aperture is opened up, the more the subject will
    get illuminated by the flash (in manual mode), so the far I leave away
    from my purpose. I did not recognize where is the point of balance. >>

    Narke-

    I think you understand. In manual mode the flash puts out full power. You
    choose a film speed and set your camera's f/stop so light intensity at a
    certain distance will give you proper exposure. You can also adjust your
    camera's shutter speed to balance ambient light with light from the flash, up
    to the maximum shutter speed for flash synchronization.

    In automatic mode the flash has a photo cell that receives light reflected from
    your subject. When it receives enough light, it stops the flash. Note that
    for ISO 100 and a Guide Number of 20 Meters, your f/5.6 setting limits you to a
    maximum distance of 20/5.6 = 3.6 meters.

    You might also consider using film with a different ISO value. For example,
    using ISO 200 film, your automatic mode would require a lens opening of f/8
    instead of f/5.6. In manual mode the guide number would be 20 times the square
    root of 2, or 28. Similarly, for ISO 400 the automatic f/stop would be f/11.
    The manual mode guide number would be 40.

    At least this is what the theory says. Some flashes may put out more or less
    light than the manufacturer claims. In addition the flash's photo cell can be
    mislead by dark or light subjects. You need to try it and see.

    Fred
     
    Fred McKenzie, Jan 11, 2005
    #10
  11. narke

    Nick Zentena Guest

    I thought you're in auto mode? If you really wanted to cover the flash I'd
    get a sheet of ND filter.

    http://www.rosco.com/us/filters/roscolux.asp

    Roscolux #397 is a 1/2 stop ND. A big sheet is pretty cheap and can be cut
    down. If you want 1/2 stop then use one piece. If you wanted 1 stop use two
    pieces.



    Depends on the situation. In manual mode you really don't have much
    control at all.

    You can use any speed lower then your max sync speed. Using a slower
    speed lets you use a smaller F/stop. This doesn't relate to the light from
    the flash but the total light.



    Not much. Less then the cost of postage.

    Nick
     
    Nick Zentena, Jan 11, 2005
    #11
  12. narke

    shesso Guest

    flash meter, test roll?
     
    shesso, Jan 11, 2005
    #12
  13. narke

    narke Guest

    Fred, Nick ...
    Thank you All !
     
    narke, Jan 12, 2005
    #13
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