Flashmeter newbie needs some guidance

Discussion in '35mm Cameras' started by Norm Dresner, Jun 9, 2005.

  1. Norm Dresner

    Norm Dresner Guest

    I just got a flashmeter which the previous owner swears isn't working but it
    does turn on and seems to respond to light -- a single flash from a
    hand-held strobe caused it to display a reading -- so far that's the extent
    of my experimentation.

    I'm a very experienced photographer (5+ decades, I guess) and somewhat of an
    electronic engineer too so even opening it up and examining the circuit
    doesn't scar me. But I have never owned a flashmeter before and I was
    hoping for at least some website with general guidance on using one.

    Also, I've been thinking that I would use an old vivitar 283 as a light
    source to test the meter since it's more or less internally calibrated. Is
    this a good idea or should I do something else like actually take pictures
    with a DSLR and determine the correct f-stop and see what the meter says?

    Any suggestions appreciated.
    Norm
     
    Norm Dresner, Jun 9, 2005
    #1
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  2. Norm Dresner

    Alan Browne Guest

    You can't test a meter against an auto flash, as the flash will cut off
    when it believes the flash exposure is correct. You have to test your
    meter with a flash that outputs a fixed amount of power each time.
    Manual power setting, IOW.

    Set up a scene with white, mid-tone (grey/beige) and white, as well as
    some color elements. (Bowl of fruit, toys, etc.)

    Setup the flash on a stand. Distance must remain constant.

    Meter the flash with the meter close to the subject, dome pointing at
    lens. The flash __must__ be in a manual power setting mode (not an auto
    mode or TTL mode).

    Set the aperture per the meter (make sure meter and camera are at same
    ISO setting, assuming you're indoors, meter can be set to at any
    reasonably close shutter speed setting, eg: 1/60 .. 1/125).

    Shoot the shot and look at the histogram. If the highlight return is as
    low as even the center of the histo, chances are very good that the
    flash meter is correct. (Ideally the highlights would be right up to
    the right, but not likely, depends too much on your sensor).

    Examine the detailed image (on computer) to see how well the color
    looks. Experiment with aperture larger and smaller to get a feel for an
    offset between the meter and the DSLR.

    Repeat the experiment with neutral slide film (such as Sensia 100).
    Keep good notes.

    Have fun.

    Cheers,
    Alan
     
    Alan Browne, Jun 9, 2005
    #2
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  3. Norm Dresner

    Norm Dresner Guest

    Thanks for the detailed procedure. I'm sure I'll have fun doing it ;-))
    Norm
     
    Norm Dresner, Jun 9, 2005
    #3
  4. Norm Dresner

    Alan Browne Guest

    UR welcome. Note that above I meant "white, mid-tone and _black_"

    Cheers,
    Alan
     
    Alan Browne, Jun 9, 2005
    #4
  5. Norm Dresner

    Joe Blow Guest

    The tricky part is that the flash uses the reflected light from the subject
    while the flash meter (usually) uses the light directly from the flash. If
    you subject does not reflect the amount of light that the flash meter is
    calibrated for (for example 18%), the flash will see a different exposure
    than the flash meter.

    My suggestion is to set the 283 to manual full power. Measure the flash with
    the flash meter at a known distance (use a measuring tape). The f-stop that
    the flash meter should indicate can be calculated by dividing the guide
    number of the 283 by the distance between the flash and the meter. The
    Vivitar 283 has a guide number of 36 (@ 100 ISO), so when measured at 4.5 m
    you should get a reading of 36/4.5 = f8 from the flash meter (@100 ISO).

    Good luck,
    Menno
     
    Joe Blow, Jun 9, 2005
    #5
  6. Norm Dresner

    johnboy Guest

    No, no, no!

    What a bunch of bullpucky. The flash meter is an incident meter. The OP has
    decades of experience. What is the friggin mystery here that a few tests
    won't reveal? Push the computer away and make it so.
     
    johnboy, Jun 9, 2005
    #6
  7. Norm Dresner

    Neil Gould Guest

    It seems that it is doing something that it's supposed to do.

    [...]
    Hmm. A roll of film would expose most issues with your flash meter. Set
    the flash on "manual", see what the meter reads, and shoot at that value
    +/- 1 or 2 stops in whatever fractions of a stop your camera allows.

    Regards,

    Neil
     
    Neil Gould, Jun 10, 2005
    #7
  8. Norm Dresner

    Norm Dresner Guest

    Actually I was planning on using a DSLR and getting instant results.

    Norm
     
    Norm Dresner, Jun 10, 2005
    #8
  9. Norm Dresner

    Norm Dresner Guest

    Well, I could use my Kodak 18% Gray Cards as part of the target, huh?
    Yeah, I checked today while moving stuff from one camera bag to another
    and did indeed verify my recollection that the 283 has a manual
    (non-automatic) mode.

    Beyond the numerical stuff, I'm planning on using the D70 DSLR to verify
    exposures as well.

    Norm
     
    Norm Dresner, Jun 10, 2005
    #9
  10. Norm Dresner

    Norm Dresner Guest

    I'll probably include the Kodak 18% Gray Card that I've carried around
    in my bag for years without ever using it in the field.

    BTW, the 283 has a "full-power", manual mode that should be perfect for
    this test.

    Norm
     
    Norm Dresner, Jun 10, 2005
    #10
  11. Norm Dresner

    Joe Blow Guest

    Exactly, the flash meter is an incident meter and the sensor in the flash is
    a reflective meter. That's why the two meters will see different exposures
    (different "amounts" of light) if the subject doesn't have the same
    reflectiveness as the flash is calibrated for. That's why the OP should NOT
    use the auto mode of the 283 flash.

    Nothing against a few tests with a camera. But just using your brain and the
    old fashioned guide number can save you some time and effort. Why do you
    think a flash manufacturer specifies a guide number? You might as well use
    it.

    Anyway, the OP has a digital SLR and I'm sure he'll be able to figure out if
    the flash meter's reading is trustworthy or not.
     
    Joe Blow, Jun 10, 2005
    #11
  12. Norm Dresner

    Bandicoot Guest

    [SNIP]
    An accessory for the 283, that at least recently was still available new, is
    the "Vari-power Module". This plugs in in place of the auto senso and gives
    you variable (manual) power from full down to about 1/32nd. If you're using
    the 283 manually with a flashmeter this is a useful thing to have
    (especially so if you have more than one gun and want to vary the ratio
    between them).


    Peter
     
    Bandicoot, Jun 10, 2005
    #12
  13. Norm Dresner

    Norm Dresner Guest

    I'll check it out. My 283 dates from IIRC the late 70's so I'll have to see
    if it's sold separately.

    Thanks for the info

    Norm
     
    Norm Dresner, Jun 10, 2005
    #13
  14. Norm Dresner

    Tony Polson Guest


    Why don't you borrow a flash meter that is known to be accurate, carry
    out a test flash with both meters and compare the readings? If you
    don't know anyone with a flash meter your local photo store or photo
    club might be able to help.
     
    Tony Polson, Jun 10, 2005
    #14
  15. Norm Dresner

    Mike Guest

    The problem with using a portable flash like the 283 is that flash duration
    (even on full power) might be quite a bit shorter than most studio units so
    I'd try to borrow a monolite from someone to use instead.
     
    Mike, Sep 27, 2005
    #15
  16. Norm Dresner

    Mike Guest

    Yep the vario-power module available separately but changes flash duration
    and some (not all) studio flash meters don't like the short flash durations.

     
    Mike, Sep 27, 2005
    #16
  17. Norm Dresner

    dadiOH Guest


    He should use the 283 on manual. I suppose it depends on the meter but
    I never had any problem reading small speed lights with any meter I ever
    used.

    Best to compare units via incident readings.

    --
    dadiOH
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    dadiOH, Sep 30, 2005
    #17
  18. That (shorter) isn't a problem.
    So there's no need to find a unit with longer flash duration (that. longer,
    could be a problem).
     
    Q.G. de Bakker, Sep 30, 2005
    #18
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