New to flash: how to use it (RZ67 and Metz 45CT-5)

Discussion in 'Lighting' started by lobko, Apr 10, 2014.

  1. lobko

    lobko Member

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    Hello everybody.

    I have a question. I am quite new to photography; I recently bought a Mamiya RZ67 and it works fine, I like it.

    Now, for my birthday, a friend of mine gave me a Metz 45CT-5 and I would like to use it, manual mode.

    According to both the camera and the flash manuals I should use this formula to set the aperture = GN / distance flash-subject.

    In my case: 45/3 = 15, so about 16. My question: how about shutter speed?

    Should I use a light meter in AV and set the aperture to 16 to have the shutter speed? I played with that and tried with some Polaroids (I have a Pola back) but every photographs appears completely black.

    What's wrong with that? How can I have a "daylight" photograph in a room with no light?

    Thank you all for the help
     
  2. Alex Muir

    Alex Muir Member

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    You get a different guide number for metres and feet, so make sure your calculation is based on the same units. In flash photography, aperture controls the flash exposure, and shutter speed controls the ambient light that records. You can work out the aperture for flash based on flash to subject distance, as you have done. You could then take an ambient light meter reading to see what shutter speed is appropriate. That should balance the exposure. Indoors at f16, the ambient light might need quite a slow speed, especially with a 100asa, or similar speed film. I'm not sure if your camera uses a leaf shutter in the lens. If it does, the flash will sync at any speed. If not , you will need to check the maximum sync speed, and stay at or below that. Instant film has quite a narrow latitude, so a small difference in exposure can have a big effect. It is similar to slide film in that respect.
    Alex
     
  3. MattKing

    MattKing Subscriber

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    If the result of your Polaroid test is completely black, I would guess that there is a problem either with the dark slide or synch.
     
  4. mgb74

    mgb74 Subscriber

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    Welcome to APUG.

    Your leaf shutter lens will sync at all speeds. The duration of the flash itself is much shorter than even the fastest speed (1/500) of your shutter. So, in theory, you can ignore the shutter speed.

    But there is an implicit assumption that the image from ambient light will not have a noticeable impact on the film. This may not be the case depending on the light (and the subject) and is, by definition, not the case when using fill flash. So (other than using fill flash) it's best to use a fast shutter speed.

    Your formula is correct. And it looks to me that you're using (correctly) both GN and distance in meters. Note that the GN rating for a flash is a function of both light output and film iso. So a GN of 45 (meter) for that flash assumes iso 100 film, which may not be the iso of your instant film.

    None of this explains why your test exposures came out black. When you used the calculator dial on the flash, did that confirm f16? Did you have the flash set to full output (the CT-5 allows you to vary the flash setting)? Were you using the flash in bounce mode (at 3 meters, I assume not)? I don't know if your lens has both "M" and "X" sync settings, but if so was it set to "X"?

    Finally, how confident are you in the Polaroid film you were using? Do you get correct exposures with it in ambient light?
     
  5. lobko

    lobko Member

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    Hi: To answer:

    I used meters for the calculation;
    The Polaback works fine, I have no problem daytime; or in ambient light;
    Yes, the ISO is 100;

    Maybe I should use the fastest speed instead of 1/2 sec.

    I haven't used the flash calculator, I used it in manual mode in full output.
    The lens has just the 'X' mode.

    Thanks
     
  6. Alex Muir

    Alex Muir Member

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    If the metered exposure for the ambient light was 1/2secs at f16, you should have had an image regardless of the flash component. Using a faster speed would lead to less exposure and a darker image of the background. If the whole image was black it suggests that neither the flash nor ambient light recorded. That sounds like a problem with the camera or the back.
    Alex
     
  7. mgb74

    mgb74 Subscriber

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    First, I forgot to take into consideration that your "film" (Polaroid) is a positive, not a negative. So while I was thinking that "completely black" meant underexposure, in your case it means overexposure.

    So your 1/2 second exposure may be too long. Although hard to imagine that the entire scene would register completely black.

    Here's the sequence I would start with:
    Set shutter to 1/250
    Using the calculator dial on the flash, set the iso then read (and set) the aperture to match the distance
    Expose indoors under typical indoor lighting, using direct flash (no bounce)
    Do the same with a 2nd lens (if you have one)
     
  8. Chan Tran

    Chan Tran Member

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    For positive material completely black is no exposure (underexposure).
     
  9. lobko

    lobko Member

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    Chan is right.

    mgb74, I've just tried (6pm circa) and I got this, at f11, 1/125, RZ67 with 250mm (result quite good):

    Scan-140411-0001.jpg

    Will try again this evening and let you know.


    Thanks