flash TTL meter and underexposure

Discussion in 'Exposure Discussion' started by Alessandro Serrao, May 15, 2010.

  1. Alessandro Serrao

    Alessandro Serrao Member

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    Hi,
    I'm told that Nikon flash systems, when used in TTL mode, read the light bounced back from the emulsion when the shutter is opening for calculating the light strenght emission.
    Now: different films has different emulsion colours. C41 and E6 has a slight brown base while b&w has a more whiter film base.

    Now, theoretically, if the system is calibrated to C41 and E6 type of reflectivity, if I use my Nikon flash in TTL with b&w films will I get underexposed images?

    Thanks...
     
  2. Anon Ymous

    Anon Ymous Member

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    Alessandro, that's called "off the film" metering. I read an interview with Yoshihisha Maitani, the mind behind the OM series cameras (Olympus), and he stated that they checked the reflectivity of about 50 different films. The differences were too small to have an effect, so film type didn't matter.
     
  3. Q.G.

    Q.G. Inactive

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    Depends.

    Different films do reflect different amounts of light.
    There is no clear division into three categories: slide, colour negative and B&W negative though.

    Here's an old chart (from the user manual of a Hasselblad flash unit). Some emulsions were changed since then. Some aren't available anymore. But you get an idea:

    [​IMG]

    If the emulsion you are using isn't listed, just run a test.
     
  4. benjiboy

    benjiboy Subscriber

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    My Canon T 90 has O.T F/ TTL flash metering the system is based I believe on the reflective index of colour print films, It has a sensor that reads the light coming through the film, I've used it with five or six different colour print, slide and monochrome films, it works perfectly with all of them.
     
  5. markbarendt

    markbarendt Subscriber

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    Not all Nikons have film plane sensors and in the end it doesn't really matter.

    This quote describes one of the ways TTL metering is done. (Text copied straight from the Nikon USA web site.)

    Some Nikon cameras did use film plane sensors but that's not the norm now.

    TTL can do amazing things but, regardless of whether your camera has a film plane sensor or not, ttl metering can still be easily fooled or foiled. Good flash photography requires the photographer to think.

    This book is a good read, Hot Shoe Diaries, lots of great ideas and info. One of the things that stood out for me in the book was that to get good shots you have to understand your equipment intimately and manipulate it appropriately. TTL is not a magic bullet.

    Practice and testing are your friends here. Shooting with strobes is a skill that most people will never master. Don't worry, you can get there, after a few hundred shots you'll start seeing how it all works. After a few thousand you may be proficient. :wink:
     
  6. Chan Tran

    Chan Tran Member

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    I found a couple of things about TTL and Nikon TTL
    1. The reflective of films varies quite a bit from type to type.
    2. Newer Nikon flash and cameras tend to underexpose while older ones are OK.
     
  7. Ian C

    Ian C Member

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    Subject Reflectance is More Important

    The differences in the reflectance of films are much less than the difference in the subject reflectance.

    Consider:

    Case 1: You photograph a fair-skinned bride in her white wedding gown against a light background.

    Case 2: You photograph a dark-skinned man in a black suit against a dark background.

    I would expect a TTL flash to produce less exposure in case 1 than in case 2. Photo #1 is likely somewhat underexposed, while photo #2 may be overexposed.

    Automatic exposure is a big advantage to quick-working photography and helps us get a high percentage of usable exposures. But no camera or flash has a brain. It helps to slow down, analyze the situation, and modify the ASA on the flash to compensate for non-standard subject reflectance—even with TTL autoflash.
     
  8. 2F/2F

    2F/2F Member

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    I was going to post something similar, but this was already here.

    Ah, the joys of in-camera reflected light meters...
     
  9. markbarendt

    markbarendt Subscriber

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    Yeah, that. :rolleyes:
     
  10. wiltw

    wiltw Subscriber

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    I just used a spotmeter to measure the reflectance of some outdated Kodak (VPH) and Fuji (NPH) color neg and Fuji color transparency (Provia) films, and and Kodak B&W (TMX) emulsion. Compared to an 18% gray card,
    B&W emulsion is +0.7EV brighter,
    Kodak color neg is +0.5EV brighter
    and Fuji color neg film is +0.6EV brighter
    the Fuji transparency film is -0.2EV.

    Nevertheless, TTL with film is heads and shoulders superior to the DSLR eTTL/iTTL/xTTL garbage we live with today!
     
  11. Chan Tran

    Chan Tran Member

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    When I got the F5 my flash pictures are always underexpsoed. I sent the camera back to Nikon twice to have it calibrated but same problem. I had to do a 1 stop + compensation and this is very inconvienient because I have to remove the compensation when shoot without flash.
    I recently read a book about Nikon flash (forgot the tittle) and in most example the author had to use + compensation. On the everage about 2/3 stop. So I am confident that Nikon intentionally made the TTL system underexpose.
     
  12. markbarendt

    markbarendt Subscriber

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    Chan,

    This is the "joy" :rolleyes: of letting the camera set your exposure.
     
  13. Alessandro Serrao

    Alessandro Serrao Member

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    I've got a F90X and an Sb-26 and, with TTL metering, I've got the same problem too, especially with b&w materials...
     
  14. TSSPro

    TSSPro Member

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    I usse the F5 w/sb-26 combo a lot, too. I havent run into too many instances where I have consistant underexposure. An example of the TTL being fooled woudl be if you were trying to photograph a lare open reception hall. I wouldnt rely on TTL metering to get it right for me. The tables, chairs, floor and ceiling in tghe foreground would be closer to being exposed properly, if not over exposed, and the BG would be entirely underexposed by several stops depending on film and other variables.

    As a rule of thumb I general overexpose my c41 to add density to the neg and prevent that under exposed haze you get with color neg; that may be whats compensating for the built-in underexposure you mentioned.