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Why not link flash to focus distance ?

Discussion in 'Lighting Forum' started by millhoud, May 10, 2018.

  1. millhoud

    millhoud Mu-43 Regular

    68
    Jun 25, 2014
    Trieste
    Hello,
    We had puppies some time ago and triyng to photograph them playing i had this thought: ttl preflash technique was too slow, and manual flash power was no good either because they were running everywhere, but the camera was able to get focus on them (well not exactly always...)so, wouldn't it be effective to output flash power depending on the subject distance ? It would be a simple firmware only option i guess. I tried searching the web but haven't found anything, so maybe it's a dumb idea, what do you knowledgeable think?
     
  2. Carbonman

    Carbonman Mu-43 All-Pro Subscribing Member

    Jul 10, 2014
    Vancouver BC
    Graham
    Canon used to have a system that worked on focus distance. CAT - Canon Auto Tuning used a flash and a cable to an adapter that bayoneted onto the front of several FD lenses and engaged a pin on the focus ring. I found it underexposed slightly as the norm. The flash was underpowered for all but the simplest work and eventually was replaced by flashes with built in sensors. Then came TTL flash metering, then film plane metering...
     
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  3. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    It's basically "guide number / distance = aperture", but rearranged to be "aperture * distance = guide number".

    Loads of film rangefinder cameras had automatic aperture using flash with the first, and Nikon used the latter for a very long time as part of their flash system.

    To work the camera would need to know the guide number of the attached flash, while there's a large amount of communication between the body and flash I don't recall if this information is part of the protocol with m4/3.
     
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  4. millhoud

    millhoud Mu-43 Regular

    68
    Jun 25, 2014
    Trieste
    So if i get this at all one would just need to dial in the guide number of the flash, not too difficult (?). But do you think the gains in speed/accuracy of flash output would be there or not ?
     
    Last edited: May 10, 2018
  5. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    It's very quick and dirty, but not at all that accurate. It's generally within 1EV or so, which is fine for negative film, but it was never as good as OTF.
    For digital? It's probably close enough for most work but... never perfect, and it's generally not fantastic with matching/blending ambient exposure to flash.

    IMO it would be a good feature to have in the toolbox (more = better!), but I probably wouldn't use it much as I don't really use direct flash and I don't really have any problems with preflash speed (unless you're using red eye reduction, which by design must be slow, the preflash should be imperceptible from the flash firing at full power).
     
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  6. millhoud

    millhoud Mu-43 Regular

    68
    Jun 25, 2014
    Trieste
    Yes in fact i never had the need for it, but these running little dogs were either too dark or too bright (or out of focus...), and the preflash got me missing the right moment (jump or whatever), any gain in speed is welcome (i was thinking abot using instead my nikon film camera...o_O )
     
  7. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    The speed increase by not using a preflash for metering would be between 1/13th (E-M5 Mk1) to 1/60th (E-M1 MkII) of a second.

    If you're seeing delays longer than this try using fill-in flash mode rather than auto, auto can choose to use redeye reduction which adds a half second delay between preflash and exposure.
     
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  8. millhoud

    millhoud Mu-43 Regular

    68
    Jun 25, 2014
    Trieste
    Thanks!! Maybe you happen to know this value for em-5 mark 2?
     
  9. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    The delay between preflash and exposure should be around 1/50th to 1/20th of a second, I'm not sure if it's using 10bit (the former) or 12bit (the latter) readout to judge exposure.
     
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  10. Ross the fiddler

    Ross the fiddler Mu-43 Hall of Famer

    If you are indoors with a white ceiling, then the best lighting is if it is bounced off the ceiling. Well it was when using the older FL50R or FL36R flashes.
     
  11. Ross the fiddler

    Ross the fiddler Mu-43 Hall of Famer

    Last edited: May 10, 2018
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  12. millhoud

    millhoud Mu-43 Regular

    68
    Jun 25, 2014
    Trieste
    this thing happened over a month ago, so i forgot that i also had put the focus in manual mode because i hated the lag on the shutter (12-40), so i hoped for a kind of lag-less actuation, but i guess one would rarely need it. Thanks again
     
  13. millhoud

    millhoud Mu-43 Regular

    68
    Jun 25, 2014
    Trieste
    thanks
     
  14. millhoud

    millhoud Mu-43 Regular

    68
    Jun 25, 2014
    Trieste
  15. exakta

    exakta Mu-43 Veteran Subscribing Member

    412
    Jun 2, 2015
    I for one would welcome it as an option. I used Canon's early GN based dedicated flash system with my old Canonet G3 and Canolite D flash. The flash had nothing but an on-off switch, no calculator chart! The camera tracked the charge on the capacitor using an extra pin on the hot shoe, enabling shooting before fully recharged if desired. The shooting aperture was displayed in the finder (aperture decreasing as the flash charged), just as with non-flash exposures.

    I used this a lot of concert photography where sensor based auto flash would give incorrect exposures. Flash was required because ISO 400 was the fastest film at the time (unless you "pushed" the processing with loss of shadow detail and increased grain). In most shots, it had the look of old newspaper shots, with the subject well lit and the backgrounds dark or totally black. I like the unnatural look but TTL flash cannot achieve it. Sadly since most cameras and lenses no longer have any indication of the focusing distance working with GNs manually is more difficult than it's ever been.

    14563322_10206839463739694_2749246343087387263_n.
     
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  16. millhoud

    millhoud Mu-43 Regular

    68
    Jun 25, 2014
    Trieste
    Yes, shooting before fully recharged could also be achieved i think, further speeding things up, and with modern electronics a simple GN-distance-aperture calculation should be a breeze.
    Great photo, am i right in thinking you posted it because an otf flash would have blown out the face of a black-dressed subject?
     
  17. inkista

    inkista Mu-43 Top Veteran

    501
    Jan 13, 2012
    San Diego, CA
    Actually, IIRC, Canon's eTTL-II already incorporates focus distance into the calculations. :)  But the lens has to be able to report the focus distance for the flash, so it also works without it. From a description of the Flash Basics on the Canon Europe learning center website:

    The pre-flash meter readings from accepted areas is weighted and averaged. It is then compared with the ambient light reading before the main flash output is calculated and stored in memory for the exposure. If the lens is able to provide distance information, this is used to determine the closeness of the subject and any highly reflective areas relative to the background. This information is used to refine the flash exposure. The result is better flash exposure for difficult subjects, such as white wedding dresses.

    I wouldn't be surprised if most digital-era TTL schemes already use distance information along with the pre-flash metering. The main issue might be getting the focus distance information to report from the lens. I don't remember ever seeing that information in my EXIF.
     
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  18. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    Focus distance and location is included in EXIF for all Olympus 4/3 cameras since about 2004, however not every program can display it.

    It's also not always entirely accurate, since it's calculated on AF steps and it can lose track of it's location.
     
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  19. Ross the fiddler

    Ross the fiddler Mu-43 Hall of Famer

    With all this talk on linking focal length to flashes, it is as far as I know since the focal length of the lens is sent to the TTL flash (Olympus FL50R & FL36R) to adjust the zoom of the flash head. That is, the angle of light spread used. Subjects colouring & background are going to affect the outcome & that is why flash compensation adjustment [+/-] is necessary.
     
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  20. millhoud

    millhoud Mu-43 Regular

    68
    Jun 25, 2014
    Trieste
    actually since the beginning the talk was about linking focus distance to flash not focal length
     
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