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Nikon iTTL and flash compensation

MichaelRMichaelR Member
edited January 2018 in flash & lighting
Hi there, and a happy new year to all of you.

I am a bit stumped with iTTL/Nikon and (flash) compensation and for the life of me I am not able to figure it out.

Problem for me ist that I have a D750/Yongnuo iTTL flash combo which might or might not be incompatible in places, so that I might bark up the wrong tree. Going manual, as Trev points it out every so often, I have no problem balancing foreground/flash and ambient/background using the diverse compensation dials on cam and on the flash in iTTL or just aperture/time/manual flash.

However, this fails horribly if I enter any one of the automatic modes. In automatic (A, S or even P), I always end up with fill flash so that within given bounds ambient and flash is always balanced.

What I am trying to achive is to change the ratio between foreground flash and abient. Imagine in a given venue, e.g. a marriage, a kind of reportage of dancing people with their surroundings correctly fill flashed (works like a charm with iTTL and any one auto mode).

Then, once in a while I want to lower the ambient just for a few shots in order to emphasize face/portraits and let the surrounding slip darker... but generally still using iTTL for the face. I was under the impression that to do so I could use the camera compensation to dial in an overall darker EC, then either leave the flash as is (fill) or give it a nudge / positive FEC to gain light in the foreground to effectively "imbalance" the flash. But, alas, effectively I will still have a balanced shot however I choose the camera dials.

Am I missing a point here (it does not work at all as I am imagining it should do) or do I possibly fight with incompatible equipment? Unfortuantely, I cannot double check with a genuine flash...

Any help highly appreciated...

-Michael



Edit by Trev:
Michael, I fixed the paragraphing for you mate. I think you may have written this out in say Word, then copied/pasted, for some reason if you do that it will not recognise any paragraphs/spacing, but if you pre-write it out in a Text Editor (like Notepad) it will retain the paragraphs.

I also deleted the bottom post where you apologised for the lack of said paras, no problems. - Trev.

There is also an 'edit' feature, I think you have up to one week. It's a tiny 'gear/cog'  symbol top right of your post, click/choose Edit - You will only have 2 choices: Edit/Delete, I think, not the ones you see in my Moderator's options.
( If you did not know that already, sorry)




Comments

  • TrevTrev Moderator
    edited January 2018
    Michael,

    The problem is once you change to an 'Auto Mode', regardless which, that is *always* going to adjust the ambient along with flash.

    You will have to be in manual, then either increase Shutter Speed, or drop ISO or close aperture down to give that darker ambient background for starters, with flash still lifting the faces you focused/locked exposure on, leaving the Flash at current value mode in iTTL to determine correct exposure for that spot.

    If you increase your flash power in any way via Camera Compensation/Flash Head Settings, it will only increase output for your targeted focus point, same with decreasing the power, leaving the ambient the same, well, at least out of flash range, if camera in manual.

    Obviously you could not try this with lots of people/objects in foreground, while targeting a subject at back without over-blowing exposure in foreground without some carefully thought out bounce/direction.
    Like pointing flash head facing forward/up/to one side to bounce off a wall/ceiling further back, and not behind you over the shoulder/right or left like you would normally do.

    By decreasing the Camera Body's Compensation, you are in fact only decreasing your target with flash power dropping, while in manual on body, ie: Face, not the general area in background/sides, but if in an Auto Mode, then naturally you are also decreasing the ambient by the Camera Body's Compensation, which will have no bearing then on flash power since the body and flash head are then talking to each other, trying to figure out what you want.

    I do hope I interpreted your question properly mate, but I would have thought just the general ambient setting in manual camera body is the deciding factor on how 'moody' you wanted to be, with flash exposing correctly for the focus point, where the flash in iTTL will determine the exposure for that focus point, ignoring (hopefully) the rest of the image.

    Two points:

    1] By dialing in Camera Compensation will only add/subtract from the flash power with body in manual, flash in iTTL, with whatever settings you determined for ambient input by camera settings.

    2] The Camera Body's Exposure Compensation has absolutely no bearing at all on the overall ambient exposure while it is in Manual Mode, only affects Flash Power, adding/subtracting from it, of course while the flash is in iTTL mode.

    The beauty of this method is if you don't have enough flash power and still stay in iTTL mode, even if you maxed out your Flash Head's +3 compensation, by dialing in the +Value on the body increases that range, so in effect you can then have up to +6 e/v on the flash, good for 'reaching' further back since if you lock focus on a distant object, with lots of foreground it may not have enough power.

    (See above for bounce position explained for further away subjects - which I am bloody sure you well know, just putting in here for others' benefits).

    Final Option: Manual on both, adjust to suit. :'(

    Trev.






  • MichaelRMichaelR Member
    edited January 2018
    Trev, thank you very much. You have indeed answered my question.

    I was under the impression by the meagre iTTL-Manuals that EC and FEC work independently regardless of cam‘s auto mode. I am aware that even the metering modes imply some fiddly behavioral changes in the iTTL environment.

    Negative EC should lower the overall light/ambient, then iTTL should within reach light up the foreground, possibly with FEC-help. This would help tremendously in changing situations. Alas, there you go. It seems that there is no free meal indeed.

    I will have to stick to manual for ambient wizardry...

    Again, thanks a lot
    -Michael
  • TrevTrev Moderator
    No worries Michael, good luck.

    I have on a couple of occasions during receptions, relied on the Nikon's feature of Camera Exposure Compensation while in manual mode to boost my speedlite's power when needed.

    Remember though, there is a trap for young players, and that is if you forget to dial back the Camera's Exposure Compensation to Zero, the next time you use it, you will be left scratching your head why there is too much power like I have done a couple of times, Doh!

    Trev.
  • The camera body exposure compensation behaves like a global adjustment, impacting both ambient and flash exposure (assuming flash is set to TTL).

    The flash exposure compensation only impacts the flash power.

    (A minor note is that if you use Auto-ISO, the EC will impact the ambient exposure even in the camera's Manual mode, by adjusting ISO.)

    If you wanted to be in, say, A mode on your camera and you wanted to bring down ambient but leave the flash exposure the way it is, you dial in negative EC (to bring down ambient) and positive FEC (to bring back up flash/subject exposure). Joe McNally in some of his books talks about shooting this way sometimes. I find it a little inconvenient, and do prefer Trev's suggestion of using M on the camera while using flash.
  • TrevTrev Moderator


    Yep, agree Nikonguy, another variable to contend with in Auto ISO, never used it in my life.



  • @Nikonguy: this behaviour is exactly what I intended to achieve in the first place. It does not work like this, my minor experience shows.

    So, still back to error analysis (error 101: sits 30 cm behind the camera). Am I doing something stupidly wrong?
    - Negative EC shows no discernible effect whatsoever.
    - I did not check Auto-ISO. Will experiment on the weekend.
    - I did change Matrix vs. Spotmetering, though.
    - My setup is a living room with subject distance 1m and walls additional 1-2m behind the subject, so diminishing light following inverse square law regarding the flash should be clearly visible.
    - I am aware that FEC must be dialed in the flash, not on the body.

    Yongnuo incompatible if setup works with SB900? Flash just too powerful to bath the living room as a whole? I would drop the latter issue because I can reach my goal on full manual. 

    Still stumped...
  • Michael, you are likely bumping into the "flash shutter speed" setting, which is the minimum shutter speed the automatic modes (P, A, S) will use when flash is turned on.

    You can determine quickly if this is the case in your test by turning off the flash. If you suddenly see the camera settings go from f/4, ISO 100, 1/60 with the flash on to f/4, ISO 100, 1/10 with it off then this would confirm it. What's happening is that the flash shutter speed (default is 1/60) is acting as a floor and is messing with your ability to change the ambient exposure conditions. In my settings example, a correct ambient exposure needs 1/10, but with flash it will bottom out at 1/60. If you put in a negative EC of -1, then it will say, ok 1/20 is the right shutter speed. But it will still use 1/60 because the "flash shutter speed" setting enforces that as the floor. So you haven't changed the ambient (it's still at 1/60), but the -1 will cause the flash output to be less unless you bring up FEC to compensate.

    Where this would work is if you are not bottoming out on the flash shutter speed. So you could bring up your ISO so you get above 1/60, then see if the EC impacts it - and it should.

    I'll play around later to confirm this. By the way, I think only the big pro bodies lack FEC ability on the body. On my D800, I can directly dial in FEC on the camera by pressing the flash lightning bolt button, and dialing the wheel to adjust.
  • That sounds about right - it never occured to me that the bottom 1/60th has got something to do with it. I had read about it and forgotten. Error 101 indeed...

    This is a great forum!

    Thank you :-))
  • I wanted to keep you updated: After some experimentation, it seems that iTTL does a great job balancing ambient and flash in whatsoever circumstances.

    To fiddle with the ratio is - aside from adjusting FEC for foreground light levels - very frustrating. The camera does its outmost to stay within sensible shutter speeds in any automatic mode. There is the bottom flash speed as Trev pointed out. Additionally, there is the shutter speed low limit regarding shake, which is dependent on focal length. ISO rampages around.

    To get the background/ambient darker, shorter shutter speed is required. In an environment with flash, this is exactly not the direction the automatic adjustments tend to go. Besides, to reach and not go over top level sync speed, there is only so much leeway, typically not more than about 2 light levels. Which is not enough to darken the background enough in the first place.

    Long matters short: fiddling with the ratio to reach a blacked out background/ambient is so counterintuitive that going there fully manual is the quicker way. To fix the internal camera bounds as required in the menus is a royal PITA.

    iTTL is great for the every day balanced shot - but just not for heavy adjustments.

    Thanks all for their input.
    -Michael
  • TrevTrev Moderator


    Thanks for update Michael.

    At least you had a play to see what will/won't work for you.

    You do need to try these things for yourself, even it only to get a better understanding of your own equipment which you now have a grasp on the boundaries imposed by said equipment.

    Cheers,
    Trev


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