Inconsistency in flash metering

Discussion in 'Canon Accessories' started by JuliaBu10, May 29, 2013.

  1. Robin_Usagani

    Robin_Usagani TPF Noob!

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    When I said system, I meant it's own calculation. It is not affected by the camera metering.

    Go set the camera to manual setting with spot metering. Point it to a dark color in the middle with bunch of white around it with ETTL VS all dark color. I bet you the 2nd one is brighter.


     
  2. Robin_Usagani

    Robin_Usagani TPF Noob!

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    I completely disagree with this. I shoot with flash at 800 and 1600 all the time.

    OP, I have a feeling your flash is working too hard. ISO800 at f/5.6 in that environment? Way too dark. Do you have a faster lens? ISO 800 is fine, but not at 5.6. I even often shot at 1600 and 2.8 to really brighten the background. That is why it takes your flash forever to recycle. You probably needed a new battery pretty quick.
     
  3. cgipson1

    cgipson1 TPF Noob!

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    So we have different styles of shooting... so what? We already knew that! I prefer lower ISO... that not make it wrong. Keep in mind that when I was learning to shoot, 1600 didn't exist yet.. and when it did finally roll around, it had a lot more grain than 100 did (almost to the point of being unusable, IMO). So I am used to shooting at lower ISO's... and prefer them.

    You are still new to photography, Robin... you have picked it up fast, and you do nice work. But don't be telling some of the older crowd that we are wrong, and you are right... that would be rude!
     
  4. o hey tyler

    o hey tyler Been spending a lot of time on here!

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    I also shoot with flash on a higher ISO. Better carry, and it doesn't work the flash so hard.
     
  5. Robin_Usagani

    Robin_Usagani TPF Noob!

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    Usagani Photography | Our own wedding photography nightmare

    Yes.. the photographer used low ASA. It sucked.

     
  6. cgipson1

    cgipson1 TPF Noob!

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    Yea.. and it was not that long ago, was it? And not long ago you didn't know enough to pick a good photographer ( you said that yourself in a previous post)! And that individuals bad photography was because they didn't know how to use that low ISO, or their camera, or flash, etc.. and probably had low end gear to begin with.

    So now you are blaming poor wedding photography on the photographers choice of ISO? lol! That doesn't make any sense.. and you know it!

     
  7. Robin_Usagani

    Robin_Usagani TPF Noob!

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    Charlie, I simply disagreed with you. The OP is photographing an event. Your method will make the whole background dark. Why would you want to shoot an event like that? Maybe if you are in a small room it is fine, not in a big room.
     
  8. cgipson1

    cgipson1 TPF Noob!

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    I have lit up entire churches, and got good shots with ISO 100 film and a single flash (of course it was a T-45 flash, that helped! lol!)... it is more how you use it, Robin. Never had a problem with dark backgrounds either... and don't have problems with recycle times, or overheating either (that is what battery packs are good for!) Dragging the shutter works just as well at low ISO as it does high ISO if you know how to use it.
     
  9. Robin_Usagani

    Robin_Usagani TPF Noob!

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  10. Vtec44

    Vtec44 Been spending a lot of time on here!

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    I have nothing to contribute to the discussion because I don't know much about Canon's. :D I had a discussion with Robin yesterday on Facebook and we both agreed that he needs to switch to Nikon. hahahaha...
     
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  11. TCampbell

    TCampbell Been spending a lot of time on here!

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    The 2nd (darker) image is a bit unusual since Charlie's EXIF viewer says you used center-weighted metering (Don't do that when using flash. You're fighting the E-TTL II system and not letting it do it's job.)

    The reflected metering system on a camera wants to assume a "middle gray" (used to be 18% but now it's almost always 12% gray). When you point it at a dark point, it wants to assume it should be capable of being "middle" gray and probably just needs more light. So it'll fire more light to attempt to compensate. This has the undesirable consequence over over-exposing the things that really were middle gray and blowing out things that were high tones.

    I grabbed my 5D II body (I usually shoot a 5D III these days, but I still have and occasionally use the 5D II), one of my 600EX-RTs, set the camera to ISO800, f/5.6 and 1/60th (to mimic your settings) and did some test shots playing with the metering modes against both white backgrounds and black backgrounds.

    As expected, if I switched to spot mode and allowed the center point to be on a black background, all the non-black things in the foreground were over-exposed. In evaluative mode it was correctly exposed.

    The 5D II will use "E-TTL II" mode (more advanced that E-TTL) with that flash. E-TTL II will read focus distance information from the lens (assuming your lens supports it, but most lenses do.) HOWEVER... distance info can ONLY be used if the flash is (a) on the camera and (b) not being bounced (pointed straight at the subject.) Generally you want to bounce or feather the flash whenever possible -- or even get it off the camera or use it in conjunction with external lights (e.g. a side-light). The problem with this is that while the camera may "know" how far the focus distance is from lens to subject, it does NOT know how far away your external lights are, nor does it know how high up your ceiling is when bouncing. That means it can't use distance info (and it knows how to detect this and wont even try) when any of those situations are true. As soon as you tilt the flash head to any position other than straight-ahead, the distance measuring data is no longer used. NOW it's going by how much of a difference it reads at with two different metering measurements. It pre-meters the scene (using no flash). Fires the pre-flash while simultaneously metering the scene again. It compares the difference between the non-flash and pre-flash metering instances to see how much of a difference the pre-flash made. It then uses that info to decide how much power to use when the shutter is open. Since you used spot metering, it was not allowed to take into account anything about your subjects (and they're basically the only thing you cared about getting exposed correctly.) That's what I meant when I said you're not letting the E-TTL II system do it's job.

    What really surprises me about that 2nd image is that I would have predicted that with your settings that not only would you not get a correct exposure, you should have had an over-exposed shot (and I'm really surprised you didn't. I cannot re-create your result with my camera and flash and I'm using the same camera, flash, and settings that Charlie says you are using.) This makes me wonder if you haven't dialed in some flash exposure compensation and didn't realize it (the EXIF data doesn't include that info, but then it also doesn't include the lens info either and usually it does. Your image only contains partial EXIF data. The camera would have included that data when it saved the image.)

    Check your Flash Exposure Compensation... on the 5D II, the third button (from the left) on the top (in front of the top LCD) is the ISO/flash± button. Press that, then the rear dial can increase or decrease flash exposure compensation. You typically want this at "0" for normal flash power when indoors and using a single light. I decrease this usually to about -1 when shooting outdoor in daytime and using the flash as fill.

    In summary...

    1. get out of spot-metering mode and go back to evaluative.
    2. check your flash exposure compensation and make sure you didn't inadvertently change that.

    I use spot-metering in concert venues, but I'm specifically targeting that center point on my subjects face to meter their skin when I use that mode. If you use spot metering, make sure you are taking the meter reading off of something reasonably close to a middle-gray value. It doesn't have to be perfect (you've got lost of adjustment latitude in post production as long as it was reasonably close. Especially avoid black or white.)
     
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  12. Robin_Usagani

    Robin_Usagani TPF Noob!

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    Tim, show me a documentation that the TTL flash metering is sampling from the same area as your camera metering. I have a black canon battery charger in the middle of a white wall. I set my cam to manual, spot meter the charger and shot it with ETTL flash. Then I shot it with center weight average. Both shots are identical. I have not seen anywhere on the manual or websearch that says the flash reading is taken from the same area as the camera metering.
     

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