Exposing for background when using OCF-TTL vs manual

[Braineack]

does the D7000 have background/foreground flash compensation?

I the D600 you can set E4 to do change the flash compensation to background only. So the flash brightness stays the same, but if you change the EV it will change the exposure to light/darken the background and the subject should stay the same. Neat little feature.

 

[WayneF]

A few thoughts: SPOT metering can lead to wildly divergent meter readings, and I would use center-weighted metering and a test exposure or two to determine the "right" exposure for the background, and how you want to render it. If the background is bright tones, like sky-tones, do NOT over-expose it and blow it out! Spot metering can vary HUGELY,depending on exactly what is being read.

Agreed, beginners seem to think Spot metering makes the image somehow be correct, or at least makes the spot correct. But it is NOT about correct - all Spot metering does is make the ambient spot be middle gray. Which might be correct, but will not be if metering a face for exampe. If a face, we have to know to add about +1 EV flash compensation to be "correct". Spot metering is very far from point&shoot, it is an advanced concept requiring some knowledge. It will get beginners in trouble.

Canon's 580 EX was very erratic and VERY focus-spot dependent; the 580 EX-II uses the ALL-NEW EX-II TTL protocol, much better consistency. Nikon's older D-TTL control was very erratic and all over the damned map...so, the ACTUAL FLASH UNIT and the camera can one, or both, control how things turn out, and affect how you use them.

I am not familiar with Canon, but that seems odd, since the cameras do the TTL metering, and then program or adjust the flash level. The flashes only flash.

Nikons, I know. Film TTL metered the reflection of the flash directly from the film surface in real time, and when that center area metered enough, it quenched the flash off. This was possibly the most accurate, however, it could not meter individual flashes individually.

D-TTL was Nikons first digital camera flash, first digital models. The anti-aliasing filter on the digital sensor did not reflect properly, so Nikon painted a light gray paint spot on the front of the focal plane shutter, and metered a preflash from that reflection. (still no metering of individual flashes).

iTTL corrected that eleven years ago, and totally changed everything. No more reflections, instead the flash light meter was in the viewfinder (with mirror still down), and it metered a preflash, including preflashes from individual multiple remotes.. The commander is required to monitor individual flashes.

Let's try again. Thank you BTW. My question has to do with the mechanics of the speedlight and (sb 700) how TTL determines the right exposure or rather, flash output. Let's say my speedlight is off camera and it is mid-day. I want to expose in camera for my ambient light and background and use the flash as fill for my subject so I adjust accordingly. Now, my SB700 is set to TTL and is positioned off camera, how and what does my flash interpret the scene and how much output to expose for? When I adjust my Nikon D7000 to expose for say, the ambient light, can TTL still be used to properly add the right amount of fill light to my subject or in this situation, or can I only manually adjust my flash to achieve proper fill?

In other words, what settings would you do in camera and on flash to accomplish this? I usually shoot aperture priority and in this circumstance, wanting to properly expose for background and not blow out the sky (mid-day problems)...I might spot meter off the sky or use matrix. That would take care of my camera settings...now for the flash??

The Nikon flash system (controlled by the camera metering) includes TTL and TTL BL modes. Some flashes (SB-800, SB-900) have a menu to select which mode the camera metering will use. Others (SB-700, SB-400, internal flash, and Commander) have a menu that just says TTL, but these are always TTL BL by default. Most third party flash models too, do TTL BL flash (the system is TTL BL).

However, camera Spot metering mode will change them to instead be TTL mode. The flash is NOT doing Spot metering, but the ambient is. If Spot metering is set, the flash just changes from TTL BL to be TTL mode (a metering method). It is the camera that meters and controls all of this. The Exif reports which flash mode was used.

TTL BL is balanced flash (in bright ambient). Balanced with ambient only just means the flash power is reduced, to serve as fill level, but specifically because the sum of a proper ambient exposure and a proper TTL exposure is two proper exposures (of the near subject), which is 2x proper exposure, which is one stop overexposed, by definition. So, TTL BL mode backs off on the flash power, which is approximately correct fill level. Typically TTL BL flash in bright sun is reduced nearly two stops ... automatically, pretty much perfect for fill flash in bright sun. That is what TTL BL is.

Whereas TTL mode comes ahead on, full metered power, regardless of if any ambient or not. In bright sun, you have to know to set about -2 EV flash compensation yourself, otherwise you get overexposed subject. TTL BL does that automatically, point&shoot.

TTL mode is good for indoor flash, when we want full metered flash level. And since the ambient is normally low indoors (where we need flash, so low enough to ignore, don't care - but DO TURN AUTO ISO OFF), then we can set Spot metering to get TTL mode on flashes that default to TTL BL, and the ambient is too low to be significant, so we don't care what Spot metering implies, it means nothing. Or camera mode M is great indoors, and Spot metering will not do anything in camera M mode (the TTL flash is still automatic flash). But Spot will change the flash metering to be TTL mode. TTL flash always meters its center spot regardless (not exactly same as Center Weighted metering, but reasonably similar).

Back to bright sun, just using camera P mode for the bright ambient, and using TTL BL flash mode (default on SB-700, SB-400, and camera internal flash - unless camera is set to Spot metering), normally gives very good point&shoot fill results on pictures of humans in bright sun. Camera A or M modes would do the same if you set the same aperture, which is saying that the photographer has to understand they have to set up near f/11 (ISO 100 and Sunny 16 bright sun) to keep shutter speed within maximum sync speed (otherwise they just see a flashing Error - wider aperture cannot work since the shutter speed cannot go faster... but P mode knows how to do this).

Some like to reduce the bright ambient exposure about two stops, and then do proper (full TTL) flash level. This makes the subject standout against the darker background, and it helps stop subject motion in fast sports. You would not call it fill flash however.

There is a lot more on this very subject at Four Flash Photography Basics we must know - Flash pictures are Double Exposures