A few scanning tips

Does Nikon Commander use TTL or TTL BL mode?

Does Nikon Commander flash mode operate in TTL or TTL BL mode?   Nikon does not say directly. Nikon does say the internal flash always operates in TTL BL mode. The system obviously is designed to do TTL BL. The speedlights default to TTL BL mode when reset. Here are quick test results which seem to confirm Commander TTL is always TTL BL mode too. Why wouldn't it?

However, Commander flash is often used indoors, and typically indoors, there is NO CONCEPT POSSIBLE about balanced flash. Indoors, there is no significant ambient to be balanced with flash.

Nikon definitions, from page 37 SB-800 manual, page 33 SB-600 manual:

That is about all we know for sure. We dont know about intended word definitions for "subject" and "background". We know the camera computer has no notion of what our subject is, so my notion is "subject" means illuminated at the center of frame during preflash, and "background" means the continuous ambient in the rest of frame before preflash.

EDIT: Nikon Capture NX shows more Exif camera settings than Adobe does, and it shows flash mode as being Commander iTTL-BL. No fun, that spoils a good debate. :)

Note that TTL BL mode has no meaning for flash indoors, where the ambient is insignificant, and there is nothing to be balanced. So when operating indoors, again, there is nothing to balance the flash with. TTL BL is not the correct mode there.

Let's see what happens. Here are quick Nikon D300 tests in four different modes:

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D300 in cloudy shadowless daylight

Here is a very quick 5 minute comparison I did against a gray sky (storm coming, windy, the hat blew off of stand once.). Quick snapshots, no comp, no WB (Auto WB), no adjustments, no nothing but the shutter button.

Cropped substantially, from 12.2MP to 1.4MP (about 2/3 frame was sky), and then resampled smaller to video size. Umbrella bracket holding hat is at center of frame.

D300 - No flash

Auto WB picked up red Nikon Flash Color Temperature Information from the flash, but the blue cloudy daylight was dominant.
D300 - TTL mode hot shoe flash - not balanced - Hat subject is better exposed than it may appear at first glance.

D300 - TTL BL mode hot shoe flash - balanced - note same brim stitching in first non-flash picture.

D300 - Remote mode, adjacent immediate left of camera commander, causing shadow at right. Looks balanced to me

Remote mode appears to be BL mode to me. Note illumination of leaves. Some think the word "background" in the BL description means "back lighted", which this is (to some extent), but I think the word means "ambient" - that which is not in center of frame and lighted during preflash duration.

Simon Stafford in his book Nikon AF Speedlight Flash System says (page 164): "Note: In all instances when you select TTL as the flash mode in the Advanced Wireless Lighting system (regardless of which speedlights are being used), the flash exposure control is performed at TTL + BL automatic balanced fill flash, although TTL is displayed on the LCD panel".

Nikon has not said, but BL surely does seem the way to bet, and the metering system is designed to do TTL BL. In my notion, TTL is the exception, not the rule. Said another way, AWL commander cannot do TTL mode (it does TTL BL mode.)

But, indoors where we usually use commander, there normally is insignificant ambient light to be blanced, and the whole question is moot (intended meaning is: "Thus, a moot point, however debatable, is one that has no practical value.")

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D300 in bright daylight

FWIW, here is the same sequence after the sun came out (wind blew this stand over once.)

Same as before, 2/3 frame is blue sky, cropped to 2MP, no adjustments of any kind.

D300 - No flash

D300 - TTL mode hot shoe flash - not balanced (manual balancing should have flash compensation, at least -1 stop)

D300 - TTL BL mode hot shoe flash - balanced (no comp, but this has that automatic compensation.)

D300 - Remote mode, adjacent immediate left of camera commander.

To get the setup idea better, here is the last one again, full frame.
I thought the sky would not be the easiest metering problem for the camera.

 

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D300 in backlighted sunlight

As before, but much less sky, still greatly cropped, but 2/3 of larger frame is green tree.

D300 - No flash

D300 - hot shoe flash, TTL mode, no comp

D300 - hot shoe flash, TTL mode, -1.3 stop flash comp, reasonable for fill in sunlight

D300 - hot shoe flash, TTL BL mode, no comp (is similar to one immediately above)

D300 - Remote mode, adjacent immediate left of camera commander, no comp (similar to BL immediately above)

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D300 and D70S indoors,
a dim room with no significant ambient to be balanced

70 mm lens, hat is at 5.5 feet, flowers at 10 feet. Manual 1/200 f/8 ISO 200 Auto WB, no processing. Cropped from 12.2MP to 2.5MP, near full frame height, and approaching 1/2 of horizontal frame width. Then resampled smaller.

The tighter zoom and darker background is to prevent need of compensation from wide expanse of lighter walls. It could have been compensated, but I am showing unprocessed images here.

No flash is a very black frame - there are no lights, nothing possible exists to balance the flash with. Not shown.

 
Nikon D300 TTL, hot shoe

 
D300 TTL BL, hot shoe

 
D300 - Remote adjacent immediate left of commander, hence shadow camera right

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  D70S, older camera body.
Nikon D70S TTL, hot shoe

D70S TTL BL, hot shoe

D70S - Remote adjacent immediate left of commander, hence shadow camera right

The D70S TTL BL does suffer in the dark room, but its commander is better, close to TTL. Of course, TTL BL has absolutely no meaning in a dark room. No possibility of more than simply "a flash exposure", good or bad.

The D300 does not seem to suffer much anywhere, in the dark room. Which is NOT to say that a white background or a light picture scene cannot fake out the light meter... See how light meters work.

Thom says (his Nikon D300 Guide, page 606) about the Nikon cameras: "DSLRs previous to the D200 tended to continue to try to balance ambient and subject light, even in dark conditions. Ones since then don't do that, as they recognize low light conditions and change the strategy of the TTL BL.... seems to do a better job of lighting the subject independently of the background exposure when you're using flash".

Independent of background is the definition of TTL mode. However, how else could it be? There is no ambient to balance the flash with, indoors.

Should we always use TTL BL by default?

Pros: Automation always has pros. TTL BL tries to do automatic point&shoot fill flash. The newer camera bodies seem to do better with BL and so better allow always using it anytime. TTL BL does use the lens CPU distance information when aimed straight forward (not a factor for bounce.)

Cons: Automation always has cons. The problem is that TTL BL makes unknown automatic adjustments. Matrix metering makes more unknown automatic adjustments. TTL BL might compensate flash by -1.3EV in backlighted sun (shown above.) It may compensate flash by -0.7 EV in daylight interiors. New cameras may not compensate at all in dark scenes. So it entirely depends on the background which exists. TTL mode does not compensate for ambient, and when both ambient and flash are properly exposed, that total is 1 stop overexposed (TTL BL compensates for the ambient, TTL does not.) If you want point&shoot fill, that is what TTL BL tries to do, and the new cameras are better at it. However, if you want more consistent results which you can directly control yourself in expected ways, to supply your own fill compensation (the value you actually want to use) without unknown changes occurring, then TTL mode and Center metering will do that. It won't help you do it, but that is the point, the plus.

Outdoors in bright ambient, we might debate the issue if the Commander uses TTL BL or not, but it clearly seems to use TTL BL. The Commander is a point&shoot system.

Indoors, the BL subject is nonsense - as there is no significant ambient, and no concept of "balancing" anything. It does appear the firmware ought to stop trying then however.

Now I need to go see about those answering machine messages, from Hollywood, wanting to sign that hat. :)