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Archive 2009 · Nikon TTL/BL explained !

DesmondD
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p.1 #1 · p.1 #1 · Nikon TTL/BL explained !

Hi , I'm new here and thought I would start off by sharing my research on Nikon TTL/BL mode . There is a lot of confusion about this mode and the official site is actually wrong since the D100 was replaced official TTL/BL site

I've done my own tests and published my own blog explaining it .

HopefullyThe 'new' TTL/BL

I also did a youtube video on it .

" target="_blank">Video on TT/BL

Hopefully it will clear up a lot of the confusion that understandably exists on the subject .

Sep 22, 2009 at 03:01 AM

Kittyk
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p.1 #2 · p.1 #2 · Nikon TTL/BL explained !

video is fine, but from my experience is that TTL works on every nikon camera a bit different. How firmware rates distance, setting and pre-flash is not consistent.
What is true however that regardless of focus/metering point, center of frame seems to be always used (together probably). I am also getting more consistent flash exposure when metering with center.
Also important is, that all dx cameras focusing flash head wrong regarding to angle of view. It works with SB900 as i heard, but didnt tried yet. On DX i get much better results when using manualy zoomed flash head.

Sep 22, 2009 at 12:48 PM

DesmondD
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p.1 #3 · p.1 #3 · Nikon TTL/BL explained !

Kittyk wrote:
video is fine, but from my experience is that TTL works on every nikon camera a bit different. How firmware rates distance, setting and pre-flash is not consistent.
What is true however that regardless of focus/metering point, center of frame seems to be always used (together probably). I am also getting more consistent flash exposure when metering with center.
Also important is, that all dx cameras focusing flash head wrong regarding to angle of view. It works with SB900 as i heard, but didnt tried yet. On DX i get much better results when using manualy zoomed flash head.

TTL doesn't use distance , only the centre of the frame . I must agree about them all working a little different . When I was doing my tests a pro photographer "Mike" decided to duplicate all my tests with his D300 and D3 . He found that TTL was giving different results between the two cameras while TTL/BL +1/3 gave the results closest to what he wanted consistently with both cameras .
Distance info is dropped when you are not using direct flash which we avoid anyway , when using bounce flash it is also good to make sure the flash head is at its widest .

I have 10 pages of 'flash' samples most with text on them if you want to see results of both systems in varying situations .photobucket

With TTL the subject needs to be central and output varies depending on size and colour of the subject .
TTL/BL however meters for the brightest focus point receiving a pre-flash and does not need the subject to be central , and you don't need to use FV lock.

http://i107.photobucket.com/albums/m300/dvdowns/Flash/zextremebl001.jpg
http://i107.photobucket.com/albums/m300/dvdowns/Flash/zextremebl002.jpg

Sep 22, 2009 at 12:59 PM

bitmaker
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p.1 #4 · p.1 #4 · Nikon TTL/BL explained !

Interesting write-up but some of your points require clarification.

Firstly, how is Russ MacDonald's (excellent TTL/BL explanation) blog entry the "official TTL/BL site"? What he writes is correct and explained in an easily understandable manner, but I see nowhere that it is "official".

Secondly, a number of your sample/test photos (those shot in the studio with "Stinky" placed against a backdrop) have little to do with TTL/BL techniques (the exception are the shots of "Stinky" in the window, which are nice examples of TTL/BL).

Your conclusions would have added depth if you included information/testing using Nikon's various methods of TTL flash exposure control: 3D multi sensor balanced fill flash, multi sensor balanced fill flash, Matrix balanced fill flash, and center weighted fill flash come quickly to mind. Each of these modes may be useful to the photographer depending on their goals for the image. Also, hardware limitations (such as non D/G lenses) may force the photographer to use one of these modes rather than a mode they prefer. Would be good to know how to balance the exposure using fill flash when forced to use one of the lesser preferred modes. Additionally, mention of Nikon's Matrix metering algorithms deserve inclusion in any TTL/BL discussion.

DesmondD wrote:
...when using bounce flash it is also good to make sure the flash head is at its widest.

The flash head zoom angle for bounce flash is more a matter of variables such as the photographer's reason for bouncing, the environment, number of subjects, subject(s) location, just a name a few. The flexibility of manually adjustable flash zoom angles is yet another nice creative tool we have at our disposal.

DesmondD wroteWith TTL the subject needs to be central and output varies depending on size and colour of the subject .

Not necessarily. Some other important factors that come into play are the flash exposure control utilized, bounce vs. direct flash, subject(s) location in the scene, brightness levels of the subject(s) and back ground.

DesmondD wroteTTL/BL however meters for the brightest focus point receiving a pre-flash and does not need the subject to be central

To clarify, 3D multi sensor is the only flash exposure mode that uses focus distance info (and only when D and G lenses are used). None of the other flash exposure modes use distance info for fill flash, so distance then becomes largely irrelevant. To assume that the brightest focus point is the sole variable in the system creating proper fill flash exposure falls short.

Regards,

Greg

Sep 22, 2009 at 04:05 PM

williamkazak
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p.1 #5 · p.1 #5 · Nikon TTL/BL explained !

I have heard that when you start compensating TTL or TTL-BL, you are fighting against the system as it was designed to do all the compensation itself. The system begins to recompensate your compensation. Is this true?
If you want to compensate, why not place the flash in M mode and begin your compensation there?

Sep 22, 2009 at 04:30 PM

DesmondD
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p.1 #6 · p.1 #6 · Nikon TTL/BL explained !

williamkazak wrote:
I have heard that when you start compensating TTL or TTL-BL, you are fighting against the system as it was designed to do all the compensation itself. The system begins to recompensate your compensation. Is this true?
If you want to compensate, why not place the flash in M mode and begin your compensation there?

The 'auto' modes get you a little closer to where you need to start with flash . It's all good using manual flash if the subject isn't moving but when something/someone moves twice as far you need 4X the power things get comlicated very quickly - depending on whether you are bouncing or using direct flash , so when the action speeds up the auto modes can save you from making a total mess of the exposure .

Sep 22, 2009 at 11:20 PM

DesmondD
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p.1 #7 · p.1 #7 · Nikon TTL/BL explained !

bitmaker wrote:
Interesting write-up but some of your points require clarification.

Firstly, how is Russ MacDonald's (excellent TTL/BL explanation) blog entry the "official TTL/BL site"? What he writes is correct and explained in an easily understandable manner, but I see nowhere that it is "official".

Secondly, a number of your sample/test photos (those shot in the studio with "Stinky" placed against a backdrop) have little to do with TTL/BL techniques (the exception are the shots of "Stinky" in the window, which are nice examples of TTL/BL).

Regards,

Greg

I'll try to answer everything here

His site may be easily understandable but it is no longer correct - technology has moved on !
Russ was on the Texas Instruments team that designed the TTL/BL chip back in the 80's and many people refer to that as the 'official' site for TTL/BL , even the Nikon agents in many countries refer people to that site when asked about TTL/BL . He also considers himself to be an expert on the subject because when I posted the results I was getting on Nikonians he stepped in and told me he knows everything about TTL/BL and it can't work without bright backlighting . When I posted examples proving him wrong he locked the thread and told me I couldn't post there anymore because my pictures are 'horrible' .
As you mention , his site is well written and it WAS correct up till the D100 was replaced . It is no longer correct with regard to newer cameras because it has become apparent that Nikon have changed the information the camera body sends to the flash .He eventually admitted via email that they have obviously changed the system but has not admitted it on his blog yet .
That is why you suggest that my tests are being done with the wrong subject matter , because you and many other people have been confused by Russ's site sayig that the subject needs to be central and there needs to be bright backlighting - not any more .

You built in speedlight is always in TTL/BL mode [ unless you are in spot metering ] , the SB400 defaults to TTL/BL mode and wireless "TTL" actually meters in TTL/BL mode .
I want you to do a test : Russ says that TTL/BL can't work indoors with no bright lights in the background . Try it , if the flash works in TTL/BL mode I am right , if it fires at its weakest .... you probably have a D100 or older camera because that WAS how TTL/BL was programmed for those cameras .
I don't emphasize the use of lens distance info much because that only works when the flash head is pointed forward - as soon as you use bounce flash [ which we should be doing ] , the flash drops the distance info and reverts to metering off the brightest focus point receiving a pre-flash reading and I can prove it .
Here we have Stinky only in the picture ....

http://i107.photobucket.com/albums/m300/dvdowns/Flash/zblexpp001.jpg

and we introduce something white to the frame

http://i107.photobucket.com/albums/m300/dvdowns/Flash/zblexpp002.jpg

TTL/BL backs off because of the white under a focus point .

Have a look at my TTL/BL consistency theory and then tell me if you still disagree TTL/B consistency

Sep 22, 2009 at 11:37 PM

DesmondD
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p.1 #8 · p.1 #8 · Nikon TTL/BL explained !

bitmaker wrote:
To clarify, 3D multi sensor is the only flash exposure mode that uses focus distance info (and only when D and G lenses are used). None of the other flash exposure modes use distance info for fill flash, so distance then becomes largely irrelevant. To assume that the brightest focus point is the sole variable in the system creating proper fill flash exposure falls short.
Regards,
Greg

Once you tilt the flash head , or as you say use a lens without distance info the difference between TTL/BL and TTL is that TTL acts like centre-weighted metering while TTL/BL finds the brightest object under a focus point reflecting a pre-flash reading , it would make sense to design the system that way to 'find' the subject .

Edited on Sep 23, 2009 at 01:13 PM · View previous versions

Sep 22, 2009 at 11:43 PM

Beni
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p.1 #9 · p.1 #9 · Nikon TTL/BL explained !

From your article:

I am saying I have discovered the 'predictable' aspect of TTL/BL bounce flash - that it meters off the lightest part of the picture - as long as it is under a focus point .....

Personally methinks I'd find this harder to work with than a 'center weighed flash' which you are saying TTL is. Especially when you want to expose for the mid tones and not the whites. At least with TTL you know that it is trying to average the data, not expose for the highlights and screw the rest of the scene.

Or am I too used to the canon system that works the way you are describing TTL when used in 'averaging mode'? I'd never use the 'evaluative' system as it sounds exactly as you are describing TTL/BL.

I prefer to know what the flash will do exactly rather than having to go through the convuluted thought process that seems to be necessary with TTL/BL which seems to underexpose with white but ignore black - if there is something else neutral in the frame and if it's big enough and if it's covered by a focus point. Seems harder to predict though less work when you do get it right.

Sep 23, 2009 at 03:06 AM

DesmondD
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p.1 #10 · p.1 #10 · Nikon TTL/BL explained !

Beni wrote:
From your article:

Personally methinks I'd find this harder to work with than a 'center weighed flash' which you are saying TTL is.

Many people assume that I am telling everyone they should be using TTL/BL , I'm not , I'm just sharing my findings - use whatever works for you but it also can't hurt to understand how the different modes work in case you find yourself in a situation where a particualr mode will be more reliable . For example , with direct flash outdoors TTL/BL will be more reliable while TTL will vary depending on the size of the subject and whether they are central or not .

http://i107.photobucket.com/albums/m300/dvdowns/Flash/zmorbl005.jpg
http://i107.photobucket.com/albums/m300/dvdowns/Flash/zmorbl006.jpg

http://i107.photobucket.com/albums/m300/dvdowns/Flash/zprogram032.jpg
http://i107.photobucket.com/albums/m300/dvdowns/Flash/zprogram033.jpg

Also remember that when you are using wireless 'TTL' it is metering in TTL/Bl mode and the Sb400 works in TTL/BL mode so it's worth getting to understand .

Sep 23, 2009 at 03:25 AM

Beni
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p.1 #11 · p.1 #11 · Nikon TTL/BL explained !

Did you apply equal plus exposure to the flash in both of those plate shots?

Sep 23, 2009 at 07:01 AM

williamkazak
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p.1 #12 · p.1 #12 · Nikon TTL/BL explained !

How is TTL-bl suppose to work in the following conditions with the SB800 and the diffusion disc in place?
1. Bride in white dress walking up the alter with father in black tux
2. Girl in black dress being seated by groomsman in black tux

Edited on Sep 23, 2009 at 12:25 PM · View previous versions

Sep 23, 2009 at 09:20 AM

mill4570
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p.1 #13 · p.1 #13 · Nikon TTL/BL explained !

DesmondD,

A very good article. It is interesting that individuals are responsible for working out things that should be in the instruction manuals.

I am confussed about one portion of your test. In the section on wireless cls, I assume you had both flash units equal distance from "Stinky" and set to 0 compensation. I also assume the white reflector was not an equal distance from the flash units but closer to B when on the right and closer A when on the left, and a focus point was on the reflector in each case. Is this correct?

Thanks for Your Work,
Richard K.

Sep 23, 2009 at 11:29 AM

DesmondD
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p.1 #14 · p.1 #14 · Nikon TTL/BL explained !

Beni wrote:
Did you apply equal plus exposure to the flash in both of those plate shots?

Yes , exactly the same settings - I just changed from TTL to TTL/BL

Sep 23, 2009 at 12:22 PM

DesmondD
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p.1 #15 · p.1 #15 · Nikon TTL/BL explained !

williamkazak wrote:
How is TTL-bl suppose to work in the following conditions with SB800 and diffusion disc;
1. Bride in white dress walking up the alter with father in black tux
2. Girl in black dress being seated by groomsman in black tux

The diffusion disc [ I'm asuming you're talking about the 'dome' diffuser ?] pushes a button on the flash head that cancels distance info so TTL/BL will seek out the brightest object which will be their faces if they all wear black and expose correctly for the faces . With the white dress it will back off and the picture will be affected by the amount of ambient exposure .
TTL/BL 'watches' your meter and if it is on zero fires very weakly as fill flash . As the meter drops below zero TTL/BL compensates accordingly and increases flash power .
I recently did a video on how the metering mode affects TTL/BL output .

" target="_blank">TTL/BL and metring - video

Sep 23, 2009 at 12:27 PM

DesmondD
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p.1 #16 · p.1 #16 · Nikon TTL/BL explained !

mill4570 wrote:
DesmondD,

A very good article. It is interesting that individuals are responsible for working out things that should be in the instruction manuals.

I am confused about one portion of your test. In the section on wireless cls, I assume you had both flash units equal distance from "Stinky" and set to 0 compensation. I also assume the white reflector was not an equal distance from the flash units but closer to B when on the right and closer A when on the left, and a focus point was on the reflector in each case. Is this correct?

Thanks for Your Work,
Richard K.

The flashes were the same distance away and I normally name the left one "a" and the right one "b" . There is no compensation on any of the shots - I let the metering decide what it wants to do .

Normally something like this and I don't move them .

http://i107.photobucket.com/albums/m300/dvdowns/Flash/zclosefocus002.jpg

Something like this - flashes on either side as shown above , a bit further back and then I start introducing objects without changing any settings or moving any flashes [ except where I state that I move the flashes ]

http://i107.photobucket.com/albums/m300/dvdowns/Flash/zgroups006.jpg

http://i107.photobucket.com/albums/m300/dvdowns/Flash/zgroups007.jpg

http://i107.photobucket.com/albums/m300/dvdowns/Flash/zgroups008.jpg

And this was to show how each flash 'group' seeks out the brightest object in the frame and exposes accordingly , and they are not affected by objects that they can't 'see' with the pre-flash for their particular group .

http://i107.photobucket.com/albums/m300/dvdowns/Flash/zgroups009.jpg

Sep 23, 2009 at 12:34 PM

bitmaker
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p.1 #17 · p.1 #17 · Nikon TTL/BL explained !

DesmondD wrote:
...because you and many other people have been confused by Russ's site sayig that the subject needs to be central and there needs to be bright backlighting - not any more .

Actually, I'm pretty comfortable working with Nikon's i-TTL system. Which means that when using the TTL/BL feature of the i-TTL system I no longer give alot of thought to whether my subject is in the center of the frame nor does scene background brightness concern me beyond ambient exposure. That's the major difference between D-TTL and i-TTL... the latter makes it much easier to gain correct exposure of off-centered subjects and goofy background brightness.

DesmondD wrote:
...as soon as you use bounce flash... the flash drops the distance info and reverts to metering off the brightest focus point receiving a pre-flash reading

This is only partially correct. Once the flash head is moved off it's "direct" position the system indeed drops distance info. However, the system does much more than simply revert to metering off the brightest focus point. You continue to emphasize the focus/defocus info the AF sensors are sending to the system while completely ignoring the other two variables included in the Matrix meter during flash exposure: Brightness and Contrast. The importance and influence of brightness and contrast in the automatic balance fill flash modes is proven by your shots of Stinky sitting on the black background.

In the first shot (Stinky alone) the exposure of him looks very nice. Skins tones are rendered quiet well, his blue shirt looks nice, and the small patch of white on his shirt is exposed nicely. The TTL/BL system did its job. In the second shot the system saw the addition of a huge (for the scene) white object that is almost as big as Stinky himself. The brightness and contrast changed drastically... to the extent that the system tried to preserve the highlights (of that big white thing it saw added to the scene) with the end result being that it decreased flash exposure and left Stinky under exposed.

With regard to your follow on post of the plate and Stinky outdoors under the overcast sky, the differences in exposure has to do with how Nikon configured Standard TTL and the various automatic balance fill flash modes. Standard TTL mode uses only the info from the TTL flash sensor(s) (some Nikon digital cameras have a single TTL flash sensor while others have two) while the automatic balance fill flash modes use the info from the TTL flash sensor(s) and the camera's TTL meter. Standard TTL keeps the camera's TTL metering system separate so that the user may gain greater control of exposure if they choose. The TTL shot of the plate was underexposed because the TTL flash sensor (and no doubt the center segment of the Matrix meter) saw the predominate white of the plate. Seeing alot of brightness it held back the flash exposure, rendering the scene under exposed. The TTL/BL shot included the camera's TTL metering and rendered the scene more accurately. The TTL/BL shot is a classic example of Nikon's CLS working as advertised. In the shots of Stinky under the overcast sky, the shot using TTL was clearly impacted by the Matrix meter's outer four segments seeing mostly sky. The end result was the camera's TTL flash sensor (working alone in TTL flash) was fooled into thinking more flash was required than was necessary. Those outer four segments of the Matrix meter completely over ruled the center segment and the subject was given too much flash exposure. In contrast, the TTL/BL shot included the camera's TTL meter in the scene evaluation and once again TTL/BL got the shot.

There's much more at play here than just focus/defocus info. Brightness and contrast will also be considered by the system, to the extent than one or more of the three variables will be given more weight in each unique scene.

Sep 23, 2009 at 12:48 PM

DesmondD
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p.1 #18 · p.1 #18 · Nikon TTL/BL explained !

bitmaker wrote:
There's much more at play here than just focus/defocus info. Brightness and contrast will also be considered by the system, to the extent than one or more of the three variables will be given more weight in each unique scene.

I'm not entirely sure what you mean by ' focus and de-focus ' , if it's about focus distance info most of the time I use bounce flash to cancel the distance info .
I won't profess to know exactly how the metering works - I can only report on my findings .
The picture outdoors with bright back-lighting is what TTL/BackLit was originally designed for but now as you can see it works indoors as well and that is no longer the sole purpose of the new TTL/BL[ Balanced Fill Flash ] - you need to forget about "BL" meaning 'Back-Lit' unless you're shooting with a D100 - technology has moved on .

I did many of my tests with the D40 once I realized how heavily weighted the TTL/BL flash metering was toward focus points and this test illustrates why I feel so strongly that it is this way .

http://i107.photobucket.com/albums/m300/dvdowns/Flash/zfocuspoints001.jpg

And one focus point touching white ....

http://i107.photobucket.com/albums/m300/dvdowns/Flash/zfocuspoints002.jpg

Sep 23, 2009 at 01:02 PM

williamkazak
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p.1 #19 · p.1 #19 · Nikon TTL/BL explained !

A very interesting discussion. It kind of suggests a starting point for making our own tests using TTL-BL. I am wondering what Desmond suggests for indoors/outdoors when things are moving along rather quickly for an event with people.

Sep 23, 2009 at 01:21 PM

bitmaker
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p.1 #20 · p.1 #20 · Nikon TTL/BL explained !

DesmondD wrote:
I'm not entirely sure what you mean by ' focus and de-focus '

Perhaps a better description would be "focus/out-of-focus" features within the scene.

Could you please do another test? Please shoot the round pouch against white background with your D90. Duplicate the exposure settings (including lens FL) you used with the shots done with the D40. Curious to see if the D90's 11 focus points will deliver different (as in: more averaged due to the 8 additional focus points) exposure evaluation data than the D40's 3 focus points.

Thanks

Sep 23, 2009 at 02:00 PM

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