Nikon flash system – TTL vs TTL BL
Nikon’s TTL flash system is generally accepted as being quite exceptional. The camera and speedlight working together according to various algorithms to control the flash exposure. The TTL flash exposure will depend on various factors – the tonality of the subject and scene; the brightness of the scene; and how the camera interprets the sections of the metering pattern. The other factors quite possibly also includes data from the lens.
How these factors inter-relate, we can only guess at. We can make educated guesses; and many photographers have taken time and effort to do test shoots to see how the cameras and speedlights work. To make things even more interesting, Nikon offers two modes of TTL flash metering: TTL and TTL BL.
The way I understand this to work, is that with TTL BL flash metering, the camera takes the ambient light into account when calculating the flash exposure. With TTL flash metering, the flash metering would appear to be de-coupled from the ambient metering.
Similarly, with Canon, you have Average / Evaluative flash metering for TTL flash. (This is set on the camera body via the custom functions.) Again, the way I understand this to work (and I’ll gladly be corrected or fine-tuned on this), is that with Evaluative TTL flash metering, the camera takes the ambient light into account. And with Average TTL flash metering, the camera is less biased by the available light..
So which TTL flash exposure mode to use? TTL or TLL BL?
In the end, I work in a fairly simplistic way …
With Nikon I keep it to TTL BL, and with Canon I mostly keep it to Evaluative TTL flash metering.
I then adjust my flash exposure compensation to taste. I do this by pre-judging the tonality of my subject and scene, and making an educated guess as to how much FEC I would need. Then I fine-tune this by looking at the image on the camera’s preview.
This does strongly imply that you have to ride the FEC as you check your results while you shoot. Shoot, check and adjust.
Ultimately you HAVE to get used to how your camera and flash responds, by getting familiar with your equipment and shooting a lot. This to me is the key point here .. being able to roughly predict how my camera will react, and what the flash exposure would be like as a result. It comes with experience and shooting a lot.
My take on it is that I am better of using one of the modes the majority of the time, and get a feel for how my camera and flash would react. Rather that, than jumping between the modes, and hoping the camera and flash will sort it out, without much input from me as the photographer.
The general approach:
Keep to TTL mode if the flash is a dominant light source.
Change to TTL BL when the flash needs to act as fill-flash or when the flash is in relation to the ambient light .
This is the approach as generally advised on various websites and forums, and is how I used to do it with the D100 and D2H and D2x.
As it is, I mostly keep to TTL-BL on my Nikon D3 bodies. There isn’t a huge difference between TTL and TTL BL modes on the Nikon D3, like there was with the Nikon D100 for example.
With the D100, I would be change between the two modes, picking TTL when the flash was a dominant source of light … and TTL BL when I wanted fill-flash, or needed the flash exposure in relation to the ambient exposure. WIth the Nikon D3, I would just use TTL BL mode and adjust from there.
In my opinion, with the latest range of Nikon D-SLRs, it doesn’t make such a difference whether you use TTL or TTL BL. Since TTL flash metering is dependent on the tonality of your subject / scene (and all the other factors), you will have to ride your FEC anyway.
Once again, this means that there has to be some familiarity in how a specific camera and speedlight works together. This is how I noticed that I needed to adjust the FEC on my D3 bodies differently than I was used to on the D2x and D2H.
So whichever TTL flash exposure mode you use, for the same situation, you’d just set your FEC to different values … and still get correct exposure by looking at your camera’s preview, and making a visual judgement of how much more or less FEC you need.
We need to accept a certain flexibility in our technique … as opposed to expecting that by meticulously analyzing how our camera and speedlight work in test situations, that we could get every image perfectly exposed from the very first frame. I believe this one of those areas where there is a danger of over-thinking it and expecting real world situations to fall withing specifically anticipated behavior … when it is much simpler and better, to simply adjust your FEC as you need, on an on-going basis while you shoot.
22 Comments, Add Your Own
1Bruno Delzant says
concerning Nikon CLS, I have found some time ago a good blog on this matter:
I have learned there very interessting stuff on the different TTL mode that Nikon offers.
Perhaps useful to read once to have objective feedback on stuff that we all try to master :-)
2Neil vN says
Hi there Bruno .. The Nikon CLS Practical Guide is about as definitive a series of articles on the topic, that you’d find on the internet. Which is why I’ve had a link to the site for quite some time now in the ‘Other Websites’ section on the right. ; )
I did change some of the text in my article now to accentuate some things hidden deeper in another paragraph.
What I was aiming for in this article, was to have a reference article for the numerous times I get asked the question … rather than it being a definitive article on the topic of TTL vs TTL BL modes. So in essence, this is how *I* approach it. It is simplistic, but it allows me to concentrate on shooting, instead of stopping short on the choice of modes.
An example from a recent wedding. I wanted a quick portrait of the bride outside, for an idea I had in mind. It was snowing, so we were limited to what we could do … so I stayed under the covered entrance way outside. This meant I could bounce flash into the ‘ceiling’ of the entrance way.
I wanted to accentuate the cold / blue tones, so I used a 1/2 CTS filter to push the difference in colour temperature between the ambient light and flash exposure, even more.
The relevance of the image here? Someone asked me on my Facebook photography page how many shots I take to get the images I do. My reply was that THAT image was one of a sequence of nine images that all look quite similar.
In other words, I anticipated what my camera and flash (Nikon D3 and SB-900) would do … and just did it. I didn’t get stuck on choosing between TTL or TTL BL.
Since I pretty much keep my D3 and SB-900 on TTL BL all the time, I had a fairly good idea of what I could expect.
My settings: 1/250 @ f3.5 @ 800 ISO
My FEC was somewhere between 0 EV and +1 EV. I can’t tell you now from the EXIF, but if I were there, I’d do it again. (If that makes sense?)
BTW .. the background is out of focus cars in the parking lot. At f3.5 at 200mm, anything further in the background kind of melts together.
I’m mostly TTL bound as I’m under the impression my batteries tend to last a little longer and the recycle times are a little faster then BL. Mind you I haven’t done any serious testing to substantiate that so take it with a grain of salt.
In terms of speed of adapting your settings, Auto Flash mode works quite well too. I usually set the flash on auto and f5.6 then simply play with the aperture to dial +/- compensation on the run. It works well for me when there’s little time to figure exposure as it gives me a base I could set quickly and work from there.
4Neil vN says
Bogdan … neither mode should use more power than the other, for correct exposure. After all, we need to convert a specific amount of electrons to photons … and how the camera and flash calculates that, has no bearing on that we need *this* amount of light for correct exposure.
I suppose that Nikon has had to modify the flash system since the new cameras shoot at such a high ISO. My D80 however, still requires a bright background and flash pointed straight ahead and matrix metering to work properly. As soon as ambient light drops too low, the pictures are underexposed.
To bounce the flash, I find spot metering and straight TTL work the best. Off camera, it is manual flash and TTL that seem to work best for me. I don’t know why but off camera flash seems to always under expose by a stop or so requiring me to start at +1 compensation.
Because of ISO requirements and low tolerance for noise on my camera coupled with slow lenses, I have never been successful using your techniques for bouncing light. Despite following your blog and your book, as soon as I hit ISO400 I’m a goner. Still love your photography though, and remain a loyal fan. Thanks for blogging all the inspiration. I’m still working on it.
6Neil vN says
Gene .. it does sound to me like you’re going shopping for a 50mm f1.4 soon. ;)
These lenses are quite affordable, and will open a new world to you with the wider apertures.
7David Holmes says
Hi Neil, thanks for the great work in your book! I have an extra copy to share :-)
Very timely article for me. I’ve been following the meticulous analysis covered at https://www.fredmiranda.com/forum/topic/816501/. I like to have some idea of the science behind it, but you are spot on regarding knowing how your equipment will respond from experience. I’ve been getting best results indoors in BL.
8ed eckels says
I did a little experimenting at a recent wedding with the AA setting on my SB-800. I discovered that it’s less likely to blow out the face of the people wearing black and also less likely to under expose the bride in white.
9Neil vN says
Ed, I wouldn’t be surprised.
With TTL, the metering is dependent strictly on what can be seen is in the viewfinder. As such, your composition will heavily influence the TTL flash metering.
With an Auto mode, the flash measures the amount of light reflected from a larger area, and is much less affected by specific composition.
From my own experience and also from various e-mails to Nikon tech support, straight TTL does push out more power then BL, when I am bouncing flash I always have it set to TTL, not BL. Actually, something that is peculiar to the SB600 (I don’t think this happens with the 800) is that if you even just put the flash head directly upwards the BL on the screen disappears and it will only let you use straight TTL.
11Neil vN says
Christian .. I think you misunderstood my comment there.
TTL does usually give off more light for the same FEC, than TTL BL does. What I was trying to explain is that you will end up using the same amount of power / juice to get correct exposure. So while you might be at -1EV for TTL, you might be at say +0.3 EV for TTL BL. Different amounts of FEC .. giving you the same flash exposure.
Which comes right back to the gist of this post .. that instead of see-sawing over the choice of TTL vs TTL BL … it might be easier just to use the one mode and get accustomed to how it responds, and adjust your FEC accordingly.
It definitely flew over my head. Thanks for clarifying.
Long time reader…first time poster. :) When shooting outdoor using TTL-BL, with -1.0 to -1.7 comp, with the SB 900, I experimented with the flash head at 60 degrees and the white card pulled out. The lighting on my subject seems a bit softer when using the white card. I like your opinion on this method of shooting TTL-BL. thanks
Is there any flashes having the TTL-BL MODE other than nikon ??? for a nikon camera ??
Hi, thanks for your clarification .. i think it might be related more to the shoot & posing the person or the group you are shooting.. if you have a TTL-BL mode its more easy & fast.. I just wanted to ask if there is any other speedlite model or brand having the TTL-BL mode compatible with nikon cams other than nikon flashes
16James M says
Will the TTL BL mode function properly on the D7200 using a SB-800 flash unit? Many thanks.
16.1Neil vN says
Was far as I know, it should. Make sure your camera isn’t in spot-metering mode.
I’m intrigued why not in spot metering Neil, does it make that much of a difference? What should I use then ? Thanks been a very long time follower. Love your techniques.
188.8.131.52Neil vN says
Cristina — in my experience, it looks as if the spot-metering affects the TTL flash exposure. And then, as you change your composition, the camera might read a different tone than before. With Matrix metering, there is less risk of this happening.
Hi just a quick question. I have a Yongnuo YN200 and YN560 TX Pro.
where should I adjust the TTL exposure compensation? On the YN200 or YN560 YX PRo or on Nikon camera?
17.1Neil vN says
I don’t know the Yongnuo range of flashes, but they should work in the same way in that you can adjust the TTL flash exposure either via the Flash Exposure Comp on the flash, or via the camera itself.
After shooting thousands of weddings I can say that setting the shutter speed to manual – flash to TTL (with the defuser card pulled out or dome in place, flash head tilted upwards and mounted on a bracket), and choosing the aperture for the preferred level of DOF or focus preference, was the best set-up for me in an indoor situations such as receptions or any other event indoor. For outdoors, I preferred to set the camera again to manual mode, do the metering, with the Shutter and aperture selected off the subjects metering, and than set the flash at the power setting that is best for fill, without over exposing the subjects. In addition, I highly recommend shooting in NEF (Nikon RAW) for any minimal corrections to be done upon uploading into Lightroom. As to the ISO and color temp. I prefer 5800K and iso may bet set at 400-800 depending on the available ambient to allow for a fast enough shutter speed to avoid movement problems.