2 TTL-BL flashes

alaios

Senior Member
Hi all,
I would like to use two TTl-BL flashes. Once at the camera axis as basic fill and one at a tripod.
When I use a setting like -1 to both flashes I just get an overexposed shot.

I have to shot the off light to -1 and camera light at -3 to start getting well lit exposures.
Any idea why is this happening?
Regards
Alex
 

WayneF

Senior Member
How are you triggering two TTL BL flashes? What trigger, what flashes, and what camera? Can you describe what you are doing? I am concerned with system compatibility. The Nikon Commander is the method Nikon provides. Are you using it?
 

WayneF

Senior Member
Looks like a nice flash. There are English descriptions at X800N Standard--PIXEL ENTERPRISE LIMITED

I am not familiar with it (so if I had known, I would have stayed out of it. :) ), but it appears to support a Nikon-Commander type interface, with master, and remote A, B, C groups. I don't know how radio might affect that, but may not change anything? The master concept requires some direct camera to flash communication, which may or may not pass through the radio system? Optical infrared is directly to the flash.

I am familiar with the Nikon Commander system. In the Nikon system, the remotes are set to Remote mode (NOT to TTL mode), and all control is done in the Commander or Master menu. In that system, the camera Flash Compensation control affects all flashes. Also individual TTL flashes can be compensated in the Master menu for that group, which is added to any camera Flash Compensation. Also Exposure Compensation adds to these, but newer camera models have an E4 menu that can isolate EC from the FC.

There are third party radio triggers that try to mimic this with all flashes instead set to TTL mode, which you'd think could be about the same if the flash triggers were individually addressable. If flashes are in TTL mode, then the flash body menu supports another flash compensation input, which is added to the camera Flash Compensation, *IF* the flash can communicate directly with the camera. My suspicion about your issue is that it might not pass through a radio trigger? Such flash menu compensation is not enabled or possible in Remote mode with Commander... the camera and commander menu handles all control.
 

alaios

Senior Member
the system works. It is more a question what should be the ratios to not get too many burned highlight. For example a -2 at camera's flash and -1 at the remote flash seem to be okayish.. Any ideas?
Alex
 

WayneF

Senior Member
There are a few ifs and buts.

Main idea is that adding two lights is always brighter than just the one brightest light.

The camera automation sets shutter speed and/or aperture for the ambient light, and then automatic flash must work into that situation.

The Nikon flash metering system has two flash modes, called TTL and TTL BL. The default is TTL BL. When the menu simply says TTL, the default is still TTL BL.

1a. Case of one TTL BL flash in bright sunlight. In A or P modes, the ambient sets the camera exposure. The TTL BL flash power is automatically reduced, perhaps -2 EV, to be more appropriate. The -2 EV does not show in the menus, but it does, and the Exif will report it. Because otherwise, proper ambient exposure and "proper" flash exposure is 2x proper, or one stop overexposed by definition (two lights added). So TTL BL tries to tend to that, and reduces the flash power. This is called Balanced Flash. Technically, it means reduced flash.

1b. Case of two TTL BL flashes - two flashes still add. Sum depends on how they are aimed, into same one area, or into two different areas. Camera does not know, so IMO, the Nikon flash metering system (the Commander for two TTL flashes) routinely underexposes one stop to account for this. We can add it back as seen needed.

I don't know what your non-Nikon Commander does, but sounds like the same thing. If your flashes optical mode is compatible with the D750 commander, it would be an interesting comparison. Your experience indicates you need -1 EV overall. My own experience with Nikon Commander is that more often I need +1 EV overall (with TTL flash).


2. But also.. default TTL BL is "Automatic flash". Regardless of what you do, it does things depending on what it deems necessary. This means it can ignore or modify or override your own flash compensation efforts. Your efforts do NOT have zero effect, but sometimes they have minor effect (on TTL BL, which is default). So you are trying to control automatic flash which has its own mind about what needs to be done. When fighting automation, automation usually wins because it's too dumb to relent. :)

A few individual flash models have their own menu to specify TTL or TTL BL flash mode, but this is disappearing. I sure miss it, seems necessary to me. Any Nikon iTTL we see now is TTL BL default. The Nikon flash metering system default mode is TTL BL. However, TTL BL is automatic compensation, and TTL mode (or Manual flash) is superior if you instead plan to control your own flash. Actual TTL flash or manual flash gets rid of the hidden other force trying to manipulate the flash.

Actual TTL flash (instead of TTL BL) does what the camera flash metering says should be necessary, regardless of ambient or any other light. TTL BL does things based on assumptions about other lights. This is the camera metering, not the actual flash, which just responds to power commands.

Setting camera metering mode to Spot Metering will force TTL metering mode instead of TTL BL mode. The flash does NOT do Spot metering then, it has its own metering system more like Center Metering (regardless). Ambient of course will respond to Spot Metering (very important outdoors, but indoors, ambient is normally too dim to much matter what it does, so indoor ambient is normally much underexposed if with flash indoors - excepting high ISO of course, when flash becomes fill to ambient). But Spot metering will change TTL BL to be TTL mode, which changes how compensation works. Your compensation efforts will be more obeyed. This TTL / TTL BL mode change is not reported in the menus, but Exif will show it afterwards.

So two choices... get used to what the TTL BL system does, and learn to live with it. Do what you see you need to do. Once you know what to expect, this seems no big deal. Sounds like you get your desired results.

Or you can use Spot metering to force TTL mode, and then numerical compensation will be more what you expect. TTL compensation is relative to the metered TTL exposure (Not relative to ambient metering).

But note that outdoors in bright light, Spot metering has very large effect on the ambient, whole different game needing understanding of Spot metering.

Three choices actually, of course manual flash allows total control.
 
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alaios

Senior Member
First of all I like your answers and thanks.
I have spent a whole evening training and this is what I found.

(My flash guns when mounted on camera they suppport TTL and TTL-BL flash, there is a mode button to switch over those. I do not know though if this "holds" in reality, i.e it was corrected implemented)

When my flash guns work in remote mode, so camera's flash is the master and the other is remote it looks like that system supports only TTL and not TTL-BL (the display writes TTL).

A. Now when I am with one flash (on body) and TTL mode the way to shoot fast and get the results I like (like here is defined flash lifting shadows and giving a slight pop where is not clear that flash was even used) is to
be at manual mode and pick an iso that underexposes the scenes around -1 stop and then set my camera flash to FEC -3.

B. When I then use two flashes (one at the body as main fill and one at a light stick) the second light should be at -2 (with the camera flash at -3). For a reason I do not know is that my ISO has to be two full stops or bit more of what I had in scenario A, assuming same light. If I have no prior information for a scene I should go around -3 stops in iso scale.

What I do not understand is the maths behind those combos that I have tested thoroughly
Alex
 

WayneF

Senior Member
First of all I like your answers and thanks.
I have spent a whole evening training and this is what I found.

(My flash guns when mounted on camera they suppport TTL and TTL-BL flash, there is a mode button to switch over those. I do not know though if this "holds" in reality, i.e it was corrected implemented)

When my flash guns work in remote mode, so camera's flash is the master and the other is remote it looks like that system supports only TTL and not TTL-BL (the display writes TTL).

The TTL vs TTL BL menu is a very strong feature for the flash, a very strong plus. Nikon flashes used to do that too, but it is disappearing, and now only the SB-910 has that choice. Even the new $600 SB-5000 does not. Extremely few third party flashes have the menu. I mostly stay with older SB-800s that have it. The default for the camera flash metering system is TTL BL, and I feel sure your master mode is default TTL BL (the metering system does that), even if its selection choice says TTL. Nikon Commander does that too. Any menu in the Nikon camera says only TTL, even when the default is TTL BL. More convenient shorter menu I suppose...

So saying, I suspect it is correctly implemented, it is only a menu choice, an on or off choice, and then communicating with the camera metering system to tell it what metering method to use. The camera does all metering and control, the flash only responds to power level instructions.
This menu is a strong plus, it is the only way for force TTL other than Spot Metering (of ambient), which then involves much complication itself. Beginners tend to NOT understand Spot Metering. But indoors with insignificant ambient (low ISO), Spot metering has no other effect.

My own use is to only use TTL mode for indoor hotshoe flash, and maybe TTL BL for automatic fill in bright sun.

The term TTL is used with at least three meanings, which can be confusing, so we sort of have to know what the subject is.

1. TTL is for Through The Lens metering, just meaning automatic flash exposure. That's what the camera menus mean, it means automatically does whatever the flash system does. That default is TTL BL.

2. TTL is the name of the Film flash metering system. Some uses of TTL absolutely implies Film TTL.
Digital requires differences, first try was named D-TTL, and now iTTL (for Nikon).

3. But digital iTTL has metering modes TTL and TTL BL, so TTL can mean that specific iTTL variation.

TTL uses whatever the metering says flash exposure should be, so flash exposure comes ahead strong, regardless of any ambient. So if in fully exposed ambient (like high ISO or bright sun), this sum will overexpose the subject one stop. So we just learn that TTL in bright sun should be routinely compensated about -1.67 stops (a commonly suggested value).

TTL BL does automatic flash compensation, and in bright sun, probably about -2 EV will be done. So any correction amount we enter should be minor, and NOT the full compensation value (because TTL BL is probably already doing about -2 EV). The camera does NOT show this number, but it does it (and the Exif should show it).

Saying, the camera menu may use shorter definition 1 of TTL, but the metering will be definition 3, or whatever the system does.

What TTL means just depends on what we are talking about. :)

The camera Exif can show the difference, saying TTL BL when it is (and showing actual TTL BL compensation sum). This requires a better Exif viewer to see it. See Camera Exif data - ExifTool



A. Now when I am with one flash (on body) and TTL mode the way to shoot fast and get the results I like (like here is defined flash lifting shadows and giving a slight pop where is not clear that flash was even used) is to
be at manual mode and pick an iso that underexposes the scenes around -1 stop and then set my camera flash to FEC -3.

B. When I then use two flashes (one at the body as main fill and one at a light stick) the second light should be at -2 (with the camera flash at -3). For a reason I do not know is that my ISO has to be two full stops or bit more of what I had in scenario A, assuming same light. If I have no prior information for a scene I should go around -3 stops in iso scale.

What I do not understand is the maths behind those combos that I have tested thoroughly
Alex

I am puzzled by your numbers too. My experience, esp with TTL BL, is that I more often need maybe +1 EV flash compensation, especially with Commander and two flashes. Your experience seems the opposite, maybe -1 EV. One difference is your ambient is up at -1 EV, and my ambient is typically far down, insignificant (low ISO).

I still think perhaps using TTL mode (instead of TTL BL) might clear confusion about compensation (because TTL BL will be in there fighting you too), but of course, that is not a menu choice for the Master/Commander mode, except for using Spot Metering indoors. But if your ambient is adjusted bright with ISO (within one stop), Spot metering will affect it too.
 
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