TTL vs Manual flash

[pmgnut]

Hi all, still new to flash photography but have been playing with both TTL and manual mode. One thing I noticed is in TTL mode there never seems to be enough output. Took a picture of my buddy 2 days ago at about 10 feet away and his face/body was just a dark silhouette. Tried same pic in manual mode on 1/1 power and it lit him up nicely. I must be doing something wrong in the TTL mode?

 

[PhotoTeach2]

Hi all, still new to flash photography but have been playing with both TTL and manual mode. One thing I noticed is in TTL mode there never seems to be enough output. Took a picture of my buddy 2 days ago at about 10 feet away and his face/body was just a dark silhouette. Tried same pic in manual mode on 1/1 power and it lit him up nicely. I must be doing something wrong in the TTL mode?

Yes, you are doing something wrong.

What is your camera and flash ???

 

[tclune]

Could you have set a negative flash compensation by mistake?

 

[pmgnut]

Hi all, still new to flash photography but have been playing with both TTL and manual mode. One thing I noticed is in TTL mode there never seems to be enough output. Took a picture of my buddy 2 days ago at about 10 feet away and his face/body was just a dark silhouette. Tried same pic in manual mode on 1/1 power and it lit him up nicely. I must be doing something wrong in the TTL mode?

Yes, you are doing something wrong.

What is your camera and flash ???

Nikon D750 and SB-700 flash

My buddy also confirmed the flash was firing {while using TTL}

 

[pmgnut]

Could you have set a negative flash compensation by mistake?

Is that even possible with TTL? I had thought TTL was fully automatic, but i'm a total newbie to flash so i'm probably mistaken

 

[PhotoTeach2]

Could you have set a negative flash compensation by mistake?

Is that even possible with TTL? I had thought TTL was fully automatic, but i'm a total newbie to flash so i'm probably mistaken

It is indeed automatic, but the parameters are preset to determine the flash-exposure relative to the ambient-exposure.

It can be preset from just a barely-noticeable "fill" (shadows) flash, or to be the dominant illumination, (w/ darker background).

Note that the max-distance is the same w/ either manual or TTL, but you are obviously in-range since it is adequately exposed in manual.

 

[SoCalAngler]

Nikon D750 and SB-700 flash

My buddy also confirmed the flash was firing {while using TTL}

Default flash mode on Nikon bodies (last 10 years or so at least) is i-TTL Balanced Fill-Flash which displays as TTL BL on the SB-700.

It attempts to balance flash power with ambient light and often does a pretty good job. But some situations can cause it to get confused and your subject comes out over or underexposed. I find this to occur most often if there is a large difference in background vs subject lighting.

Also if you have auto ISO engaged you may get odd results as well as using EC and Flash EC in TTL BL, so I try to avoid messing with these.

If I'm not getting something I like I switch to Standard TTL mode and put the camera in M mode (not the flash). The easiest way to set the camera to Standard TTL is to change metering to spot. This automatically changes to the camera and flash to Standard TTL with Nikon bodies.

Then I set aperture and shutter speed manually for good exposure for the background (ambient light). Then I make sure the focus point for spot metering is on the subject, and shoot. The camera is still calculating flash output, but is now basing the output on the subject (it fires a pre flash to do this, just like in TTL BL mode). If subject is over exposed then I will try some negative flash exposure compensation. If underexposed then I will try some positive flash exposure compensation. Rarely do I need to drop below -1.0 EV when using the flash as primary light for the subject. Rarely have I needed to dial in positive flash exposure compensation.

If I only need the flash for fill flash, such as when most of subject is well lit but maybe a hat is casting a shadow or I have the sun off to the side, then I may use between -1.0 and -2.0 flash exposure compensation.

I don't recall ever putting the flash in Manual mode when on camera. I have a few times when off camera and doing some close up/macro

Some of this I figured out myself through experimentation but I picked up more details, many more, from Thom Hogan's book on the D7100 and my Z5 works the same with flash. I'm using the SB-700 too. The D750 works about the same: there may be a couple of additional or different settings for special cases. I have seen similar suggestions in other writings but I have seen different ones too.

I am hardly an expert with flash but this works well for me with my Nikon bodies.

 

[J Peters]

TTL mode fires the flashgun twice. It triggers a pre-flash from which it calculates the amount of power needed for the "real" flash. This happens so quickly that you perceive it as a single burst.

I can't think how this might happen, but I guess it is possible for the camera and flash to be mismatched in their settings. If the camera thinks TTL mode is on, but the flash doesn't, then the flash could deliver one big burst when the camera thinks it should be giving only the pre-flash.

There is an easy way to test this. Take a picture in a mirror so you can see the flash gun in the shot. If you see a flash with your eyes but the flashgun is clearly off in the photo, then the above is the issue. The flash is firing a millisecond before the shutter is open.

 

[Aberaeron]

Could you have set a negative flash compensation by mistake?

Is that even possible with TTL? I had thought TTL was fully automatic, but i'm a total newbie to flash so i'm probably mistaken

Yes it is. In the camera’s flash menu you will have flash power compensation adjustment, which is quite distinct from the camera’s normal EV compensation in that it alters only the flash intensity.

 

[thinkinginimages]

Since I don't have the same camera gear I have to generalize a bit. Manual flash is pretty much all math. This much output at this distance and ISO = this f/stop. (The shutter speed is usually the max sync speed). It doesn't take into account balancing ambient, reflectance of the subject, etc. That's what GN (guide number) is all about.

TTL tries to balance a whole box of variables. Sometimes it gets it right, but there's a lot a settings that can make it go wrong. I'm guessing, since I don't have your cameras. Mode and metering may affect the overall exposure. Some cameras are more intelligent about Auto mode than others. There may be an exposure, or flash bias set, or both.

There's a lot to explore when you mix flash and ambient.

 

[pmgnut]

If it helps, my camera was in manual mode as usual. ISO 100

 

[thinkinginimages]

Manual mode may be the cause. I can't say for sure since I wasn't there. In broad strokes in TTL mode the camera probably tried to juggle the ambient settings but you locked them down. The flash couldn't compensate because there wasn't enough output for the given situation. Maybe.

Let me try to make this more sensible and throw out a few things to consider. Because focal plane shutters and flash units create limitations you will have a maximum (but low) shutter speed because of the flash. Let's say 1/250. (It may be lower on your camera.)

Keep in mind your shutter speed can be lower in Manual mode and the flash will still work fine. Let's say 1/15 to 1/250 for handheld work.

You also have the limitations of the lens aperture. Let's make that range f:/3.5 to F:/16.

Now with the flash off, if your manual exposure can't be calculated within those limitation because of lighting, your ambient exposure is going to be "off". The flash exposure may be the dominant light source. In effect, ambient is the fill lighting.

If the flash was on manual you could calculate the exposure easy enough using the Guide Number of the flash. (The guide number of a flash is the product of the f/stop of the exposure at a given distance at ISO 100, i.e.: f:/8 at 10 feet, at ISO100=GN80.)

The point I'm wandering towards is there needs to be a dominant exposure flash or ambient, or a balance of the two. Locking the camera in Manual you may have miscalculated.

Yes, this is tricky stuff.

TTL can be a blessing, or not. It may be misreading the scene/subject. It may not know how to bias the lighting (is ambient or flash dominant?)

I suspect that I've just made this a lot more confusing.

 

[Leonard Migliore]

I have the same camera and flash. I always have the camera in manual mode and the flash in TTL. If I have any exposure automation at all (aperture priority or auto ISO) things get weird. The D750 defaults to fill flash in aperture priority or P mode, which is usually not what I want.

 

[pmgnut]

Manual mode may be the cause. I can't say for sure since I wasn't there. In broad strokes in TTL mode the camera probably tried to juggle the ambient settings but you locked them down. The flash couldn't compensate because there wasn't enough output for the given situation. Maybe.

Let me try to make this more sensible and throw out a few things to consider. Because focal plane shutters and flash units create limitations you will have a maximum (but low) shutter speed because of the flash. Let's say 1/250. (It may be lower on your camera.)

Keep in mind your shutter speed can be lower in Manual mode and the flash will still work fine. Let's say 1/15 to 1/250 for handheld work.

You also have the limitations of the lens aperture. Let's make that range f:/3.5 to F:/16.

Now with the flash off, if your manual exposure can't be calculated within those limitation because of lighting, your ambient exposure is going to be "off". The flash exposure may be the dominant light source. In effect, ambient is the fill lighting.

If the flash was on manual you could calculate the exposure easy enough using the Guide Number of the flash. (The guide number of a flash is the product of the f/stop of the exposure at a given distance at ISO 100, i.e.: f:/8 at 10 feet, at ISO100=GN80.)

The point I'm wandering towards is there needs to be a dominant exposure flash or ambient, or a balance of the two. Locking the camera in Manual you may have miscalculated.

Yes, this is tricky stuff.

TTL can be a blessing, or not. It may be misreading the scene/subject. It may not know how to bias the lighting (is ambient or flash dominant?)

I suspect that I've just made this a lot more confusing.

I did some research and watched a ton of videos before buying the flash, the consensus was that TTL was easier to use, however I find just the opposite, so far anyway. I'm sure once i totally learn it that may change. So I can hand hold the camera a slow as 1/15 sec with a flash?

 

[PhotoTeach2]

Manual mode may be the cause. I can't say for sure since I wasn't there. In broad strokes in TTL mode the camera probably tried to juggle the ambient settings but you locked them down. The flash couldn't compensate because there wasn't enough output for the given situation. Maybe.

Let me try to make this more sensible and throw out a few things to consider. Because focal plane shutters and flash units create limitations you will have a maximum (but low) shutter speed because of the flash. Let's say 1/250. (It may be lower on your camera.)

Keep in mind your shutter speed can be lower in Manual mode and the flash will still work fine. Let's say 1/15 to 1/250 for handheld work.

You also have the limitations of the lens aperture. Let's make that range f:/3.5 to F:/16.

Now with the flash off, if your manual exposure can't be calculated within those limitation because of lighting, your ambient exposure is going to be "off". The flash exposure may be the dominant light source. In effect, ambient is the fill lighting.

If the flash was on manual you could calculate the exposure easy enough using the Guide Number of the flash. (The guide number of a flash is the product of the f/stop of the exposure at a given distance at ISO 100, i.e.: f:/8 at 10 feet, at ISO100=GN80.)

The point I'm wandering towards is there needs to be a dominant exposure flash or ambient, or a balance of the two. Locking the camera in Manual you may have miscalculated.

Yes, this is tricky stuff.

TTL can be a blessing, or not. It may be misreading the scene/subject. It may not know how to bias the lighting (is ambient or flash dominant?)

I suspect that I've just made this a lot more confusing.

I did some research and watched a ton of videos before buying the flash, the consensus was that TTL was easier to use, however I find just the opposite, so far anyway.

TTL is absolutely easier/faster (but w/ conditions).

Keep in mind that in manual, you have to measure EACH and EVERY distance and CALCULATE the f/stop ... for EVERY shot. Very time-consuming.

In TTL you only have to be concerned if your subject is either a REFLECTIVE-white or ABSORDENT-black.

I'm sure once i totally learn it that may change.

Yes ... you are doing something "basic/SIMPLE" wrong. Do you have a camera store or other (friend) professional photographer close by you could simply show him and see if he sees anything ???

BUT ... since the flash-power (in manual) is adequate ... I am thinking your flash (TTL-circuity) is bad.

So I can hand hold the camera a slow as 1/15 sec with a flash?

Yes ... technically ... but NO in practice, because it will then expose the background light and probably be shaky w/ that long shutter-speed.

But that is indeed OFTEN DONE, but only w/ precautions if you don't want a shaky background.

Keep in mind that an image w/ flash is a combination of both the ambient-(background) and the (close-up)-flash exposure. By careful choices of shutter-speed and (ratio) of flash-power, you can decide if you want the subject to be highlighted brighter than the background, or simply "filled" equally, (as often done outdoors to simply fill "shadows").

 

[thinkinginimages]

Short answer, yes you can hand hold camera at 1/15 using the flash because the flash burst if effectively the shutter.

I'm glad that you made that observation because it helps to make this clearer (maybe). Let's set aside TTL for a bit. It's only going to confuse this next bit.

If the flash unit is the dominant light source that "pop" of the flash is extremely short, even in a dark setting. We're talking thousand's of a second. The camera's shutter only real function is to make sure the entire sensor is exposed during that extremely brief "pop".

I need to go into how a focal plane shutter works for that to make sense. Skip this part if you know. A focal plane shutter is basically a moving "slit", exposing the sensor in sequential sections as it swipes across it. EXCEPT that below certain shutter speeds, let's say 1/250 and lower, the entire sensor is exposed. 1/250 is the maximum flash sync speed. There is no minimum shutter speed (theoretically). The flash pop acts as the shutter.

Back to TTL: TTL Flash reads the burst of light coming into the camera lens at the time of exposure. With compatible flash units the camera body is aware of the flash units and can control the flash units, as well as the shutter and aperture. You might see exposure bias for the flash units, as well as the ambient exposure, in the camera's menus.

In Manual mode you're stopping the camera from adjusting the shutter, aperture, and ISO AND the flash from adjusting as well. That's fine if you're familiar with all the variables.

Like I said, this is tricky. You're trying to juggle a lot of complex variables. There's a lot to absorb here, but I think you're starting to "get it".

 

[SoCalAngler]

S

Back to TTL: TTL Flash reads the burst of light coming into the camera lens at the time of exposure. With compatible flash units the camera body is aware of the flash units and can control the flash units, as well as the shutter and aperture. You might see exposure bias for the flash units, as well as the ambient exposure, in the camera's menus.

In Manual mode you're stopping the camera from adjusting the shutter, aperture, and ISO AND the flash from adjusting as well. That's fine if you're familiar with all the variables.

Like I said, this is tricky. You're trying to juggle a lot of complex variables. There's a lot to absorb here, but I think you're starting to "get it".

At least with Nikon bodies, if camera in manual exposure mode, i-TTL still automatically makes flash adjustments. If in balanced fill flash control mode (TTL BL), which is the default with matrix metering, it tries to balance subject and background. If in standard i-TTL (automatic when camera is set to spot metering, balanced is not available when spot metering), then it adjusts flash for subject only and ignores background

 

[thinkinginimages]

Thanks for bringing me up to speed on Nikons. I use them if I'm not carrying my own cameras (Panasonic) but there's a difference between "using" and "knowing" a camera. The same hold true for flash units.

 

[henrya41]

Spot Metering was my first thought. If the camera was set to Spot Metering rather than matrix metering it could give results like the OP mentioned. If the camera was using a spot on a bright background for both the flash and ambient exposure, It could severely under-expose the foreground subject. Whenever my flash is acting strange the first thing I always check is that the exposure meter is set to Matrix.

 

[pmgnut]

I have the same camera and flash. I always have the camera in manual mode and the flash in TTL. If I have any exposure automation at all (aperture priority or auto ISO) things get weird. The D750 defaults to fill flash in aperture priority or P mode, which is usually not what I want.

Leonard- are there any other settings I need to check for TTL and the camera in manual mode? To me the flash in TTL seems weak but I have a hunch something is set wrong. The flash is basically new. Just played with it again in TTL mode, flash fires but is so weak it wont light any subjects up.

Note: Just played with it again, TTL seems to work fine when I crank it up to +3EV but if no compensation is set {0.00EV } the subject will come out dark and not illuminated at all.

Camera is set to 1/160 for both flash sync speed and flash shutter speed in the D750

I'm wondering if it's only the pre-flash that's actually firing in TTL