TTL Flash in Manual Mode

[Lobalobo]

Just started using an inherited D80 and discovered something puzzling with the pop-up flash used in a dimly lit room:

• With camera set to Auto, ISO 200, and Pop-Up Flash set to TTL, pressing the shutter button produces a well-lit image taken at a shutter speed of 1/60 of a second and aperture of f5.6.
• With camera set to Manual, ISO 200, Pop-Up Flash set to TTL, shutter speed set to 1/60 second, and aperture set at f5.6, pressing the shutter button produces a deeply underexposed image. (Same settings but with Pop-Up Flash set to Full Power, and the image is almost properly exposed, slightly overexposed.)

So, apparently, TTL does not work in Manual Mode (and seemingly not in P, A, or S mode either). Why would that be? Is there a setting I'm missing? Thanks in advance.

 

[SoCalAngler]

Just started using an inherited D80 and discovered something puzzling with the pop-up flash used in a dimly lit room:

• With camera set to Auto, ISO 200, and Pop-Up Flash set to TTL, pressing the shutter button produces a well-lit image taken at a shutter speed of 1/60 of a second and aperture of f5.6.
• With camera set to Manual, ISO 200, Pop-Up Flash set to TTL, shutter speed set to 1/60 second, and aperture set at f5.6, pressing the shutter button produces a deeply underexposed image. (Same settings but with Pop-Up Flash set to Full Power, and the image is almost properly exposed, slightly overexposed.)

So, apparently, TTL does not work in Manual Mode (and seemingly not in P, A, or S mode either). Why would that be? Is there a setting I'm missing? Thanks in advance.

The default TTL method is i-TTL Balanced Fill Flash. This is what the camera uses when using matrix or center weighted metering. The camera attempts to create a balance between the subject and ambient or background exposure. This often works quite well but with some combinations of subject and background it can get thrown off.

When in the green Auto mode the camera uses Auto ISO. Even though you had set ISO to 200, was the ISO actually used 200 or did the camera bump it up to compensate for the dim lighting? I am guessing, perhaps incorrectly, that the actual ISO used was something higher than 200. Maybe at least 400.

When in Manual mode with auto ISO off and aperture and shutter speed fixed the only thing the camera can vary is flash output. The built in flash isn't particularly powerful and depending on the size of the room, brightness, shades of color or background and what the camera thinks is the subject it might have picked a lower flash power to try to get the subject and background exposure the same, possibly resulting in lower exposure. So perhaps both subject and background dim if the flash cant sufficiently light the background. According to the manual the effective range of the built in flash at ISO 200 and f/5.6 is 2-10 feet. ISO 400 and f/5.6 its 2-15 feet and so on

To get out of the balanced fill flash mode when in manual mode (or A and S, I don't recall off hand what it does in P) you can change the metering mode to Spot which will change the flash mode from Balanced i-TTL fill to Standard i-TTL fill. In Standard i-TTL the camera chooses a flash power to expose the subject, based on the selected focus point, and ignores the background. Depending on the subject you may need to dial in some negative flash exposure compensation.

Note that in P and Auto modes the maximum aperture (lowest numerical F number) is constrained by ISO with higher ISO restricting how wide you can open the aperture. For example at ISO 400 max aperture is f/5.6 and at ISO 1600 it is f/8!

I have learned that in M and A modes ( I dont use P, S, and Auto with flash) I get the best results if I use spot metering, set the shutter speed, aperture, and ISO for the background ambient light and exposure I want and thus let the camera chose the flash exposure for the subject. If the subject is too bright I will try again with some negative flash exposure compensation dialed in.

[ a little update:]

After writing all that above I decided to grab a camera and run a quick test. I have a room in my house that is 30' by 18'. At one end the wall is covered floor to ceiling with oak book shelves packed with books. There is a fire place in the middle and above that a light colored space in which is hung a large dark toned framed print. The room was lit at the time with two lights each with a 60wt warm tinted LED bulb. Its fairly dim. I stood five feet from the opposite wall on the long axis. 8 feet from me I set a golden brown colored stuffed animal on the back of a chair. The wall was at the far end of the range of the effective range of the flash at high ISO.

I put the camera in green auto mode so the camera is going to use matrix metering and auto ISO. The flash automatically deployed. I had set ISO 200 in the camera. Focused on the stuffed animal and took a photo. Lens was a variable zoom that I chose a focal length that it couldn't open any wider than f/5.6. In Auto the camera chose a shutter speed of 1/60 and an ISO of 1600 and produced a fairly well exposed image with the subject exposure pretty well balanced with the back wall. Since it illuminated the back wall it was probably a full power flash burst.

I then went to manual mode, ISO 200 (auto ISO off), shutter speed 1/60, aperture f/5.6, matrix metering, and captured an image. Subject stuffed animal was pretty dark as was the back wall but both were about the same brightness and thus balanced. But not a very useful image.

Next I changed to spot metering thus now in standard i-TTL. Subject well exposed, perhaps a bit bright and background much darker since the camera ignored the background though the subject. Captured another exposure with -0.3 flash compensation and the subject looked a better.

I then changed the shutter speed to 1/8 (3 stop difference roughly correlating to the camera boosting ISO from 200 to 1600 in auto mode) and captured a shot. Basically changing shutter speed to get a good exposure of the background. A long exposure but subject and background brightness closer to the initial shot made in Auto mode.

--
If cameras and lenses can have autofocus then why can't I?

 

[Lobalobo]

Thanks for such a thoughtful and detailed reply, but you said:

• The built in flash isn't particularly powerful and depending on the size of the room, brightness, shades of color or background and what the camera thinks is the subject it might have picked a lower flash power to try to get the subject and background exposure the same, possibly resulting in lower exposure. So perhaps both subject and background dim if the flash cant sufficiently light the background.

But this can't be the explanation because (as you yourself discovered, I guess, in replicating), everything was too dim when the camera is on Manual; and the flash was plenty powerful at ISO 200 for the scene because when the flash was manually set to Full Power, the image was slightly overexposed. So, it remains a mystery why TTL didn't work properly when set to Auto. Your experiment seems to verify this, and it is a mystery.

 

[Mako2011]

So, it remains a mystery why TTL didn't work properly when set to Auto. Your experiment seems to verify this, and it is a mystery.

Check the post shot ISO's (look at the EXIF) actually used manual vs auto. Should also show flash power used and mode

 

[David Lal]

With camera set to Manual, ISO 200, Pop-Up Flash set to TTL, shutter speed set to 1/60 second, and aperture set at f5.6, pressing the shutter button produces a deeply underexposed image.

I don't have a D80 but do have D70; D90; D300 and D750. Also, I use flash a lot. I found your post interesting so I tried out your settings on several of these cameras.

I could not really replicate your results. I did see some underexposure but not the dire results you describe. Actually, I don't ever use manual mode + iTTL flash. To me, that is not a manual setup. On the D80 I think the popup flash tube has a guide number of 12M, so a subject approximately 2m distant requires about F6 at ISO=100. I tried that and achieved acceptable results

 

[SoCalAngler]

Thanks for such a thoughtful and detailed reply, but you said:

• The built in flash isn't particularly powerful and depending on the size of the room, brightness, shades of color or background and what the camera thinks is the subject it might have picked a lower flash power to try to get the subject and background exposure the same, possibly resulting in lower exposure. So perhaps both subject and background dim if the flash cant sufficiently light the background.

But this can't be the explanation because (as you yourself discovered, I guess, in replicating), everything was too dim when the camera is on Manual; and the flash was plenty powerful at ISO 200 for the scene because when the flash was manually set to Full Power, the image was slightly overexposed. So, it remains a mystery why TTL didn't work properly when set to Auto. Your experiment seems to verify this, and it is a mystery.

When you use flash, there are two exposures: the ambient light or background exposure and the flash exposure.

The flash can only provide correct exposure at one distance. Light intensity falls off with the square of the distance. If the flash is lighting a subject 8 feet away, the light intensity has already fallen to 1/2 of the light at the subject by 11 feet. (1 stop fall off). So something farther away than the subject will get less illumination and something closer will get more intense lighting.

When in Auto mode your camera can adjust ISO, shutter speed, aperture ( restricted by limits of the lens) to deal with ambient light in the scene by changing exposure or brightness.. When the flash is used it fixes the shutter speed at 1/60. It can adjust the flash to illuminate the subject and also attempt to balance the background exposure and scene brightness so they are close to the same. The camera is using i-TTL Blanced Fill flash so it will adjust flash for the subject and it can bump up ISO to brighten the background where you also get some diminishing illumination from the flash.

When in manual mode you had shutter speed, aperture and ISO fixed. All that is left to adjust is the flash. With i-TTL Balanced Fill the camera attempts to keep a balance between the subject flash exposure and the background ambient exposure. With i-TTL the camera fires a pre-flash and meters to determine the flash power to use. Since the flash intensity falls off with distance and the camera is trying to balance the the subject and background, if it can't sufficiently illuminate the background, its next and only option to balance the subject and background exposure is to reduce the flash power so the subject isn't much brighter than the background since the other parameters are fixed. Of course this produces an undesirable image but the camera did do what we asked - balance the subject and background even if that meant both seemed underexposed. This is what happened in the example I created in Manual mode with my camera.

In both Auto and Manual mode the camera attempted to balance the subject and background but in Auto it had an additional parameter available to change (i.e. ISO).

When you manually set the flash to full power, the closer subject was overexposed but you added more light on top of the ambient light to the background. The subject was likely close enough for to be overexposed but the greater power provided more illumination for the background.

Much of the time i-TTL Balanced Fill works pretty well but in many situations it doesn't, depending on the scene and the camera settings that it can change automatically.

If you use i-TTL Standard Fill Flash, which is the type used when Spot metering is selected, you have more more repeatable control over your overall exposure because you can set aperture, shutter, speed, and ISO for the ambient light and the camera chooses flash power for the subject. The camera is no longer trying to automagically balance the brightness of everything in the scene, which isn't possible in some situations and/or combinations of camera settings.

--
If cameras and lenses can have autofocus then why can't I?

 

[fotowbert]

Just started using an inherited D80 and discovered something puzzling with the pop-up flash used in a dimly lit room:

• With camera set to Auto, ISO 200, and Pop-Up Flash set to TTL, pressing the shutter button produces a well-lit image taken at a shutter speed of 1/60 of a second and aperture of f5.6.
• With camera set to Manual, ISO 200, Pop-Up Flash set to TTL, shutter speed set to 1/60 second, and aperture set at f5.6, pressing the shutter button produces a deeply underexposed image. (Same settings but with Pop-Up Flash set to Full Power, and the image is almost properly exposed, slightly overexposed.)

So, apparently, TTL does not work in Manual Mode (and seemingly not in P, A, or S mode either). Why would that be? Is there a setting I'm missing? Thanks in advance.

Like David Lal I was intrigued by your post and I do have a D80 so I tried to replicate your issue. Unfortunately I could not.

Using the green "Auto" on the mode dial in my kitchen I get 1/30, f/4.5, ISO 200 and the flash pops up. Exposure looks good. I transferred these values to "M" mode and get the same looking image. The two histograms are almost identical (I was hand-holding the camera and framing was slightly different). "A" mode without flash shows ambient light level is 1/4, f/4.5, ISO 200 so the flash shutter speed is underexposing the ambient by 3 stops. Using matrix metering btw.

I suspect you may have uncovered some defect with the TTL system and suggest you make more tests to confirm the repeatability of this issue. The most likely cause for TTL not producing the light you know the flash is capable of is the capacitor hasn't had enough time to recharge. Fire off a sequence of full power flashes to see how long it takes for the "flash ready" light to come back on. It is good practice to exercise you flash at least once or twice a year to keep the capacitors in good shape. Perhaps with use your issue will go away.

• John

--
"[If you don't sweat the details] the magic doesn't work." Brooks, F. P., The Mythical Man-Month, Addison-Wesley, 1975, page 8.

 

[SoCalAngler]

So, it remains a mystery why TTL didn't work properly when set to Auto. Your experiment seems to verify this, and it is a mystery.

Check the post shot ISO's (look at the EXIF) actually used manual vs auto. Should also show flash power used and mode

I don't think flash power used is recorded when using i-TTL. At least I don't find it. It is recorded when setting flash power manually.

 

[SoCalAngler]

I suspect you may have uncovered some defect with the TTL system and suggest you make more tests to confirm the repeatability of this issue.

I don't think this is a bug or defect.

I believe the camera is trying to do exactly what you want (though you may not realize that) when using the default i-TTL BL flash mode, which tries to balance ambient and flash exposure.

Nikon did change their TTL BL algorithm at some point to work differently in low light (Thom Hogan mentions this in his books) do use a different strategy. My D7100 and later bodies seem to give more priority to the subject over background in low light conditions compared to the the older D40 and D80 where were both released in 2006. The difference is most noticeable in Manual mode when aperture, shutter, and ISO are fixed.

The most likely cause for TTL not producing the light you know the flash is capable of is the capacitor hasn't had enough time to recharge. Fire off a sequence of full power flashes to see how long it takes for the "flash ready" light to come back on. It is good practice to exercise you flash at least once or twice a year to keep the capacitors in good shape. Perhaps with use your issue will go away.

• John

 

[Mako2011]

So, it remains a mystery why TTL didn't work properly when set to Auto. Your experiment seems to verify this, and it is a mystery.

Check the post shot ISO's (look at the EXIF) actually used manual vs auto. Should also show flash power used and mode

I don't think flash power used is recorded when using i-TTL.

I get a reading with the D7K...may not with the D80

--
My opinions are my own and not those of DPR or its administration. They carry no 'special' value (except to me and Lacie of course)

 

[Lobalobo]

The flash can only provide correct exposure at one distance. Light intensity falls off with the square of the distance. If the flash is lighting a subject 8 feet away, the light intensity has already fallen to 1/2 of the light at the subject by 11 feet. (1 stop fall off). So something farther away than the subject will get less illumination and something closer will get more intense lighting.

Thanks for the time you took to write this long post (partially quoted above) but your reply was not responsive. Yes, I know how a flash works. But, as my post explains, I looked at the ISO, Shutter Speed, and Aperture setting the TTL chose in Auto mode and replicated those in Manual Mode, then captured the same image in that mode with TTL set. Thus, there was no chance that the flash was incapable of proper exposure at the distance needed; it just didn't do it. When I turned the flash to manual mode along with the camera, I was again able to get proper exposure. All I can conclude from this is that TTL does not work when the camera is in manual mode, and that can't be a feature (at least not a rational one).

 

[Lobalobo]

Actually, I don't ever use manual mode + iTTL flash. To me, that is not a manual setup. On the D80 I think the popup flash tube has a guide number of 12M, so a subject approximately 2m distant requires about F6 at ISO=100. I tried that and achieved acceptable results

Often, I use a Flash to fill and want to control Shutter Speed and Aperture for the effect I want in the portion of a scene exposed for ambient light. Thus, this is a function I would use, if it worked. And, yes, the flash is not underpowered as it exposed the scene properly both when the camera is in Auto mode and when the camera and the flash are in Manual mode. So, the mystery remains, or perhaps I just have a defective camera, or I've inadvertently activated a setting that limits TTL to Auto mode. But I can't figure it out.

 

[Mako2011]

But, as my post explains, I looked at the ISO, Shutter Speed, and Aperture setting the TTL chose in Auto mode

How did you determine the ISO used?

 

[Lobalobo]

The most likely cause for TTL not producing the light you know the flash is capable of is the capacitor hasn't had enough time to recharge. Fire off a sequence of full power flashes to see how long it takes for the "flash ready" light to come back on. It is good practice to exercise you flash at least once or twice a year to keep the capacitors in good shape. Perhaps with use your issue will go away.

Good suggestions, and thank you. But TTL works fine when the camera is in Auto mode, and I've replicated the problem on my camera a number of times, with plenty of time between shots. Always the same: TTL works flawlessly when camera is in Auto mode; exposure of the same season works as expected when both the camera and the flash are in Manual mode; but when the camera is in Manual mode, TTL underexposes the scene significantly (even when ISO, Shutter Speed, and Aperture are manually set to replicate the camera's chosen values when in full Automatic mode).

 

[Lobalobo]

The camera is trying to do exactly what you want (though you may not realize that) when using the default i-TTL BL flash mode, which tries to balance ambient and flash exposure.

When I manually set ISO, Shutter Speed, and Aperture to exactly the same settings that the camera chose in Auto mode, and then engage TTL, everything in the scene is dramatically underexposed; this can hardly be by design.

It's possible, I suppose, that I've misread the one of the parameters chosen by the camera in Auto mode (though I'm not sure how I could have done that), but even if I have, that doesn't explain the results because leaving the chosen ISO, Shutter Speed, and Aperture in Manual mode and changing only the Flash from Auto to Manual, I can (slightly) overexpose the scene by putting the flash on Full Power; so it utterly escapes me why the TTL would choose to underexpose everything when the flash has the ability to properly, even over, expose the scene. There must be something wrong with the camera, or I must have an errant setting somewhere, but it's hard to see what defect or error would produce this precise pattern of results.

 

[Lobalobo]

But, as my post explains, I looked at the ISO, Shutter Speed, and Aperture setting the TTL chose in Auto mode

How did you determine the ISO used?

Excellent question. Hitting Play Back and then Display, the data from the shot appear. Is that not reliable? Even if it's not, though, there is still a mystery because, with the camera in Manual mode, when I leave all the parameters unchanged, but switch the flash from TTL to Manual, I can properly expose (even overexpose) the scene, so it's hard to understand why the TTL would choose to significantly underexpose the entire scene when the flash has sufficient power to avoid this outcome.

 

[Mako2011]

But, as my post explains, I looked at the ISO, Shutter Speed, and Aperture setting the TTL chose in Auto mode

How did you determine the ISO used?

Excellent question. Hitting Play Back and then Display, the data from the shot appear. Is that not reliable?

Not nessesarily. Best to check the EXIF. Was it a non-CPU lens?

Even if it's not, though, there is still a mystery because, with the camera in Manual mode, when I leave all the parameters unchanged, but switch the flash from TTL to Manual, I can properly expose (even overexpose) the scene, so it's hard to understand why the TTL would choose to significantly underexpose the entire scene when the flash has sufficient power to avoid this outcome.

Some good info:

Nikon D80 Review - Flash - Imaging Resource

Nikon D80 Review - D80 Flash

www.imaging-resource.com

 

[fotowbert]

SoCalAngler wrote in part:

fotowbert wrote in part:

I suspect you may have uncovered some defect with the TTL system and suggest you make more tests to confirm the repeatability of this issue.

I don't think this is a bug or defect.

I believe the camera is trying to do exactly what you want (though you may not realize that) when using the default i-TTL BL flash mode, which tries to balance ambient and flash exposure.

I have to disagree. My experience with a D80 in low ambient light conditions is that Nikon's TTL BL flash mode does not produce what the OP describes as a "deeply underexposed image".

I backed that up by saying (in the portion of my post you did not quote) that I performed a test and couldn't replicate the OP's issue with my D80. Is it my D80 that's the defective one?

IMO the reported behavior by the OP isn't typical for the D80. Something other than TTL BL is responsible.

• John

 

[fotowbert]

Just started using an inherited D80 and discovered something puzzling with the pop-up flash used in a dimly lit room:

• With camera set to Auto, ISO 200, and Pop-Up Flash set to TTL, pressing the shutter button produces a well-lit image taken at a shutter speed of 1/60 of a second and aperture of f5.6.
• With camera set to Manual, ISO 200, Pop-Up Flash set to TTL, shutter speed set to 1/60 second, and aperture set at f5.6, pressing the shutter button produces a deeply underexposed image. (Same settings but with Pop-Up Flash set to Full Power, and the image is almost properly exposed, slightly overexposed.)

So, apparently, TTL does not work in Manual Mode (and seemingly not in P, A, or S mode either). Why would that be? Is there a setting I'm missing? Thanks in advance.

Upon studying my D80 manual I noticed that FEC (Flash Exposure Compensation) doesn't apply to the green Auto mode but does apply to PSAM exposures modes. If that was set to something like -3EV (the max ) that could explain your issue.

On a more general note it is a good practice to reset all the parameters back to factory defaults when you receive a camera from someone else. You want to start from a clean defined state, not how someone else left the camera. See the user manual on how to do this.

John

 

[SoCalAngler]

The flash can only provide correct exposure at one distance. Light intensity falls off with the square of the distance. If the flash is lighting a subject 8 feet away, the light intensity has already fallen to 1/2 of the light at the subject by 11 feet. (1 stop fall off). So something farther away than the subject will get less illumination and something closer will get more intense lighting.

Thanks for the time you took to write this long post (partially quoted above) but your reply was not responsive. Yes, I know how a flash works. But, as my post explains, I looked at the ISO, Shutter Speed, and Aperture setting the TTL chose in Auto mode

Ok good. In your original post you wrote that the camera was set to "...Auto, ISO 200..." but it wasn't clear that you meant that you had set the camera to ISO 200 or the camera chose ISO 200. A couple of responses mentioned Auto mode controlling ISO but you hadn't clarified whether ISO 200 was what the camera used and what was recorded in the EXIF. Hence my misunderstanding.

At the time it was released there was a lot of discussion about how well the matrix meter worked (or not). I no longer have access to the D80 but I recall having some issues with i-TTL BL at the time in some conditions. But it worked fine most of the time.

and replicated those in Manual Mode, then captured the same image in that mode with TTL set. Thus, there was no chance that the flash was incapable of proper exposure at the distance needed; it just didn't do it. When I turned the flash to manual mode along with the camera, I was again able to get proper exposure. All I can conclude from this is that TTL does not work when the camera is in manual mode, and that can't be a feature (at least not a rational one).

But there is another camera setting that affects the jpeg output. These are settings that are applied to the jpeg, including the embedded jpeg in the .NEF file

The D80 has a setting called Optimize Image as I'm sure you know. This was replaced by Picture Controls in the D90 and later cameras.

When you are shooting Auto the camera automatically chooses values for the Optimize Image parameters. When shooting in P, A, S, M modes you can select something else like Vivid, Black and White, Portrait, Custom, etc. When Custom is chosen you can pick different values for sharpening, saturation, tone, and color. When I set Optimize Image on my D40 to Custom with Tone Compensation set to "-2 Less contrast" and did the flash shot in manual the jpeg looked much closer to the image captured in Auto.

I don't think the Optimize Image setting is necessarily the answer to your issue, but it does have a demonstrable effect on the jpeg output.

Also verify that flash exposure compensation is not set to a large negative value. That is ignored in green Auto mode.

--
If cameras and lenses can have autofocus then why can't I?