Does Metering System works with Flash ?
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I'm fairly new to flash photography, but as I understand it,TTL mode will get you Through The Lens metering.
Fred Kingston
Senior Member
No. The meter can't measure something that hasn't occurred. The meter (when the camera is in iTTL mode, will shut off the flash after it has received enough light.
Things to remember about flash.
All flash is at maximum power. Flash is controlled by "duration"... that's the time the flash is ON... Flash is controlled by controlling the duration or time... the electronics turn the flash ON, and then turns the flash OFF when the meter has measured enough light... IF you could watch the meter during a flash's very fast sequence, you would see it move from under-exposed to 0, and the back to under-exposed...
Nikon's external flashes have the same sensing system in them... the flash turns on at full power, and measures the reflected light at the sensor, and shuts OFF the flash...
Things to remember about flash.
All flash is at maximum power. Flash is controlled by "duration"... that's the time the flash is ON... Flash is controlled by controlling the duration or time... the electronics turn the flash ON, and then turns the flash OFF when the meter has measured enough light... IF you could watch the meter during a flash's very fast sequence, you would see it move from under-exposed to 0, and the back to under-exposed...
Nikon's external flashes have the same sensing system in them... the flash turns on at full power, and measures the reflected light at the sensor, and shuts OFF the flash...
Horoscope Fish
Senior Member
What flash are you using and what settings are you using on your camera?
With the right combination the flash and camera do "talk" to one another to help ensure proper exposure. This communication can be thwarted however by incorrect camera or flash settings.
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Fred, this is not how iTTL works. In iTTL mode the flash sends a low-level flash, with the lens wide open, before the mirror is raised, so the camera's meter can measure the amount of light reflected from the subject. Then, the camera decides how much light is required, sets the flash's power to the the appropriate level and takes the picture.
PS. I don't think you can control flash duration. There is a capacitor in the flash unit and when the flash is triggered it is discharged into the flash tube. I don't think you can stop this process, once it has started. Also, when the shutter is open, the camera cannot measure light and tell the flash to stop.
PS. I don't think you can control flash duration. There is a capacitor in the flash unit and when the flash is triggered it is discharged into the flash tube. I don't think you can stop this process, once it has started. Also, when the shutter is open, the camera cannot measure light and tell the flash to stop.
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Fred Kingston
Senior Member
Not according to Nikon's documentation... it controls the duration... all flash charges a capacitor and have a timing circuit that shunts the voltage stream... flash is max.... the duration is simply shortened based on the pre-flashes measurement... It appears to the naked eye that the flash is at less than full power... it isn't... it's the duration that's shortened... 
I think we have diverged too far from the original question. When you measure light with the flash on, the meter shows you the exposure without the flash. So, if you are in a dark room, the shutter speed is at 1/60 s, ISO is at 100 and even with the lens wide open there is no enough external light. So, the meter tells you that your shot will be underexposed. However, since you have the flash on, it will balance the exposure by adding the appropriate amount of light.
This is a rather simplified description, just to explain why your meter shows underexposed when you take a picture. Proper balancing flash and external light is more complicated and requites some knowledge and experience.
Fred Kingston
Senior Member
Cameras only have Reflective light meters... they can only measure reflected light.
An incident light meter will allow you to "preflash" the subject, and make the necessary aperture/iso/speed adjustments prior to a shutter release... they also take into account multiple sources of light...
An incident light meter will allow you to "preflash" the subject, and make the necessary aperture/iso/speed adjustments prior to a shutter release... they also take into account multiple sources of light...
Thanks for the answer I was looking for. But the problem is I use SB700 with the flash direction upwards so thats more complicated to measure the light since there is no direct flash light. Also i have experienced that TTL flash doesnot work properly in this way as the picture is always underexposed so now i am struggling to get to know my flash in manual mode
Horoscope Fish
Senior Member
If that's the case, and assuming your gear is in proper working order, you're doing something wrong, need to adjust a setting(s) or both. I routinely bounce flash my SB700 using TTL metering and I get spot-on exposure.
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The bit that's missing here is that two exposures are occurring. The ambient one, typically the background behind the subject and the closer flash illuminated subject. The meter showing under exposed is referring to the ambient part. You can adjust the exposure in the normal way to balance everything but that is a trade off as you will end up slowing the shutter or increasing the ISO.
The flash TTL part has been answered in the other replies.
Sent from my iPad using Tapatalk HD
The flash TTL part has been answered in the other replies.
Sent from my iPad using Tapatalk HD
what settings should i use , i dont take a lot of flash photography ,i have a d7100 and i bought a yongnuo 560-111 , do i shoot and focus manually and then set shutter speed to below sync speed 1/250 , do i have to worry about focal length to shutter speed or concentrate on aperture? , problem i have when shooting in other modes is i cant focus so i cant press the shutter and i also get very slow shutter speeds and that forces me to go very high isos
What metering mode do you use? If your camera is set to matrix metering, it will try to balance natural light and the flash. If it is in spot metering, it will ignore external light and will try to set the flash to exposure your measured spot. If your spot is set at something bright, it might result in underexposed photos.
But this is only a wild guess. There might be various reasons for underexposing. Some of them quite simple: you might have exposure or flash exposure compensation set to underexpose. Or, your ceiling is too high or too dark to reflect enough light. Or, your subject might be too far.
Go through all your camera and flash settings and make sure there is nothing unusual there.
Thanks for the answer I was looking for. But the problem is I use SB700 with the flash direction upwards so thats more complicated to measure the light since there is no direct flash light. Also i have experienced that TTL flash doesnot work properly in this way as the picture is always underexposed so now i am struggling to get to know my flash in manual mode
Ok, I have written about this here somewhere here but can't find it so here it is again. First understand how the flash works - power is controlled by the duration -see the spec here -scroll down to "Flash duration" for the SB700 At full power 1/1, the duration is 1/1024 sec and at 1/128 power the duration is 1/40,000 of a sec. Now, this is how TTL works in Nikon - you set the camera in M(anual) mode but you are NOT in Manual - you have transferred the automatic function from the camera to the flash. Because the flash speed is faster than your shutter speed, your shutter speed contribute very little to the exposure - so just set it to 1/200 or 1/250 ie fastest sync speed.
Now, set your aperture for your liking base on depth of field you want. (That's the fundament art of photography - right?) When you take a picture, the flash sends out a "pre-flash" and the camera reads the reflected light level and based on its zoom setting and aperture, instructs the flash what power to use to light the subject - and this is when you are set on spot metering - meter the subject. It doesn't matter if you are pointing the flash head straight at the subject (Never do that unless you have a soft-box) or up the ceiling or in many cases, behind you with a white wall. The camera by reading the preflash light level will tell the flash the proper level to use. IGNORE THE LIGHT METER READING - it doesn't apply here! If you turn on the beep in the SB700, you can by the beeps tell if there's enough light after you press the shutter - 3-beeps means not enough power - put light closer to subject or set up a 2nd or 3rd speedlight!
Now, if you are using the flash as a fill-in flash, (BL mode) then use Matrix or Center-weight. Here, the shutter speed will control the brightness of the background but the TTL flash will control the brightness of your subject.
A note about pointing to the ceiling - the ceiling is the best softbox ever but only if it's lower than a 10ft ceiling and a white or off white ceiling. If you bounce off a 20ft ceiling, you won't have enough light power with an SB700 - I use 3 when I do that. If the ceiling is not white, you'll need to change your white balance, in-camera or post-production. When using the SB700 or any Nikon, set white balance to "Cloudy" - not "flash." When you have high ceiling like convention halls, try bouncing off a wall behind you! Or invest in a $50 portable softbox or one of Gary Fong's rubbermaid cups!! In any case, don't fret about having to manually compensate for the non-direct lighting or any light-modifiers - the TTL system will take care of that for you.
Hope this clarifies how TTL flash works. With NIKON, when using TTL speedlites always shoot in MANUAL mode - even if you have never done so, don't panic - you are not really in manual - the exposure is taken over by the speedlite based on what the camera tells it the setting is.
Now, High-Speed Sync (HSS) aka FP mode next ... never mind...
Now, set your aperture for your liking base on depth of field you want. (That's the fundament art of photography - right?) When you take a picture, the flash sends out a "pre-flash" and the camera reads the reflected light level and based on its zoom setting and aperture, instructs the flash what power to use to light the subject - and this is when you are set on spot metering - meter the subject. It doesn't matter if you are pointing the flash head straight at the subject (Never do that unless you have a soft-box) or up the ceiling or in many cases, behind you with a white wall. The camera by reading the preflash light level will tell the flash the proper level to use. IGNORE THE LIGHT METER READING - it doesn't apply here! If you turn on the beep in the SB700, you can by the beeps tell if there's enough light after you press the shutter - 3-beeps means not enough power - put light closer to subject or set up a 2nd or 3rd speedlight!
Now, if you are using the flash as a fill-in flash, (BL mode) then use Matrix or Center-weight. Here, the shutter speed will control the brightness of the background but the TTL flash will control the brightness of your subject.
A note about pointing to the ceiling - the ceiling is the best softbox ever but only if it's lower than a 10ft ceiling and a white or off white ceiling. If you bounce off a 20ft ceiling, you won't have enough light power with an SB700 - I use 3 when I do that. If the ceiling is not white, you'll need to change your white balance, in-camera or post-production. When using the SB700 or any Nikon, set white balance to "Cloudy" - not "flash." When you have high ceiling like convention halls, try bouncing off a wall behind you! Or invest in a $50 portable softbox or one of Gary Fong's rubbermaid cups!! In any case, don't fret about having to manually compensate for the non-direct lighting or any light-modifiers - the TTL system will take care of that for you.
Hope this clarifies how TTL flash works. With NIKON, when using TTL speedlites always shoot in MANUAL mode - even if you have never done so, don't panic - you are not really in manual - the exposure is taken over by the speedlite based on what the camera tells it the setting is.
Now, High-Speed Sync (HSS) aka FP mode next ... never mind...
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Re this original question.... the camera light meter that we see is only about the ambient exposure. TTL flash is metered too, but it has its own invisible system that we cannot see.
The ambient metering sets the camera settings, like shutter speed and aperture and Auto ISO. Then when the shutter button is pressed, the flash has to deal with those settings, and provide the correct flash power level to match them. Speedlight power level is controlled with flash duration. Film TTL cameras just quenched the flash off when exposure was seen to be enough. Current iTTL cameras instead meter a low level preflash, and then compute and set the flash power level directly, in advance of the actual flash.
There are several ifs and buts, some differences in camera modes (A,S,P, M), and some Auto ISO differences in camera models.
In the general theory, the ambient metering and settings are the same regardless if flash is used or not (the ambient is what it is). However, there are common exceptions. For example, with the flash turned off, in camera A mode, maybe you set f/5.6. Then if you meter a scene indoors, perhaps it says 1/4 second shutter speed (dim, and too slow, so we need flash). Reach up and turn on the flash, and shutter probably changes to 1/60 second, which is a Minimum shutter speed with flash (in modes A or P, but some models can change that with an E2 menu). This is not about exposure, the system just assumes if we are using flash, we don't need 1/4 second.
Or if outdoors in bright light, a fast shutter speed is reduced to Maximum sync speed (1/200 or 1/250 second).... again, NOT about flash exposure, but the change may affect ambient exposure. Auto ISO may be substantially reduced too, in the older and the few latest newer iTTL cameras. But there is a midrange period of models when the flash was always working into high ISO, set for the less bright ambient.
Auto ISO is hardest to describe, because it has changed a couple of times. Older iTTL cameras up through the D300, never allowed Auto ISO to advance at all if flash was detected used. We are using flash instead of ISO. There was one exception, a hot shoe flash might allow Auto ISO to increase some if the flash power was not otherwise sufficient for the metering.
But then starting with the D300S, all camera models ignored flash when determining Auto ISO value, so in a dim room, Auto ISO was always very high, even with flash.
Then the last few newer models (starting with D800) corrected this, and now will only allow Auto ISO to advance 2 stops (ISO 100 to ISO 400) if hot shoe flash is detected used (the internal flash still always sees high ISO). And same exception, if the hot shoe flash limits out on power, Auto ISO can advance more then. That is very much more reasonable.
Bounce normally does need ISO 400, but if you see that your camera is using very high ISO with flash, you probably should turn Auto ISO off.
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That is common, and using flash compensation is this answer. SB-700 does TTL BL, so try routinely setting up to +1 EV flash compensation if needed.
In camera A or P modes (or Auto modes), the shutter speed should be a 1/60 second MINIMUM shutter speed anytime flash is used (and recognized). If you are seeing the normal slow dim ambient shutter speed, then you have to get out of Slow Sync or Rear Curtain Sync modes to see this faster minimum shutter speed. Slow Sync or Rear Curtain Sync retains and uses the slow ambient shutter speed, but normal sync mode imposes this minimum shutter speed if in A or P modes. There is a menu E2 where you can make this Minimum even slower, but I doubt that has been changed.
But the flash really does not care about shutter speed, and using camera M mode will let you set it as you wish (if not exceeding maximum sync speed). This is very handy (and usual) indoors, when the ambient exposure is too dim to be concerned about.
Using high ISO and/or slow shutter speed will bring up the ambient, which is usually orange incandescent light indoors, and not necessarily a good thing.
But when using flash indoors, we normally don't care about the ambient, and so it is well underexposed, but we are using flash instead.
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