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Thread: Flash and exposure...

  1. #1

    Default Flash and exposure...

    Hey guys..I have a question I wanna ask..done quite abit of reading up but haven't got a very definite answer to what I'm looking for..

    Basically it's this..let's just say in a low light condition, to get correct exposure in manual mode, settings are ISO 1600 1/80 f5.6..supposedly I can go wide open at f2.8 thus reducing ISO but let's say i prefer to leave it at f5.6..because of the high ISO noise tends to be quite bad..most of the guys recommend using a on-camera flash unit to help in this situation..my question is..with the flash on eTTL and using a bounce card..do you change any of the settings? Or because there is fill light now you can lower the ISO and still get the correct exposure?

    For event or wedding shoots, is it ok that the photos are underexposed and then use post-processing to correct it(assuming shooting in RAW)? This is the initial thought that brought me to the question above!

    If you think I'm asking a stupid question I'm sorry I wasted your time reading this..if someone can help me out with this question it'll be greatly appreciated!

  2. #2

    Default Re: Flash and exposure...

    f5.6 so dark if ever that is the scenario try to use direct flash and use a stofen you can adjust the power of your ttl but adjust the setting in you cam flash setting... the under exposed is better than the over exposed but dont practice doing it. i hope i did help you.
    Last edited by bujay; 29th June 2011 at 07:46 AM.

  3. #3
    Moderator Octarine's Avatar
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    Default Re: Flash and exposure...

    Each system acts a bit differently, but one thing is clear: Normal exposure metering and flash exposure metering are 2 different pairs of shoes. Normal exposure metering takes the ambient light and measures the entire scene, flash exposure measures the foreground where the main object is. Now the challenge is to blend both settings. For Canon, you might find all what you need to know in the Canon Flash Bible.
    Do note the different approaches of the camera when using Auto and P, compared to Tv, Av and Manual. Other systems might act differently, you need to check then for their specific behaviour.
    EOS

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    Senior Member ZerocoolAstra's Avatar
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    Default Re: Flash and exposure...

    Quote Originally Posted by SmOcKxY View Post
    Hey guys..I have a question I wanna ask..done quite abit of reading up but haven't got a very definite answer to what I'm looking for..

    Basically it's this..let's just say in a low light condition, to get correct exposure in manual mode, settings are ISO 1600 1/80 f5.6..supposedly I can go wide open at f2.8 thus reducing ISO but let's say i prefer to leave it at f5.6..because of the high ISO noise tends to be quite bad..most of the guys recommend using a on-camera flash unit to help in this situation..my question is..with the flash on eTTL and using a bounce card..do you change any of the settings? Or because there is fill light now you can lower the ISO and still get the correct exposure?

    For event or wedding shoots, is it ok that the photos are underexposed and then use post-processing to correct it(assuming shooting in RAW)? This is the initial thought that brought me to the question above!

    If you think I'm asking a stupid question I'm sorry I wasted your time reading this..if someone can help me out with this question it'll be greatly appreciated!
    Flash is a bit tricky because the distance between the flash and the subject affects the level of illumination greatly.

    Based on my trial-and-error with my Nikon TTL flash unit, if subject is well-exposed in manual exposure mode, and I then add a flash unit (without changing any other settings), most likely the subject will end up overexposed.
    What I usually do is meter for the background to be reasonably well-exposed (usually this setting would result in the subject being underexposed), then let the flash fill-in the rest. It by no means guarantees a good result. Still a bit of trial-and-error before the event helps.

    You can try experimenting with this at home or any indoor space
    Exploring! :)

  5. #5
    Senior Member ZerocoolAstra's Avatar
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    Default Re: Flash and exposure...

    Quote Originally Posted by bujay View Post
    f5.6 so dark if ever that is the scenario try to use direct flash and use a stofen you can adjust the power of your ttl but adjust the setting in you cam flash setting... the under exposed is better than the over exposed but dont practice doing it. i hope i did help you.
    woah... can explain in plain English (with appropriate use of punctuation) for us lesser mortals, please?
    Exploring! :)

  6. #6

    Default Re: Flash and exposure...

    Here is MHO,

    let's say i prefer to leave it at f5.6..because of the high ISO noise tends to be quite bad..most of the guys recommend using a on-camera flash unit to help in this situation
    >>Firstly, you need to know if ISO1600 is acceptable for your camera. It does not need to be great at pixel peeping levels but needs to be pushable in PP (in case you need it) and be good enough for normal viewing.
    By setting f5.6, ISO1600; 1/80 in your example, you have the camera exposing for the scene.
    For the flash, you need to decide how you want to expose for the subject, and set the flash power accordingly.


    with the flash on eTTL and using a bounce card..do you change any of the settings? Or because there is fill light now you can lower the ISO and still get the correct exposure?
    >> Each camera brand will have its own algorithm to do this. However, it can depend if you are on an 'auto'/semi-auto mode or 'M' mode.



    For event or wedding shoots, is it ok that the photos are underexposed and then use post-processing to correct it(assuming shooting in RAW)? This is the initial thought that brought me to the question above
    >> You should try to expose correctly. You can underexpose the scene a bit (eg. 1 stop) if necessary, but the flash should aim to expose the subjects properly. Note the distinction between scene and subject.


    I try to elaborate more on exposing for the scene and subject.
    Scene meters at f5.6, ISO1600; 1/80
    If you shoot w/o flash, everything is exposed correctly (assuming camera metering is correct).

    Using flash (a few things can happen or be achieved)

    1. Ambient stays the same (f5.6, ISO1600; 1/80); flash exposes for the subject the same - the flash is more of a fill flash in this case.
    2. Ambient stays the same (f5.6, ISO1600; 1/80); flash does a key shift and exposes for the subject slightly higher (say +0.5 to +1 stop)- the subject 'stand out' more than the scene.
    3. Ambient exposure is dropped (eg. (f5.6, ISO800; 1/80); flash exposes for the subject properly - the subject 'stand out' more than the scene.
    4. Camera tries to light up the whole scene. In this case, shutter speed typically becomes irrelevant and exposure is controlled by flash power, ISO, f-stop. Typically not practical in large spaces and the o/p power is either too large for the strobe, or the power is too large and uneven that the nearer objects get over exposed.


    This is a site with very good reading on the subject.
    http://neilvn.com/tangents/flash-pho...-camera-flash/

  7. #7

    Default Re: Flash and exposure...

    Quote Originally Posted by pinholecam View Post
    Here is MHO,

    let's say i prefer to leave it at f5.6..because of the high ISO noise tends to be quite bad..most of the guys recommend using a on-camera flash unit to help in this situation
    >>Firstly, you need to know if ISO1600 is acceptable for your camera. It does not need to be great at pixel peeping levels but needs to be pushable in PP (in case you need it) and be good enough for normal viewing.
    By setting f5.6, ISO1600; 1/80 in your example, you have the camera exposing for the scene.
    For the flash, you need to decide how you want to expose for the subject, and set the flash power accordingly.


    with the flash on eTTL and using a bounce card..do you change any of the settings? Or because there is fill light now you can lower the ISO and still get the correct exposure?
    >> Each camera brand will have its own algorithm to do this. However, it can depend if you are on an 'auto'/semi-auto mode or 'M' mode.



    For event or wedding shoots, is it ok that the photos are underexposed and then use post-processing to correct it(assuming shooting in RAW)? This is the initial thought that brought me to the question above
    >> You should try to expose correctly. You can underexpose the scene a bit (eg. 1 stop) if necessary, but the flash should aim to expose the subjects properly. Note the distinction between scene and subject.


    I try to elaborate more on exposing for the scene and subject.
    Scene meters at f5.6, ISO1600; 1/80
    If you shoot w/o flash, everything is exposed correctly (assuming camera metering is correct).

    Using flash (a few things can happen or be achieved)

    1. Ambient stays the same (f5.6, ISO1600; 1/80); flash exposes for the subject the same - the flash is more of a fill flash in this case.
    2. Ambient stays the same (f5.6, ISO1600; 1/80); flash does a key shift and exposes for the subject slightly higher (say +0.5 to +1 stop)- the subject 'stand out' more than the scene.
    3. Ambient exposure is dropped (eg. (f5.6, ISO800; 1/80); flash exposes for the subject properly - the subject 'stand out' more than the scene.
    4. Camera tries to light up the whole scene. In this case, shutter speed typically becomes irrelevant and exposure is controlled by flash power, ISO, f-stop. Typically not practical in large spaces and the o/p power is either too large for the strobe, or the power is too large and uneven that the nearer objects get over exposed.


    This is a site with very good reading on the subject.
    http://neilvn.com/tangents/flash-pho...-camera-flash/
    Very nice explain and Very good article to read. Thank you for sharing

  8. #8

    Default Re: Flash and exposure...

    Thanks for the response guys..i do understand that at the end of the day it's still pretty much down to skill and perception of the photographer to put all the knowledge to good use..now i'm trying to gain knowledge so i know what i can practise on..

    Thanks pinholecam for the link! Quite a good read..i've found an article on that website that may just help me out..so correct me if i'm wrong here..given that i meter the exposure correctly on manual mode on the camera..adding on-camera flash will over expose the subject/subjects if i don't change any if the setting..in the article and also pinholecam and ZerocoolAstra have mentioned..i can meter for the ambient to be slightly under-exposed and with the flash on eTTL..it will compensate for the exposure and light up the subject..make it stand out in the scene..which i feel is pretty much the case for shooting people in an event or wedding..am i right to say that?

    I guess the only guesstimation i have to do is how much i underexpose by changing ISO..i understand that flash power is lost when using a lambency diffuser or bounce card..Ok now i'm starting to get an idea of how it works..any more things i should take note off?

    Thanks guys for all the help so far!!
    Last edited by SmOcKxY; 29th June 2011 at 12:56 PM.

  9. #9

    Default Re: Flash and exposure...

    errr...in big hall like expo/suntec convention hall, for flash exposure, u meter the background or meter the subject?

  10. #10
    Moderator Octarine's Avatar
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    Default Re: Flash and exposure...

    Quote Originally Posted by baggiolee View Post
    errr...in big hall like expo/suntec convention hall, for flash exposure, u meter the background or meter the subject?
    Can your flash illuminate the hall? Why would you want to meter for it?
    EOS

  11. #11

    Default Re: Flash and exposure...

    Quote Originally Posted by SmOcKxY View Post
    Thanks for the response guys..i do understand that at the end of the day it's still pretty much down to skill and perception of the photographer to put all the knowledge to good use..now i'm trying to gain knowledge so i know what i can practise on..

    Thanks pinholecam for the link! Quite a good read..i've found an article on that website that may just help me out..so correct me if i'm wrong here..given that i meter the exposure correctly on manual mode on the camera..adding on-camera flash will over expose the subject/subjects if i don't change any if the setting..in the article and also pinholecam and ZerocoolAstra have mentioned..i can meter for the ambient to be slightly under-exposed and with the flash on eTTL..it will compensate for the exposure and light up the subject..make it stand out in the scene..which i feel is pretty much the case for shooting people in an event or wedding..am i right to say that?

    I guess the only guesstimation i have to do is how much i underexpose by changing ISO..i understand that flash power is lost when using a lambency diffuser or bounce card..Ok now i'm starting to get an idea of how it works..any more things i should take note off?

    Thanks guys for all the help so far!!
    Not really. Assuming you are on 'auto' or 'semi-auto' mode, it really depends on the cameras algorithm in determining flash exposure. Its supposed to give the correct exposure by controlling the flash power from whatever the lens 'sees; (TTL = thru the lens). Then again, all this is what the camera thinks and can be tricked in many conditions, TTL systems are supposed to be good, but the flash exposure compensation is there for a reason
    Fudge accordingly with the flash exp. compensation if necessary.

    I'm a manual flash guy, cause I don't trust the TTL on my system.
    To me, M mode on camera and flash give the control I need.

    On 'auto' or 'semi-auto' modes, in an ideal world, you don't need to control anything

    On 'M' mode, your controls are :
    Ambient - ISO; aperture; shutter speed
    Flash - Distance to subject; ISO; aperture; flash power


    My few cents on recycling time.
    We can be happy that we fire TTL (no control over power) or full power and get the shot at say ISO200, but the cost is battery life (though the duration of the event) and recycling time.
    If say I can shoot acceptably at ISO400 f4 and use 1/4 power per shot than 1/1 at ISO200 f5.6, that is something worth considering.
    Else, at 1/1, you may have to wait a few seconds between each shot, or get varying o/p from a not fully charged up capacitor.

  12. #12

    Default Re: Flash and exposure...

    Quote Originally Posted by baggiolee View Post
    errr...in big hall like expo/suntec convention hall, for flash exposure, u meter the background or meter the subject?
    They are separate right?

    You can :

    For Ambient
    =========
    1. Meter the ambient and expose 'as is' for the ambient.
    2. Meter the ambient, key shift it down a little (ie. under expose say -1 stop) to have less bkgnd emphasis (or to get a hand holdable speed)
    3. Totally ignore the ambient and use a setting that will actually give a totally 'black' photo if you don't use a flash on the subject
    4. Meter the ambient and overexpose it a bit (for creative effect)

    Flash
    =====
    1. Fill flash (ie. just enough flash power such that the subject is filled or a bit underexposed by the flash)
    2. Normal exposed flashed
    3. Key shift (up)


    You will never be able to light up such a big place with a strobe.
    How you want the ambient to be exposed is up to you.
    Your flash will only be used to expose your subject properly.

  13. #13
    Moderator catchlights's Avatar
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    Default Re: Flash and exposure...

    Quote Originally Posted by bujay View Post
    f5.6 so dark if ever that is the scenario try to use direct flash and use a stofen you can adjust the power of your ttl but adjust the setting in you cam flash setting... the under exposed is better than the over exposed but dont practice doing it. i hope i did help you.
    shooting underexposed and pump up during post will get more noise and also lost of shadow details.
    you will get better results in exposed to the right especially shooting in raw.
    Shoot to Live, Live to Shoot
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  14. #14

    Default Re: Flash and exposure...

    Quote Originally Posted by pinholecam View Post
    Not really. Assuming you are on 'auto' or 'semi-auto' mode, it really depends on the cameras algorithm in determining flash exposure. Its supposed to give the correct exposure by controlling the flash power from whatever the lens 'sees; (TTL = thru the lens). Then again, all this is what the camera thinks and can be tricked in many conditions, TTL systems are supposed to be good, but the flash exposure compensation is there for a reason
    Fudge accordingly with the flash exp. compensation if necessary.

    I'm a manual flash guy, cause I don't trust the TTL on my system.
    To me, M mode on camera and flash give the control I need.

    On 'auto' or 'semi-auto' modes, in an ideal world, you don't need to control anything

    On 'M' mode, your controls are :
    Ambient - ISO; aperture; shutter speed
    Flash - Distance to subject; ISO; aperture; flash power


    My few cents on recycling time.
    We can be happy that we fire TTL (no control over power) or full power and get the shot at say ISO200, but the cost is battery life (though the duration of the event) and recycling time.
    If say I can shoot acceptably at ISO400 f4 and use 1/4 power per shot than 1/1 at ISO200 f5.6, that is something worth considering.
    Else, at 1/1, you may have to wait a few seconds between each shot, or get varying o/p from a not fully charged up capacitor.
    Thanks for your inputs again..to make it simple i'd be shooting in M on the camera and leaving the flash in eTTL mode..my 430 EX II can't do ISO and aperture even on manual..and the easiest to adjust on the fly would be shutter speed cos of the dial near the shutter button..or would it be better to just do test shots before the start..use the flash on M mode too and determine the power of the flash and leave it there? This will mean that the subject distance from me would more or less be the same and the ambient light doesn't change by much?

    Noted your comments on the recycling time of the flash..that will also be a consideration when shooting.

  15. #15

    Default Re: Flash and exposure...

    Quote Originally Posted by SmOcKxY View Post
    Thanks for your inputs again..to make it simple i'd be shooting in M on the camera and leaving the flash in eTTL mode..my 430 EX II can't do ISO and aperture even on manual..and the easiest to adjust on the fly would be shutter speed cos of the dial near the shutter button..or would it be better to just do test shots before the start..use the flash on M mode too and determine the power of the flash and leave it there? This will mean that the subject distance from me would more or less be the same and the ambient light doesn't change by much?

    Noted your comments on the recycling time of the flash..that will also be a consideration when shooting.
    You have to try out if your system works as you described/intend (ie. M on the camera and leaving the flash in eTTL mode).

    Fastest is still leave camera on semi-auto modes (eg. Av, Tv, x-sync) and flash on TTL. Shoot, check if its acceptable and then compensate flash exposure accordingly.

    M mode on camera and flash is also ok and becomes rather straightforward with some practice.
    M modes are good if you want to have full control over all aspects of exposure (both ambient and subject).

    Most important thing is to read and try out. If its wrong, just think and adjust again.
    Gd luck

  16. #16

    Default

    Hmm...shooting in Av mode in low light conditions most of the time the camera sets the shutter too slow..i only use Av when i'm doing street or at least in bright places where ambient light is bright and just use flash as fill in..so indoors wise i think i'll still be using M mode..

  17. #17
    Moderator daredevil123's Avatar
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    Default

    Quote Originally Posted by SmOcKxY
    Hmm...shooting in Av mode in low light conditions most of the time the camera sets the shutter too slow..i only use Av when i'm doing street or at least in bright places where ambient light is bright and just use flash as fill in..so indoors wise i think i'll still be using M mode..
    Or you can bump up the iso.

  18. #18

    Default Re: Flash and exposure...

    Quote Originally Posted by daredevil123 View Post
    Or you can bump up the iso.
    Yah I also tried that before..there are some low light places I shoot..on Av mode with f2.8 and ISO 1600 and the camera sets the shutter at 1/50..still a bit too slow to go handheld..but of cos with the flash I can still the subjects by going rear curtain sync..

    The reason why I'm almost reluctant to bump up ISO past 1600 is that the noise control on my 2 yr old camera is not so good!

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    Default Re: Flash and exposure...

    Quote Originally Posted by SmOcKxY View Post
    Yah I also tried that before..there are some low light places I shoot..on Av mode with f2.8 and ISO 1600 and the camera sets the shutter at 1/50..still a bit too slow to go handheld..but of cos with the flash I can still the subjects by going rear curtain sync..

    The reason why I'm almost reluctant to bump up ISO past 1600 is that the noise control on my 2 yr old camera is not so good!
    Use M or Tv instead to control the shutter speed.
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  20. #20
    Moderator daredevil123's Avatar
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    Default Re: Flash and exposure...

    Quote Originally Posted by SmOcKxY View Post
    Yah I also tried that before..there are some low light places I shoot..on Av mode with f2.8 and ISO 1600 and the camera sets the shutter at 1/50..still a bit too slow to go handheld..but of cos with the flash I can still the subjects by going rear curtain sync..

    The reason why I'm almost reluctant to bump up ISO past 1600 is that the noise control on my 2 yr old camera is not so good!
    I meant, bump up your ISO when using external flash...

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