off camera flash question, white wall became black background in photo

Discussion in 'Photography Beginners' Forum' started by minn, Jan 16, 2016.

  1. minn

    minn TPF Noob!

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    Hi, All

    I thought this subject probably is at intermediate level of photographing, and I am newbie though. Simply curious how the white wall could become a dark background using one bare flash off camera. please see the image attached for understanding my question

    I have been searching for answer quite while, and still could not get there. can anyone please help me? thank you

    Kindest Regards
    Minn


     
  2. Trever1t

    Trever1t Been spending a lot of time on here!

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    the light falling on the wall is exponentially less than on the subject. What's that formula? Anyhow, if she was closer to the wall it's be lit somewhat more. If you truly want the white background you'll need to put lights on it.
     
  3. minn

    minn TPF Noob!

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    Thanks, Trever. what I wanted is the dark background, the trick here is to convert the white wall into black.

    I knew the shutter speed controls the ambient light, so, I can purposely lower the exposure to make it looks dark.

    in the meantime, the aperture controls the flash light. I can cast the highlight on to the model

    now, the problem is once the flash sparkles, the light goes everywhere to turn the background back to white again. how to fix that, and keep the background still dark but the model in good spot light?
     
  4. dcbear78

    dcbear78 No longer a newbie, moving up!

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    Add more light. Turn it up higher, use higher aperture to balance exposure. Try something like f8 or f11.

    Unless you have a HSS capable flash (probably unlikely) there is only so far you can got with shutter speed.
     
  5. Didereaux

    Didereaux Been spending a lot of time on here!

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    Decrease your shutter speed. in some mode take the shot for proper exposure (without flash) this will show the background. make note of the cameras choices ISO shutter ap. Then set camera to Manual and enter those settings turn on the flash and take your shot. Usually a tripod is mandatory in such a shot to prevent blurring the background unless that is the effect you want. The main subject will not be blurred as it is illuminated by the very fast flash. ETTL mode on the flash is easiest for this, but you can manually set the power with a little experimenting. This is a common technique used to when taking a subject in the foreground against say a late sunset or interior.
     
  6. petrochemist

    petrochemist TPF junkie!

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    As Trever1t mentioned it's to do with light fall off. As the distance from the light source increases it has to cover larger areas. (Numerically its an inverse square relation ship.)

    To light your subject but not the background the light would be much closer to the subject than the background. Ideally this involves having the background reasonably far from the subject as having the light source close to the subject tends to produce hard shadows, which can be dramatic but is not flattering.

    With off axis lighting flags can be used to control the parts of the image that are lit so with side lighting it's possible to arrange the lighting to fall on the subject but not on the visible background.
     
  7. minn

    minn TPF Noob!

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    Thank you all for the good advices, here is what I did
    - aperture set to f13 which is the maximum I could do, otherwise, the camera doesn't shoot. don't know why though
    - shutter speed set to 200 which is the maximum when using the speedlight E-TTL mode
    - ISO 100

    I feel closing by the flash to the subject made it happen if I am not wrong, thank you Petrochemist, and it is true the light is not flattering.

    just don't quite sure what do you mean by "With off axis lighting flags can be used to control the parts of the image ... ... ". probably I need to digest a while before understanding this trick.

    Hi, Didereaux, thank you too for shedding me the light, the issue with me is I am still blind to what you suggested, I am sorry for this. I thought decreasing shutter speed will increase the amount of the light hitting the sensor, how is it possible doing this would preserve the dark background which I adjusted my parameters to catch ?
     
  8. Didereaux

    Didereaux Been spending a lot of time on here!

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    the ETTL on the camera/ reads the light on your focus point. What happens with slow shutter is this. You will see the subject and bckground but if you do it right the background is slightly underexposed, as well as the subject. While the shutter is open light from all sources is coming in, since the flash is NOT reaching the background when the flash goes off (it is very very fast thousandths of a sec you in effect have a double exposure....the background then the flash lit subject. Play with it, it is easier to do and understand than to read about it. As I said this is a very common technique used by pros and advanced amateurs alike.

    The simple advice you will read usually is something along the lines of this: Expose for the background light the subject with the flash.
     
  9. Braineack

    Braineack Been spending a lot of time on here!

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    Setup camera, without flash, so you get the background you want.

    add flash to the subject to fill in where needed.
     
    Last edited: Jan 17, 2016
  10. minn

    minn TPF Noob!

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    Thank you, Sir, I will try to experiment this and see the good results

     
  11. petrochemist

    petrochemist TPF junkie!

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    Perhaps I can explain better. If the flash is near the camera it will be sending light in much the same direction as the camera is looking. Move the flash to the side or up (~45° is common) then a a flag (dark sheet/card etc) can be used to block the light that would fall on the background behind the subject. This can still be done with large diffuse light sources. Together with a reflector to fill in the shadows it can produce a nice soft light while still not lighting your background. Getting it right probably takes quite a bit of practice :)
     
  12. minn

    minn TPF Noob!

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    Good explanation, Sir.

    The reflector thing, do you mean the reflector serves reflection and blocking purpose ? I guess it will be placed opposite to the key light, if this is the case, probably there is a need to prevent the key light from spillover particularly when using large diffuser at 45 and not far enough away from background such as in a living room, correct me if I am wrong
     

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